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1
Labun, Ján, Pavol Kurdel, Marek Češkovič, Alexey Nekrasov e Ján Gamec. "Low Altitude Measurement Accuracy Improvement of the Airborne FMCW Radio Altimeters". Electronics 8, n. 8 (12 agosto 2019): 888. http://dx.doi.org/10.3390/electronics8080888.
Testo completoAbstract (sommario):
This manuscript focuses on the analysis of a critical height of radio altimeters that can help for the development of new types of aeronautical radio altimeters with increased accuracy in measuring low altitudes. Altitude measurement accuracy is connected with a form of processing the difference signal of a radio altimeter, which carries information on the measured altitude. The definition of the altitude measurement accuracy is closely linked to the value of a critical height. Modern radio altimeters with digital processing of a difference signal could shift the limit of accuracy towards better values when the basics of the determination of critical height are thoroughly known. The theory results from the analysis and simulation of dynamic formation and the dissolution of the so-called stable and unstable height pulses, which define the range of the critical height and are presented in the paper. The theory is supported by a new method of derivation of the basic equation of a radio altimeter based on a critical height. The article supports the new theory of radio altimeters with the ultra-wide frequency deviation that lead to the increase the accuracy of a low altitude measurement. Complex mathematical analysis of the dynamic formation of critical height and a computer simulation of its course supported by the new form of the derivation of the basic equation of radio altimeter guarantee the correctness of the new findings of the systematic creation of unstable height pulses and the influence of their number on the altitude measurement accuracy. Application of the presented findings to the aviation practice will contribute to increasing the accuracy of the low altitude measurement from an aircraft during its landing and to increasing air traffic safety.
2
Partington, K. C., J. K. Ridley, C. G. Rapley e H. J. Zwally. "Observations of the Surface Properties of the Ice Sheets by Satellite Radar Altimetry". Journal of Glaciology 35, n. 120 (1989): 267–75. http://dx.doi.org/10.3189/s0022143000004603.
Testo completoAbstract (sommario):
Abstract By comparing modelled and averaged satellite altimeter return, it is demonstrated that time profiles of altimeter return can be used to provide important information on the surface properties of the ice sheets. Altimeter ice-sheet radar echoes from low altitudes and/or relatively low latitudes are, in general, dominated by surface scattering and, in Greenland, the area of surface-dominated return broadly coincides with the zone of summer melting. Seasonal variations in the echo wave-form shapes are negligible in all regions studied, with the possible exception of an area near the margin of the Greenland dry-snow zone. In general, the model explains well the observed variations in mean wave-form shape, but small discrepances between the model wave forms and the recorded wave forms indicate that sub-surface layers may be influencing the shape of the return. The possibility of deriving quantitative estimates of surface properties is explored by fitting model returns to averaged altimeter wave forms from the Wilkes Land plateau in Antarctica. Surface roughness can be measured unambiguously from the wave-form data, but estimations of other parameters, such as grain-size, snow density, and snow temperature are found to be ambiguous because different surface parameters have a similar influence on the shape of the return. Despite this, the derived estimates compare well with ground-based observations and suggest that the satellite altimeter may have an important role to play in providing information on the surface properties of the ice sheets.
3
Plana-Fattori, Artemio, Gérard Brogniez, Patrick Chervet, Martial Haeffelin, Olga Lado-Bordowsky, Yohann Morille, Frédéric Parol et al. "Comparison of High-Cloud Characteristics as Estimated by Selected Spaceborne Observations and Ground-Based Lidar Datasets". Journal of Applied Meteorology and Climatology 48, n. 6 (1 giugno 2009): 1142–60. http://dx.doi.org/10.1175/2009jamc1964.1.
Testo completoAbstract (sommario):
Abstract The characterization of high clouds as performed from selected spaceborne observations is assessed in this article by employing a number of worldwide ground-based lidar multiyear datasets as reference. Among the latter, the ground lidar observations conducted at Lannion, Bretagne (48.7°N, 3.5°W), and Palaiseau, near Paris [the Site Instrumental de Recherche par Télédétection Atmosphérique (SIRTA) observatory: 48.7°N, 2.2°E], both in France, are discussed in detail. High-cloud altitude statistics at these two sites were found to be similar. Optical thicknesses disagree, and possible reasons were analyzed. Despite the variety of instruments, observation strategies, and methods of analysis employed by different lidar groups, high-cloud optical thicknesses from the Geoscience Laser Altimeter System (GLAS) on board the Ice, Cloud and land Elevation Satellite (ICESat) were found to be consistent on the latitude band 40°–60°N. Respective high-cloud altitudes agree within 1 km with respect to those from ground lidars at Lannion and Palaiseau; such a finding remains to be verified under other synoptic regimes. Mean altitudes of high clouds from Lannion and Palaiseau ground lidars were compared with altitudes of thin cirrus from the Television and Infrared Observation Satellite (TIROS) Operational Vertical Sounder (TOVS) Path-B 8-yr climatology for a common range of optical thicknesses (0.1–1.4). Over both sites, the annual altitude distribution of thin high clouds from TOVS Path-B is asymmetric, with a peak around 8–9.5 km, whereas the distribution of high clouds retrieved from ground lidars seems symmetric with a peak around 9.5–11.5 km. Additional efforts in standardizing ground lidar observation and processing methods, and in merging high-cloud statistics from complementary measuring platforms, are recommended.
4
Baskakov, A. I., A. A. Komarov e M. S. Mikhailov. "Methodical Errors of a High-Precision Airborne Radio Altimeter Operating at Low Altitudes Above the Sea Surface". Radiophysics and Quantum Electronics 60, n. 6 (novembre 2017): 467–74. http://dx.doi.org/10.1007/s11141-017-9815-x.
Testo completo
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Hodge, Steven M., David L. Wright, Jerry A. Bradley, Robert W. Jacobel, Neils Skou e Bruce Vaughn. "Determination of the Surface and Bed Topography in Central Greenland". Journal of Glaciology 36, n. 122 (1990): 17–30. http://dx.doi.org/10.1017/s0022143000005505.
Testo completoAbstract (sommario):
AbstractThe surface and bottom topography of the central Greenland ice sheet was determined from airborne ice-radar soundings over a 180 km by 180 km grid centered on the 1974 “Summit” site (lat. 72°18′N., long. 37°55′W.), using the Technical University of Denmark 60 MHz ice radar. Over 6100 km of high-quality radar data were obtained, covering over 99'% of the grid, along lines spaced 12.5 km apart in both north-south and east-west directions. Aircraft location was done with an inertial navigation system (INS) and a pressure altimeter, with control provided by periodically flying over a known point at the center of the grid. The ice radar was used to determine ice thickness; the surface topography was determined independently using height-above-terrain measurements from the aircraft’s radar altimeter. The calculated surface topography is accurate to about ±6 m, with this error arising mostly from radar-altimeter errors. The ice thickness and bottom topography are accurate to about ±50 m, with this error dominated by the horizontal navigation uncertainties due to INS drift; this error increases to about ±125 m in areas of rough bottom relief (about 12% of the grid).The highest point on Greenland is at lat. 72°34′ N., long. 37°38′W., at an altitude of 3233 ± 6 m a.s.l. The ice surface at this point divides into three sectors, one facing north, one east-south-east, and one west-south-west, with each having a roughly uniform slope. The ice divide between the last two sectors is a well-defined ridge running almost due south. The ice is about 3025 m thick at the summit. Excluding the mountainous north-east corner of the grid, where the ice locally reaches a thickness of about 3470 m and the bed dips to about 370 m below sea-level, the maximum ice thickness, approximately 3375 m, occurs about 97 km south-south-west of the summit. The average bed altitude over the entire grid is 180 m and the average ice thickness is 2975 ± 235 m. The ice in most of the south-west quadrant of the grid is over 3200 m thick, and overlies a relatively smooth, flat basin with altitudes mostly below sea-level. There is no predominant direction to the basal topography over most of the grid; it appears to be undulating, rolling terrain with no obvious ridge/valley structure. The summit of the ice sheet is above the eastern end of a relatively large, smooth, flat plateau, about 10–15 km wide and extending about 50 km to the west. If the basal topography were the sole criterion, then a site somewhere on this plateau or in the south-west basin would be suitable for the drilling of a new deep ice core.
6
Hodge, Steven M., David L. Wright, Jerry A. Bradley, Robert W. Jacobel, Neils Skou e Bruce Vaughn. "Determination of the Surface and Bed Topography in Central Greenland". Journal of Glaciology 36, n. 122 (1990): 17–30. http://dx.doi.org/10.3189/s0022143000005505.
Testo completoAbstract (sommario):
AbstractThe surface and bottom topography of the central Greenland ice sheet was determined from airborne ice-radar soundings over a 180 km by 180 km grid centered on the 1974 “Summit” site (lat. 72°18′N., long. 37°55′W.), using the Technical University of Denmark 60 MHz ice radar. Over 6100 km of high-quality radar data were obtained, covering over 99'% of the grid, along lines spaced 12.5 km apart in both north-south and east-west directions. Aircraft location was done with an inertial navigation system (INS) and a pressure altimeter, with control provided by periodically flying over a known point at the center of the grid. The ice radar was used to determine ice thickness; the surface topography was determined independently using height-above-terrain measurements from the aircraft’s radar altimeter. The calculated surface topography is accurate to about ±6 m, with this error arising mostly from radar-altimeter errors. The ice thickness and bottom topography are accurate to about ±50 m, with this error dominated by the horizontal navigation uncertainties due to INS drift; this error increases to about ±125 m in areas of rough bottom relief (about 12% of the grid).The highest point on Greenland is at lat. 72°34′ N., long. 37°38′W., at an altitude of 3233 ± 6 m a.s.l. The ice surface at this point divides into three sectors, one facing north, one east-south-east, and one west-south-west, with each having a roughly uniform slope. The ice divide between the last two sectors is a well-defined ridge running almost due south. The ice is about 3025 m thick at the summit. Excluding the mountainous north-east corner of the grid, where the ice locally reaches a thickness of about 3470 m and the bed dips to about 370 m below sea-level, the maximum ice thickness, approximately 3375 m, occurs about 97 km south-south-west of the summit. The average bed altitude over the entire grid is 180 m and the average ice thickness is 2975 ± 235 m. The ice in most of the south-west quadrant of the grid is over 3200 m thick, and overlies a relatively smooth, flat basin with altitudes mostly below sea-level. There is no predominant direction to the basal topography over most of the grid; it appears to be undulating, rolling terrain with no obvious ridge/valley structure. The summit of the ice sheet is above the eastern end of a relatively large, smooth, flat plateau, about 10–15 km wide and extending about 50 km to the west. If the basal topography were the sole criterion, then a site somewhere on this plateau or in the south-west basin would be suitable for the drilling of a new deep ice core.
7
Haardenog-Pedersen, G., K. Keller, C. C. Tscherning e N. Gundestrup. "Modeling the signature of a transponder in altimeter return data and determination of the reflection surface of the ice cap near the GRIP camp, Greenland". Journal of Glaciology 44, n. 148 (1998): 625–33. http://dx.doi.org/10.3189/s0022143000002124.
Testo completoAbstract (sommario):
AbstractUsing an active transponder with the ERS-I and ERS-2 radar altimeters, the distance to the satellite was measured at a location close to the GRIP site, Greenland, at an altitude of 3.2 km. The measurement was executed while the transponder was in the “ice-tracking mode”. It includes a bias due to the propagation delay. The location of the transponder was determined using the global positioning system.The transponder signal was modeled and the distance from the altimeter to the effective reflection point of the transponder was determined. Since the transponder was located within 1 km of the ground tracks, the measurement was corrected for this offset. A correction was also done for the surface slope, resulting in the distance (plus bias) to the closest sub-satellite point on the surface of the (compact) snow.The transponder signal was then removed from the radar altimeter waveform, enabling the determination of the distance (plus bias from the altimeter to the first reflective surface within the snow. The différence between this distance and that obtained using the transponder was < 2 m. This shows that the surface which gives rise to the first return of the reflection agrees with the surface of the (compact, dry) snow at this high-altitude location. This is an important result to be used when studying ice-cap topography using satellite radar altimetry.
8
Haardenog-Pedersen, G., K. Keller, C. C. Tscherning e N. Gundestrup. "Modeling the signature of a transponder in altimeter return data and determination of the reflection surface of the ice cap near the GRIP camp, Greenland". Journal of Glaciology 44, n. 148 (1998): 625–33. http://dx.doi.org/10.1017/s0022143000002124.
Testo completoAbstract (sommario):
Abstract Using an active transponder with the ERS-I and ERS-2 radar altimeters, the distance to the satellite was measured at a location close to the GRIP site, Greenland, at an altitude of 3.2 km. The measurement was executed while the transponder was in the “ice-tracking mode”. It includes a bias due to the propagation delay. The location of the transponder was determined using the global positioning system. The transponder signal was modeled and the distance from the altimeter to the effective reflection point of the transponder was determined. Since the transponder was located within 1 km of the ground tracks, the measurement was corrected for this offset. A correction was also done for the surface slope, resulting in the distance (plus bias) to the closest sub-satellite point on the surface of the (compact) snow. The transponder signal was then removed from the radar altimeter waveform, enabling the determination of the distance (plus bias from the altimeter to the first reflective surface within the snow. The différence between this distance and that obtained using the transponder was < 2 m. This shows that the surface which gives rise to the first return of the reflection agrees with the surface of the (compact, dry) snow at this high-altitude location. This is an important result to be used when studying ice-cap topography using satellite radar altimetry.
9
Davis, Curt H., e Richard K. Moore. "A combined surface-and volume-scattering model for ice-sheet radar altimetry". Journal of Glaciology 39, n. 133 (1993): 675–86. http://dx.doi.org/10.1017/s0022143000016579.
Testo completoAbstract (sommario):
AbstractOver the last 15 years, satellite-altimeter data have been used to produce surface-elevation maps of the Greenland and Antarctic ice sheets with a 2 m accuracy. Analysis of Seasat and Geosat cross-over points showed that satellite altimeters can measure changes in the mass balance of the ice sheets. The retracking algorithm used to extract surface elevations from Seasat and Geosat return wave forms is based upon a modified form of the Brown surface-scattering model. Recent work has shown that altimeter wave forms over higher-altitude regions of the ice sheets are affected by sub-surface volume-scattering. Here, we develop a theoretical model for altimeter return wave forms over the ice sheets that is based on a combination of surface-and volume-scattering. By approximating the altimeter’s antenna pattern and transmitted pulse shape with Gaussian functions, we derive a closed-form analytical solution for the return-power volume-scattered from beneath the ice-sheet surface. We then combine the volume-scattering model with the Brown model and apply it to average wave forms from the Greenland and Antarctic ice sheets. The results show that the combined model accurately describes variations in altimeter wave-form shapes that are produced by differing contributions of surface-and volume-scattering to the received power. The combined model is then used to simulate return wave forms from a dual-frequency altimeter. The simulation shows that a two-frequency system can provide quantitative estimates of the absorption and scattering coefficients for near-surface snow.
10
Davis, Curt H., e Richard K. Moore. "A combined surface-and volume-scattering model for ice-sheet radar altimetry". Journal of Glaciology 39, n. 133 (1993): 675–86. http://dx.doi.org/10.3189/s0022143000016579.
Testo completoAbstract (sommario):
AbstractOver the last 15 years, satellite-altimeter data have been used to produce surface-elevation maps of the Greenland and Antarctic ice sheets with a 2 m accuracy. Analysis of Seasat and Geosat cross-over points showed that satellite altimeters can measure changes in the mass balance of the ice sheets. The retracking algorithm used to extract surface elevations from Seasat and Geosat return wave forms is based upon a modified form of the Brown surface-scattering model. Recent work has shown that altimeter wave forms over higher-altitude regions of the ice sheets are affected by sub-surface volume-scattering. Here, we develop a theoretical model for altimeter return wave forms over the ice sheets that is based on a combination of surface-and volume-scattering. By approximating the altimeter’s antenna pattern and transmitted pulse shape with Gaussian functions, we derive a closed-form analytical solution for the return-power volume-scattered from beneath the ice-sheet surface. We then combine the volume-scattering model with the Brown model and apply it to average wave forms from the Greenland and Antarctic ice sheets. The results show that the combined model accurately describes variations in altimeter wave-form shapes that are produced by differing contributions of surface-and volume-scattering to the received power. The combined model is then used to simulate return wave forms from a dual-frequency altimeter. The simulation shows that a two-frequency system can provide quantitative estimates of the absorption and scattering coefficients for near-surface snow.
11
Durban, J. W., H. Fearnbach, L. G. Barrett-Lennard, W. L. Perryman e D. J. Leroi. "Photogrammetry of killer whales using a small hexacopter launched at sea". Journal of Unmanned Vehicle Systems 3, n. 3 (settembre 2015): 131–35. http://dx.doi.org/10.1139/juvs-2015-0020.
Testo completoAbstract (sommario):
Conventional aircraft have been used for photogrammetry studies of free-ranging whales, but are often not practical in remote regions or not affordable. Here we report on the use of a small, unmanned hexacopter (APH-22; Aerial Imaging Solutions) as an alternative method for collecting photographs to measure killer whales (Orcinus orca) at sea. We deployed and retrieved the hexacopter by hand during 60 flights (average duration 13.2 min, max 15.7 min) from the upper deck of an 8.2 m boat, utilizing the aircraft's vertical takeoff and landing (VTOL) capability. The hexacopter was quiet and stable in flight, and therefore could be flown at relatively low altitudes without disturbing whales. The payload was a Micro Four-Thirds system camera that was used to obtain 18920 still images from an altitude of 35–40 m above the whales. Tests indicated a ground-resolved distance of <1.4 cm across the full extent of a flat and undistorted field of view, and an onboard pressure altimeter enabled measurements in pixels to be scaled to true size with an average accuracy of 5 cm. As a result, the images were sharp enough to differentiate individual whales using natural markings (77 whales in total) and preliminary estimates resolved differences in whale lengths ranging from 2.6 to 5.8 m. This first application at sea demonstrated the APH-22 hexacopter to be a safe and cost-effective platform for collecting photogrammetry images to fill key scientific data gaps about whales, and we anticipate this utility will extend to studies of other wildlife species.
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Zakharchenko, Vladimir, Sergey Zakharchenko e Andrey Yakimets. "Numeric Modeling of Low-Altitude Altimeter with Double Frequency Modulation". Mathematical Physics and Computer Simulation, n. 3 (dicembre 2020): 5–11. http://dx.doi.org/10.15688/mpcm.jvolsu.2020.3.1.
Testo completoAbstract (sommario):
This study is concerned with the problem of increasing the accuracy of a low-altitude altimeter employing the frequency modulation principle. A way to suppress the "discrete error" of the altimeter by employing additional «slow» frequency modulation of the carrier wave and averaging the resulting counts is considered. The benefit of such approach is simplicity of technical implementation manifesting in minimal changes in the microwave path and the recording device, which needs to run in averaging count mode. It is shown that, given a limited frequency band, the linear modulation form is not optimal. Results of error calculations presented are obtained via mathematical modelling of the altimeter’s operation for different shapes of the additional prequency modulation. It is shown that using complex shapes of the «slow» modulation with positive third derivative and optimizing for a given altitude range allows to reduce the average measurement error 2–3 times additionally relatively to the linear modulation form without expanding the occupied frequency band.
13
Zakharchenko, Vladimir, e Sergey Zakharchenko. "Numeric Low-Altitude Altimeter Modeling with Computation of Additional Modulation Frequencies Using a Genetic Algorithm". Mathematical Physics and Computer Simulation, n. 2 (luglio 2021): 18–26. http://dx.doi.org/10.15688/mpcm.jvolsu.2021.2.2.
Testo completoAbstract (sommario):
This study is concerned with the problem of increasing the accuracy of a low-altitude altimeter employing the frequency modulation principle. A way to suppress the “discrete error” of the altimeter by employing additional frequency modulation of the carrier wave and averaging the resulting counts is considered. The benefit of such approach is simplicity of technical implementation manifesting in minimal changes in the microwave path and the recording device, which needsto run in averaging count mode. This work presents a genetic algorithm for computing the array of additional modulation frequencies which can be used to reduce the mean square of the discrete error given a limited frequency band. Results of error calculations presented are obtained via mathematical modeling of the altimeter’s operation. It is shown that using additional modulation frequencies obtained by the genetic algorithm allows to reduce the average measurement error two times relatively to the linear modulation form without expanding the occupied frequency band.
14
Ichikawa, Kaoru, Takuji Ebinuma, Masanori Konda e Kei Yufu. "Low-Cost GNSS-R Altimetry on a UAV for Water-Level Measurements at Arbitrary Times and Locations". Sensors 19, n. 5 (26 febbraio 2019): 998. http://dx.doi.org/10.3390/s19050998.
Testo completoAbstract (sommario):
Together with direct Global Navigation Satellite System (GNSS) signals, the signals reflected at the water surface can be received by an unmanned aerial vehicle (UAV). From the range difference between two GNSS signal paths, the height of the UAV above the water level can be geometrically estimated using the weighted least squares method, called GNSS reflectometry (GNSS-R) altimetry. Experimental low-cost GNSS-R altimetry flights with a UAV were conducted at the coast of Lake Biwa, Japan. Although the height estimated by the GNSS-R altimeter included large short-term noises up to 8 m amplitude, it agreed well with the UAV altitude measured by the post-processed kinematic positioning. By selecting better weight functions in the least square method and using sufficient temporal averaging, the GNSS-R altimetry achieved accuracy in the order of 0.01 m if a sufficient number of GNSS satellites with high elevation angles were available. The dependency of the results on the weight functions is also discussed.
15
Wang, Haihong, Yonghai Chu, Zhengkai Huang, Cheinway Hwang e Nengfang Chao. "Robust, Long-term Lake Level Change from Multiple Satellite Altimeters in Tibet: Observing the Rapid Rise of Ngangzi Co over a New Wetland". Remote Sensing 11, n. 5 (7 marzo 2019): 558. http://dx.doi.org/10.3390/rs11050558.
Testo completoAbstract (sommario):
Satellite altimetry has been successfully applied to monitoring water level variation of global lakes. However, it is still difficult to retrieve accurate and continuous observations for most Tibetan lakes, due to their high altitude and rough terrain. Aiming to generate long-term and accurate lake level time series for the Tibetan lakes using multi-altimeters, we present a robust strategy including atmosphere delay corrections, waveform retracking, outlier removal and inter-satellite bias adjustment. Apparent biases in dry troposphere corrections from different altimeter products are found, and such correctios must be recalculated using the same surface pressure model. A parameter is defined to evaluate the performance of the retracking algorithm. The ICE retracker outperforms the 20% and 50% threshold retrackers in the case of Ngangzi Co, where a new wetland has been established. A two-step algorithm is proposed for outlier removal. Two methods are adopted to estimate inter-satellite bias for different cases of with and without overlap. Finally, a 25-year-long lake level time series of Ngangzi Co are constructed using the TOPEX/Poseidon-family altimeter data from October 1992 to December 2017, resulting in an accuracy of ~17 cm for TOPEX/Poseidon and ~10 cm for Jason-1/2/3. The accuracy of retrieved lake levels is on the order of decimeter. Because of no gauge data available, ICESat and SARAL data with the accuracy better than 7 cm are used for validation. A correlation more than 0.9 can be observed between the mean lake levels from TOPEX/Poseidon-family satellites, ICESat and SARAL. Compared to the previous studies and other available altimeter-derived lake level databases, our result is the most robust and has resulted in the maximum number of continuous samples. The time series indicates that the lake level of Ngangzi Co increased by ~8 m over 1998–2017 and changed with different rates in the past 25 years (-0.39 m/yr in 1992–1997, 1.03 m/yr in 1998–2002 and 0.32 m/yr in 2003–2014). These findings will enhance the understanding of water budget and the effect of climate change.
16
Nazarali, Samir, Henry Liu, Maleeha Syed, Terry Wood, Samuel Asanad, Alfredo A. Sadun e Rustum Karanjia. "Aircraft Cabin Pressurization and Concern for Non-Arteritic Anterior Ischemic Optic Neuropathy". Aerospace Medicine and Human Performance 91, n. 9 (1 settembre 2020): 715–19. http://dx.doi.org/10.3357/amhp.5498.2020.
Testo completoAbstract (sommario):
BACKGROUND: Cabin pressurization is the process by which aircraft maintain a comfortable and safe environment for passengers flying at high altitudes. At high altitudes, most patients can tolerate changes in pressurization; however, passengers at high risk of hypoxia may experience ischemic events. The purpose of this study was to evaluate variations in pressurization of commercial aircraft at cruising altitude and describe its relevance in relation to patients with non-arteritic anterior ischemic optic neuropathy (NAION).METHODS: Altimeters were used to measure altitude and cabin altitude at cruising altitude aboard 113 commercial flights, including 53 narrow-body and 60 wide-body aircraft.RESULTS: Cabin altitude ranged from 4232 ft to 7956 ft at cruising altitudes ranging from 30,000 ft to 41,000 ft. The mean cabin altitude for all flights was 6309 876 ft. Narrow-body aircraft had a significantly higher mean cabin altitude (6739 829 ft) compared to wide-body aircraft (5929 733 ft). For all flights, the mean cruising altitude was 35,369 2881 ft with narrow-body aircraft cruising at a lower altitude of 34,238 2389 ft compared to wide-body aircraft at 36,369 2925 ft. Newer generation aircraft had a mean cabin altitude of 6066 837 ft, which was lower than the mean cabin altitude of older aircraft (6616 835 ft).DISCUSSION: Innovation in flight design has offered the ability for aircraft to fly at greater altitudes while maintaining lower cabin altitude. Those at high risk of hypoxia-induced complications may consider aircraft type when air travel is required.Nazarali S, Liu H, Syed M, Wood T, Asanad S, Sadun AA, Karanjia R. Aircraft cabin pressurization and concern for non-arteritic anterior ischemic optic neuropathy. Aerosp Med Hum Perform. 2020; 91(9):715719.
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Enßle, F., A. Fritz e B. Koch. "COMPARING ICESAT/GLAS BASED ELEVATION HEIGHTS WITH PHOTOGRAMMETRIC TERRAIN HEIGHTS FROM UAV-IMAGERY ON THE EAST TIBETAN PLATEAU". ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XL-3/W3 (19 agosto 2015): 385–90. http://dx.doi.org/10.5194/isprsarchives-xl-3-w3-385-2015.
Testo completoAbstract (sommario):
Digital elevation models (DEMs) and height measurements are broadly used in environmental studies. Two common elevation sources are the Ice Cloud and land elevation Satellite (ICESat), which acquired laser range measurements with the Geoscience Laser Altimeter System (GLAS) across the globe and elevation data from the Shuttle Radar Topography Mission (SRTM). Current developments of small unmanned aerial vehicles (UAV) provide the opportunity to collect aerial images of remote areas at a high spatial resolution. These can be further processed to digital surface models by stereophotogrammetry and provide a reliable data source to evaluate coarse scale Digital Elevation Models (DEMs). <br><br> This study compares ICESat/GLAS and SRTM90 elevation data against photogrammetric terrain heights within GLAS footprints on high altitudes on the East Tibetan Plateau. Without vegetation-bias, we were able to examine height differences under different topographic conditions and of different acquisition dates. Several resampling techniques were applied to SRTM90 data and averaged height within each footprint was calculated. ICESat/GLAS heights (n = 148) are most similar to UAV data based elevations with an averaged difference of −0.8m ±3.1m. Results furthermore indicate the validity of ICESat/GLAS heights, which are usually removed from analyses by applying different quality flags. Smallest difference of SRTM90 to UAV based heights could be observed by a natural neighbour resampling technique (averaged 3.6m ±14m), whereat other techniques achieved quite similar results. It can be confirmed that within a range of 3,800–4,200m above mean sea level the ICESat/GLAS heights are a precise source to determine elevation at footprint geolocation.
18
Botsyun, Svetlana, Pierre Sepulchre e Camille Risi. "Comprendre la dynamique atmosphérique pour mieux reconstituer l'altitude passée des chaînes de montagnes". La Météorologie, n. 109 (2020): 023. http://dx.doi.org/10.37053/lameteorologie-2020-0043.
Testo completoAbstract (sommario):
Comprendre la dynamique de soulèvement d'une chaîne de montagne nécessite d'en estimer l'altitude passée. C'est le but de la paléoaltimétrie. La méthode la plus répandue utilise la composition isotopique en oxygène des roches carbonatées formées dans les sols et à partir des sédiments lacustres. Celle-ci reflète la composition de la pluie passée qui, dans le monde actuel et dans la plupart des chaînes de montagnes, s'appauvrit progressivement en isotopes lourds avec l'altitude. En supposant que cet appauvrissement reste valide dans le passé, l'altitude du plateau tibétain à l'Éocène (il y a environ 42 millions d'années) est estimée à 4 000 m environ. Mais d'autres marqueurs de l'altitude passée indiquent au contraire des altitudes inférieures à 2 000 m. La relation entre composition isotopique des pluies et altitude observée aujourd'hui s'applique-t-elle à l'Éocène ? C'est ce que nous avons essayé de vérifier en utilisant un modèle de circulation générale atmosphérique, LMDZ-iso. On trouve qu'à l'Éocène la circulation atmosphérique et les processus hydrologiques étaient tellement différents de l'actuel que les observations isotopiques dans les roches carbonatées se trouvent finalement être cohérentes avec des altitudes relativement faibles. Les différentes méthodes de paléo-altimétrie se retrouvent ainsi réconciliées et en accord avec un soulèvement récent (post-Éocène) du plateau tibétain. Understanding the uplift dynamics of a mountain range requires estimating past altitude. This is the purpose of the paleo-altimetry. The most commonly applied paleo-altimetry method is based on the isotopic oxygen composition of the carbonate archives. It reflects the composition of past rain, which at present-day and in the most mountain ranges becomes progressively more depleted in heavy isotopes with altitude. Assuming that this depletion remains valid in the past, the elevation of the Tibetan Plateau in the Eocene (about 42 millions years ago) is estimated to be about 4 000 m. However, other proxy data indicate on the contrary low altitudes. Is the relationship between the rain isotopic composition and the altitude that is observed today applicable to the Eocene? This is what we tried to verify using an atmospheric general circulation model, LMDZ-iso. We find that in the Eocene, the atmospheric circulation and hydrological processes were so different to the present-day that the isotopic observations in the Eocene carbonates are actually consistent with relatively low altitudes of the Plateau. This allows us to reconcile different methods of paleo-altimetry in agreement with more recent (post-Eocene) uplift of the Tibetan Plateau.
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Labun, Ján, Martin Krchňák, Pavol Kurdel, Marek Češkovič, Alexey Nekrasov e Mária Gamcová. "Possibilities of Increasing the Low Altitude Measurement Precision of Airborne Radio Altimeters". Electronics 7, n. 9 (11 settembre 2018): 191. http://dx.doi.org/10.3390/electronics7090191.
Testo completoAbstract (sommario):
The paper focuses on the new trend of increasing the accuracy of low altitudes measurement by frequency-modulated continuous-wave (FMCW) radio altimeters. The method of increasing the altitude measurement accuracy has been realized in a form of a frequency deviation increase with the help of the carrier frequency increase. In this way, the height measurement precision has been established at the value of ±0.75 m. Modern digital processing of a differential frequency cannot increase the accuracy limitation considerably. It can be seen that further increase of the height measurement precision is possible through the method of innovatory processing of so-called height pulses. This paper thoroughly analyzes the laws of height pulse shaping from the differential frequency presented by the number that represents the information about the measured altitude for this purpose. This paper presents the results of the laboratory experimental altitude measurement with the use of a so-called double-channel method. The application of obtained results could contribute to the increase of air traffic safety, mainly in the phase of the aircraft approaching for landing and landing itself.
20
Chu, Cun Shan, e Jia Yua Shan. "Application of Passive Seeker/Altimeter in Air Guided Munition’s End-Guidance Phase". Advanced Materials Research 433-440 (gennaio 2012): 6959–64. http://dx.doi.org/10.4028/www.scientific.net/amr.433-440.6959.
Testo completoAbstract (sommario):
Inertial navigation system’s position error and velocity error are accumulated over time, it certainly affect the end guidance accuracy of the air munitions. To solve this problem, the information which includes altitude angle, azimuth angle, their angle velocity and altitude provided by passive seeker and altimeter is used for amending INS error with UKF algorithm in end-guidance phase. Through computer simulation the feedback filter with altimeter is better than that without altimeter.
21
Guinn, Thomas A., Daniel J. Halperin e Christopher G. Herbster. "Climatology of Estimated Altimeter Error due to Nonstandard Temperatures". Journal of Applied Meteorology and Climatology 60, n. 3 (marzo 2021): 377–90. http://dx.doi.org/10.1175/jamc-d-20-0159.1.
Testo completoAbstract (sommario):
AbstractGeneral aviation (GA) accidents involving controlled flight into terrain often occur when pilots are unaware that their aircraft’s true altitude is lower than the altitude indicated by the pressure altimeter as a result of colder-than-standard temperatures. However, little guidance is available that quantifies the magnitude of these altimeter errors and their variation with season. In this study, the fifth-generation European Centre for Medium-Range Weather Forecasts atmospheric reanalysis of the global climate (ERA5) dataset is combined with the pressure–altitude equation to construct a 30-yr monthly climatology, covering much of the United States and Canada, of D value (i.e., true altitude minus pressure altitude) corrected for the standard-atmosphere height separation between the altimeter setting and standard mean sea level pressure. This “corrected” D value therefore provides a useful estimate of the error between true and altimeter-indicated altitude. During winter, the mean corrected D values reach values as low as −350 m (~−1200 ft) in northern, low-terrain regions for flights near a pressure altitude of 3600 m, meaning the aircraft would be nearly 350 m lower than the altimeter indicates. Furthermore, the minimum (i.e., maximum negative) corrected D values are nearly double their mean values for the same time period. In addition, the reanalysis-based corrected D values are compared with estimated values calculated using a simple rule of thumb that is based solely on the air temperature at altitude and the surface elevation. The rule of thumb tends to underpredict the magnitude of the estimated error, in some cases by 70 m (~200 ft), and therefore gives a lower margin of safety.
22
Mercenaro, Luca, Ana Fernandes de Oliveira, Massimiliano Cocco e Giovanni Nieddu. "Yield and grape quality of three red grapevine cultivars (Vitis vinifera L.) in relation to altimetry". BIO Web of Conferences 13 (2019): 02002. http://dx.doi.org/10.1051/bioconf/20191302002.
Testo completoAbstract (sommario):
Environment has a great impact on berry composition. In this context we investigated the quality of extremely widespread grape varieties in Sardinia, cvs. Cannonau, Bovale sardo and Monica, cultivated at different altitudes. The work was conducted in a two-year period in two vineyards located respectively at 500 and 700 meters above sea level. Viticultural model and cultivation practices were the same for both vineyards. The following measurements were noted: (i) main phenological phases, (ii) yield and its components, (iii) must quality from veraison to harvest, and (iv) anthocyanin qualitative profiles at harvest. At higher altitude the phenological phases are delayed. Yield was not statistically influenced by altitude. The ripening of the main technological parameters, although similar among the vineyards, suggests that the effects of the different altitude are clear, but they vary according to year and are cultivar dependent. In cv. Cannonau, higher altitude promoted higher total soluble solids. The extractable anthocyanins were not influenced by altitude, although in all tested varieties the higher altitude favored a decrease in the ratio between non-acylated and acylated anthocyanins.
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Bierlich, KC, RS Schick, J. Hewitt, J. Dale, JA Goldbogen, AS Friedlaender e DW Johnston. "Bayesian approach for predicting photogrammetric uncertainty in morphometric measurements derived from drones". Marine Ecology Progress Series 673 (2 settembre 2021): 193–210. http://dx.doi.org/10.3354/meps13814.
Testo completoAbstract (sommario):
Increasingly, drone-based photogrammetry has been used to measure size and body condition changes in marine megafauna. A broad range of platforms, sensors, and altimeters are being applied for these purposes, but there is no unified way to predict photogrammetric uncertainty across this methodological spectrum. As such, it is difficult to make robust comparisons across studies, disrupting collaborations amongst researchers using platforms with varying levels of measurement accuracy. Here we built off previous studies quantifying uncertainty and used an experimental approach to train a Bayesian statistical model using a known-sized object floating at the water’s surface to quantify how measurement error scales with altitude for several different drones equipped with different cameras, focal length lenses, and altimeters. We then applied the fitted model to predict the length distributions and estimate age classes of unknown-sized humpback whales Megaptera novaeangliae, as well as to predict the population-level morphological relationship between rostrum to blowhole distance and total body length of Antarctic minke whales Balaenoptera bonaerensis. This statistical framework jointly estimates errors from altitude and length measurements from multiple observations and accounts for altitudes measured with both barometers and laser altimeters while incorporating errors specific to each. This Bayesian model outputs a posterior predictive distribution of measurement uncertainty around length measurements and allows for the construction of highest posterior density intervals to define measurement uncertainty, which allows one to make probabilistic statements and stronger inferences pertaining to morphometric features critical for understanding life history patterns and potential impacts from anthropogenically altered habitats.
24
Zhu, Quansheng, Wanshou Jiang, Ying Zhu e Linze Li. "Geometric Accuracy Improvement Method for High-Resolution Optical Satellite Remote Sensing Imagery Combining Multi-Temporal SAR Imagery and GLAS Data". Remote Sensing 12, n. 3 (8 febbraio 2020): 568. http://dx.doi.org/10.3390/rs12030568.
Testo completoAbstract (sommario):
With the widespread availability of satellite data, a single region can be described using multi-source and multi-temporal remote sensing data, such as high-resolution (HR) optical imagery, synthetic aperture radar (SAR) imagery, and space-borne laser altimetry data. These have become the main source of data for geopositioning. However, due to the limitation of the direct geometric accuracy of HR optical imagery and the effect of the small intersection angle of HR optical imagery in stereo pair orientation, the geometric accuracy of HR optical imagery cannot meet the requirements for geopositioning without ground control points (GCPs), especially in uninhabited areas, such as forests, plateaus, or deserts. Without satellite attitude error, SAR usually provides higher geometric accuracy than optical satellites. Space-borne laser altimetry technology can collect global laser footprints with high altitude accuracy. Therefore, this paper presents a geometric accuracy improvement method for HR optical satellite remote sensing imagery combining multi-temporal SAR Imagery and GLAS data without GCPs. Based on the imaging mechanism, the differences in the weight matrix determination of the HR optical imagery and SAR imagery were analyzed. The laser altimetry data with high altitude accuracy were selected and applied as height control point in combined geopositioning. To validate the combined geopositioning approach, GaoFen2 (GF2) optical imagery, GaoFen6 (GF6) optical imagery, GaoFen3 (GF3) SAR imagery, and the Geoscience Laser Altimeter System (GLAS) footprint were tested. The experimental results show that the proposed model can be effectively applied to combined geopositioning to improve the geometric accuracy of HR optical imagery. Moreover, we found that the distribution and weight matrix determination of SAR images and the distribution of GLAS footprints are the crucial factors influencing geometric accuracy. Combined geopositioning using multi-source remote sensing data can achieve a plane accuracy of 1.587 m and an altitude accuracy of 1.985 m, which is similar to the geometric accuracy of geopositioning of GF2 with GCPs.
25
Wufu, Adilai, Hongwei Wang, Yun Chen, Yusufujiang Rusuli, Ligang Ma, Shengtian Yang, Fei Zhang, Dan Wang, Qian Li e Yinbo Li. "Lake water volume fluctuations in response to climate change in Xinjiang, China from 2002 to 2018". PeerJ 8 (20 agosto 2020): e9683. http://dx.doi.org/10.7717/peerj.9683.
Testo completoAbstract (sommario):
Climate change has a global impact on the water cycle and its spatial patterns, and these impacts are more pronounced in eco-fragile regions. Arid regions are significantly affected by human activities like farming, and climate change, which influences lake water volumes, especially in different latitudes. This study integrates radar altimetry data from 2002 to 2018 with optical remote sensing images to analyze changes in the lake areas, levels, and volumes at different altitudes in Xinjiang, China. We analyzed changes in lake volumes in March, June, and October and studied their causes. The results showed large changes in the surface areas, levels, and volumes of lakes at different altitudes. During 2002–2010, the lakes in low- and medium-altitude areas were shrinking but lakes in high altitude areas were expanding. Monthly analysis revealed more diversified results: the lake water levels and volumes tended to decrease in March (−0.10 m/year, 37.55×108 m3) and increase in June (0.03 m/year, 3.48×108 m3) and October (0.04 m/year, 26.90×108 m3). The time series lake water volume data was reconstructed for 2011 to 2018 based on the empirical model and the total lake water volume showed a slightly increasing trend during this period (71.35×108 m3). We hypothesized that changes in lake water at high altitudes were influenced by temperature-induced glacial snow melt and lake water in low- to medium-altitude areas was most influenced by human activities like agricultural irrigation practices.
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Brozena, John M., e Mary F. Peters. "An airborne gravity study of eastern North Carolina". GEOPHYSICS 53, n. 2 (febbraio 1988): 245–53. http://dx.doi.org/10.1190/1.1442459.
Testo completoAbstract (sommario):
The Naval Research Laboratory (NRL) has developed a prototype airborne gravity measurement system. The core of the system is a LaCoste and Romberg air‐sea gravity meter mounted on a three‐axis stable platform. Corrections to the gravimeter data for altitude and variations in altitude are determined from a combination of highly precise radar and pressure altimeters. The original prototype system was designed for use over oceanic areas. We recently incorporated the pressure measurement to extend use of the airborne system to terrestrial regions where occasional radar altitudes over points of known topographic height can be obtained. The radar heights are used to relate the pressure altitudes to absolute altitudes and to determine the slopes of the isobaric surfaces. Vertical accelerations due to horizontal velocity over a curved, rotating earth (the Eötvös correction) and precise two‐dimensional positions are determined from a Texas Instrument P-code global positioning system. The updated system was tested over eastern North Carolina and the Outer Banks, an area that is difficult to survey by conventional means. Over one‐third of the region consists of low lying swampy terrain and another one‐third is the shallow water of the Pamlico and Albemarle Sounds. Neither the land method nor the shipboard gravity surveying method is well suited for these types of areas. Flying at an altitude of 600 m at 375 km/hr, we were able to cover an area over [Formula: see text] with a nominal track spacing of 9 km by 9 km in less than 18 hours of flying time. A comparison by the Defense Mapping Agency showed a 2.8 mGal rms and a −0.2 mGal mean difference between ground truth data and the airborne data at grid points when both data sets were interpolated to a common 9 km grid.
27
Labun, Ján, Miloš Soták e Pavol Kurdel. "Innovative Technique of Using the Radar Altimeter for Prediction of Terrain Collision Threats". Journal of the American Helicopter Society 57, n. 4 (1 ottobre 2012): 1–3. http://dx.doi.org/10.4050/jahs.57.045002.
Testo completoAbstract (sommario):
The Technical Note presents the possibility of applying the classical onboard aviation radar altimeter in the function of a simple anticollision system. Currently, classical radar altimeter offers two important pieces of information for pilots: actual flight altitude and aircraft descent at the level of decision making. The goal here is to draw attention to the innovative technique of using the radar altimeter to generate further crucial information for the pilot of a helicopter or small aircraft for predicting the threat of collision with the terrain. This new technique is based on the evaluation of the Doppler frequency in the differential signal of the radar altimeter. The theoretical assumptions have been verified by simulation and experiment.
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Neiman, Yu M., e L. S. Sugaipova. "On determining parameters of the returned altimetry signal". Geodesy and Cartography 954, n. 12 (20 gennaio 2020): 10–19. http://dx.doi.org/10.22389/0016-7126-2019-954-12-10-19.
Testo completoAbstract (sommario):
The authors summarize the principle underlying the modern satellite altimetry. Careful analysis of the shape of the reflected signal enables estimating the flight altitude of the satellite altimeter above sea level, and other important parameters of the sea surface in the area under study quite reliably. Important in doing so is the reflected signal power model used. The Brown-Hayne model seems to be the most common one. The values of these parameters are determined from measurements using certain optimization methods. It is especially noted that the problem in question can be successfully solved by methods based on modern theory of artificial neural networks. Numerical experiments using real altimetric data were carried out in MATLAB environment. In this regard, the basic concepts of this theory are described and the possibilities of its use as an effective approximation of any dependence are emphasized. The Levenberg-Marquardt method and the genetic algorithm of artificial neural networks show the same results, but the latter does not require setting initial values of parameters, only limits of their possible change.
29
Makshakov, A. V., Yu I. Shtern, O. S. Volkova e K. A. Vasilchenko. "Method and Hardware-Software for Measuring Altitude of Aircraft and Descent Facilities with Increased Accuracy". Proceedings of Universities. Electronics 25, n. 5 (ottobre 2020): 452–64. http://dx.doi.org/10.24151/1561-5405-2020-25-5-452-464.
Testo completoAbstract (sommario):
Reliable, accident-free operation of extra light aviation, drone aircraft, the parachute equipment for landing of people and loads, demands to increase an accuracy of determination of height for the purpose of their safe maneuvering, descent and landing. In the work the critical analysis of existing methods of the height measurement has been carried out for the purpose of defining the most accurate ones and the preference has been given to the barometric method. To decrease the measurement errors, the smart altimeter sensors (SAS) intellectual sensors have been developed, and on their basis the prototype of a barometric altimeter have been designed. In the course of computer modeling and prototyping it has been determined that in designing the altimeter it is necessary to use several SAS, and the accuracy of measurements is essentially affected by an arrangement of sensors on a flying object. The developed method of the height measurement using SAS includes the hardware-software compensation of the errors, caused by the atmospheric phenomena and aerodynamic parameters of the flying object design. The hardware – software for processing the measured data has been developed as well as the software for functioning of intelligent pressure sensor, automatic data processing and the information output to the altimeter display. The tests on the offered technique and hardware – software have been carried out in actual practice of operation. The developed altimeter has been installed on the equipment of a parachutist. In the test result it has been determined that the developed original method and the hardware – software permit to significantly decrease the errors of measurements, which do not exceed 1 meter while the airflow moving at speeds up to 8 meters per second 5 meters up to 70 meters per second
30
Ali, Busyairah Syd, e Nur Asheila Taib. "A Study on Geometric and Barometric Altitude Data in Automatic Dependent Surveillance Broadcast (ADS-B) Messages". Journal of Navigation 72, n. 5 (8 maggio 2019): 1140–58. http://dx.doi.org/10.1017/s0373463319000201.
Testo completoAbstract (sommario):
In Air Traffic Control (ATC), aircraft altitude data is used to keep an aircraft within a specified minimum distance vertically from other aircraft, terrain and obstacles to reduce the risk of collision. Two types of altitude data are downlinked by radar; actual flight level (Mode C) and selected altitude (Mode S). Flight level indicates pressure altitude, also known as barometric altitude used by controllers for aircraft vertical separation. ‘Selected altitude’ presents intent only, and hence cannot be used for separation purposes. The emergence of Global Navigation Satellite Systems (GNSSs) has enabled geometric altitude on board and to the controllers via the Automatic Dependent Surveillance-Broadcast (ADS-B) system. In addition, ADS-B provides quality indicator parameters for both geometric and barometric altitudes. Availability of this information will enhance Air Traffic Management (ATM) safety. For example, incidents due to Altimetry System Error (ASE) may potentially be avoided with this information. This work investigates the use and availability of these parameters and studies the characteristics of geometric and barometric data and other data that complement the use of these altitude data in the ADS-B messages. Findings show that only 8·7% of the altitude deviation is < 245 feet (which is a requirement of the International Civil Aviation Organization (ICAO) to operate in Reduced Vertical Separation Minimum (RVSM) airspace). This work provides an alert/guidance for future ground or airborne applications that may utilise geometric/barometric altitude data from ADS-B, to include safety barriers that can be found or analysed from the ADS-B messages itself to ensure ATM safety.
31
Jung, Jung-Soo, Ho-Jun Lee e Young-Kil Kwag. "Altitude Error Analysis of Helicopter-Borne FMCW Radar Altimeter". Journal of Korean Institute of Electromagnetic Engineering and Science 23, n. 2 (29 febbraio 2012): 258–61. http://dx.doi.org/10.5515/kjkiees.2012.23.2.258.
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32
Reineman, Benjamin D., Luc Lenain, Nicholas M. Statom e W. Kendall Melville. "Development and Testing of Instrumentation for UAV-Based Flux Measurements within Terrestrial and Marine Atmospheric Boundary Layers". Journal of Atmospheric and Oceanic Technology 30, n. 7 (1 luglio 2013): 1295–319. http://dx.doi.org/10.1175/jtech-d-12-00176.1.
Testo completoAbstract (sommario):
Abstract Instrumentation packages have been developed for small (18–28 kg) unmanned aerial vehicles (UAVs) to measure momentum fluxes as well as latent, sensible, and radiative heat fluxes in the atmospheric boundary layer (ABL) and the topography below. Fast-response turbulence, hygrometer, and temperature probes permit turbulent momentum and heat flux measurements, and shortwave and longwave radiometers allow the determination of net radiation, surface temperature, and albedo. UAVs flying in vertical formation allow the direct measurement of fluxes within the ABL and, with onboard high-resolution visible and infrared video and laser altimetry, simultaneous observation of surface topography or ocean surface waves. The low altitude required for accurate flux measurements (typically assumed to be 30 m) is below the typical safety limit of manned research aircraft; however, with advances in laser altimeters, small-aircraft flight control, and real-time kinematic differential GPS, low-altitude flight is now within the capability of small UAV platforms. Flight tests of instrumented BAE Systems Manta C1 UAVs over land were conducted in January 2011 at McMillan Airfield (Camp Roberts, California). Flight tests of similarly instrumented Boeing Insitu ScanEagle UAVs were conducted in April 2012 at the Naval Surface Warfare Center, Dahlgren Division (Dahlgren, Virginia), where the first known measurements of water vapor, heat, and momentum fluxes were made from low-altitude (down to 30 m) UAV flights over water (Potomac River). This study presents a description of the instrumentation, summarizes results from flight tests, and discusses potential applications of these UAVs for (marine) atmospheric boundary layer studies.
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Vieira, Telmo, M. Joana Fernandes e Clara Lázaro. "Modelling the Altitude Dependence of the Wet Path Delay for Coastal Altimetry Using 3-D Fields from ERA5". Remote Sensing 11, n. 24 (11 dicembre 2019): 2973. http://dx.doi.org/10.3390/rs11242973.
Testo completoAbstract (sommario):
Wet path delay (WPD) for satellite altimetry has been provided from external sources, raising the need of converting this value between different altitudes. The only expression available for this purpose considers the same altitude reduction, irrespective of geographic location and time. The focus of this study is the modelling of the WPD altitude dependence, aiming at developing improved expressions. Using ERA5 pressure level fields (2010–2013), WPD vertical profiles were computed globally. At each location and for each vertical profile, an exponential function was fitted using least squares, determining the corresponding decay coefficient. The time evolution of these coefficients reveals regions where they are highly variable, making this modelling more difficult, and regions where an annual signal exists. The output of this modelling consists of a set of so-called University of Porto (UP) coefficients, dependent on geographic location and time. An assessment with ERA5 data (2014) shows that for the location where the Kouba coefficient results in a maximum Root Mean Square (RMS) error of 3.2 cm, using UP coefficients this value is 1.2 cm. Independent comparisons with WPD derived from Global Navigation Satellite Systems and radiosondes show that the use of UP coefficients instead of Kouba’s leads to a decrease in the RMS error larger than 1 cm.
34
Baskakov, Aleksandr I., Alexey A. Komarov, Anna V. Ruban e Min-Ho Ka. "Limiting Accuracy of Height Measurement for a Precision Radar Altimeter in a Low Altitude Flying Vehicle above the Sea Surface". Remote Sensing 13, n. 14 (6 luglio 2021): 2660. http://dx.doi.org/10.3390/rs13142660.
Testo completoAbstract (sommario):
This study presents mathematical analysis and numerical modeling for the estimation of measurement errors of height estimation over the sea surface for a precision radar altimeter installed in a low altitude flying vehicle. Reflective properties of the electromagnetic signals from the sea surface are determined by the local backscattering patterns of the sea surface illuminated. The height estimation of the flying vehicle from the received echo signals at the output of its tracking system is the sum of three factors: the first factor is the height to the average sea level the second is the bias of the estimation of the height, which is time-varying and depends on the slope of large-scale roughness; the third is the terms related to the surface topography. For the calculation of the estimation errors of the height measurement of a low altitude precision radar altimeter, a reasonable approximation of the large roughness of the sea surface by a deterministic function is necessary. In this study, we performed the derivation of the estimation function and the analysis of the limiting accuracy of the height measurement using the calculation of the estimation errors in spectral domain method describing the large-scale sea surface roughness. The results obtained for the limiting accuracy of a flying vehicle at low altitude above the sea surface, allows to obtain reasonable system parameters minimizing height errors of the flight altitude.
35
Canas, António Costa, Magda Ramires Marabujo e Teresa Sousa. "Coutinho's Method for the Altitude". Journal of Navigation 73, n. 4 (11 dicembre 2019): 861–73. http://dx.doi.org/10.1017/s0373463319000961.
Testo completoAbstract (sommario):
In the first aerial crossing of the South Atlantic, by Gago Coutinho and Sacadura Cabral in 1922, several methods of astronomical maritime navigation were used with adaptions to aerial navigation. In order to apply these methods, the navigator needed to know the approximate altitude of the aircraft so that its position could be determined. The instrument available at that time, the altimeter, did not give reliable values for altitude. Therefore, Coutinho had to devise a method that enabled the navigator to determine the altitude quickly and efficiently. The method Coutinho devised is based on a mathematical and geometrical procedure. In this paper, we study in detail Coutinho's method to determine altitude, with diagrams to aid understanding of the deductions and calculations. We also present a real example of how this method would be used during the flight.
36
Stosius, R., G. Beyerle, A. Helm, A. Hoechner e J. Wickert. "Simulation of space-borne tsunami detection using GNSS-Reflectometry applied to tsunamis in the Indian Ocean". Natural Hazards and Earth System Sciences 10, n. 6 (25 giugno 2010): 1359–72. http://dx.doi.org/10.5194/nhess-10-1359-2010.
Testo completoAbstract (sommario):
Abstract. Within the German-Indonesian Tsunami Early Warning System project GITEWS (Rudloff et al., 2009), a feasibility study on a future tsunami detection system from space has been carried out. The Global Navigation Satellite System Reflectometry (GNSS-R) is an innovative way of using reflected GNSS signals for remote sensing, e.g. sea surface altimetry. In contrast to conventional satellite radar altimetry, multiple height measurements within a wide field of view can be made simultaneously. With a dedicated Low Earth Orbit (LEO) constellation of satellites equipped with GNSS-R, densely spaced sea surface height measurements could be established to detect tsunamis. This simulation study compares the Walker and the meshed comb constellation with respect to their global reflection point distribution. The detection performance of various LEO constellation scenarios with GPS, GLONASS and Galileo as signal sources is investigated. The study concentrates on the detection performance for six historic tsunami events in the Indian Ocean generated by earthquakes of different magnitudes, as well as on different constellation types and orbit parameters. The GNSS-R carrier phase is compared with the PARIS or code altimetry approach. The study shows that Walker constellations have a much better reflection point distribution compared to the meshed comb constellation. Considering simulation assumptions and assuming technical feasibility it can be demonstrated that strong tsunamis with magnitudes (M) ≥8.5 can be detected with certainty from any orbit altitude within 15–25 min by a 48/8 or 81/9 Walker constellation if tsunami waves of 20 cm or higher can be detected by space-borne GNSS-R. The carrier phase approach outperforms the PARIS altimetry approach especially at low orbit altitudes and for a low number of LEO satellites.
37
Paek, Inchan, Sangil Lee, Joohwan Chun, Hyukjung Lee e Jong Hun Jang. "Simulation Study of Altitude and Angle Estimation with an InSAR Altimeter". Journal of Korean Institute of Electromagnetic Engineering and Science 25, n. 8 (31 agosto 2014): 838–48. http://dx.doi.org/10.5515/kjkiees.2014.25.8.838.
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Choi, Kyeung-Sik, Jung-Wook Hyun, Jae-Won Jang, Dong-Man Ahn e Gyo-Young Hong. "Ground Altitude Measurement Algorithm using Laser Altimeter and Ultrasonic Rangefinder for UAV". Journal of Korea Navigation Institute 17, n. 6 (30 dicembre 2013): 749–56. http://dx.doi.org/10.12673/jkoni.2013.17.6.749.
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Marchenko, N., N. P. Yarema e T. R. Pavliv. "GEODYNAMICS". GEODYNAMICS 1(10)2011, n. 1(10) (28 giugno 2011): 27–30. http://dx.doi.org/10.23939/jgd2011.01.027.
Testo completoAbstract (sommario):
The study of Black Sea and Mediterranean Sea surface altitudes was carried out based on satellite altimetry data. The model of the Black Sea and Mediterranean Sea surface topography (SST) was build. The comparison of received results with the European quasigeoid was done.
40
Beamish, David. "The canopy effect in airborne EM". GEOPHYSICS 67, n. 6 (novembre 2002): 1720–28. http://dx.doi.org/10.1190/1.1527073.
Testo completoAbstract (sommario):
Airborne electromagnetic (AEM) surveys may be used to provide environmental subsurface assessments. Trial fixed‐wing AEM surveys were conducted in the central English Midlands for such purposes. This paper investigates a specific issue, that of the canopy effect, which needs to be addressed when high‐resolution AEM data are to be interpreted accurately. Any elevated feature (typically tree cover) that gives rise to underestimated altimeter readings causes the canopy effect. Half‐space models obtained from conventional, half‐space procedures together with formal numerical inversion techniques form the basis of the study. Both theory and survey data are used to assess the significance of the canopy thickness on the resistivity models. The pseudolayer half‐space method has a stated immunity to altitude errors. The method is found to be highly effective in returning resistivity estimates unbiased by altimeter errors. The associated positive apparent depths provide realistic estimates of canopy thickness while, elsewhere, negative values may be returned. Published numerical inversion schemes do not discuss any corresponding requirement to reduce canopy effect bias. Underestimated altitude measurements introduce false high‐resistivity zones with high wavenumber content unless an equivalent pseudolayer concept is used. The study indicates a requirement for a formal pseudolayer (an at‐surface perfect resistor of variable depth) to be included in the model when canopy zones are present.
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Rémy, Frédérique, e Benoit Legrésy. "Antarctic non-stationary signals derived from Seasat-ERS-1 altimetry comparison". Annals of Glaciology 27 (1998): 81–85. http://dx.doi.org/10.3189/1998aog27-1-81-85.
Testo completoAbstract (sommario):
Geographical changes in the height of the Antarctic ice sheet between 1978 and 1992 are mapped using altimeter data from Seasat and ERS-1 via an inverse technique that allows us to take imo account the whole altimctric error budget. in a belt between 70° and 72° S and between 150° and 80° E, a precision better than 40 cm is found for the surface elevation change, while the change in height averaged in the along-slopc direction has a precision of around 10-20 cm, leading to a precision better than 10% of the mass balance. These data suggest a relative positive imbalance of around 20% in this sector for the western and high-altitude areas, and a relative negative imbalance in some areas of lower altitude.
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Dibarboure, G., F. Boy, J. D. Desjonqueres, S. Labroue, Y. Lasne, N. Picot, J. C. Poisson e P. Thibaut. "Investigating Short-Wavelength Correlated Errors on Low-Resolution Mode Altimetry". Journal of Atmospheric and Oceanic Technology 31, n. 6 (1 giugno 2014): 1337–62. http://dx.doi.org/10.1175/jtech-d-13-00081.1.
Testo completoAbstract (sommario):
Abstract The observation of ocean scales smaller than 100 km with low-resolution mode (LRM) altimetry products is degraded by the existence of a “hump artifact” visible on sea surface height (SSH) spectra. Through an analysis of simulations and actual data from multiple missions, this paper shows that the hump originates in a response to inhomogeneities in backscatter strength. Current retrackers cannot fit their Brown model properly because they were designed for a scene with homogeneous backscatter properties. The error is also smoothed along track because of the size and shape of the LRM disc-shaped footprint. Therefore, the hump is modulated by the altimeter design and altitude and by the retracker used. Because of the random nature of the phenomenon, a large majority of long topography segments (e.g., hundreds to thousands of kilometers) is affected. However, within these segments, a substantial fraction of the corruption is contained in small subsets of data (e.g., less than 10%). This paper shows that oceanography users interested in small-scale SSH signals can mitigate the hump corruption by using better editing and postprocessing algorithms on the 20-Hz rate of current products. Last, the thin stripe-shaped footprint of Cryosat-2’s synthetic aperture radar mode (SARM) is not affected by the hump artifact, thus improving the observation of topography features ranging from 30 to 100 km. The differences between SARM and pseudo-LRM sigma0 can also be used to detect major hump events on pseudo-LRM data, which might be an asset to design/validate a new generation of algorithms aimed at reducing the hump artifact on the existing LRM record.
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Adamov, Yu, K. Boriak e V. Zavalniuk. "ON IMPROVEMENT OF PARACHUTE-RETROROCKET AIRDROP SYSTEM". Collection of scientific works of the Military Institute of Kyiv National Taras Shevchenko University, n. 64 (2019): 5–13. http://dx.doi.org/10.17721/2519-481x/2019/64-01.
Testo completoAbstract (sommario):
The paper is devoted to the study of the prospects for improving the parachute-retrorocket airdrop system (PRS) in order to increase its reliability and enable the ability to adjust the orientation of a load in the horizontal plane depending on the slope of the earth's surface at the landing site. The primary task is to improve the accuracy of the altimeter, which determines the triggering moment of the PRS jet engines. The replacement of a mechanical altimeter of an outdated design with a modern electronic radio altimeter based on phased array radar is proposed, which allows to improve the accuracy of determining the absolute altitude(distance to the ground) and to take into account a roll of the load during the descent. The ways of determining the slope of earth's surface at the estimated landing site are also discussed. The results obtained make it possible to increase the accuracy of radio altimeter operation and significantly reduce the probability of an error in determining the absolute altitude due to rocking or static roll of the object. In addition to determining the current values of the height and speed of the descent of the vehicle, the use of a scanning radar makes it possible to estimate the inclination angle of the Earth’s surface at the landing site (in the radar scanning plane). If a certain angle of inclination of the earth surface at the landing site turns out to be too large, the probability of a successful landing can be increased by correcting the object's descent path, taking into account the information received. One of the easiest ways to correct a descent trajectory is to equip an object with small aerodynamic elements (rudders) and electromechanical actuators, ensuring their necessary orientation based on the results of determining the surface relief with radar. As one of the options, the authors propose the use of additional jet engines, which are structurally located on opposite sides of the object of landing in such a way as to form a torque of rotation of the object in a space from 0 ° to 90 ° in the horizontal plane due to the kinetic energy of motion from the actuation of jet engines. The triggering moment of the squibs is calculated based on determining the optimal distance of the object to the ground surface, and the need for triggering the squibs to rotate the object (correcting its position in space) depends on a certain value of the slope angle of the earth surface and comparing it with the admissible critical values of the angle, at which the object loses its stability during landing.
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Lee, Jungshin, Chang-Ky Sung, Juhyun Oh, Kyungjun Han, Sangwoo Lee e Myeong-Jong Yu. "A Pragmatic Approach to the Design of Advanced Precision Terrain-Aided Navigation for UAVs and Its Verification". Remote Sensing 12, n. 9 (28 aprile 2020): 1396. http://dx.doi.org/10.3390/rs12091396.
Testo completoAbstract (sommario):
Autonomous unmanned aerial vehicles (UAVs) require highly reliable navigation information. Generally, navigation systems with the inertial navigation system (INS) and global navigation satellite system (GNSS) have been widely used. However, the GNSS is vulnerable to jamming and spoofing. The terrain referenced navigation (TRN) technique can be used to solve this problem. In this study, to obtain reliable navigation information even if a GNSS is not available or the degree of terrain roughness is not determined, we propose a federated filter based INS/GNSS/TRN integrated navigation system. We also introduce a TRN system that combines batch processing and an auxiliary particle filter to ensure stable flight of UAVs even in a long-term GNSS-denied environment. As an altimeter sensor for the TRN system, an interferometric radar altimeter (IRA) is used to obtain reliable navigation accuracy in high altitude flight. In addition, a parallel computing technique with general purpose computing on graphics processing units (GPGPU) is applied to process a high resolution terrain database and a nonlinear filter in real-time on board. Finally, the performance of the proposed system is verified through software-in-the-loop (SIL) tests and captive flight tests in a GNSS unavailable environment.
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Nesterov, M. Yu, e A. A. Monakov. "Estimation of flight altitude in the aperture synthesizing mode for altimeter with continuous probing signal". Radioelectronics and Communications Systems 57, n. 11 (novembre 2014): 489–94. http://dx.doi.org/10.3103/s0735272714110028.
Testo completo
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Nebylov, Alexander, Gennady Jatchevitch e Vladimir Nebylov. "New Structures and Algorithms of Altimeters for Controlling Vehicles Motion at Low and Superlow Altitudes". IFAC Proceedings Volumes 45, n. 1 (2012): 196–201. http://dx.doi.org/10.3182/20120213-3-in-4034.00037.
Testo completo
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Khajeh, S., A. A. Ardalan e H. Schuh. "INTERFEROMETRIC PATH MODELS FOR GNSS GROUND-BASED PHASE ALTIMETRY". ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-4/W18 (18 ottobre 2019): 597–603. http://dx.doi.org/10.5194/isprs-archives-xlii-4-w18-597-2019.
Testo completoAbstract (sommario):
Abstract. Altimetry by using GNSS (Global Navigation Satellite Systems) reflectometry is regarded as a new promising technique. One important step to utilize this technique is modeling the interferometric path (the difference between the direct and the reflected signal paths). This paper evaluates three models: the planar model, the planar model with tropospheric correction and a model based on ray-tracing. If decimeter level accuracy for water surface fluctuation is required, the planar model cannot be used when a receiver is at an altitude of a few hundred meters and observations are taken at low elevation angles. On the other hand, depending on the mapping function and zenith total delay in the tropospheric correction, the planar model with tropospheric correction can provide decimeter level accuracy for low altitude stations. If simulated observations with a 1 cm accuracy have been employed to estimate Sea Surface Height (SSH) by the model based on ray-tracing the numerical results present 1 cm as RMSE for phase retrieval and 5 cm for Doppler retrieval. The planar model with tropospheric correction does not yield RMSE better than some decimeters for the same condition.
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Assorov, Nikita A., Evgeniy E. Nechaev e Pavel S. Surint. "ABOUT THE TRANSITION TO QNH PRESSURE IN THE RUSSIAN FEDERATION". Civil Aviation High TECHNOLOGIES 21, n. 6 (26 dicembre 2018): 8–19. http://dx.doi.org/10.26467/2079-0619-2018-21-6-8-19.
Testo completoAbstract (sommario):
This article discusses the advantages and disadvantages of transition to QNH pressure. The analysis of various factors affecting the flight safety has been conducted. A comparative analysis of the two types of altitude reading while approaching the airport has been carried out. The first type is the altitude reading relative to the airfield when at an aerodrome surface an altimeter altitude is equal to zero. This pressure is called QFE. The second one is estimated relatively to the sea level; in this case the aerodrome elevation must be taken into account. Such pressure is called QNH. These both pressures are used in aviation. Historically, QFE pressure was used in the USSR, and after the disintegration of the Soviet Union this type of pressure was used during takeoff and landing. In the mid - 2000s, the majority of Russian airlines began to use the foreign aircraft, mainly the airplanes produced by Boeing and Airbus Companies. Since these aircraft are produced in Western countries, they use QNH pressure, so there are some difficulties of correct altitude setting while approaching an aerodrome, this causes an aircraft descent below the level prescribed by STAR, consequently, decent below minimum safe altitude. The conclusion of necessary transition to QNH pressure was made using the example of aircraft. The article also explains why the transition to QNH pressure flights in the Russian Federation is a top priority and a necessary step for maintaining proper level of flight safety.
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Sang, Shengbo, Ruiyong Zhai, Wendong Zhang, Qirui Sun e Zhaoying Zhou. "A self-developed indoor three-dimensional pedestrian localization platform based on MEMS sensors". Sensor Review 35, n. 2 (16 marzo 2015): 157–67. http://dx.doi.org/10.1108/sr-07-2014-682.
Testo completoAbstract (sommario):
Purpose – This study aims to design a new low-cost localization platform for estimating the location and orientation of a pedestrian in a building. The micro-electro-mechanical systems (MEMS) sensor error compensation and the algorithm were improved to realize the localization and altitude accuracy. Design/methodology/approach – The platform hardware was designed with common low-performance and inexpensive MEMS sensors, and with a barometric altimeter employed to augment altitude measurement. The inertial navigation system (INS) – extended Kalman filter (EKF) – zero-velocity updating (ZUPT) (INS-EKF-ZUPT [IEZ])-extended methods and pedestrian dead reckoning (PDR) (IEZ + PDR) algorithm were modified and improved with altitude determined by acceleration integration height and pressure altitude. The “AND” logic with acceleration and angular rate data were presented to update the stance phases. Findings – The new platform was tested in real three-dimensional (3D) in-building scenarios, achieved with position errors below 0.5 m for 50-m-long route in corridor and below 0.1 m on stairs. The algorithm is robust enough for both the walking motion and the fast dynamic motion. Originality/value – The paper presents a new self-developed, integrated platform. The IEZ-extended methods, the modified PDR (IEZ + PDR) algorithm and “AND” logic with acceleration and angular rate data can improve the high localization and altitude accuracy. It is a great support for the increasing 3D location demand in indoor cases for universal application with ordinary sensors.
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Frei, Jiří. "Implementation of Harmonised European Transition Altitude (HETA)". MAD - Magazine of Aviation Development 4, n. 19 (15 luglio 2016): 5. http://dx.doi.org/10.14311/mad.2016.19.01.
Testo completoAbstract (sommario):
<span style="font-family: 'Times New Roman',serif; font-size: 10pt; mso-fareast-font-family: 'MS Mincho'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;" lang="EN-US">Since 2010 there has been a noticeable effort to implement harmonized European transition altitude (HETA). This effort resulted in establishing of several working groups. As outputs were proposed three options but no mandatory implementation rules for European countries (resp. air navigation services providers). Nowadays each country evaluates impacts of implementation of one of three proposed solutions and some countries even implement kind of harmonized transition altitude in cooperation with neighboring countries (Slovakia, Hungary and Austria). This article briefly describes the general problem in section I and II. Impacts of all three proposed options by working group on involved subjects such as crew, controllers, but also environment or safety are evaluated. The end of the article describes in details the way of implementation in Slovakia and some case studies related to </span><span style="font-family: 'Times New Roman',serif; font-size: 10pt; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;" lang="EN-US">altimeter setting rules in the area of common interest at the interface between FIR Prague, Bratislava and Vienna</span><span style="font-family: 'Times New Roman',serif; font-size: 10pt; mso-fareast-font-family: 'MS Mincho'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;" lang="EN-US">.</span>