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Magnetospheric diurnal electron concentration variation from Faraday polarization rotation and differential Doppler frequency measurements of lunar radar echoes
This oral presentation examines the use of lunar radar data in the study of the moon's crust. Examined are long-wavelength (70-cm and 7.5-meter) radar scatter from the lunar surface in order to gain some insight into its structure and chemical composition.
Radar echo measurements for determining lunar scattering properties
Lunar exploration conference - radar echo, radar data interpretation, photographic photometry, lunar volcanics, & manned exploration
Ground-based bistatic radar astronomy technique using distantly spaced receiver and transmitter in trial measurement of lunar angular size
Dielectric constants, composition, and depths of layers of moon based on two-layer lunar model using radar echoes
A method for extracting surface-slope frequency distributions from bistatic-radar data has been developed and applied to the lunar surface. Telemetry transmissions from orbiting Apollo spacecraft were received on the earth after reflection from the lunar surface. The echo-frequency spectrum was related analytically to the probability distribution of lunar slopes. Standard regression techniques were used to solve the inverse problem of finding slope distributions from observed echo-frequency spectra. Data taken simultaneously at two wavelengths, 13 and 116 cm, have yielded diverse slope statistics.
An examination was made of radar data on depolarized radar echoes for the general areas of (1) the Apollo 11, 12, 14, 15, 16, and 17 landing sites, (2) Ranger 7, 8, and 9 impact sites, and (3) the Surveyor 1, 3, 5, and 7 landing sites. These data were then compared with photographic data. Surveyor 6 was excluded because it landed near the center of the lunar disk where echo data are poor. Three problems concerning the echo data are (1) the frequency distributions of echo strengths from site to site, (2) the areal distribution of echoes, and (3) detailed correlation of echoes with the photographs of the Apollo 17 landing area.
Radar echoes intensity distribution maps from lunar surface surrounding crater Tycho
Radio and radar studies of lunar and planetary ionospheres, atmospheres, and surfaces, sun echoes, and spacecraft instrumentation
Supersynthesis and delay-Doppler methods of mapping radar echo power distribution across lunar surface
Three sets of polarized radar-echo images of the Moon were examined to establish the relation between radar resolution and landform-identification resolution. After comparison with lunar maps and photographs, real and apparent landforms on the radar images were grouped into one of seven classes. Results show strong relations between radar resolution and diameter or relief of landforms that are clearly identified and those that would probably be correctly identified (class 1 and class 2). Landforms are not detected (class 5) at all diameters and reliefs, but the percentage of undetected landforms decreases with increasing mean diameter and mean relief. Landforms are simply detected (class 4) at most mean diameters and reliefs. Ambiguous arrays (class 6) portrayed by the radar constitute up to about 16, 22, and 15% of the landforms at various diameters and relief values for the 3.8 cm, 70 cm high resolution, and 70 cm low resolution images, respectively. Only a few percent of the landforms portrayed by the radar images at various diameters and relief values are fictitious (class 7).
Since 1990, much effort has been devoted to optimizing Goldstone's capability to study near-Earth objects (NEOs). Three different configurations are now available. The nominal system on the 70-m antenna (DSS 14) uses separate feed horns for transmitting and receiving, and the 15-plus seconds required for transmit-to-receive switching renders the system useless for targets much closer than about 0.025 AU (about 10 lunar distances, about 25 seconds of echo time delay) and unwieldy even for targets twice that far. However, an additional, recently installed single horn system shrinks switching time to about 5 seconds, letting DSS 14 observe NEOs as close as about 5 lunar distances. Closer targets will require two-station observations, with DSS 14 transmitting continuously while DSS 13, a 34-m antenna 22 km away, receives. That configuration, first used for Toutatis, will also be required for delay-Doppler imaging that places thousands of pixels on any NEO whose rotation period P(h) and echo roundtrip time delay RTT (s) satisfy P > RTT. Between January 1990 and June 1994, the Goldstone radar has detected 11 asteroids. During the next 2 years, seven asteroids are scheduled for Goldstane observations. After completion of the Arecibo upgrade, Goldstone will play an important complementary role to that much more sensitive instrument.
As NASA seeks to fulfill its mission of extending humanity’s reach through exploration as delineated in the Moon to Mars Strategy and Objectives Development and the Moon to Mars Architecture Definition Document, accurate and timely position, navigation, and timing (PNT) services are critical in the architecture, identifying a need to expand a PNT capability to the full lunar proximity service volume. This is echoed in the White House Office of Science, Technology, and Policy Cislunar Science and Technology Strategy, which pinpoints the fundamental need for PNT infrastructure to enable and sustain a vibrant cislunar ecosystem. While the Human Lunar Return segment seeks commercial services to provide a PNT service over a South Pole service volume for a limited period per Earth day, meeting the Sustained Lunar Evolution segment requires a Lunar Navigation System (LNS) focused on delivery of precise and resilient PNT services across the lunar globe and near-Moon space. This presentation describes the pre-Phase A system concept for an orbital constellation, the requisite lunar surface-based in-situ monitor and control segment, and an Earth control segment to provide lunar PNT services out to 200km altitude above the surface. The LNS leverages the foundational efforts on lunar reference system components such as the Lunar Geodetic System, Lunar Time System, and lunar ephemeris and orientation critical to safe, accurate, and seamless navigation.
Lunar radar backscattering data for Apollo program obtained over lunar-like terrain by scatterometer using echoes from fan-beam antenna
The international program of lunar telemetry, which has been in operation for three and one-half years, is intended to supply basic information for study of the lunar motion and the internal physics of the moon and the earth, particularly with reference to movement of the pole and displacements of plates. Laser echoes were obtained on Jan. 23, 1973 from the French reflector placed on the moon by Luna 21. Two series of firings, made with a 3-J laser radiated by the 2.7-m telescope of the McDonald Observatory (Texas) made it possible to identify significant echoes of an intensity comparable to those obtained with the reflector set down by Apollo 15. The path time measurements are compatible with normal coordinates.
Geometric optics used with Fresnel coefficients to interpret data on radar echoes from Moon
The Apollo 15, 16, and 17 core tubes show that the uppermost few meters of the lunar regolith are interlaced layers of a fine grained powders and blocky crater ejecta. The layers of crater ejecta have dielectric constants in the range of 7-9 while the fine-grained powders has dielectric constant on the order of 2.7. These differences in dielectric constant, in turn, create radar reflections that are both refracted and reflected back through the space-regolith interface. Note that for a dielectric constant of 2.7 for the lunar regolith, radio waves incident on the lunar surface at the angle of 30-degrees from the normal will propagate in the regolith at an angle of 18-degrees. At the limb, radio waves incident on the lunar surface at an angle near 90-degrees from the normal will propagate in the regolith at an angle of about 37-degrees. These angles are within the range where radar backscatter is in the quasi-specular regime. When these buried crater ejecta layers are modeled using Hagfors' formulation (Hagfors,1963), echo powers match the behavior observed for average lunar backscatter at centimeter wavelengths for higher (30 to 90) angles of incidence. In addition, Hagfors et al. (1965) conducted an experiment where the Moon was illuminated at 23-cm wavelength with circular polarization and the differences were observed in orthogonal linear polarizations. Modeling of these observations and assuming again that the buried crater ejecta scatter in a quasi-specular manner, echo differences in horizontal and vertical linear polarizations are in good agreement with the observations.