共查询到20条相似文献，搜索用时 15 毫秒
1.
T. W. Thompson H. Masursky R. W. Shorthill G. L. Tyler S. H. Zisk 《Earth, Moon, and Planets》1974,10(1):87-117
Between 1000 and 2000 infrared (eclipse) and radar anomalies have been mapped on the nearside hemisphere of the Moon. A study of 52 of these anomalies indicates that most are related to impact craters and that the nature of the infrared and radar responses is compatible with a previously developed geologic model of crater aging processes. The youngest craters are pronounced thermal and radar anomalies; that is, they have enhanced eclipse temperatures and are strong radar scatterers. With increasing crater age, the associated thermal and radar responses become progressively less noticeable until they assume values for the average lunar surface. The last type of anomaly to disappear is radar enhancement at longer wavelengths. A few craters, however, have infrared and radar behaviors not predicted by the aging model. One previously unknown feature - a field strewn with centimeter-sized rock fragments - has been identified by this technique of comparing maps at the infrared, radar, and visual wavelengths. 相似文献
2.
J.D. Mathews M.P. Sulzer C.A. Tepley R. Bernard J.L. Fellous M. Glass M. Massebeuf S. Ganguly R.M. Harper R.A. Behnke J.C.G. Walker 《Planetary and Space Science》1981,29(3):341-348
The results of simultaneous meteor and Thomson scatter radar wind measurements in the 65–105 km altitude region are presented. The two radars are located in Puerto Rico where the 430-MHz Thomson scatter radar at Arecibo Observatory is employed along with the French (CNET) portable meteor radar which is at a 40-km distance. The two sets of wind measurements compare quite favorably during periods of coincident observation. The meteor radar yields continuous results while the Thomson scatter radar is usable only during daylight hours. The Thomson scatter results, on the other hand, extend down to 65 km altitude and are available with better height and time resolutions than the meteor radar results. The two measurement techniques are therefore complementary. 相似文献
3.
A. D. M. Walker 《Astrophysics and Space Science》1995,230(1-2):415-430
Ionospheric radars are an important tool for studying magnetospheric dynamics. The nature of such instruments is described and their application to a number of important problems is discussed, emphasizing South African work. A study of the theory of reflection from irregularities is discussed. The nature of ULF pulsations of more than one type has been elucidated by radar studies. An improvement of the understanding of magnetospheric convection has been achieved. A new HF radar experiment being developed for operation at SANAE, Antarctica, is described. An HF radar will be operated at SANAE in conjunction with the British radar at Halley to provide vector information about magnetospheric convection within that part of the magnetosphere which maps to a large portion of the Antarctic continent. The radar will be part of the SuperDARN international network of radars. 相似文献
4.
The auroragraph is a device for the analysis of any movements of patterns on movie films. Its application to the PPI record from an auroral radar is described, and examples from Syowa Station, Antarctica are given. The radar auroragraph has advantages over other more conventional methods of deriving the speed and direction of movement of auroral radar echoes in space. 相似文献
5.
High-resolution lunar radar map at 70-cm wavelength 总被引：4，自引：0，他引：4
T. W. Thompson 《Earth, Moon, and Planets》1987,37(1):59-70
New radar observations of the Moon in 1981–1984 were made using the 430 MHz (70 cm wavelength) radar at the Arecibo observatory, Puerto Rico. The new observations have produced a high resolution lunar radar map with radar cell-sizes near 2–5 km. This new resolution is a three-fold improvement over the previous mapping done in the late 1960's. Since the Arecibo radar antenna beam is only ten arc-minutes (about one-third of the width of the lunar disk), this new map is a mosaic of some eighteen observations. A radarmetric control between the various pieces of the mosaic was obtained via a beam-swing, limb-to-limb calibration.When the limb-to-limb calibration was combined with the mosaic, there were significant radar scattering differences across the maria. Eastern Mare Tranquillitatis and western Oceanus Procellarum have weaker echoes than other maria, while the central portion of Mare Serenitatis and northern Mare Imbrium have stronger echoes. There is a radar scattering difference across the southern terra as areas nearer Mare Orientale have stronger echoes than areas further from Mare Orientale. 相似文献
6.
7.
Michael W. Busch Shrinivas R. Kulkarni Steven J. Ostro Lance A.M. Benner Michael C. Nolan 《Icarus》2010,209(2):535-541
Knowing the shapes and spin states of near-Earth asteroids is essential to understanding their dynamical evolution because of the Yarkovsky and YORP effects. Delay-Doppler radar imaging is the most powerful ground-based technique for imaging near-Earth asteroids and can obtain spatial resolution of <10 m, but frequently produces ambiguous pole direction solutions. A radar echo from an asteroid consists of a pattern of speckles caused by the interference of reflections from different parts of the surface. It is possible to determine an asteroid’s pole direction by tracking the motion of the radar speckle pattern. Speckle tracking can potentially measure the poles of at least several radar targets each year, rapidly increasing the available sample of NEA pole directions. We observed the near-Earth asteroid 2008 EV5 with the Arecibo planetary radar and the Very Long Baseline Array in December 2008. By tracking the speckles moving from the Pie Town to Los Alamos VLBA stations, we have shown that EV5 rotates retrograde. This is the first speckle detection of a near-Earth asteroid. 相似文献
8.
地基雷达观测可以提供太阳系天体目标的地形地貌、物理特征、轨道动力等信息。聚焦利用地基雷达天文技术开展月球观测的原理方法和科学意义,介绍了基于我国现有深空雷达上行装置、射电望远镜条件以及非相干散射雷达等系统,初步开展的特高频段(Ultra High Frequency,UHF)和X频段的地基雷达观测月球试验。通过月球反射回波的信号处理,获得了延迟、多普勒频移等参数,得到了一致的与近表层物质密度相关的月面雷达反射率,并得到了月球的左右旋圆极化率,反映了与波长同尺度的月球近表层结构。文章积累的数据处理经验将为我国的小行星预警、行星历表等地基雷达观测研究提供技术基础。 相似文献
9.
During Cassini’s T44 flyby of Titan (May 28, 2008), the Cassini SAR (synthetic aperture radar) revealed sinuous channels in the Southwest of Xanadu. These channels feature very large radar cross-sections, up to 5 dB, whereas the angle of incidence was relatively high, ∼20°. This backscatter is larger than allowed by the coherent backscatter model considered to explain the unusual reflective and polarization properties of the icy satellites and only a few radar scattering mechanisms can be responsible for such high radar returns. The presence of rounded (icy) pebbles with size larger than the radar wavelength (2.18 cm) is proposed to explain the large radar cross-sections measured in these units. The radar-bright channels are thus interpreted as riverbeds, where debris, likely shaped and transported by fluvial activity, have been deposited. Similar debris were observed in the landing site of the Huygens probe. This work may point the way to an explanation for the enhanced brightness of other fluvial regions of Titan. 相似文献
10.
Initial studies of the Sun's corona using a solar radar were done in the 1960s and provided measurements of the Sun's radar cross-section at about 38 MHz. These initial measurements were done at a time when the large-scale phenomenon known as a coronal mass ejection was unknown; however, these data suggest that coronal mass ejections (CMEs) may have been detected but were unrecognized. That solar radar facility, which was located at El Campo, TX, no longer exists. New solar radar investigations are motivated by our modern understanding of CMEs and their effects on the Earth. A radar echo from an Earthward-directed coronal mass ejection may be expected to have a frequency shift proportional to velocity; thus providing a good estimate of arrival time at Earth and the possible occurrence of geomagnetic storms. Solar radar measurements may also provide new information on electron densities in the corona. The frequencies of interest for solar radars fall in the range of about 10–100 MHz, corresponding to the lower range planned for the low-frequency array. In combination with existing or new high-power transmitters, it is possible to use the low-frequency array to re-initiate radar studies of the Sun's corona. In this report, we review the basic requirements of solar radars, as developed in past studies and as proposed for future investigations. 相似文献
11.
The problem of subsurface radar sounding of the martian polar caps [Ilyushin, 2004. Martian northern polar cap: layering and possible implications for radar sounding. Planet. Space Sci. 52, 1195–1207] is considered from the point of view of incoherent radiative transfer theory. Since it has been previously shown that the radar signal field within the polar cap has diffuse structure, there is a need for a statistical approach to the problem. Radiative transfer theory, which is now well developed, seems to be the most appropriate formalism for this approach.Several physical models of polar caps have been formulated. The asymptotic solutions for all proposed models are derived here. In the present paper only the case of orbital ground penetrating radar is considered, because it is of great interest in relationship to currently developed radar experiments. In principle, the approach is believed to be applicable to a wide class of short pulse and compressed chirp radar experiments, including both orbital and landed instruments and media more complicated than a simple plane parallel geometry. This work, however, is postponed to future papers.Techniques for retrieval of physical properties of polar caps from the radar measurements are proposed. From the observational data, the macroscopic parameters of the medium appearing in radiative transfer theory, i.e. the single scattering albedo and volume extinction coefficient can be estimated. These estimates put certain constraints on the physical parameters of the medium model introduced in the paper. With some additional information, known a priori or from other observations, these estimates can be used to retrieve physically meaningful information, for example, the average content of impurities in the ice. 相似文献
12.
Study of a Bistatic Radar System Using VLBI Technologies for Detecting Space Debris and the Experimental Verification of its Validity 总被引：1，自引：0，他引：1
Masanobu Yajima Kazutomo Tsuchikawa Toshiyuki Murakami Kazuyoshi Katsumoto Tadashi Takano 《Earth, Moon, and Planets》2007,100(1-2):57-76
Space debris are increasing around the Earth. The observation of space debris is a key issue for the investigation and monitoring
of space environment. But the observation opportunities and the detection ability are limited in existing monostatic radar
systems. This paper proposes a bistatic radar which is composed of a transmitting station and a receiving-only station. A
carrier wave modulated by PN-PSK signals is used in combination with a VLBI (Very Long Baseline Interferometry) recorder for
range measurement between space debris and stations. The receiving radio wave is processed on the basis of VLBI techniques.
Accordingly, the system is shown to have significant advantages over a monostatic radar. We actually formed a bistatic radar
system, and observed a satellite in order to experimentally verify the validity. The configuration of the system, data analysis
and the experimental results are described. 相似文献
13.
The surface of Venus viewed in Arecibo radar images has a small population of bright ring-shaped features. These features are interpreted as the rough or blocky deposits surrounding craters of impact or volcanic origin. Population densities of these bright ring features are small compared with visually identified impact craters on the surface of the Moon and volcanic craters on Io. However, they are comparable to the short-lived radar-bright haloes associated with ejecta deposits of young craters on the Moon. This suggests that bright radar signatures of the deposits around Venusian craters are obliterated by an erosional or sedimentary process. We have evaluated the hypothesis that bright radar crater signatures were obliterated by a global mantle deposited after impacts of very large bolides. The mechanism accounts satisfactorily for the population of features with internal diameters greater than 64 km. The measured population of craters with internal diameters between 32 and 64 km is difficult to account for with the model but it may be underestimated because of poor radar resolution (5 to 20 km). Other possible mechanisms for the removal of radar bright crater signatures include in situ chemical weathering of rocks and mantling by young volcanic deposits. All three alternatives may be consistent with existing radar roughness and cross-section data and Venera 8, 9, and 10 data. However, imaging observations from a lander on the rolling plains or lowlands may verify or disprove the proposed global mantling. New high-resolution ground-based radar data can also contribute new information on the nature and origin of these radar bright ring features. 相似文献
14.
The entire earth-facing lunar surface has been mapped at a resolution of 2 km using the 3.8-cm radar of Haystack Observatory. The observations yield the distribution of relative radar backscattering efficiency with an accuracy of about 10% for both the polarized (primarily quasispecular or coherent) and depolarized (diffuse or incoherent) scattered components. The results show a variety of discrete radar features, many of which are correlated with craters or other features of optical photographs. Particular interest, however, attaches to those features with substantially different radio and optical contrasts. An anomaly near 63° is noted in the mean angular scattering law obtained from a summary of the radar data. 相似文献
15.
We review the results of radar studies of the Sun made at El Campo, Texas 1961–69 with particular emphasis on the record of observed solar radar cross sections. Using ray traces which include the effects of refraction, absorption, and scattering in non-spherically symmetric models of the corona, we investigate the role of focusing by large-scale coronal geometries in enhancing the radar cross section. We find that certain coronal geometries (e.g. disk-center coronal holes) can, in principle, significantly increase the radar cross section. However the observations of large cross sections do not correspond very well with periods when such large-scale focusing geometries existed in the corona. We conclude that the present dataset does not support the hypothesis that radar observations of the Sun will be useful in determining the properties of large-scale coronal features.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
16.
Ya.A. Ilyushin 《Planetary and Space Science》2009,57(12):1458-1466
The effect of the ionospheric scintillations on the performance of the dekameter wave band synthetic aperture radar (SAR) is considered. The numerical model for computer simulations, based on the multiple phase screen technique and accounting for diffraction, is formulated. The result of numerical simulations of the radar pulses is presented and analyzed. The role of the various features of the ionospheric disturbances and their influence on the radar pulse characteristic parameters is figured out and discussed. Both effects of anisotropy of the correlation function of plasma irregularities and their temporal variations are studied numerically. 相似文献
17.
T. W. Thompson W. J. Roberts W. K. Hartmann R. W. Shorthill S. H. Zisk 《Earth, Moon, and Planets》1979,21(3):319-342
Radar, infrared, and photogeologic properties of lunar craters have been studied to determine whether there is a systematic difference in blocky craters between the maria and terrae and whether this difference may be due to a deep megaregolith of pulverized material forming the terra surface, as opposed to a layer of semi-coherent basalt flows forming the mare surface. Some 1310 craters from about 4 to 100 km diameter have been catalogued as radar and/or infrared anomalies. In addition, a study of Apollo Orbital Photography confirmed that the radar and infrared anomalies are correlated with blocky rubble around the crater.Analysis of the radar and infrared data indicated systematic terra—mare differences. Fresh terra craters smaller than 12 km were less likely to be infrared and radar anomalies than comparable mare craters: but terra and mare craters larger than 12 km had similar infrared and radar signatures. Also, there are many terra craters which are radar bright but not infrared anomalies.Our interpretation of these data is that while the maria are rock layers (basaltic flow units) where craters eject boulder fields, the terrae are covered by relatively pulverized megaregolith at least 2 km deep, where craters eject less rocky rubble. Blocky rubble, either in the form of actual rocks or partly consolidated blocks, contributes to the radar and infrared signatures of the crater. However, aging by impacts rapidly destroys these effects, possibly through burial by secondary debris or by disintegration of the blocks themselves, especially in terra regions.PSI Contribution No. 110. 相似文献
18.
Walter E. Brown Jr. 《Earth, Moon, and Planets》1972,4(1-2):113-127
The Apollo Lunar Sounder Experiment that is scheduled to orbit the Moon on Apollo 17 consists of a three frequency coherent radar system and an optical recorder. The coherent radar can be used to measure both phase and amplitude characteristics of the radar echo. Measurement methods that are related to the phase and amplitude will be used to determine the surface profile, locate subsurface features and ascertain near surface electrical properties of the lunar surface. The key to the coherent radar measurement is a highly stable oscillator that preserves an accurate phase reference (2 or 3 electrical degrees) over a long period of time. This reference provides a means for reducing surface clutter so that subsurface features are more easily detected and also provides a means of measuring range to the surface to within a fraction of a wavelength. 相似文献
19.
V. M. Smirnov V. N. Marchuk O. V. Yushkova V. V. Abramov A. S. Bazhanov B. S. Lifantsev 《Solar System Research》2010,44(5):423-437
The specific features of the radar sounding of the soil of Phobos during the performance of the Russian Phobos-Grunt project have been considered. The parameters of the long-wave subsurface sounding radar designed in order to study the electrophysical
characteristics of the soil of Phobos, reveal the depth structure, estimate the rock density, and perform radar mapping of
the satellite relief and surface roughness have been justified. The scheme of the experimental sounding of the soil of Phobos
is presented. 相似文献
20.
There is a correlation between Martian thermal inertia and radar cross section data centered on +22° latitude. The correlation is strongest with 70-cm radar, except between longitudes 10 and 90° where there is a slight anticorrelation, and gets progressively weaker at 12.5- and 3.8-cm wavelengths, respectively. A correlation is expected because of the dependence of both properties on density, but an increase in the average particle size of the surface with increasing dielectric constant is also required in order to explain the data. This may take the form of an increased number of small rocks. The anticorrelation may result from either the effects of atmospheric dust on the surface temperature or from the effects on radar of local variations in large-scale roughness or scattering by rocks. The relative behavior between the wavelengths can be understood in terms of appropriately sized rocks which act as radar scatterers. The trend of the correlation agrees with the dichotomy of the planet into two types of terrain, as noted in other remote-sensing data, and is consistent with an erosional versus depositional surface nature. Variations in the surface dielectric constant, inferred from the 3.8-cm radar data, can explain discrepancies between 2.8-cm radio emission observations and a simple model based on the global distribution of thermal inertia and albedo. 相似文献