Articoli di riviste: "Optical radar Observations"

1

Ogawa, T. "Radar observations of ionospheric irregularities at Syowa Station, Antarctica: a brief overview". Annales Geophysicae 14, n. 12 (31 dicembre 1996): 1454–61. http://dx.doi.org/10.1007/s00585-996-1454-z.

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Abstract. We briefly overview the radar observations that have been made for 30 years at Syowa Station, Antarctica for studying small-scale electron-density irregularities in the southern high-latitude E- and F-region ionosphere. Some observational results (i.e., long-term variations of radio aurora, Doppler spectra with narrow spectral widths and low Doppler velocities, and simultaneous observations of radar and optical auroras) from VHF radars capable of detecting 1.3- to 3-m scale irregularities are presented. A new 50-MHz radar system equipped with phased-antenna arrays began operation in February 1995 to observe two-dimensional behaviours of E-region irregularities. An HF radar experiment also began in February 1995 to explore decameter-scale E- and F-region irregularities in the auroral zone and polar cap. These two radars will contribute to a better understanding of the ionospheric irregularities and ionospheric physics at southern high latitudes.

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Huyan, Zongbo, Yu Jiang, Hengnian Li, Pengbin Ma e Dapeng Zhang. "Bistatic Radar Observations Correlation of LEO Satellites Considering J2 Perturbation". Mathematics 10, n. 13 (23 giugno 2022): 2197. http://dx.doi.org/10.3390/math10132197.

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Space debris near Earth severely interferes with the development of space, and cataloging space objects is increasingly important. Since optical telescopes and radars used to detect space debris only provide short-arc observations, mathematical algorithms are needed to solve problems in the correlation of observations. In this work, an efficient mathematical algorithm based on J2 analytic solutions is put forward. Initial orbit determination (IOD) serves as the starter and orbit determination (OD) with the weighted least-squares method (WLSM) is used to improve the accuracy of the estimated orbit. Meanwhile, the effect of the weight of different observation types is analyzed. The correlation criteria for bistatic radar observations are accordingly developed. Lastly, the variation in and evolution of the error of bistatic radar ranging are discussed.

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3

Brosch, N., D. Polishook, R. Helled, S. Schijvarg e M. Rosenkrantz. "Radar and optical leonids". Atmospheric Chemistry and Physics Discussions 4, n. 2 (9 marzo 2004): 1425–47. http://dx.doi.org/10.5194/acpd-4-1425-2004.

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Abstract. We present joint optical-radar observations of meteors collected near the peak of the leonid activity in 2002. We show four examples of joint detections with a large, phased array L-band radar and with intensified video cameras. The general characteristic of the radar-detected optical meteors is that they show the radar detection below the termination of the optical meteor. Therefore, at least some radar events associated with meteor activity are neither head echoes nor trail echoes, but probably indicate the formation of "charged clouds" after the visual meteor is extinguished.

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Brosch, N., D. Polishook, R. Helled, S. Schijvarg e M. Rosenkrantz. "Radar and optical leonids". Atmospheric Chemistry and Physics 4, n. 4 (6 luglio 2004): 1063–69. http://dx.doi.org/10.5194/acp-4-1063-2004.

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Abstract. We present joint optical-radar observations of meteors collected near the peak of the Leonid activity in 2002. We show four examples of joint detections with a large, phased array L-band radar and with intensified video cameras. The general characteristic of the radar-detected optical meteors is that they show the radar detection below the termination of the optical meteor. Therefore, at least some radar events associated with meteor activity are neither head echoes nor trail echoes, but probably indicate the formation of "charged clouds" after the visual meteor is extinguished.

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Mann, Ingrid, Asta Pellinen-Wannberg e Anders Tjulin. "Meteor studies applying incoherent scatter radar instruments". Proceedings of the International Astronomical Union 10, H16 (agosto 2012): 181. http://dx.doi.org/10.1017/s1743921314005353.

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AbstractOne of the interesting aspects of optical meteor studies is that the spectral composition of the brightness reveals information about the element composition of the solid particles that enter Earthfs atmosphere from interplanetary space. Deriving composition from optical spectra requires understanding the entry process during which the entering solid interacts with atmospheric species. This is especially so, because most meteors are observed at altitudes where the mean free path changes from tens of meters to millimeters, that is in the 120 km to 80 km altitude range within the atmosphere. The ionization that causes optical emission also reflects radio waves, so that meteors are observed with different kinds of radar instruments. Incoherent scatter radar facilities are in particular designed to study the upper atmosphere by using the backscattering from free electrons and are basically High Power Large Aperture radars. During the past 15 years they have been increasingly used for meteor studies. The phased-array incoherent scatter radars that are currently under development, such as the planned EISCAT-3Dsystem in northern Scandinavia, will further improve the spatial and time resolution of radar observations and will allow simultaneous measurements of the meteors and of the parameters of the surrounding ionosphere. Radar backscattering is also sensitive to objects that are smaller than those detected optically, so that the observations also permit studying the extension of the meteoroid size distribution to smaller sizes. In this presentation we consider the possibilities for measurements with the future EISCAT-3D as a new path of studying the physics of meteor phenomena with high accuracy.

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Cline, Don, Simon Yueh, Bruce Chapman, Boba Stankov, Al Gasiewski, Dallas Masters, Kelly Elder et al. "NASA Cold Land Processes Experiment (CLPX 2002/03): Airborne Remote Sensing". Journal of Hydrometeorology 10, n. 1 (1 febbraio 2009): 338–46. http://dx.doi.org/10.1175/2008jhm883.1.

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Abstract This paper describes the airborne data collected during the 2002 and 2003 Cold Land Processes Experiment (CLPX). These data include gamma radiation observations, multi- and hyperspectral optical imaging, optical altimetry, and passive and active microwave observations of the test areas. The gamma observations were collected with the NOAA/National Weather Service Gamma Radiation Detection System (GAMMA). The CLPX multispectral optical data consist of very high-resolution color-infrared orthoimagery of the intensive study areas (ISAs) by TerrainVision. The airborne hyperspectral optical data consist of observations from the NASA Airborne Visible/Infrared Imaging Spectrometer (AVIRIS). Optical altimetry measurements were collected using airborne light detection and ranging (lidar) by TerrainVision. The active microwave data include radar observations from the NASA Airborne Synthetic Aperture Radar (AIRSAR), the Jet Propulsion Laboratory’s Polarimetric Ku-band Scatterometer (POLSCAT), and airborne GPS bistatic radar data collected with the NASA GPS radar delay mapping receiver (DMR). The passive microwave data consist of observations collected with the NOAA Polarimetric Scanning Radiometer (PSR). All of the airborne datasets described here and more information describing data collection and processing are available online.

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Maki, Masayuki, Masato Iguchi, Takeshi Maesaka, Takahiro Miwa, Toshikazu Tanada, Tomofumi Kozono, Tatsuya Momotani, Akihiko Yamaji e Ikuya Kakimoto. "Preliminary Results of Weather Radar Observations of Sakurajima Volcanic Smoke". Journal of Disaster Research 11, n. 1 (1 febbraio 2016): 15–30. http://dx.doi.org/10.20965/jdr.2016.p0015.

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Preliminary results of quantitative analysis of volcanic ash clouds observed over the Sakurajima volcano in Kagoshima, Japan, were obtained by using weather radar and surface instruments. The Ka-band Doppler radar observations showed the inner structure of a volcanic ash column every two minutes after an eruption. Operational X-band polarimetric radar provides information on three-dimensional ash fall amount distribution. The terminal fall velocity of ash particles was studied by using optical disdrometers, together with the main specifications of observation instruments.

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8

Safargaleev, V., A. Kozlovsky, T. Sergienko, T. K. Yeoman, M. Uspensky, D. M. Wright, H. Nilsson, T. Turunen e A. Kotikov. "Optical, radar, and magnetic observations of magnetosheath plasma capture during a positive IMF Bz impulse". Annales Geophysicae 26, n. 3 (26 marzo 2008): 517–31. http://dx.doi.org/10.5194/angeo-26-517-2008.

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Abstract. We present a multi-instrument study of the ionospheric response to a northward turning of the IMF. The observations were made in the near-noon (11:00 MLT) sector on Svalbard (at 75° MLAT). The data set includes auroral observations, ionospheric flows obtained from the EISCAT and CUTLASS radars, the spectral width of the HF radar backscatter, particle precipitation and plasma flow data from the DMSP F13 satellite, and Pc1 frequency band pulsations observed by induction magnetometers. Careful collocation of all the observations has been made with the HF radar backscatter located by a ray-tracing procedure utilizing the elevation angle of arrival of the signals and an ionospheric plasma density profile. Prior to IMF turning northward, three auroral arcs were observed at the poleward boundary of the closed llbl, inside the llbl, and in the equatorward part of the llbl, respectively. The northward IMF turning was accompanied by enhanced HF radar returns with a broad Doppler spectrum collocated with the arcs. The auroral arcs shifted poleward whereas the backscatter region moved in the opposite direction, which is consistent, respectively, with reconnection beyond the cusp and the capturing of magnetosheath plasma during northward IMF. Locally, magnetic noise enhancement in the Pc1 frequency band occurred simultaneously with the anomalous radar backscatter, and the absence of such signals at more remote magnetic observatories indicates a local generation of the Pc1 turbulence, which is collocated with the radar backscatter. Finally, we discuss possible interpretation errors which may be caused by limited observational data.

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9

Sekar, R., D. Chakrabarty, R. Narayanan, S. Sripathi, A. K. Patra e K. S. V. Subbarao. "Characterization of VHF radar observations associated with equatorial Spread F by narrow-band optical measurements". Annales Geophysicae 22, n. 9 (23 settembre 2004): 3129–36. http://dx.doi.org/10.5194/angeo-22-3129-2004.

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Abstract. The VHF radars have been extensively used to investigate the structures and dynamics of equatorial Spread F (ESF) irregularities. However, unambiguous identification of the nature of the structures in terms of plasma depletion or enhancement requires another technique, as the return echo measured by VHF radar is proportional to the square of the electron density fluctuations. In order to address this issue, co-ordinated radar backscatter and thermospheric airglow intensity measurements were carried out during March 2003 from the MST radar site at Gadanki. Temporal variations of 630.0-nm and 777.4-nm emission intensities reveal small-scale ("micro") and large-scale ("macro") variations during the period of observation. The micro variations are absent on non-ESF nights while the macro variations are present on both ESF and non-ESF nights. In addition to the well-known anti-correlation between the base height of the F-region and the nocturnal variation of thermospheric airglow intensities, the variation of the base height of the F-layer, on occasion, is found to manifest as a bottomside wave-like structure, as seen by VHF radar on an ESF night. The micro variations in the airglow intensities are associated with large-scale irregular plasma structures and found to be in correspondence with the "plume" structures obtained by VHF radar. In addition to the commonly observed depletions with upward movement, the observation unequivocally reveals the presence of plasma enhancements which move downwards. The observation of enhancement in 777.4-nm airglow intensity, which is characterized as plasma enhancement, provides an experimental verification of the earlier prediction based on numerical modeling studies.

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10

Ostro, S. J. "Radar and Optical Observations of Asteroid 1998 KY26". Science 285, n. 5427 (23 luglio 1999): 557–59. http://dx.doi.org/10.1126/science.285.5427.557.

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Nam, Christine C. W., e Johannes Quaas. "Evaluation of Clouds and Precipitation in the ECHAM5 General Circulation Model Using CALIPSO and CloudSat Satellite Data". Journal of Climate 25, n. 14 (15 luglio 2012): 4975–92. http://dx.doi.org/10.1175/jcli-d-11-00347.1.

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Abstract Observations from Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and CloudSat satellites are used to evaluate clouds and precipitation in the ECHAM5 general circulation model. Active lidar and radar instruments on board CALIPSO and CloudSat allow the vertical distribution of clouds and their optical properties to be studied on a global scale. To evaluate the clouds modeled by ECHAM5 with CALIPSO and CloudSat, the lidar and radar satellite simulators of the Cloud Feedback Model Intercomparison Project’s Observation Simulator Package are used. Comparison of ECHAM5 with CALIPSO and CloudSat found large-scale features resolved by the model, such as the Hadley circulation, are captured well. The lidar simulator demonstrated ECHAM5 overestimates the amount of high-level clouds, particularly optically thin clouds. High-altitude clouds in ECHAM5 consistently produced greater lidar scattering ratios compared with CALIPSO. Consequently, the lidar signal in ECHAM5 frequently attenuated high in the atmosphere. The large scattering ratios were due to an underestimation of effective ice crystal radii in ECHAM5. Doubling the effective ice crystal radii improved the scattering ratios and frequency of attenuation. Additionally, doubling the effective ice crystal radii improved the detection of ECHAM5’s highest-level clouds by the radar simulator, in better agreement with CloudSat. ECHAM5 was also shown to significantly underestimate midlevel clouds and (sub)tropical low-level clouds. The low-level clouds produced were consistently perceived by the lidar simulator as too optically thick. The radar simulator demonstrated ECHAM5 overestimates the frequency of precipitation, yet underestimates its intensity compared with CloudSat observations. These findings imply compensating mechanisms in ECHAM5 balance out the radiative imbalance caused by incorrect optical properties of clouds and consistently large hydrometeors in the atmosphere.

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Takewaka, Satoshi. "Visibility of River Plume Fronts with an X-Band Radar". Journal of Sensors 2016 (2016): 1–11. http://dx.doi.org/10.1155/2016/6594847.

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A land-based X-band radar was employed to observe river plume fronts at the mouth of the Tenryu River, Japan. Time-averaged radar images captured fronts extending offshore from the river’s mouth as bright streaks. Comparisons between satellite optical images and radar images confirm that streaky features in the radar image represent color river plume fronts. Further corroboration comes from field observations of water temperature, salinity, and turbidity conducted simultaneously with the radar measurements. When a survey ship crossed the front, the measured properties varied discontinuously, suggesting that water from the river and sea converged there and also that a downwards current was present. Variation of visibility of the fronts was assessed and compared with the rate of variation of water level and the wind speed and direction. The radar is able to image fronts when the water level is decreasing during ebb tide and the wind speed is over 3 m/s along shore. Surface ripple waves are generated by the local wind, and if they propagate across the front, wave heights increase, causing higher backscatter of the emitted radar beam. This observation gives further evidence on the imaging mechanism of river plume fronts with X-band radars in relation to wind direction.

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Kastinen, Daniel, Torbjørn Tveito, Juha Vierinen e Mikael Granvik. "Radar observability of near-Earth objects using EISCAT 3D". Annales Geophysicae 38, n. 4 (15 luglio 2020): 861–79. http://dx.doi.org/10.5194/angeo-38-861-2020.

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Abstract. Radar observations can be used to obtain accurate orbital elements for near-Earth objects (NEOs) as a result of the very accurate range and range rate measureables. These observations allow the prediction of NEO orbits further into the future and also provide more information about the properties of the NEO population. This study evaluates the observability of NEOs with the EISCAT 3D 233 MHz 5 MW high-power, large-aperture radar, which is currently under construction. Three different populations are considered, namely NEOs passing by the Earth with a size distribution extrapolated from fireball statistics, catalogued NEOs detected with ground-based optical telescopes and temporarily captured NEOs, i.e. mini-moons. Two types of observation schemes are evaluated, namely the serendipitous discovery of unknown NEOs passing the radar beam and the post-discovery tracking of NEOs using a priori orbital elements. The results indicate that 60–1200 objects per year, with diameters D>0.01 m, can be discovered. Assuming the current NEO discovery rate, approximately 20 objects per year can be tracked post-discovery near the closest approach to Earth. Only a marginally smaller number of tracking opportunities are also possible for the existing EISCAT ultra-high frequency (UHF) system. The mini-moon study, which used a theoretical population model, orbital propagation, and a model for radar scanning, indicates that approximately seven objects per year can be discovered using 8 %–16 % of the total radar time. If all mini-moons had known orbits, approximately 80–160 objects per year could be tracked using a priori orbital elements. The results of this study indicate that it is feasible to perform routine NEO post-discovery tracking observations using both the existing EISCAT UHF radar and the upcoming EISCAT 3D radar. Most detectable objects are within 1 lunar distance (LD) of the radar. Such observations would complement the capabilities of the more powerful planetary radars that typically observe objects further away from Earth. It is also plausible that EISCAT 3D could be used as a novel type of an instrument for NEO discovery, assuming that a sufficiently large amount of radar time can be used. This could be achieved, for example by time-sharing with ionospheric and space-debris-observing modes.

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Shchukin, G. G., e V. V. Bulkin. "Meteorological passive-active radar observations". Journal of Communications Technology and Electronics 56, n. 5 (maggio 2011): 509–30. http://dx.doi.org/10.1134/s1064226911030089.

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Shuygina, N. V., e E. I. Yagudina. "The FK5 equinox and equator from combined radar and optical data of the near-earth asteroids". Symposium - International Astronomical Union 172 (1996): 469–74. http://dx.doi.org/10.1017/s0074180900127895.

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Minor planets optical observations have long been used for the purpose of establishing a Celestial reference frame. Being in existence since the early 1960s modern high-accuracy radar measurements of the so-called near-Earth asteroids (NEAs) have been widely extended to the orbit determination process and predicting of the next apparition of the asteroid. Even few radar measurements, when added to optical ones, significantly improve asteroid's ephemeris and reduce standard deviations of the orbital elements (Yeomans et al., 1987). The idea to connect optical and radar data in the problem of the catalogue zero-point determination has been stated by several scientists (Boiko, 1975). And even the first attempt of the authors (Krivova et al., 1994) with actual optical and radar observations of two NEAs: (4179) Toutatis and (1862) Apollo appears to have considerable promise. It was demonstrated the possibility of obtaining standard deviations of catalogue orientation parameters 1.5–2 times better with radar data included.

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Milan, S. E., M. Lester, S. W. H. Cowley, J. Moen, P. E. Sandholt e C. J. Owen. "Meridian-scanning photometer, coherent HF radar, and magnetometer observations of the cusp: a case study". Annales Geophysicae 17, n. 2 (28 febbraio 1999): 159–72. http://dx.doi.org/10.1007/s00585-999-0159-5.

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Abstract. The dynamics of the cusp region and post-noon sector for an interval of predominantly IMF By, Bz < 0 nT are studied with the CUTLASS Finland coherent HF radar, a meridian-scanning photometer located at Ny Ålesund, Svalbard, and a meridional network of magnetometers. The scanning mode of the radar is such that one beam is sampled every 14 s, and a 30° azimuthal sweep is completed every 2 minutes, all at 15 km range resolution. Both the radar backscatter and red line (630 nm) optical observations are closely co-located, especially at their equatorward boundary. The optical and radar aurora reveal three different behaviours which can interchange on the scale of minutes, and which are believed to be related to the dynamic nature of energy and momentum transfer from the solar wind to the magnetosphere through transient dayside reconnection. Two interpretations of the observations are presented, based upon the assumed location of the open/closed field line boundary (OCFLB). In the first, the OCFLB is co-located with equatorward boundary of the optical and radar aurora, placing most of the observations on open field lines. In the second, the observed aurora are interpreted as the ionospheric footprint of the region 1 current system, and the OCFLB is placed near the poleward edge of the radar backscatter and visible aurora; in this interpretation, most of the observations are placed on closed field lines, though transient brightenings of the optical aurora occur on open field lines. The observations reveal several transient features, including poleward and equatorward steps in the observed boundaries, "braiding" of the backscatter power, and 2 minute quasi-periodic enhancements of the plasma drift and optical intensity, predominantly on closed field lines.Key words. Ionosphere (auroral ionosphere; plasma convection) · Magnetospheric physics (magnetopause · cusp · and boundary layers)

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Ohsawa, Ryou, Akira Hirota, Kohei Morita, Shinsuke Abe, Daniel Kastinen, Johan Kero, Csilla Szasz et al. "Relationship between radar cross section and optical magnitude based on radar and optical simultaneous observations of faint meteors". Planetary and Space Science 194 (dicembre 2020): 105011. http://dx.doi.org/10.1016/j.pss.2020.105011.

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Rodger, A. S., S. B. Mende, T. J. Rosenberg e K. B. Baker. "Simultaneous optical and HF radar observations of the ionospheric cusp". Geophysical Research Letters 22, n. 15 (1 agosto 1995): 2045–48. http://dx.doi.org/10.1029/95gl01797.

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Frey, H. U., G. Haerendel, D. Knudsen, S. Buchert e O. H. Bauer. "Optical and radar observations of the motion of auroral arcs". Journal of Atmospheric and Terrestrial Physics 58, n. 1-4 (gennaio 1996): 57–69. http://dx.doi.org/10.1016/0021-9169(95)00019-4.

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Zambrano-Marin, Luisa Fernanda, Ellen S. Howell, Patrick A. Taylor, Sean E. Marshall, Maxime Devogèle, Anne K. Virkki, Dylan C. Hickson, Edgard G. Rivera-Valentín, Flaviane C. F. Venditti e Jon D. Giorgini. "Radar and Optical Characterization of Near-Earth Asteroid 2019 OK". Planetary Science Journal 3, n. 6 (1 giugno 2022): 138. http://dx.doi.org/10.3847/psj/ac63cd.

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Abstract We conducted radar observations of near-Earth asteroid 2019 OK on 2019 July 25 using the Arecibo Observatory S-band (2380 MHz, 12.6 cm) planetary radar system. Based on Arecibo and optical observations the apparent diameter is between 70 and 130 m. Combined with an absolute magnitude of H = 23.3 ± 0.3, the optical albedo of 2019 OK is likely between 0.05 and 0.17. Our measured radar circular polarization ratio of μ C = 0.33 ± 0.03 indicates 2019 OK is likely not a V- or E-type asteroid and is most likely a C- or S-type. The measured radar echo bandwidth of 39 ± 2 Hz restricts the apparent rotation period to be approximately between 3 minutes (0.049 hr, D = 70 m) and 5 minutes (0.091 h, D = 130 m). Together, the apparent diameter and rotation period suggest that 2019 OK is likely not a rubble-pile body bound only by gravity. 2019 OK is one of a growing number of fast-rotating near-Earth asteroids that require some internal strength to keep them from breaking apart.

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Belavin, N. A., A. B. Silantyev, Yu V. Babkin, V. I. Kim e A. V. Timoshenko. "RESOURCE EFFICIENT CONTROL OF LONG-RANGE DETECTION RADAR FOR MONITORING OF HIGH EARTH ORBIT OBJECTS WITH SIMULTANEOUS CONTROL OF BARRIER ZONE". T-Comm 16, n. 9 (2022): 4–12. http://dx.doi.org/10.36724/2072-8735-2022-16-9-4-12.

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Radar surveillance (RS) of space objects has a number of advantages over the optical one. An urgent task is the RS of remote spacecraft, including high Earth orbit (HEO) spacecraft with the apogee height of more than 2500 km above the Earth's surface. In modern radars, well-known models, methods and technical solutions for observing remote spacecraft are implemented by increasing the duration (energy) of transmitted signals and observation time. This restriction does not allow to simultaneously detect and track objects of the "barrier zone" (BZ) while solving routine tasks using a long-range detection (LRD) radar. As a result, the radar throughput may decrease. It is proposed to use resource-efficient methods of multi-scanning monitoring (MSM). The methods make it possible to efficiently accumulate the energy of echo signals received during several radar observations. Purpose. In this paper, we research how to ensure the required throughput of the LRD radar when monitoring the BZ and observing the HEO objects using the MSM methods in conditions of a limited time resource. The study sets and solves the task of resource-efficient management of the LRD radar. This method consists in planning and organizing RS of the LRD radar for observation of the HEO objects with simultaneous control (detection and tracking) of BZ objects. In general, we formulate the task of RS of remote spacecraft and substantiate the algorithm for planning and organizing a RS for monitoring the HEO objects in conditions of a limited energy (time) resource. Methods. Analytical methods are used to substantiate the algorithm of resource-efficient control of the LRD radar using the MSM methods. Resource-efficient management is based on the use of a priori information about the parameters of the HEO objects trajectories, planning, organization and joint processing of RS results. The model of the LRD radar with the MSM channel is also substantiated in the form of a queuing system for assessing the radar throughput. Results. The simulation results indicate maintenance of the required throughput of the radar during the observations of the radar. It confirms the operability and effectiveness of the radar control method for solving the problem of simultaneous observation of the radar and monitoring of the objects of the BZ. Conclusion. The structure of the radar with the MSM channel and the method of resource-efficient management allow to implement the monitoring of the HEO objects with simultaneous detection and tracking of BZ objects. In contrast to the existing ones, the proposed algorithm for planning and control of the surveillance provides the required radar throughout during monitoring of the HEO objects.

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Milan, S. E., M. Lester, N. Sato, H. Takizawa e J. P. Villain. "Investigation of the relationship between optical auroral forms and HF radar E region backscatter". Annales Geophysicae 18, n. 6 (30 giugno 2000): 608–17. http://dx.doi.org/10.1007/s00585-000-0608-7.

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Abstract. The SuperDARN HF radars have been employed in the past to investigate the spectral characteristics of coherent backscatter from L-shell aligned features in the auroral E region. The present study employs all-sky camera observations of the aurora from Husafell, Iceland, and the two SuperDARN radars located on Iceland, Þykkvibær and Stokkseyri, to determine the optical signature of such backscatter features. It is shown that, especially during quiet geomagnetic conditions, the backscatter region is closely associated with east-west aligned diffuse auroral features, and that the two move in tandem with each other. This association between optical and radar aurora has repercussions for the instability mechanisms responsible for generating the E region irregularities from which radars scatter. This is discussed and compared with previous studies investigating the relationship between optical and VHF radar aurora. In addition, although it is known that E region backscatter is commonly observed by SuperDARN radars, the present study demonstrates for the first time that multiple radars can observe the same feature to extend over at least 3 h of magnetic local time, allowing precipitation features to be mapped over large portions of the auroral zone.Key words: Ionosphere (particle precipitation; plasma waves and instabilities)

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Koustov, A., K. Hosokawa, N. Nishitani, T. Ogawa e K. Shiokawa. "Rankin Inlet PolarDARN radar observations of duskward moving Sun-aligned optical forms". Annales Geophysicae 26, n. 9 (12 settembre 2008): 2711–23. http://dx.doi.org/10.5194/angeo-26-2711-2008.

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Abstract. On 15 February 2007, several duskward moving sun-aligned (SA) auroral forms have been observed by the all-sky camera at Resolute Bay, Nunavut (Canada). Concurrent observations with the Rankin Inlet (RANK) PolarDARN HF radar within the field-of-view of the camera showed signatures of moving auroral forms in all signal parameters with the most remarkable effects being the echo power drop and velocity reversal as the arc reached a specific radar beam/gate. Spatial and temporal variations of the velocity in the vicinity of the SA form are investigated. It is shown that the form-associated convection reversal was located poleward (duskward) of the global-scale convection reversal associated with the dawn cell of the large-scale convection pattern. Thus, the RANK radar was monitoring the polar cap portion of the global-scale convection pattern and its transition from the IMF By<0 to the By>0 situation. Magnetic perturbations associated with the SA form passing the zenith of several magnetometers are investigated. It is shown that although magnetometer signatures of the moving form were clear, the convection pattern derivation from magnetometer records alone is not straightforward.

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Tsuda, T., T. Nakamura, A. Nomura, T. D. Kawahara, C. Nagasawa, M. Abo, S. Okano, M. Taguchi e M. Ejiri. "Coordinated observations of the mesopause region with radar and optical techniques". Advances in Space Research 26, n. 6 (gennaio 2000): 907–16. http://dx.doi.org/10.1016/s0273-1177(00)00029-6.

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25

Michell, R. G., D. Janches, M. Samara, J. L. Hormaechea, C. Brunini e I. Bibbo. "Simultaneous optical and radar observations of meteor head-echoes utilizing SAAMER". Planetary and Space Science 118 (dicembre 2015): 95–101. http://dx.doi.org/10.1016/j.pss.2015.04.018.

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26

Narziev, Mirhusen. "Physical properties of the meteoroids using simultaneous radar and optical observations". Planetary and Space Science 173 (settembre 2019): 42–48. http://dx.doi.org/10.1016/j.pss.2018.11.011.

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27

Samara, M., e R. G. Michell. "Optical and radar observations of small-scale polar cap auroral structures". Journal of Atmospheric and Solar-Terrestrial Physics 105-106 (dicembre 2013): 308–12. http://dx.doi.org/10.1016/j.jastp.2012.11.016.

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28

Larsen, M. F., D. L. Hysell, Q. H. Zhou, S. M. Smith, J. Friedman e R. L. Bishop. "Imaging coherent scatter radar, incoherent scatter radar, and optical observations of quasiperiodic structures associated with sporadicElayers". Journal of Geophysical Research: Space Physics 112, A6 (giugno 2007): n/a. http://dx.doi.org/10.1029/2006ja012051.

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29

Клунко, Евгений, Evgeny Klunko, Максим Еселевич, Maxim Eselevich, Владимир Тергоев e Vladimir Tergoev. "Progress cargo spacecraft observed with the AZT-33IK optical telescope". Solar-Terrestrial Physics 2, n. 3 (27 ottobre 2016): 22–31. http://dx.doi.org/10.12737/22282.

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Abstract (sommario):

In this paper, we describe a telescope and measuring equipment used for optical observations of Progress cargo spacecraft (PCS), which were made during Radar–Progress space experiment sessions. We also demonstrate object tracking and measurement techniques. The observations were made with the optical telescope AZT-33IK at the Sayan Solar Observatory of ISTP SB RAS. During many of the sessions, we registered optical phenomena that occurred in regions of space surrounding the PCS and appeared due to the work of PCS onboard engines. The data we obtained can be used to independently control the geometry of the experiment and to analyze physical conditions in outer space.

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30

Michell, R. G., K. A. Lynch, C. J. Heinselman e H. C. Stenbaek-Nielsen. "High time resolution PFISR and optical observations of naturally enhanced ion acoustic lines". Annales Geophysicae 27, n. 4 (1 aprile 2009): 1457–67. http://dx.doi.org/10.5194/angeo-27-1457-2009.

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Abstract. Observations of naturally enhanced ion acoustic lines (NEIALs) taken with the Poker Flat Incoherent Scatter Radar (PFISR) using a mode with very high time resolution are presented. The auroral event took place over Poker Flat, Alaska on 8 February 2007 at 09:35 UT (~22:00 MLT), and the radar data are complemented by common-volume high-resolution auroral imaging. The NEIALs occurred during only one of the standard 15-s integration periods. The raw data of this time show very intermittent NEIALs which occur only during a few very short time intervals (≤1 s) within the 15-s period. The time sampling of the raw data, ~19 ms on average, allows study of the time development of the NEIALs, though there are indications that even finer time resolution would be of interest. The analysis is based on the assumption that the NEIAL returns are the result of Bragg scattering from ion-acoustic waves that have been enhanced significantly above thermal levels. The spectra of the raw data indicate that although the up- and down-shifted shoulders can both become enhanced at the same time, (within 19 ms), they are most often enhanced individually. The overall power in the up-and down-shifted shoulders is approximately equal throughout the event, with the exception of one time, when very large up-shifted power was observed with no corresponding down-shifted power. This indicates that during the 480 μs pulse, the strongly enhanced ion-acoustic waves were only traveling downward and not upward. The exact time that the NEIALs occurred was when the radar beam was on the boundary of a fast-moving (~10 km/s), bright auroral structure, as seen in the high resolution auroral imaging of the magnetic zenith. When viewed with high time resolution, the occurrence of NEIALs is associated with rapid changes in auroral luminosity within the radar field of view due to fast-moving auroral fine structures.

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31

Dorozhkin, N. S., V. Yu Zhukov e V. M. Mel'nikov. "Doppler observations with stock meteorological radar". Radiophysics and Quantum Electronics 37, n. 11 (novembre 1994): 910–13. http://dx.doi.org/10.1007/bf01057280.

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32

Jin, Huiran, e Giorgos Mountrakis. "Fusion of optical, radar and waveform LiDAR observations for land cover classification". ISPRS Journal of Photogrammetry and Remote Sensing 187 (maggio 2022): 171–90. http://dx.doi.org/10.1016/j.isprsjprs.2022.03.010.

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33

LIU, Jianjun, Hongqiao HU, Desheng HAN, Yonghua LIU, Qinghe ZHANG e S. Yukimatu Akira. "Optical and SuperDARN radar observations of duskside shock aurora over Zhongshan Station". ADVANCES IN POLAR SCIENCE 24, n. 1 (7 gennaio 2014): 60–68. http://dx.doi.org/10.3724/sp.j.1085.2013.00060.

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34

Gustavsson, B., M. J. Kosch, A. Senior, A. J. Kavanagh, B. U. E. Brändström e E. M. Blixt. "Combined EISCAT radar and optical multispectral and tomographic observations of black aurora". Journal of Geophysical Research: Space Physics 113, A6 (giugno 2008): n/a. http://dx.doi.org/10.1029/2007ja012999.

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35

Yeoman, T. K., M. Lester, S. W. H. Cowley, S. E. Milan, J. Moen e P. E. Sandholt. "Simultaneous observations of the cusp in optical, DMSP and HF radar data". Geophysical Research Letters 24, n. 17 (1 settembre 1997): 2251–54. http://dx.doi.org/10.1029/97gl02072.

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36

Frey, H. U., S. Frey, B. S. Lanchester e M. Kosch. "Optical tomography of the aurora and EISCAT". Annales Geophysicae 16, n. 10 (31 ottobre 1998): 1332–42. http://dx.doi.org/10.1007/s00585-998-1332-y.

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Abstract (sommario):

Abstract. Tomographic reconstruction of the three-dimensional auroral arc emission is used to obtain vertical and horizontal distributions of the optical auroral emission. Under the given experimental conditions with a very limited angular range and a small number of observers, algebraic reconstruction methods generally yield better results than transform techniques. Different algebraic reconstruction methods are tested with an auroral arc model and the best results are obtained with an iterative least-square method adapted from emission-computed tomography. The observation geometry used during a campaign in Norway in 1995 is tested with the arc model and root-mean-square errors, to be expected under the given geometrical conditions, are calculated. Although optimum geometry was not used, root-mean-square errors of less than 2% for the images and of the order of 30% for the distribution could be obtained. The method is applied to images from real observations. The correspondence of original pictures and projections of the reconstructed volume is discussed, and emission profiles along magnetic field lines through the three-dimensionally reconstructed arc are calibrated into electron density profiles with additional EISCAT measurements. Including a background profile and the temporal changes of the electron density due to recombination, good agreement can be obtained between measured profiles and the time-sequence of calculated profiles. These profiles are used to estimate the conductivity distribution in the vicinity of the EISCAT site. While the radar can only probe the ionosphere along the radar beam, the three-dimensional tomography enables conductivity estimates in a large area around the radar site.Key words. Tomography · Aurora · EISCAT · Ionosphere · Conductivity

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37

Peña-Luque, Santiago, Sylvain Ferrant, Mauricio C. R. Cordeiro, Thomas Ledauphin, Jerome Maxant e Jean-Michel Martinez. "Sentinel-1&2 Multitemporal Water Surface Detection Accuracies, Evaluated at Regional and Reservoirs Level". Remote Sensing 13, n. 16 (19 agosto 2021): 3279. http://dx.doi.org/10.3390/rs13163279.

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Abstract (sommario):

Water stock monitoring is a major issue for society on a local and global scale. Sentinel-1&2 satellites provide frequent acquisitions to track water surface dynamics, proxy variables to enable water surface volume monitoring. How do we combine such observations along time for each sensor? What advantages and disadvantages of single-date, monthly or time-windowed estimations? In this context, we analysed the impact of merging information through different types and lengths of time-windows. Satellite observations were processed separately on optical (Sentinel-2) and radar (Sentinel-1) water detectors at 10 m resolution. The analysis has been applied at two scales. First, validating with 26 large scenes (110 × 110 km) in different climatic zones in France, time-windows yielded an improvement on radar detection (F1-score improved from 0.72 to 0.8 for 30 days on average logic) while optical performances remained stable (F1-score 0.89). Second, validating reservoir area estimations with 29 instrumented reservoirs (20–1250 ha), time-windows presented in all cases an improvement on both optical and radar error for any window length (5–30 days). The mean relative absolute error in optical area detection improved from 16.9% on single measurements to 12.9% using 15 days time-windows, and from 22.15% to 15.1% in radar detection). Regarding reservoir filling rates, we identified an increased negative bias for both sensors when the reservoir is nearly full. This work helped to compare accuracies of separate optical and radar capabilities, where optical statistically outperforms radar at both local and large scale to the detriment of less frequent measurements. Furthermore, we propose a geomorphological indicator of reservoirs to predict the quality of radar area monitoring (R2 = 0.58). In conclusion, we suggest the use of time-windows on operational water mapping or reservoir monitoring systems, using 10–20 days time-windows with average logic, providing more frequent and faster information to water managers in periods of crisis (e.g., water shortage) compared to monthly estimations.

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38

Milan, S. E., M. Lester, N. Sato e H. Takizawa. "On the altitude dependence of the spectral characteristics of decametre-wavelength E region backscatter and the relationship with optical auroral forms". Annales Geophysicae 19, n. 2 (28 febbraio 2001): 205–17. http://dx.doi.org/10.5194/angeo-19-205-2001.

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Abstract. Observations of E region backscatter by the Ice-land East SuperDARN HF radar from the 30 minute period 2330 to 2400 UT on 13 September 1999 are presented, along with simultaneous observations of auroral luminosity from two all-sky cameras. Interferometric techniques are employed to estimate the altitude of origin of each echo observed by the radar. Under investigation is a region of backscatter which is L-shell aligned and exists in a region of low auroral luminosity bounded to the north and the south by two auroral arcs. The spectral characteristics of the backscatter fall into three main populations: broad, low Doppler shift spectra; narrow, high Doppler shift spectra; and exceptionally narrow, low Doppler shift spectra. The first two populations are similar to type II and type I spectra observed with VHF radars, respectively. These populations scatter from near the peak of the E region. The high Doppler shift population appears to exist in a region of sub-critical electric field. The third population originates below the E region peak at altitudes between 80 and 100 km. We argue that a non-coherent scattering process is responsible for this backscatter.Key words. Ionosphere (auroral ionosphere; ionospheric irregularities)

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39

Kavanagh, A. J., J. A. Wild e F. Honary. "Observations of omega bands using an imaging riometer". Annales Geophysicae 27, n. 11 (6 novembre 2009): 4183–95. http://dx.doi.org/10.5194/angeo-27-4183-2009.

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Abstract. We present a case study of an omega band current system from 11 May 1998 using data from the Imaging Riometer for Ionospheric Studies (IRIS) in Finland. For the first time, images of a substorm-related omega band in cosmic noise absorption are shown. The substorm in question was one of a string that occurred on that day; inspection of geostationary satellite data indicates that this was a sawtooth event. Using a previously established statistical relationship, the IRIS data is used to provide maps of Hall conductance and compared with previous estimates utilising both HF and VHF coherent-scatter radars. Discrepancies are discussed with reference to precipitation spectrum and the geometry of the experimental set-up. The imaging riometer data provides a higher spatial resolution than the combined magnetometer-radar pairing for determining the Hall conductance and can also be used to identify the extent of the precipitation in the absence of optical data.

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40

Rożek, A., S. C. Lowry, M. C. Nolan, P. A. Taylor, L. A. M. Benner, A. Fitzsimmons, T. J. Zegmott et al. "Shape model and spin-state analysis of PHA contact binary (85990) 1999 JV6 from combined radar and optical observations". Astronomy & Astrophysics 631 (novembre 2019): A149. http://dx.doi.org/10.1051/0004-6361/201936302.

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Abstract (sommario):

Context. The potentially hazardous asteroid (85990) 1999 JV6 has been a target of previously published thermal-infrared observations and optical photometry. It has been identified as a promising candidate for possible Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect detection. Aims. The YORP effect is a small thermal-radiation torque considered to be a key factor in spin-state evolution of small Solar System bodies. In order to detect YORP on 1999 JV6 we developed a detailed shape model and analysed the spin-state using both optical and radar observations. Methods. For 1999 JV6, we collected optical photometry between 2007 and 2016. Additionally, we obtained radar echo-power spectra and imaging observations with Arecibo and Goldstone planetary radar facilities in 2015, 2016, and 2017. We combined our data with published optical photometry to develop a robust physical model. Results. We determine that the rotation pole resides at negative latitudes in an area with a 5° radius close to the south ecliptic pole. The refined sidereal rotation period is 6.536787 ± 0.000007 h. The radar images are best reproduced with a bilobed shape model. Both lobes of 1999 JV6 can be represented as oblate ellipsoids with a smaller, more spherical component resting at the end of a larger, more elongated component. While contact binaries appear to be abundant in the near-Earth population, there are only a few published shape models for asteroids in this particular configuration. By combining the radar-derived shape model with optical light curves we determine a constant-period solution that fits all available data well. Using light-curve data alone we determine an upper limit for YORP of 8.5 × 10−8 rad day−2. Conclusions. The bifurcated shape of 1999 JV6 might be a result of two ellipsoidal components gently merging with each other, or a deformation of a rubble pile with a weak-tensile-strength core due to spin-up. The physical model of 1999 JV6 presented here will enable future studies of contact binary asteroid formation and evolution.

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41

Chapuis, Anne, Cecilie Rolstad e Richard Norland. "Interpretation of amplitude data from a ground-based radar in combination with terrestrial photogrammetry and visual observations for calving monitoring of Kronebreen, Svalbard". Annals of Glaciology 51, n. 55 (2010): 34–40. http://dx.doi.org/10.3189/172756410791392781.

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AbstractA ground-based radar has been used successfully for monitoring calving events and velocities at Kronebreen, Svalbard, for two test seasons in 2007 and 2008. We use daily terrestrial optical photogrammetry and continuous visual observation to validate the interpretation of a 116 hour ground-based radar amplitude of return signal data recorded from 26 to 30 August 2008. The radar was placed –4 km from the glacier. It measured at high temporal rate (2 Hz) and the antenna lobe covered a width of –700 m of the front. The calving-front geometry was extracted from the optical images, and its effect on radar backscatter, together with the movement of the glacier, was identified in the plot of the amplitude of the radar return signal. Calving events were detected applying an automated change-detection technique to the radar dataset. This technique allowed us to detect 92% of the events that were observed during the same time. In this paper, we focus on the method rather than on data interpretation. However, future use of this method, combined with meteorological data, tides and ocean temperature, will be valuable for calving-process studies.

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42

Vandemark, D., B. Chapron, J. Sun, G. H. Crescenti e H. C. Graber. "Ocean Wave Slope Observations Using Radar Backscatter and Laser Altimeters". Journal of Physical Oceanography 34, n. 12 (1 dicembre 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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43

Ostro, Steven J. "Radar Contributions to Asteroid Astrometry and Dynamics". International Astronomical Union Colloquium 165 (1997): 87–96. http://dx.doi.org/10.1017/s0252921100046406.

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Abstract (sommario):

Almost every radar observation of asteroids has measured some characteristics of the distribution of echo power in time delay (range) and Doppler frequency (radial velocity). Such measurements, which are orthogonal to optical plane-of-sky angular astrometry, are also done in the well-known, “absolute” reference frame of the planetary ephemerides, often with fractional precision that is much finer than can be achieved with other kinds of groundbased observations; they therefore can dramatically refine orbits and ephemerides. This statement is most true for near-Earth asteroids (NEAs), which constitute the most prolifically observed radar targets and are likely to be observed in increasing abundance as instrumental capabilities improve and CCD-based, NEA search programs expand. Moreover, studies of closely approaching NEAs benefit tremendously from the inverse fourthpower dependence of echo strength on target distance. For these reasons, I devote the bulk of this paper to NEAs

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44

Khan, H., M. Lester, J. A. Davies, S. E. Milan e P. E. Sandholt. "Multi-instrument study of the dynamic cusp during dominant IMF By conditions". Annales Geophysicae 21, n. 3 (31 marzo 2003): 693–708. http://dx.doi.org/10.5194/angeo-21-693-2003.

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Abstract. We present multi-instrument observations using the meridian scanning photometer (MSP) at NyAlesund, the EISCAT Svalbard radar (ESR) and the CUTLASS Finland HF radar, to investigate the dynamics of the cusp region during pulsed reconnection events. The optical data obtained from the MSP indicate the presence of several poleward-moving auroral forms (PMAFs) which have been previously identified as the auroral signature of pulsed reconnection. Furthermore, the optical green line (557.7 nm) luminosity indicates a loss of emission equatorward of the location of the onset of the PMAFs, characteristic of magnetospheric plasma escaping to the magnetosheath along newly opened field lines. This reduction in green line luminosity creates a "dark region", the equatorward edge of which is found to lie close to the boundary between high and low spectral widths observed by the CUTLASS Finland radar. High spectral widths on the dayside have previously been identified as a good indicator of cusp backscatter. Both of these boundaries have been suggested to provide an accurate representation of the location of the open/closed field line boundary. The ESR observations show enhancements in electron density and electron temperature occurring in conjunction with the optical PMAFs. The observations demonstrate some correspondence with the theoretical predictions of Davis and Lockwood (1996), who used an auroral precipitation model to predict ESR observations in the vicinity of the cusp. However, the limitations of this model are apparent under conditions of large plasma flows in the ionosphere. Finally, convection velocities obtained from the HF radar data illustrate a flow regime similar to that predicted to be driven by strong IMF By, as described by Cowley and Lockwood (1992), demonstrating an initial azimuthal flow followed by a rotation to more poleward directions.Key words. Ionosphere (ionosphere-magnetosphere interactions; particle precipitation) – Magnetospheric physics (magnetopause, cusp and boundary layers)

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Gorbatsky, V., N. Shpilev e Ye Lebedeva. "Sea currents monitoring in the coastal areas by the remote observation methods". Transactions of the Krylov State Research Centre 1, n. 399 (15 marzo 2022): 159–67. http://dx.doi.org/10.24937/2542-2324-2022-1-399-159-167.

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Abstract (sommario):

Object and purpose of research. The compare analysis carried out on the vorticies structure optical satellite pictures observation of the sea surface and the velocities field obtained by the ground HF Doppler radar. The purpose of this research is estimation of the possibility on fast monitoring feasibility assessment for the changes in littoral waters dynamics through joint application of satellite surveillance, radar probing of sea currents, wind data and numerical simulation of water circulation in the area under investigation. Materials and methods. The Sea surface observation data obtained by the satellites Sentinel 1 and 2 and by the coastal Doppler HF radar Sea Sonde in the South-east Black Sea area are analyzing. The additional data on the satellite observation of this area and on the wind condition is used from LANCE processing system [9, 10] and reanalysis NCEP/NCAR [11, 12]. The comparative analysis is carried out on the large vertical structures (LVS) establishing in the research coastal area. The numerical modeling of the water mass circulation in this area is carried out by the software package COHERENS (Belgian Institute of Natural Science) to investigate the role of the wind conditions at LVS appearance in the research area. Main results. The LVS in the vicinity of Sea coast line could be generated, as satellites observations demonstrated, by the vortices arrived along the coast line from the east-south direction in accordance with the Black Sea general circulation flow. Such vortices could be induced by the bottom roughness, rivers discharges and another local sources. Another LVS source could be connected with the wind impact in some affordable direction as demonstrated by the numerical modeling of the coastal water circulation. The continuous currents measurements at the Sea surface by Doppler HF coastal Radar supply the valuable data for further details on the space –time variation of LVS parameters and operational forecast of the hydrology regime in the aquatic areas. The operative numerical modelling of the wind impact to the surface currents structures formation provides the efficient estimation of the local large vorticity structure appearance in the research area. Conclusion. Satellite radar and optical observation provide the large scale control on the Sea surface dynamics conditions, but that is limited by relatively long interval between satellite tracks over the region of interest and do not acquire optical data at the cloud cover. The additional data could be operative obtain from the open internet resource in satellite optical, radar and meteorological data (LANCE, NCEP/NCAR), to get the more details development of the Sea surface dynamics. Sub-satellite Sea currents measurements by HF Doppler radar are useful for the reliable interpretation of satellite pictures and for the proper forecast of the aquatic area dynamics. Operative numerical modelling of the Sea coastal water circulation in accordance with variable meteo data combining with dynamic processes remote measurements could be efficient for the forecast of the environment parameters variation due the water mass transfer. In general the presented results demonstrates the combined application possibilities of the satellite observations, coastal Doppler radar measurements, internet data and operative numerical modelling for operational oceanographic and ecological monitoring of Sea coastal areas with heavy pollution load.

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Schroeder, Dustin M., Julian A. Dowdeswell, Martin J. Siegert, Robert G. Bingham, Winnie Chu, Emma J. MacKie, Matthew R. Siegfried, Katherine I. Vega, John R. Emmons e Keith Winstein. "Multidecadal observations of the Antarctic ice sheet from restored analog radar records". Proceedings of the National Academy of Sciences 116, n. 38 (3 settembre 2019): 18867–73. http://dx.doi.org/10.1073/pnas.1821646116.

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Abstract (sommario):

Airborne radar sounding can measure conditions within and beneath polar ice sheets. In Antarctica, most digital radar-sounding data have been collected in the last 2 decades, limiting our ability to understand processes that govern longer-term ice-sheet behavior. Here, we demonstrate how analog radar data collected over 40 y ago in Antarctica can be combined with modern records to quantify multidecadal changes. Specifically, we digitize over 400,000 line kilometers of exploratory Antarctic radar data originally recorded on 35-mm optical film between 1971 and 1979. We leverage the increased geometric and radiometric resolution of our digitization process to show how these data can be used to identify and investigate hydrologic, geologic, and topographic features beneath and within the ice sheet. To highlight their scientific potential, we compare the digitized data with contemporary radar measurements to reveal that the remnant eastern ice shelf of Thwaites Glacier in West Antarctica had thinned between 10 and 33% between 1978 and 2009. We also release the collection of scanned radargrams in their entirety in a persistent public archive along with updated geolocation data for a subset of the data that reduces the mean positioning error from 5 to 2.5 km. Together, these data represent a unique and renewed extensive, multidecadal historical baseline, critical for observing and modeling ice-sheet change on societally relevant timescales.

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47

Zegmott, Tarik J., S. C. Lowry, A. Rożek, B. Rozitis, M. C. Nolan, E. S. Howell, S. F. Green, C. Snodgrass, A. Fitzsimmons e P. R. Weissman. "Detection of the YORP effect on the contact binary (68346) 2001 KZ66 from combined radar and optical observations". Monthly Notices of the Royal Astronomical Society 507, n. 4 (3 settembre 2021): 4914–32. http://dx.doi.org/10.1093/mnras/stab2476.

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Abstract (sommario):

Abstract The Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect is a small thermal-radiation torque experienced by small asteroids, and is considered to be crucial in their physical and dynamical evolution. It is important to understand this effect by providing measurements of YORP for a range of asteroid types to facilitate the development of a theoretical framework. We are conducting a long-term observational study on a selection of near-Earth asteroids to support this. We focus here on (68346) 2001 KZ66, for which we obtained both optical and radar observations spanning a decade. This allowed us to perform a comprehensive analysis of the asteroid’s rotational evolution. Furthermore, radar observations from the Arecibo Observatory enabled us to generate a detailed shape model. We determined that (68346) is a retrograde rotator with its pole near the southern ecliptic pole, within a 15○ radius of longitude 170○ and latitude −85○. By combining our radar-derived shape model with the optical light curves, we developed a refined solution to fit all available data, which required a YORP strength of $(8.43\pm 0.69)\times 10^{-8} \rm ~rad ~d^{-2}$. (68346) has a distinct bifurcated shape comprising a large ellipsoidal component joined by a sharp neckline to a smaller non-ellipsoidal component. This object likely formed either from the gentle merging of a binary system or from the deformation of a rubble pile due to YORP spin-up. The shape exists in a stable configuration close to its minimum in topographic variation, where regolith is unlikely to migrate from areas of higher potential.

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Pellinen-Wannberg, A., A. Westman, G. Wannberg e K. Kaila. "Meteor fluxes and visual magnitudes from EISCAT radar event rates: a comparison with cross-section based magnitude estimates and optical data". Annales Geophysicae 16, n. 11 (30 novembre 1998): 1475–85. http://dx.doi.org/10.1007/s00585-998-1475-x.

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Abstract (sommario):

Abstract. Incoherent scatter radars (ISR) are versatile instruments for continuous monitoring of ionisation processes in the Earth's atmosphere. EISCAT, The European Incoherent Scatter facility has proven effective also in meteor studies. The time resolution of the radar can be reduced to a few milliseconds, sufficient to resolve the passage of individual meteors through the narrow ISR beam. Methods for group and phase velocity determination of the meteoroids and the discrepancy between the results related to the target behaviour are presented. The radar cross sections of echoes associated with moving meteoroids ("meteor head echoes") are very small and increase with decreasing wavelength. The parent meteoroids are found to have visual magnitudes far below the detection limit of most optical observations. The equivalent visual magnitude limit of the smallest objects observed by EISCAT in the current experiments has been estimated by two different methods, both from the cross-section measurements and from the measured event rates. Both methods give a limit value of +10 for the smallest objects while the upper limit is +4. The lower limit of the visual magnitude for the collocated optical measurement system is +4. Thus the two detection systems observe two different meteor size ranges, with the radar almost reaching micrometeorite population. Meteor fluxes estimated from the event rates and the radar system parameters agree well with previous extrapolated values for this size range.Key words. Ionosphere (ionization mechanisms). Radio science (ionospheric physics). Space plasma physics (ionization processes)

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Vinogradova, T. A., O. M. Kochetova, Yu A. Chernetenko, V. A. Shor e E. I. Yagudina. "The orbit of asteroid (99942) Apophis as determined from optical and radar observations". Solar System Research 42, n. 4 (30 luglio 2008): 271–80. http://dx.doi.org/10.1134/s0038094608040011.

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Michell, R. G., M. DeLuca, D. Janches, R. Chen e M. Samara. "Simultaneous optical and dual-frequency radar observations of small mass meteors at Arecibo". Planetary and Space Science 166 (febbraio 2019): 1–8. http://dx.doi.org/10.1016/j.pss.2018.07.015.

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