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Brunt, Kelly M., Robert L. Hawley, Eric R. Lutz, Michael Studinger, John G. Sonntag, Michelle A. Hofton, Lauren C. Andrews y Thomas A. Neumann. "Assessment of NASA airborne laser altimetry data using ground-based GPS data near Summit Station, Greenland". Cryosphere 11, n.º 2 (8 de marzo de 2017): 681–92. http://dx.doi.org/10.5194/tc-11-681-2017.
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Abstract. A series of NASA airborne lidars have been used in support of satellite laser altimetry missions. These airborne laser altimeters have been deployed for satellite instrument development, for spaceborne data validation, and to bridge the data gap between satellite missions. We used data from ground-based Global Positioning System (GPS) surveys of an 11 km long track near Summit Station, Greenland, to assess the surface–elevation bias and measurement precision of three airborne laser altimeters including the Airborne Topographic Mapper (ATM), the Land, Vegetation, and Ice Sensor (LVIS), and the Multiple Altimeter Beam Experimental Lidar (MABEL). Ground-based GPS data from the monthly ground-based traverses, which commenced in 2006, allowed for the assessment of nine airborne lidar surveys associated with ATM and LVIS between 2007 and 2016. Surface–elevation biases for these altimeters – over the flat, ice-sheet interior – are less than 0.12 m, while assessments of measurement precision are 0.09 m or better. Ground-based GPS positions determined both with and without differential post-processing techniques provided internally consistent solutions. Results from the analyses of ground-based and airborne data provide validation strategy guidance for the Ice, Cloud, and land Elevation Satellite 2 (ICESat-2) elevation and elevation-change data products.
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Toffoli, A., A. V. Babanin, M. A. Donelan, B. K. Haus y D. Jeong. "Estimating Sea Spray Volume with a Laser Altimeter". Journal of Atmospheric and Oceanic Technology 28, n.º 9 (1 de septiembre de 2011): 1177–83. http://dx.doi.org/10.1175/2011jtecho827.1.
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Abstract Down-looking laser altimeters are commonly used to measure the sea surface elevation. However, because the laser radiation is attenuated by spray droplets suspended along the transmission path, it is presumed that altimeters may also provide an indirect measure of the sea spray volume. Here, this conjecture is discussed by means of laboratory experiments, which have been conducted in a wind-wave flume. A large number of wind conditions were considered between equivalent 10-m wind speeds of 20 and 60 m s−1 in order to generate different spray volumes above the water surface. The facility was equipped with a laser and side-looking camera system to estimate the spray volume as well as a nearby down-looking laser altimeter. Results confirm that there is a robust degradation of the laser intensity for increasing wind speed and hence the amount of spray droplets above the water surface. A simple regression model to extract spray volume from the average intensity of the laser radiation is presented, demonstrating the promise of laser altimeters for making in situ spray observations. Additional observations will be required to calibrate the altimeters for applications in the open ocean marine environment.
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Farrell, Sinéad L., Kelly M. Brunt, Julia M. Ruth, John M. Kuhn, Laurence N. Connor y Kaitlin M. Walsh. "Sea-ice freeboard retrieval using digital photon-counting laser altimetry". Annals of Glaciology 56, n.º 69 (2015): 167–74. http://dx.doi.org/10.3189/2015aog69a686.
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AbstractAirborne and spaceborne altimeters provide measurements of sea-ice elevation, from which sea-ice freeboard and thickness may be derived. Observations of the Arctic ice pack by satellite altimeters indicate a significant decline in ice thickness, and volume, over the last decade. NASA’s Ice, Cloud and land Elevation Satellite-2 (ICESat-2) is a next-generation laser altimeter designed to continue key sea-ice observations through the end of this decade. An airborne simulator for ICESat-2, the Multiple Altimeter Beam Experimental Lidar (MABEL), has been deployed to gather pre-launch data for mission development. We present an analysis of MABEL data gathered over sea ice in the Greenland Sea and assess the capabilities of photon-counting techniques for sea-ice freeboard retrieval. We compare freeboard estimates in the marginal ice zone derived from MABEL photon-counting data with coincident data collected by a conventional airborne laser altimeter. We find that freeboard estimates agree to within 0.03 m in the areas where sea-ice floes were interspersed with wide leads, and to within 0.07 m elsewhere. MABEL data may also be used to infer sea-ice thickness, and when compared with coincident but independent ice thickness estimates, MABEL ice thicknesses agreed to within 0.65 m or better.
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Xie, J., R. Liu, F. Mo, H. Tang, H. Jiao, Y. Mei y C. Yang. "POINTING BIAS CALIBRATION OF GAOFEN-7 LASER ALTIMETER BASED ON SINGLE LASER FOOTPRINT IMAGE". ISPRS Annals of Photogrammetry, Remote Sensing and Spatial Information Sciences V-2-2020 (3 de agosto de 2020): 113–19. http://dx.doi.org/10.5194/isprs-annals-v-2-2020-113-2020.
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Abstract. The GaoFen-7 (GF-7) satellite is successfully launched on November 3, 2019, and its laser altimeter system is officially and firstly employed as the main payload for earth observations in China, which includes two sets of laser altimeters and laser footprint cameras. The Laser Footprint Image (LFI) is used to capture laser spots on the ground. In order to make up for the shortcomings of high cost field work for the traditional laser altimeter ground detector-based calibration method, this paper proposes a novel laser altimeter calibration method based on LFI. Firstly, the spaceborne laser calibration model and the Laser Footprint Camera (LFC) geolocation model are established. Secondly, the image coordinates of laser spot centroid are extracted from LFI, and the ground location of is obtained by ray intersecting with the reference Digital Surface Model (DSM). Finally, the centroid of laser spot is considered as Ground Control Point (GCP), and the pointing bias of GF-7 laser altimeter is calibrated by the Least Squares Estimation (LSE). The ALOS Global Digital Surface Model “ALOS World 3D-30m” (AW3D30) is used to evaluate the elevation accuracy of GF-7 laser altimeter before and after the calibration. The results indicate that elevation accuracy of the GF-7 laser altimeter is improved significantly after calibration. The proposed method can be effectively applied for high-frequency geometric calibration of GF-7 laser altimeter.
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Sun, J., S. P. Burns, D. Vandemark, M. A. Donelan, L. Mahrt, Timothy L. Crawford, T. H. C. Herbers, G. H. Crescenti y J. R. French. "Measurement of Directional Wave Spectra Using Aircraft Laser Altimeters". Journal of Atmospheric and Oceanic Technology 22, n.º 7 (1 de julio de 2005): 869–85. http://dx.doi.org/10.1175/jtech1729.1.
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Abstract A remote sensing method to measure directional oceanic surface waves by three laser altimeters on the NOAA LongEZ aircraft is investigated. To examine feasibility and sensitivity of the wavelet analysis method to various waves, aircraft motions, and aircraft flight directions relative to wave propagation directions, idealized surface waves are simulated from various idealized aircraft flights. In addition, the wavelet analysis method is also applied to two cases from field measurements, and the results are compared with traditional wave spectra from buoys. Since the wavelet analysis method relies on the “wave slopes” measured through phase differences between the time series of the laser distances between the aircraft and sea surface at spatially separated locations, the resolved directional wavenumber and wave propagation direction are not affected by aircraft motions if the resolved frequencies of the aircraft motion and the wave are not the same. However, the encounter wave frequency, which is directly resolved using the laser measurement from the moving aircraft, is affected by the Doppler shift due to aircraft motion relative to wave propagations. The wavelet analysis method could fail if the aircraft flies in the direction such that the aircraft speed along the wave propagation direction is the same as the wave phase speed (i.e., the aircraft flies along wave crests or troughs) or if two waves with different wavelengths and phase speed have the same encountered wavelength from the aircraft. In addition, the data noise due to laser measurement uncertainty or natural isotropic surface elevation perturbations can also affect the relative phase difference between the laser distance measurements, which in turn affects the accuracy of the resolved wavenumber and wave propagation direction. The smallest waves measured by the lasers depend on laser sampling rate and horizontal distances between the lasers (for the LongEZ this is 2 m). The resolved wave direction and wavenumber at the peak wave from the two field experiments compared well with on-site buoy observations. Overall, the study demonstrates that three spatially separated laser altimeters on moving platforms can be utilized to resolve two-dimensional wave spectra.
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Gardner, C. S. "Ranging performance of satellite laser altimeters". IEEE Transactions on Geoscience and Remote Sensing 30, n.º 5 (1992): 1061–72. http://dx.doi.org/10.1109/36.175341.
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Zhang, Yi Fei y Hui Yang. "Design of a Signal Processing System for Digital Laser Altimeter". Applied Mechanics and Materials 333-335 (julio de 2013): 592–96. http://dx.doi.org/10.4028/www.scientific.net/amm.333-335.592.
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Laser altimeters are used to measure the elevation and detect the topography of terrain, which have been widely applied in military and civilian field. In the course of measurement, errors will inevitably generate as a result of ground settlement, surface relief and tilt, etc. In order to reduce measurement errors, the technology of laser waveform digitalization was researched. Firstly, the principle of error generation was introduced. Secondly, the basic scheme of signal processing system for digital laser altimeter was present. System components and signal processing procedure were researched. Next, the technology of extracting echo waveform parameters was discussed. Finally the method of using digital waveform parameters to correct measurement errors was provided. The principle of target classification and identification based on echo waveform parameters was introduced also.
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Kornienko, Yu V., I. A. Dulova y N. V. Bondarenko. "INVOLVEMENT OF ALTIMETRY INFORMATION INTO THE IMPROVED PHOTOCLINOMETRY METHOD FOR RELIEF RETRIEVAL FROM A SLOPE FIELD". Radio physics and radio astronomy 26, n.º 2 (23 de junio de 2021): 173–88. http://dx.doi.org/10.15407/rpra26.02.173.
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Purpose: The paper discusses the possibility for increasing the planet’s surface relief retrieving accuracy with the improved photoclinometry method through the reference of the desired relief to the altimetry data. The general approach to solving the problem is proposed. The use of altimeters having both wide and narrow beam patterns are discussed, but the narrow beam pattern altimeter data is studied more in detail. The spatial resolution of the retrieved relief calculated with the improved photoclinometry method conforms to the one of the source images. Altimetry allows absolute reference to the surface heights and improves the accuracy of the relief determination. Design/metodology/approach: The work is based on the improved photoclinometry method for the planet’s surface relief retrieving from images. This method is mathematically rigorous and uses the Bayesian statistical approach, that allows calculation of the most probable relief according to available observations. Findings: An approach to determining the optimal statistical estimate of the surface heights from images in the frames of the improved photoclinometry method is proposed and an expression for the optimal filter which converts source images along with the wide beam pattern altimetry data into the most probable relief of the planet surface area is presented. The reference technique for the narrow beam pattern altimeter data is formulated. The efficiency of the method has been verified with the computer simulation. The relief of the surface area in Mare Imbrium on the Moon was retrieved using three images and laser altimeter data taken by the “Lunar Reconnaissance Orbiter” spacecraft. Conclusions: Accounting for the narrow beam pattern altimeter data increases the accuracy of the relief determination. Using the narrow beam pattern altimeter data turns out to be more preferable over the involving wide beam pattern altimeter data. Computer simulation has shown that accounting for the narrow beam pattern altimeter data significantly increases the accuracy of the calculated heights as against using images exclusively and helps to speed up the calculation procedure. Key words: planet surface relief; photometry; altimetry; optimal filtering; statistical estimation of random value
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Levinsen, J. F., I. M. Howat y C. C. Tscherning. "Improving maps of ice-sheet surface elevation change using combined laser altimeter and stereoscopic elevation model data". Journal of Glaciology 59, n.º 215 (2013): 524–32. http://dx.doi.org/10.3189/2013jog12j114.
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AbstractWe combine the complementary characteristics of laser altimeter data and stereoscopic digital elevation models (DEMs) to construct high-resolution (∼100 m) maps of surface elevations and elevation changes over rapidly changing outlet glaciers in Greenland. Measurements from spaceborne and airborne laser altimeters have relatively low errors but are spatially limited to the ground tracks, while DEMs have larger errors but provide spatially continuous surfaces. The principle of our method is to fit the DEM surface to the altimeter point clouds in time and space to minimize the DEM errors and use that surface to extrapolate elevations away from altimeter flight lines. This reduces the DEM registration errors and fills the gap between the altimeter paths. We use data from ICESat and ATM as well as SPOT 5 DEMs from 2007 and 2008 and apply them to the outlet glaciers Jakobshavn Isbræ (JI) and Kangerdlugssuaq (KL). We find that the main trunks of JI and KL lowered at rates of 30–35 and 7–20 m a−1,respectively. The rates decreased inland. The corresponding errors were 0.3–5.2 m a−1for JI and 0.3–5.1 m a−1for KL, with errors increasing proportionally with distance from the altimeter paths.
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Quartly, Graham D., Eero Rinne, Marcello Passaro, Ole B. Andersen, Salvatore Dinardo, Sara Fleury, Amandine Guillot et al. "Retrieving Sea Level and Freeboard in the Arctic: A Review of Current Radar Altimetry Methodologies and Future Perspectives". Remote Sensing 11, n.º 7 (11 de abril de 2019): 881. http://dx.doi.org/10.3390/rs11070881.
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Spaceborne radar altimeters record echo waveforms over all Earth surfaces, but their interpretation and quantitative exploitation over the Arctic Ocean is particularly challenging. Radar returns may be from all ocean, all sea ice, or a mixture of the two, so the first task is the determination of which surface and then an interpretation of the signal to give range. Subsequently, corrections have to be applied for various surface and atmospheric effects before making a comparison with a reference level. This paper discusses the drivers for improved altimetry in the Arctic and then reviews the various approaches that have been used to achieve the initial classification and subsequent retracking over these diverse surfaces, showing examples from both LRM (low resolution mode) and SAR (synthetic aperture radar) altimeters. The review then discusses the issues concerning corrections, including the choices between using other remote-sensing measurements and using those from models or climatology. The paper finishes with some perspectives on future developments, incorporating secondary frequency, interferometric SAR and opportunities for fusion with measurements from laser altimetry or from the SMOS salinity sensor, and provides a full list of relevant abbreviations.
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RITCHIE, JERRY C. "Remote sensing applications to hydrology: airborne laser altimeters". Hydrological Sciences Journal 41, n.º 4 (agosto de 1996): 625–36. http://dx.doi.org/10.1080/02626669609491529.
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Sun, X., F. M. Davidson, L. Boutsikaris y J. B. Abshire. "Receiver characteristics of laser altimeters with avalanche photodiodes". IEEE Transactions on Aerospace and Electronic Systems 28, n.º 1 (1992): 268–75. http://dx.doi.org/10.1109/7.135452.
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Brunt, Kelly M., Thomas A. Neumann y Christopher F. Larsen. "Assessment of altimetry using ground-based GPS data from the 88S Traverse, Antarctica, in support of ICESat-2". Cryosphere 13, n.º 2 (18 de febrero de 2019): 579–90. http://dx.doi.org/10.5194/tc-13-579-2019.
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Abstract. We conducted a 750 km kinematic GPS survey, referred to as the 88S Traverse, based out of South Pole Station, Antarctica, between December 2017 and January 2018. This ground-based survey was designed to validate spaceborne altimetry and airborne altimetry developed at NASA. The 88S Traverse intersects 20 % of the ICESat-2 satellite orbits on a route that has been flown by two different Operation IceBridge airborne laser altimeters: the Airborne Topographic Mapper (ATM; 26 October 2014) and the University of Alaska Fairbanks (UAF) Lidar (30 November and 3 December 2017). Here we present an overview of the ground-based GPS data quality and a quantitative assessment of the airborne laser altimetry over a flat section of the ice sheet interior. Results indicate that the GPS data are internally consistent (1.1±4.1 cm). Relative to the ground-based 88S Traverse data, the elevation biases for ATM and the UAF lidar range from −9.5 to 3.6 cm, while surface measurement precisions are equal to or better than 14.1 cm. These results suggest that the ground-based GPS data and airborne altimetry data are appropriate for the validation of ICESat-2 surface elevation data.
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Vandemark, D., B. Chapron, J. Sun, G. H. Crescenti y H. C. Graber. "Ocean Wave Slope Observations Using Radar Backscatter and Laser Altimeters". Journal of Physical Oceanography 34, n.º 12 (1 de diciembre de 2004): 2825–42. http://dx.doi.org/10.1175/jpo2663.1.
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Abstract Combination of laser and radar aboard an aircraft is used to directly measure long gravity wave surface tilting simultaneously with nadir-viewing microwave backscatter from the sea surface. The presented dataset is extensive, encompassing varied wind conditions over coastal and open-ocean wave regimes. Laser-derived slope statistics and Ka-band (36 GHz) radar backscatter are detailed separately to document their respective variations versus near-surface wind speed. The slope statistics, measured for λ > 1–2 m, show good agreement with Cox and Munk's oil-slickened sea measurements. A notable exception is elevated distribution peakedness and an observed wind dependence in this likely proxy for nonlinear wave–wave interactions. Aircraft Ka-band radar data nearly mimic Ku-band satellite altimeter observations in their mean wind dependence. The present calibrated radar data, along with relevant observational and theoretical studies, suggest a large (−5 dB) bias in previous Ka-band results. Next, wave-diverse inland, coastal, and open-ocean observations are contrasted to show wind-independent long-wave slope variance changes of a factor of 2–3, always increasing as one heads to sea. Combined long-wave and radar data demonstrate that this long-wave tilt field variability is largely responsible for radar backscatter variations observed at a given wind speed, particularly at wind speeds below 5–7 m s−1. Results are consistent with, and provide quantititative support for, recent satellite altimeter studies eliciting signatures of long-wave impacts resident in the radar backscatter. Under a quasi-optical scattering assumption, the results illustrate long-wave control on the variance of the total mean square slope parameter due to changes in the directional long-wave spectrum, with high-wavenumbers being relatively unaffected in a mean sense. However, further analysis suggests that for winds above 7 m s−1 the high-wavenumber subrange also varies with change in the longer wave field slope and/or energy, the short gravity wave roughness being measurably greater for smoother seas.
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Li, Shaoning, Chaokui Li, Guo Zhang y Yanan Wang. "Geometric calibration of satellite laser altimeters based on waveform matching". Photogrammetric Record 36, n.º 174 (7 de mayo de 2021): 104–23. http://dx.doi.org/10.1111/phor.12362.
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Farrell, Sinéad L., Thorsten Markus, Ron Kwok y Laurence Connor. "Laser altimetry sampling strategies over sea ice". Annals of Glaciology 52, n.º 57 (2011): 69–76. http://dx.doi.org/10.3189/172756411795931660.
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AbstractWith the conclusion of the science phase of the Ice, Cloud and land Elevation Satellite (ICESat) mission in late 2009, and the planned launch of ICESat-2 in late 2015, NASA has recently established the IceBridge program to provide continuity between missions. A major goal of IceBridge is to obtain a sea-ice thickness time series via airborne surveys over the Arctic and Southern Oceans. Typically two laser altimeters, the Airborne Topographic Mapper (ATM) and the Land, Vegetation and Ice Sensor (LVIS), are utilized during IceBridge flights. Using laser altimetry simulations of conventional analogue systems such as ICESat, LVIS and ATM, with the multi-beam system proposed for ICESat-2, we investigate differences in measurements gathered at varying spatial resolutions and the impact on sea-ice freeboard. We assess the ability of each system to reproduce the elevation distributions of two sea-ice models and discuss potential biases in lead detection and sea-surface elevation, arising from variable footprint size and spacing. The conventional systems accurately reproduce mean freeboard over 25 km length scales, while ICESat-2 offers considerable improvements over its predecessor ICESat. In particular, its dense along-track sampling of the surface will allow flexibility in the algorithmic approaches taken to optimize the signal-to-noise ratio for accurate and precise freeboard retrieval.
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Yi Hong, Li Song, Ma Yue, Huang Ke, Zhou Hui y Shi Guang-Yuan. "On-orbit calibration of satellite laser altimeters based on footprint detection". Acta Physica Sinica 66, n.º 13 (2017): 134206. http://dx.doi.org/10.7498/aps.66.134206.
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Filin, S. "Calibration of spaceborne laser Altimeters-an algorithm and the site selection problem". IEEE Transactions on Geoscience and Remote Sensing 44, n.º 6 (junio de 2006): 1484–92. http://dx.doi.org/10.1109/tgrs.2005.863295.
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Bierlich, KC, RS Schick, J. Hewitt, J. Dale, JA Goldbogen, AS Friedlaender y DW Johnston. "Bayesian approach for predicting photogrammetric uncertainty in morphometric measurements derived from drones". Marine Ecology Progress Series 673 (2 de septiembre de 2021): 193–210. http://dx.doi.org/10.3354/meps13814.
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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.
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van Tiggelen, Maurice, Paul C. J. P. Smeets, Carleen H. Reijmer, Bert Wouters, Jakob F. Steiner, Emile J. Nieuwstraten, Walter W. Immerzeel y Michiel R. van den Broeke. "Mapping the aerodynamic roughness of the Greenland Ice Sheet surface using ICESat-2: evaluation over the K-transect". Cryosphere 15, n.º 6 (11 de junio de 2021): 2601–21. http://dx.doi.org/10.5194/tc-15-2601-2021.
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Abstract. The aerodynamic roughness of heat, moisture, and momentum of a natural surface are important parameters in atmospheric models, as they co-determine the intensity of turbulent transfer between the atmosphere and the surface. Unfortunately this parameter is often poorly known, especially in remote areas where neither high-resolution elevation models nor eddy-covariance measurements are available. In this study we adapt a bulk drag partitioning model to estimate the aerodynamic roughness length (z0m) such that it can be applied to 1D (i.e. unidirectional) elevation profiles, typically measured by laser altimeters. We apply the model to a rough ice surface on the K-transect (west Greenland Ice Sheet) using UAV photogrammetry, and we evaluate the modelled roughness against in situ eddy-covariance observations. We then present a method to estimate the topography at 1 m horizontal resolution using the ICESat-2 satellite laser altimeter, and we demonstrate the high precision of the satellite elevation profiles against UAV photogrammetry. The currently available satellite profiles are used to map the aerodynamic roughness during different time periods along the K-transect, that is compared to an extensive dataset of in situ observations. We find a considerable spatio-temporal variability in z0m, ranging between 10−4 m for a smooth snow surface and 10−1 m for rough crevassed areas, which confirms the need to incorporate a variable aerodynamic roughness in atmospheric models over ice sheets.
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Singh, Bharat Raj y Onkar Singh. "Global Trend of Glacier Melting or Growing and its Impact on Heavy Storms". SAMRIDDHI : A Journal of Physical Sciences, Engineering and Technology 8, n.º 01 (25 de junio de 2016): 43–55. http://dx.doi.org/10.18090/samriddhi.v8i1.11411.
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Scientists calculate how much the ice sheet is growing or shrinking from the changes in surface height that are measured by the satellite altimeters. In locations where the amount of new snowfall accumulating on an ice sheet is not equal to the ice flow downward and outward to the ocean, the surface height changes and the ice-sheet mass grows or shrinks. But it might only take a few decades for Antarctica’s growth to reverse, according to Zwally. If the losses of the Antarctic Peninsula and parts of West Antarctica continue to increase at the same rate they’ve been increasing for the last two decades, the losses will catch up with the long-term gain in East Antarctica in 20 or 30 years and it is questionable whether there will be enough snowfall increase to offset these losses. The study analyzed changes in the surface height of the Antarctic ice sheet measured by radar altimeters on two European Space Agency European Remote Sensing (ERS) satellites, spanning from 1992 to 2001, and by the laser altimeter on NASA’s Ice, Cloud, and land Elevation Satellite (ICESat) from 2003 to 2008. The good news is that Antarctica is not currently contributing to sea level rise, but is taking 0.23 millimeters per year away. But, this is also bad news. If the 0.27 millimeters per year of sea level rise attributed to Antarctica in the IPCC report is not really coming from Antarctica, there must be some other contribution to sea level rise that is not accounted for. On other hand, globally every country is facing heavy storm, disastrous rain fall and variance in Climate Change, causing greater loss in production of food grain, disruption of smooth living and development and enhancement of hazardous deceases on account of Global Warming and Climatic Changes. This paper focuses on the current issues and its remedial efforts to be made essentially to curb these issues and save human life and beautiful creatures on the globe.
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Levinsen, J. F., K. Khvorostovsky, F. Ticconi, A. Shepherd, R. Forsberg, L. S. Sørensen, A. Muir et al. "ESA's Ice Sheets CCI: validation and inter-comparison of surface elevation changes derived from laser and radar altimetry over Jakobshavn Isbræ, Greenland – Round Robin results". Cryosphere Discussions 7, n.º 6 (15 de noviembre de 2013): 5433–60. http://dx.doi.org/10.5194/tcd-7-5433-2013.
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Abstract. In order to increase the understanding of the changing climate, the European Space Agency has launched the Climate Change Initiative (ESA CCI), a program which joins scientists and space agencies into 13 projects either affecting or affected by the concurrent changes. This work is part of the Ice Sheets CCI and four parameters are to be determined for the Greenland Ice Sheet (GrIS), each resulting in a dataset made available to the public: Surface Elevation Changes (SEC), surface velocities, grounding line locations, and calving front locations. All CCI projects have completed a so-called Round Robin exercise in which the scientific community was asked to provide their best estimate of the sought parameters as well as a feedback sheet describing their work. By inter-comparing and validating the results, obtained from research institutions world-wide, it is possible to develop the most optimal method for determining each parameter. This work describes the SEC Round Robin and the subsequent conclusions leading to the creation of a method for determining GrIS SEC values. The participants used either Envisat radar or ICESat laser altimetry over Jakobshavn Isbræ drainage basin, and the submissions led to inter-comparisons of radar vs. altimetry as well as cross-over vs. repeat-track analyses. Due to the high accuracy of the former and the high spatial resolution of the latter, a method, which combines the two techniques will provide the most accurate SEC estimates. The data supporting the final GrIS analysis stem from the radar altimeters on-board Envisat, ERS-1 and ERS-2. The accuracy of laser data exceeds that of radar altimetry; the Round Robin analysis has, however, proven the latter equally capable of dealing with surface topography thereby making such data applicable in SEC analyses extending all the way from the interior ice sheet to margin regions. This shows good potential for a~future inclusion of ESA CryoSat-2 and Sentinel-3 radar data in the analysis, and thus for obtaining reliable SEC estimates throughout the entire GrIS.
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Reineman, Benjamin D., Luc Lenain, Nicholas M. Statom y 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.º 7 (1 de julio de 2013): 1295–319. http://dx.doi.org/10.1175/jtech-d-12-00176.1.
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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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Bilous, A. M., P. P. Diachuk, R. M. Zadorozhniuk, M. S. Matsala y M. M. Burianchuk. "Accuracy of selected methods of measurement of tree heights". Ukrainian Journal of Forest and Wood Science 12, n.º 1 (31 de marzo de 2021): 6–16. http://dx.doi.org/10.31548/forest2021.01.001.
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In this paper, the possibilities of using stereophotogrammetry methods for measurements using unmanned aerial vehicles (UAVs) for the conditions of a mature pine stand with uneven density are examined. Here, we carried out a comparison of measurements using altimeters and remote sensing data collected with a UAV optical camera. In particular, the height of growing trees was estimated by three different field-based devices and applying the three methods of data collection and processing with UAVs. Specifically, one method implied the direct measurements using on-board UAV equipment. The following two methods are based on the data provided by the stereophotogrammetrical approach, while the aerial images for that were collected using a UAV optical camera. In particular, there was a modeling of the points cloud from one-sided vertical shooting of sample trees and determination of height of trees from digital canopy height model (CHM) from data of aerial photography of horizontal spans over a stand. Our investigation confirmed the highest accuracy of laser measuring tools among the ground measuring devices used in research. Respective value of the average random measurement error was less than 3 % (0.88 m). Among the results obtained from the analysis of the original data collected by UAVs, the best method was to utilize the CHM, namely, the average random error was less than 2% (0.64 m). This exceeds the accuracy of laser altimeter measurements 33 %. Thus, this method of measuring height in pine stands meets the standards of accuracy in determining the height for production assessment, according to the “Inventory guidelines for the forest fund of Ukraine”, and can be used for survey, inventory, forest management and other works related to forestry and monitoring the changes in forest ecosystems.
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Massom, Robert. "Satellite remote sensing of polar snow and ice: present status and future directions". Polar Record 31, n.º 177 (abril de 1995): 99–114. http://dx.doi.org/10.1017/s0032247400013607.
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AbstractPolar snow and ice masses exert a profound influence on global climate and ocean circulation, and are in turn influenced by climate. Satellite remote sensing constitutes the only practical and systematic means of gaining long-term overviews of any change or variability that may be occurring in key snow and ice parameters. Current relevant satellite sensors are reviewed and future developments evaluated to determine how these may lead to improved retrievals of the key parameters. Sensors to be launched on satellite platforms planned for the end of the century and beyond include both improved versions of existing sensors (such as MODIS) and new classes of sensors (such as imaging spectrometers and laser rangers/altimeters) applied to polar remote sensing for the first time.
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Li, G., X. Tang, X. Gao, J. P. Huang, J. Chen y J. Lu. "POINTING ANGLE CALIBRATION OF ZY3-02 SATELLITE LASER ALTIMETER USING TERRAIN MATCHING". ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-1/W1 (31 de mayo de 2017): 205–10. http://dx.doi.org/10.5194/isprs-archives-xlii-1-w1-205-2017.
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After GLAS (Geo-science Laser Altimeter System) loaded on the ICESat (Ice Cloud and land Elevation Satellite), satellite laser altimeter attracts more and more attention. ZY3-02 equipped with the Chinese first satellite laser altimeter has been successfully launched on 30<sup>th</sup> May, 2016. The geometric calibration is an important step for the laser data processing and application. The method to calculate the laser pointing angle error based on existed reference terrain data is proposed in this paper. The public version terrain data, such as 90m-SRTM and 30m-AW3D30, can be used to estimate the pointing angle of laser altimeter. The GLAS data with simulated pointing error and actual ZY3-02 laser altimetry data is experimented to validate the algorithm. The conclusion will be useful for the future domestic satellite laser altimeter.
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Li, G., J. Guo, X. Tang, F. Ye, Z. Zuo, Z. Liu, J. Chen y Y. Xue. "PRELIMINARY QUALITY ANALYSIS OF GF-7 SATELLITE LASER ALTIMETER FULL WAVEFORM DATA". ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLIII-B1-2020 (6 de agosto de 2020): 129–34. http://dx.doi.org/10.5194/isprs-archives-xliii-b1-2020-129-2020.
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Abstract. The full-waveform data is the core data of GaoFen-7 (GF-7) satellite laser altimeter, and evaluation of waveform data quality is an important step and premise for satellite laser altimetry and quality control. In this paper, the full waveform data quality assessment and analysis of GF-7 laser altimeter is implemented during the period of on-orbit experiment, and the real waveform data of many orbits is used to quantitatively describe the characteristic parameters of the transmitted waveform and the signal-to-noise ratio (SNR), and the result of two beam lasers is compared. The conclusion is validated that the GF-7 laser altimeter can obtain effective waveform data and the echo waveform availability of the experimental data is approximate 72.59%, moreover, the quality of beam 1 is slightly better than that of the beam 2. The laser temperature is an important indication of the quality of transmitted waveform according to the SNR changing. The good SNR value of the waveform and small footprint size will be helpful for the terrain information extraction and analysis, although the repetition frequency is low.
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Krieger, Lukas, Undine Strößenreuther, Veit Helm, Dana Floricioiu y Martin Horwath. "Synergistic Use of Single-Pass Interferometry and Radar Altimetry to Measure Mass Loss of NEGIS Outlet Glaciers between 2011 and 2014". Remote Sensing 12, n.º 6 (19 de marzo de 2020): 996. http://dx.doi.org/10.3390/rs12060996.
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Mass balances of individual glaciers on ice sheets have been previously reported by forming a mass budget of discharged ice and modelled ice sheet surface mass balance or a complementary method which measures volume changes over the glaciated area that are subsequently converted to glacier mass change. On ice sheets, volume changes have been measured predominantly with radar and laser altimeters but InSAR DEM differencing has also been applied on smaller ice bodies. Here, we report for the first time on the synergistic use of volumetric measurements from the CryoSat-2 radar altimetry mission together with TanDEM-X DEM differencing and calculate the mass balance of the two major outlet glaciers of the Northeast Greenland Ice Stream: Zachariæ Isstrøm and Nioghalvfjerdsfjorden (79North). The glaciers lost 3.59 ± 1.15 G t a − 1 and 1.01 ± 0.95 G t a − 1 , respectively, between January 2011 and January 2014. Additionally, there has been substantial sub-aqueous mass loss on Zachariæ Isstrøm of more than 11 G t a − 1 . We attribute the mass changes on both glaciers to dynamic downwasting. The presented methodology now permits using TanDEM-X bistatic InSAR data in the context of geodetic mass balance investigations for large ice sheet outlet glaciers. In the future, this will allow monitoring the mass changes of dynamic outlet glaciers with high spatial resolution while the superior vertical accuracy of CryoSat-2 can be used for the vast accumulation zones in the ice sheet interior.
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Zhang, Zhiyu, Nan Xu, Yue Ma, Xinyuan Liu, Wenhao Zhang y Song Li. "Land and snow-covered area classification method based on the background noise for satellite photon-counting laser altimeters". Optics Express 28, n.º 11 (13 de mayo de 2020): 16030. http://dx.doi.org/10.1364/oe.392904.
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Legkiĭ, V. N., S. A. Litvinenko, I. Yu Balasov, A. O. Bashmakov, O. V. Sankov, B. V. Galun y V. A. Shumeĭko. "Construction principles of noise-suppressing miniature laser pulse rangefinders, altimeters, and sensors for on-board and transport systems". Journal of Optical Technology 78, n.º 5 (31 de mayo de 2011): 332. http://dx.doi.org/10.1364/jot.78.000332.
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Li, Binbin, Huan Xie, Xiaohua Tong, Yinqiao Cai y Zhijie Zhang. "Research on the Control Point Extraction Method of Chinese Gaofen 7 Satellite Using Altimeter and Footprint Camera". EPJ Web of Conferences 237 (2020): 01016. http://dx.doi.org/10.1051/epjconf/202023701016.
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Satellite laser altimetry is one of the most advanced information acquisition technologies in Earth observation system. It can provide high-accuracy elevation information, however, due to the lack of detail intensity information, its planimetric accuracy is usually worse than the elevation accuracy. Gaofen 7 (GF-7) satellite scheduled for launch in 2019 will be equipped with laser altimeter, footprint camera, stereo mapping camera, etc. The laser altimeter together with the footprint camera was designed to provide high accuracy ground control point of satellite mapping. The laser altimeter can provide the high-accuracy elevation information and the joint processing of footprint camera and stereo mapping camera can provide high-accuracy planimetric information. Therefore, this paper mainly studies the technology of extracting high-accuracy control points based on GF-7 satellite’s altimeter, footprint camera and stereo mapping camera using a simulated dataset extracted from Quickbird image and ICESat altimetric data.
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Weissling, B. P. y S. F. Ackley. "Antarctic sea-ice altimetry: scale and resolution effects on derived ice thickness distribution". Annals of Glaciology 52, n.º 57 (2011): 225–32. http://dx.doi.org/10.3189/172756411795931679.
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AbstractThree ice type regimes at Ice Station Belgica (ISB), during the 2007 International Polar Year SIMBA (Sea Ice Mass Balance in Antarctica) expedition, were characterized and assessed for elevation, snow depth, ice freeboard and thickness. Analyses of the probability distribution functions showed great potential for satellite-based altimetry for estimating ice thickness. In question is the required altimeter sampling density for reasonably accurate estimation of snow surface elevation given inherent spatial averaging. This study assesses an effort to determine the number of laser altimeter ‘hits’ of the ISB floe, as a representative Antarctic floe of mixed first- and multi-year ice types, for the purpose of statistically recreating the in situ-determined ice-thickness and snow depth distribution based on the fractional coverage of each ice type. Estimates of the fractional coverage and spatial distribution of the ice types, referred to as ice ‘towns’, for the 5 km2 floe were assessed by in situ mapping and photo-visual documentation. Simulated ICESat altimeter tracks, with spot size ~70m and spacing ~170 m, sampled the floe’s towns, generating a buoyancy-derived ice thickness distribution. 115 altimeter hits were required to statistically recreate the regional thickness mean and distribution for a three-town assemblage of mixed first- and multi-year ice, and 85 hits for a two-town assemblage of first-year ice only: equivalent to 19.5 and 14.5 km respectively of continuous altimeter track over a floe region of similar structure. Results have significant implications toward model development of sea-ice sampling performance of the ICESat laser altimeter record as well as maximizing sampling characteristics of satellite/airborne laser and radar altimetry missions for sea-ice thickness.
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Lacroix, P., B. Legrésy, K. Langley, S. E. Hamran, J. Kohler, S. Roques, F. Rémy y M. Dechambre. "In situ measurements of snow surface roughness using a laser profiler". Journal of Glaciology 54, n.º 187 (2008): 753–62. http://dx.doi.org/10.3189/002214308786570863.
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AbstractThe snow surface roughness at centimetre and millimetre scales is an important parameter related to wind transport, snowdrifts, snowfall, snowmelt and snow grain size. Knowledge of the snow surface roughness is also of high interest for analyzing the signal from radar sensors such as SAR, altimeters and scatterometers. Unfortunately, this parameter has seldom been measured over snow surfaces. The techniques used to measure the roughness of other surfaces, such as agricultural or sand soils, are difficult to implement in polar regions because of the harsh climatic conditions. In this paper we develop a device based on a laser profiler coupled with a GPS receiver on board a snowmobile. This instrumentation was tested successfully in midre Lovénbreen, Svalbard, in April 2006. It allowed us to generate profiles of 3 km sections of the snow-covered glacier surface. Because of the motion of the snowmobile, the roughness signal is mixed with the snowmobile signal. We use a distance/frequency analysis (the empirical mode decomposition) to filter the signal. This method allows us to recover the snow surface structures of wavelengths between 4 and 50 cm with amplitudes of >1 mm. Finally, the roughness parameters of snow surfaces are retrieved. The snow surface roughness is found to be dependent on the scales of the observations. The retrieved RMS of the height distribution is found to vary between 0.5 and 9.2 mm, and the correlation length is found to be between 0.6 and 46 cm. This range of measurements is particularly well adapted to the analysis of GHz radar response on snow surfaces.
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Filin, Sagi y Beáta Csathó. "Improvement of elevation accuracy for mass-balance monitoring using in-flight laser calibration". Annals of Glaciology 34 (2002): 330–34. http://dx.doi.org/10.3189/172756402781817563.
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AbstractTo exploit the high accuracy potential of laser ranging, suitable laser-altimeter calibration procedures combining laboratory and in-flight calibration steps are needed. Previous calibration schemes have limited the calibration process to flying over planar surfaces, and systematic errors remained in the system. In this paper we present a laser calibration algorithm that utilizes natural surfaces as calibration sites. This is especially important for calibrating systems in the interior of ice sheets. The proposed approach is demonstrated in calibrating the U.S. National Science Foundation Support Office for Aerogeophysical Research laser altimetry system. The results show a significant improvement in accuracy.
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Wang, Y., J. Fang y Y. Ai. "SPACE-BORNE LASER ALTIMETER GEOLOCATION ERROR ANALYSIS". ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-2 (30 de mayo de 2018): 1169–74. http://dx.doi.org/10.5194/isprs-archives-xlii-2-1169-2018.
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This paper reviews the development of space-borne laser altimetry technology over the past 40 years. Taking the ICESAT satellite as an example, a rigorous space-borne laser altimeter geolocation model is studied, and an error propagation equation is derived. The influence of the main error sources, such as the platform positioning error, attitude measurement error, pointing angle measurement error and range measurement error, on the geolocation accuracy of the laser spot are analysed by simulated experiments. The reasons for the different influences on geolocation accuracy in different directions are discussed, and to satisfy the accuracy of the laser control point, a design index for each error source is put forward.
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Zhou, M., L. S. Chen, J. H. Wang, G. E. Teng, C. R. Li, Q. Q. Yao y J. Y. Chen. "ANALYSIS OF INFLUENCING FACTORS OF CURVE MATCHING BASED GEOMETRIC CALIBRATION FOR ZY3-02 ALTIMETER DATA". ISPRS Annals of Photogrammetry, Remote Sensing and Spatial Information Sciences IV-2/W7 (16 de septiembre de 2019): 221–26. http://dx.doi.org/10.5194/isprs-annals-iv-2-w7-221-2019.
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<p><strong>Abstract.</strong> High-precision on-orbit geometric calibration of spaceborne laser altimetry data is essential to its effective applications. Firstly, the existing calibration methods for laser altimeter data are analyzed. Then, a geometric calibration method based on curve matching is proposed. Compared to the existing methods, the proposed method does not rely on ground calibration field. Thus, it is efficiency in expense and time. Notably, three factors, i.e. matching method, initial control point selection and the step size of matching step, which significantly affect the results of calibration are analyzed respectively. The analysis was validated based on the original laser altimetry data obtained by ZY3-02 satellite. According to the results, the following conclusions can be drawn preliminarily: (1) Both the correlation coefficient maximum (COR) criterion and the mean square error minimum (MSD) criterion in the curve matching can be used to correct the systematic error in altimetry data. (2) The initial control points of the selected track should have a significant change trend and the slope within the laser footprints should be less than 15&deg;. (3) Current experimental data show that the best step size for matching search is 10&thinsp;m. The relevant conclusions can provide reference for the research of geometrical calibration and data processing of the same type of laser altimetry satellite.</p>
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Zuo, Zhiqiang, Xinming Tang, Guoyuan Li, Yue Ma, Wenhao Zhang y Song Li. "Inversion of Terrain Slope and Roughness with Satellite Laser Altimeter Full-Waveform Data Assisted by Shuttle Radar Topographic Mission". Remote Sensing 13, n.º 3 (26 de enero de 2021): 424. http://dx.doi.org/10.3390/rs13030424.
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Slope and roughness are basic geophysical properties of terrain surface, and also sources of error in satellite laser altimetry systems. The full-waveform satellite laser altimeter records the complete echo waveform backscattered from the target surface worldwide, so it may be used for both range measurement and inversion analysis of geometric parameters of the target surface. This paper proposes a new method for inversion of slope and roughness of the bare or near-bare terrain within laser footprint using full-waveform satellite laser altimeter data, Shuttle Radar Topographic Mission (SRTM) and topographic prior knowledge. To solve the non-uniqueness of the solution to the inversion problem, this paper used the SRTM and airborne Light Detection and Ranging (LiDAR) data in North Rhine-Westphalia, Germany, to establish a priori hypothesis about real information of topographic parameters. Then, under the constraints of prior hypothesis, the theoretical formulas and rules for slope and roughness inversion using the pulse-width broadening knowledge of satellite laser altimeter echo full-waveform were developed. Finally, based on the full-waveform data from the Geoscience Laser Altimeter System (GLAS) that was borne on ICE, Cloud, and Land Elevation Satellite (ICESat) and SRTM in the West Valley City, Utah and Jackson City, Wyoming, United States of America, the inversion was carried out. The experiment compares the results of proposed method with those of existing ones and evaluates the inversion results using high precision terrain slope and roughness information, which indicates that our proposed method is superior to the state-of-the-art methods, and the inversion accuracy for slope is 0.667° (Mean Absolute Error, MAE) and 1.054° (Root Mean Square Error, RMSE), the inversion accuracy for roughness is 0.171 m (MAE) and 0.250 m (RMSE).
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Chen, Jian Ping, Hong Li Liu y Min Guo. "The High Resolution Lunar Planet DEM Based on the Altimetry Data of 400-Circle CE-1 Laser Altimeter (2B)". Applied Mechanics and Materials 142 (noviembre de 2011): 28–31. http://dx.doi.org/10.4028/www.scientific.net/amm.142.28.
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Recent years, considering the decreasing amount of nature resource on Earth, It’s very important to expand the field of scientific research, and to develop new resources. Based on 400 rail CE-1 laser altimeter altimetry data (2B data), to process the data, delete the singular of data, and import the remaining data into ERDAS IMAGINE9.1 generating lunar planet DEM. Its spatial resolution is more accurate than the existing model of the lunar DEM.
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Steinbrügge, G., A. Stark, H. Hussmann, F. Sohl y J. Oberst. "Measuring tidal deformations by laser altimetry. A performance model for the Ganymede Laser Altimeter". Planetary and Space Science 117 (noviembre de 2015): 184–91. http://dx.doi.org/10.1016/j.pss.2015.06.013.
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Yuan, Cui, Peng Gong y Yuqi Bai. "Performance Assessment of ICESat-2 Laser Altimeter Data for Water-Level Measurement over Lakes and Reservoirs in China". Remote Sensing 12, n.º 5 (28 de febrero de 2020): 770. http://dx.doi.org/10.3390/rs12050770.
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Although the Advanced Topographic Laser Altimeter System (ATLAS) onboard the Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) was primarily designed for glacier and sea-ice measurement, it can also be applied to monitor lake surface height (LSH). However, its performance in monitoring lakes/reservoirs has rarely been assessed. Here, we report an accuracy evaluation of the ICESat-2 laser altimetry data over 30 reservoirs in China using gauge data. To show its characteristics in large-scale lake monitoring, we also applied an advanced radar altimeter SARAL (Satellite for ARgos and ALtika) and the first laser altimeter ICESat (Ice, Cloud and land Elevation Satellite) to investigate all lakes and reservoirs (>10 km2) in China. We found that the ICESat-2 has a greatly improved altimetric capability, and the relative altimetric error was 0.06 m, while the relative altimetric error was 0.25 m for SARAL. Compared with SARAL and ICESat data, ICESat-2 data had the lowest measurement uncertainty (the standard deviation of along-track heights; 0.02 m vs. 0.17 m and 0.07 m), the greatest temporal frequency (3.43 vs. 1.35 and 1.48 times per year), and the second greatest lake coverage (636 vs. 814 and 311 lakes). The precise LSH profiles derived from the ICESat-2 data showed that most lakes (90% of 636 lakes) had a quasi-horizontal LSH profile (measurement uncertainty <0.05 m), and special methods are needed for mountainous lakes or shallow lakes to extract precise LSHs.
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Slater, Thomas, Andrew Shepherd, Malcolm McMillan, Alan Muir, Lin Gilbert, Anna E. Hogg, Hannes Konrad y Tommaso Parrinello. "A new digital elevation model of Antarctica derived from CryoSat-2 altimetry". Cryosphere 12, n.º 4 (2 de mayo de 2018): 1551–62. http://dx.doi.org/10.5194/tc-12-1551-2018.
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Abstract. We present a new digital elevation model (DEM) of the Antarctic ice sheet and ice shelves based on 2.5×108 observations recorded by the CryoSat-2 satellite radar altimeter between July 2010 and July 2016. The DEM is formed from spatio-temporal fits to elevation measurements accumulated within 1, 2, and 5 km grid cells, and is posted at the modal resolution of 1 km. Altogether, 94 % of the grounded ice sheet and 98 % of the floating ice shelves are observed, and the remaining grid cells north of 88∘ S are interpolated using ordinary kriging. The median and root mean square difference between the DEM and 2.3×107 airborne laser altimeter measurements acquired during NASA Operation IceBridge campaigns are −0.30 and 13.50 m, respectively. The DEM uncertainty rises in regions of high slope, especially where elevation measurements were acquired in low-resolution mode; taking this into account, we estimate the average accuracy to be 9.5 m – a value that is comparable to or better than that of other models derived from satellite radar and laser altimetry.
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Münchow, Andreas, Laurie Padman y Helen A. Fricker. "Interannual changes of the floating ice shelf of Petermann Gletscher, North Greenland, from 2000 to 2012". Journal of Glaciology 60, n.º 221 (2014): 489–99. http://dx.doi.org/10.3189/2014jog13j135.
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AbstractPetermann Gletscher, northwest Greenland, drains 4% of the Greenland ice sheet into Nares Strait. Its floating ice shelf retreated from 81 to 48 km in length during two large calving events in 2010 and 2012. We document changes in the three-dimensional ice-shelf structure from 2000 to 2012, using repeated tracks of airborne laser altimetry and ice radio-echo sounding, ICESat laser altimetry and MODIS visible imagery. The recent ice-shelf velocity, measured by tracking surface features between flights in 2010 and 2011, is ~1.25 km a−1, ~15–30% faster than estimates made before 2010. The steady- state along-flow ice divergence represents 6.3 Gta−1 mass loss through basal melting (~5Gta−1) and surface melting and sublimation (~1.0Gta−1). Airborne laser altimeter data reveal thinning, both along a thin central channel and on the thicker ambient ice shelf. From 2007 to 2010 the ice shelf thinned by ~5 m a−1, which represents a non-steady mass loss of ~4.1 Gta−1. We suggest that thinning in the basal channels structurally weakened the ice shelf and may have played a role in the recent calving events.
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Bavle, Hriday, Jose Sanchez-Lopez, Paloma Puente, Alejandro Rodriguez-Ramos, Carlos Sampedro y Pascual Campoy. "Fast and Robust Flight Altitude Estimation of Multirotor UAVs in Dynamic Unstructured Environments Using 3D Point Cloud Sensors". Aerospace 5, n.º 3 (6 de septiembre de 2018): 94. http://dx.doi.org/10.3390/aerospace5030094.
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This paper presents a fast and robust approach for estimating the flight altitude of multirotor Unmanned Aerial Vehicles (UAVs) using 3D point cloud sensors in cluttered, unstructured, and dynamic indoor environments. The objective is to present a flight altitude estimation algorithm, replacing the conventional sensors such as laser altimeters, barometers, or accelerometers, which have several limitations when used individually. Our proposed algorithm includes two stages: in the first stage, a fast clustering of the measured 3D point cloud data is performed, along with the segmentation of the clustered data into horizontal planes. In the second stage, these segmented horizontal planes are mapped based on the vertical distance with respect to the point cloud sensor frame of reference, in order to provide a robust flight altitude estimation even in presence of several static as well as dynamic ground obstacles. We validate our approach using the IROS 2011 Kinect dataset available in the literature, estimating the altitude of the RGB-D camera using the provided 3D point clouds. We further validate our approach using a point cloud sensor on board a UAV, by means of several autonomous real flights, closing its altitude control loop using the flight altitude estimated by our proposed method, in presence of several different static as well as dynamic ground obstacles. In addition, the implementation of our approach has been integrated in our open-source software framework for aerial robotics called Aerostack.
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Zhao, H., R. Xu y G. Qiao. "COMPARISON OF CRYOSAT-2 AND ICESAT-2 ON WATER LEVEL MONITORING OF NAM CO LAKE". International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLIII-B3-2021 (28 de junio de 2021): 527–32. http://dx.doi.org/10.5194/isprs-archives-xliii-b3-2021-527-2021.
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Abstract. There are more than 1,000 lakes (> 1 km2) on the Tibetan Plateau and lake level is an important physical feature of lake changes. Lake level change is an important indicator to reflect changes of climate and environment in a certain area. The development of satellite altimetry has provided data support for the monitoring of lake level and effectively compensated for the deficiencies of traditional water level monitoring in alpine regions. In this study, the laser altimeter of ICESat-2 and the radar altimeter of CryoSat-2 are used to provide lake level of the Nam Co lake during the period of 2010–2020. The result showed that the standard deviation (SD) of ICESat-2 (0.0895 m) was lower than the SD of CryoSat-2 (0.2556 m) and the months with higher SD values were mostly during the ice period of Nam Co lake. ICESat-2 had a considerably decreased measurement uncertainty. There are systematic differences in lake levels extracted by different altimetry satellites and the mean bias between ICESat-2 and CryoSat-2 was around 0.45 m. After removing inter-altimeter biases, the continuous lake levels from 2010 to 2020 were constructed. The inter-annual changes in lake levels were flat or even slightly decreased and the lake level has dropped by about 0.80 m in general. The water level generally reached the highest from September to October of the year in terms of intra-annual changes. Besides, temperature and precipitation changes were closely related to lake level tendency.
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Young, Duncan A., Laura E. Lindzey, Donald D. Blankenship, Jamin S. Greenbaum, Alvaro Garcia De Gorordo, Scott D. Kempf, Jason L. Roberts et al. "Land-ice elevation changes from photon-counting swath altimetry: first applications over the Antarctic ice sheet". Journal of Glaciology 61, n.º 225 (2015): 17–28. http://dx.doi.org/10.3189/2015jog14j048.
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AbstractSatellite altimetric time series allow high-precision monitoring of ice-sheet mass balance. Understanding elevation changes in these regions is important because outlet glaciers along ice-sheet margins are critical in controlling flow of inland ice. Here we discuss a new airborne altimetry dataset collected as part of the ICECAP (International Collaborative Exploration of the Cryosphere by Airborne Profiling) project over East Antarctica. Using the ALAMO (Airborne Laser Altimeter with Mapping Optics) system of a scanning photon-counting lidar combined with a laser altimeter, we extend the 2003–09 surface elevation record of NASA’s ICESat satellite, by determining cross-track slope and thus independently correcting for ICESat’s cross-track pointing errors. In areas of high slope, cross-track errors result in measured elevation change that combines surface slope and the actual Δz/Δt signal. Slope corrections are particularly important in coastal ice streams, which often exhibit both rapidly changing elevations and high surface slopes. As a test case (assuming that surface slopes do not change significantly) we observe a lack of ice dynamic change at Cook Ice Shelf, while significant thinning occurred at Totten and Denman Glaciers during 2003–09.
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Steinbrügge, Gregor, Teresa Steinke, Robin Thor, Alexander Stark y Hauke Hussmann. "Measuring Ganymede’s Librations with Laser Altimetry". Geosciences 9, n.º 7 (20 de julio de 2019): 320. http://dx.doi.org/10.3390/geosciences9070320.
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Jupiter’s moon Ganymede might be in possession of a subsurface ocean located between two ice layers. However, from Galileo data it is not possible to unambiguously infer the thickness and densities of the individual layers. The upcoming icy satellite mission JUICE (JUpiter ICy moons Explorer) will have the possibility to perform more detailed investigations of Ganymede’s interior structure with the radio science experiment 3GM and the GAnymede Laser Altimeter (GALA). Here we investigate the possibility to derive the rotational state of the outer ice shell by using topography measured by laser altimetry. We discuss two different methods to invert synthetic laser altimetry data. Method 1 is based on a spherical harmonics expansion and Method 2 solves for B-splines on a rectangular grid. While Method 1 has significant limitations due to the omission of high degrees of the global expansion, Method 2 leads to stable results allowing for an estimate of the in-orbit measurement accuracy. We estimate that GALA can measure the amplitude of Ganymede’s librations with an accuracy of 2.5–6.6 μ rad (6.6–17.4 m at the equator). This allows for determining the thickness of an elastic ice shell, if decoupled from the deeper interior by a subsurface ocean, to about an accuracy of 24–65 km.
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Donghui, Yi y Charles R. Bentley. "Geoscience Laser Altimeter System waveform simulation and its applications". Annals of Glaciology 29 (1999): 279–85. http://dx.doi.org/10.3189/172756499781821580.
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AbstractTo study the relationship between surface topography and satellite laser altimetry waveform, a numerical model that simulates an ideal satellite laser altimeter has been developed. It has a Gaussian beam pattern and a Gaussian pulse shape. Different three-dimensional surface topographies have been used in the simulation to generate waveforms. Using a non-linear least-squares method, the generated waveforms were fitted to theoretical models to calculate surface roughness and surface slope. The outputs from the models were then compared with the values calculated from the given assumed surfaces. There is no way to distinguish between a horizontal, randomly rough surface and a smoothly sloping surface from waveform fitting alone. However, if either the surface roughness or the surface slope can be acquired independently, the other one can be determined through waveform fitting.
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Marsh, O. J. y W. Rack. "A method of calculating ice-shelf surface velocity using ICESat altimetry". Polar Record 48, n.º 1 (29 de noviembre de 2011): 25–30. http://dx.doi.org/10.1017/s0032247411000362.
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ABSTRACTVery high precision satellite altimeter measurements from the Geoscience Laser Altimeter System onboard NASA's Ice, Cloud and Land Elevation Satellite (ICESat) have allowed a method of feature tracking to be developed for floating ice which relies on recording the movement of large surface undulations. This method is applied to a section of the Ross Ice Shelf downstream of the grounding line of the Beardmore Glacier, Antarctica. The altimetry method has benefits over established optical and interferometric remote sensing techniques due to high pointing accuracy for geo-location, ability to deal with tidal fluctuations and to measure velocity where visible surface features are absent. Initial processing of a single sequence of ICESat tracks gives encouraging results for unidirectional ice flow with correlations between surface profiles in consecutive years exceeding 90% and producing high internal consistency in velocity between independent tracks. Velocities of 331 ± 28 m a−1 near to the grounding line are also consistent with available ground measurements for the area.
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Helm, V., A. Humbert y H. Miller. "Elevation and elevation change of Greenland and Antarctica derived from CryoSat-2". Cryosphere 8, n.º 4 (20 de agosto de 2014): 1539–59. http://dx.doi.org/10.5194/tc-8-1539-2014.
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Abstract. This study focuses on the present-day surface elevation of the Greenland and Antarctic ice sheets. Based on 3 years of CryoSat-2 data acquisition we derived new elevation models (DEMs) as well as elevation change maps and volume change estimates for both ice sheets. Here we present the new DEMs and their corresponding error maps. The accuracy of the derived DEMs for Greenland and Antarctica is similar to those of previous DEMs obtained by satellite-based laser and radar altimeters. Comparisons with ICESat data show that 80% of the CryoSat-2 DEMs have an uncertainty of less than 3 m ± 15 m. The surface elevation change rates between January 2011 and January 2014 are presented for both ice sheets. We compared our results to elevation change rates obtained from ICESat data covering the time period from 2003 to 2009. The comparison reveals that in West Antarctica the volume loss has increased by a factor of 3. It also shows an anomalous thickening in Dronning Maud Land, East Antarctica which represents a known large-scale accumulation event. This anomaly partly compensates for the observed increased volume loss of the Antarctic Peninsula and West Antarctica. For Greenland we find a volume loss increased by a factor of 2.5 compared to the ICESat period with large negative elevation changes concentrated at the west and southeast coasts. The combined volume change of Greenland and Antarctica for the observation period is estimated to be −503 ± 107 km3 yr−1. Greenland contributes nearly 75% to the total volume change with −375 ± 24 km3 yr−1.
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Lindzey, Laura E., Lucas H. Beem, Duncan A. Young, Enrica Quartini, Donald D. Blankenship, Choon-Ki Lee, Won Sang Lee, Jong Ik Lee y Joohan Lee. "Aerogeophysical characterization of an active subglacial lake system in the David Glacier catchment, Antarctica". Cryosphere 14, n.º 7 (15 de julio de 2020): 2217–33. http://dx.doi.org/10.5194/tc-14-2217-2020.
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Abstract. In the 2016–2017 austral summer, the University of Texas Institute for Geophysics (UTIG) and the Korea Polar Research Institute (KOPRI) collaborated to perform a helicopter-based radar and laser altimeter survey of lower David Glacier with the goals of characterizing the subglacial water distribution that supports a system of active subglacial lakes and informing the site selection for a potential subglacial access drilling project. This survey overlaps with and expands upon an earlier survey of the Drygalski Ice Tongue and the David Glacier grounding zone from 2011 and 2012 to create a 5 km resolution survey extending 200 km upstream from the grounding zone. The surveyed region covers two active subglacial lakes and includes reflights of ICESat ground tracks that extend the surface elevation record in the region. This is one of the most extensive aerogeophysical surveys of an active lake system and provides higher-resolution boundary conditions and basal characterizations that will enable process studies of these features. This paper introduces a new helicopter-mounted ice-penetrating radar and laser altimetry system, notes a discrepancy between the original surface-elevation-derived lake outlines and locations of possible water collection based on basal geometry and hydraulic potential, and presents radar-based observations of basal conditions that are inconsistent with large collections of ponded water despite laser altimetry showing that the hypothesized active lakes are at a highstand.