High circular polarization ratios in radar scattering from geologic targets

Campbell, B. A.

doi:10.1029/2012je004061

Cited by 88 publications

(76 citation statements)

References 47 publications

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“…In the case of the former, geologically fresh surfaces (such as ejecta from young craters) create high degrees of surface roughness at wavelength-scales. Such roughness results in the creation of corner-reflectors that increase the amount of same-sense (double-bounce) reflections and thus, result in high CPR [Campbell, 2012]. Alternatively, if deposits of low-loss media (such as ice) exist on the Moon, they will also exhibit high CPR, in this case caused by both enhanced same-sense returns (through high degrees of volume scattering and corresponding multibounce) and from the coherent backscatter opposition effect (CBOE) [Hapke, 1990;Mishchenko, 1992].…”

Section: Discussionmentioning

confidence: 99%

“…This 18 km diameter crater appears to be moderately old (late Imbrian) [Scott and Pohn, 1972], but does not display high CPR exterior to its rim. However, long (several kilometers) debris flows occur in the walls of this crater, creating extensive block fields that are likely to be responsible for the high CPR in the crater interior (Figure 10) [see also Campbell, 2012]. Direct evidence for the association of high CPR and surface roughness caused by debris flows from the crater rim is also found in the walls of Linné crater (27.7°N, 11.8°E ; 2.2 km diameter) in Mare Serenitatis .…”

Section: Discussionmentioning

confidence: 99%

“…[19] High CPR on the Moon may be caused by one or both of two principal factors (1) large degrees of wavelength-scale surface roughness [e.g., Campbell, 2002Campbell, , 2012 or (2) the presence of water ice [e.g., Nozette et al, 1996Nozette et al, , 2001]. In the case of the former, geologically fresh surfaces (such as ejecta from young craters) create high degrees of surface roughness at wavelength-scales.…”

Section: Discussionmentioning

confidence: 99%

“…Ice deposits are known to have high CPR [e.g., Ostro, 2002;Campbell, 2002] caused by both volumetric backscatter and the coherent backscatter opposition effect (CBOE) [Mishchenko, 1992;Peters, 1992;Black et al, 2001;Nozette et al, 2001], an interferometeric enhancement of backscatter seen at very low beta (phase) angles. Surface scattering from dry, fine-grained planetary regolith typically has CPR less than unity [Campbell, 2002;Heggy et al, 2007], with increasing CPR seen in geologic units that have high degrees of surface roughness at scales similar to the wavelength of the imaging radar [Campbell, 2002[Campbell, , 2012.…”

Section: Experiments Design and Instrument Descriptionmentioning

confidence: 99%

“…The differences in appearance between the lunar and mercurian polar craters suggest that more ice is present on Mercury than on the Moon, probably a result of the higher cometary flux near Mercury compared with the Moon [e.g., Hartmann et al, 1981] and the fact that the higher surface gravity on Mercury (~0.3 g) means that body will retain more water on its surface. The values assigned to these end-members are based on observations of fresh craters on the Moon, which have typical CPR values at 12.5 cm wavelength of 1, with extreme examples showing CPR as high as 1.5-2.5 [Campbell, 2012] and on theoretical considerations of the CPR of pure ice reflectors [e.g., Peters, 1992].…”

Section: Modeling the Radar Backscatter Of Rough And Icy Cratersmentioning

confidence: 99%

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Evidence for water ice on the Moon: Results for anomalous polar craters from the LRO Mini‐RF imaging radar

et al. 2013

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[1] The Mini-RF radar instrument on the Lunar Reconnaissance Orbiter spacecraft mapped both lunar poles in two different RF wavelengths (complete mapping at 12.6 cm S-band and partial mapping at 4.2 cm X-band) in two look directions, removing much of the ambiguity of previous Earth-and spacecraft-based radar mapping of the Moon's polar regions. The poles are typical highland terrain, showing expected values of radar cross section (albedo) and circular polarization ratio (CPR). Most fresh craters display high values of CPR in and outside the crater rim; the pattern of these CPR distributions is consistent with high levels of wavelength-scale surface roughness associated with the presence of block fields, impact melt flows, and fallback breccia. A different class of polar crater exhibits high CPR only in their interiors, interiors that are both permanently dark and very cold (less than 100 K). Application of scattering models developed previously suggests that these anomalously high-CPR deposits exhibit behavior consistent with the presence of water ice. If this interpretation is correct, then both poles may contain several hundred million tons of water in the form of relatively "clean" ice, all within the upper couple of meters of the lunar surface. The existence of significant water ice deposits enables both long-term human habitation of the Moon and the creation of a permanent cislunar space transportation system based upon the harvest and use of lunar propellant.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Experiments Design and Instrument Descriptionmentioning

confidence: 99%

Section: Modeling the Radar Backscatter Of Rough And Icy Cratersmentioning

confidence: 99%

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Evidence for water ice on the Moon: Results for anomalous polar craters from the LRO Mini‐RF imaging radar

et al. 2013

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Improved discrimination of volcanic complexes, tectonic features, and regolith properties in Mare Serenitatis from Earth-based radar mapping

Campbell

Hawke

Morgan

et al. 2014

J. Geophys. Res. Planets

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Radar images at 70 cm wavelength show 4-5 dB variations in backscatter strength within regions of relatively uniform spectral reflectance properties in central and northern Mare Serenitatis, delineating features suggesting lava flow margins, channels, and superposition relationships. These backscatter differences are much less pronounced at 12.6 cm wavelength, consistent with a large component of the 70 cm echo arising from the rough or blocky transition zone between the mare regolith and the intact bedrock. Such deep probing is possible because the ilmenite content, which modulates microwave losses, of central Mare Serenitatis is generally low (2-3% by weight). Modeling of the radar returns from a buried interface shows that an average regolith thickness of 10 m could lead to the observed shifts in 70 cm echo power with a change in TiO 2 content from 2% to 3%. This thickness is consistent with estimates of regolith depth (10-15 m) based on the smallest diameter for which fresh craters have obvious blocky ejecta. The 70 cm backscatter differences provide a view of mare flow-unit boundaries, channels, and lobes unseen by other remote sensing methods. A localized pyroclastic deposit associated with Rima Calippus is identified based on its low radar echo strength. Radar mapping also improves delineation of units for crater age dating and highlights a 250 km long, east-west trending feature in northern Mare Serenitatis that we suggest is a large graben flooded by late-stage mare flows.

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The relationship between radar scattering and surface roughness of lunar volcanic features

et al. 2014

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Lunar roughness measurements derived from the Lunar Orbiter Laser Altimeter are compared to 12.6 cm wavelength radar data collected by the Miniature Radio Frequency instrument and 70 cm wavelength radar data collected by the Arecibo Observatory. These data are compared to assess how surface and subsurface roughness are correlated and affected by parameters including age and composition at length scales between 0.1 and 100 m. A range of features are analyzed including volcanic domes (Marius Hills, Rümker Hills, Gruithuisen, and Mairan Domes); mare (Imbrium, Serenitatis, and Oceanus Procellarum); pyroclastic dark mantle deposits (Sinus Aestuum, Sulpicius Gallus, and Mare Vaporum); and two young craters (Copernicus and Tycho). Statistically significant positive correlations exist between topographic roughness and both P-and S-band circular polarization ratios. The strongest correlation is observed at the longest length scales. Correlations weaken as length scales become less similar, potentially due to distinct processes controlling surface modification. Roughness is not significantly correlated with local slope. Although the Marius Hills are compositionally distinct from the Gruithuisen and Mairan domes, they are indistinguishable in roughness characteristics. Conversely, the Rümker Hills, mare, and dark mantle deposits are smoother at the length scales examined, possibly due to fine-grained mantling of regolith or pyroclastic deposits. The floor and ejecta of Tycho are the roughest surfaces measured in this study, while the floor and ejecta of Copernicus overlap the roughness distribution of the volcanic features. This study shows that many factors control the evolution of roughness over time on various length scales.

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High circular polarization ratios in radar scattering from geologic targets

Cited by 88 publications

References 47 publications

Evidence for water ice on the Moon: Results for anomalous polar craters from the LRO Mini‐RF imaging radar

Evidence for water ice on the Moon: Results for anomalous polar craters from the LRO Mini‐RF imaging radar

Improved discrimination of volcanic complexes, tectonic features, and regolith properties in Mare Serenitatis from Earth-based radar mapping

The relationship between radar scattering and surface roughness of lunar volcanic features

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