Icy Galilean Satellites: Modeling Radar Reflectivities as a Coherent Backscatter Effect

Black, G. J.; Campbell, D. B.; Nicholson, P.

doi:10.1006/icar.2001.6616

Cited by 81 publications

(61 citation statements)

References 36 publications

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“…The icy Galilean satellites' albedo drop from 13 to 70 cm wavelength has been interpreted as a reduction in the number of scatterers at the larger wavelength (Black et al, 2001b). The drop between wavelengths observed on lapetus was suggested by Ostro et al (2006) to result from a relatively shallow scattering layer.…”

Section: Discussionmentioning

confidence: 95%

“…The result of any added absorption at 13 cm wavelength is thus to reduce both the radar albedo and the polarization ratio. Conversely, the polarization ratios of the icy Galilean satellites may remain high at all wavelengths because their albedo drop with wavelength is due instead to a lack of scatterers available at the largest scales (Black et al, 2001b), effectively diminishing the number of scattering paths without preferentially selecting against longer ones.…”

Section: Discussionmentioning

confidence: 99%

“…All rely on subsurface scattering and range from those that consider the effects of buried structures such as craters (Baron et al, 2003;Gurrola, 1995;Eshleman, 1986), randomly oriented facets (Goldstein and Green, 1980), or refractive lenses (Hagfors et al, 1997), to models of distributions of non-specific but efficient scatterers (Black et al, 2001b) that produce a coherent enhancement in the backscatter direction (cf. Hapke, 1990;Peters, 1992).…”

Section: Introductionmentioning

confidence: 99%

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Arecibo radar observations of Rhea, Dione, Tethys, and Enceladus

Black

Campbell

Carter

2007

Icarus

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Section: Discussionmentioning

confidence: 95%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Arecibo radar observations of Rhea, Dione, Tethys, and Enceladus

Black

Campbell

Carter

2007

Icarus

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“…This quantity is defined to be the magnitude of the same sense (i.e., the left or right sense of the transmitted circular polarization) divided by the opposite sense polarized signals that are received. 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%

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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“…Polarimetric analysis methods can suggest the occurrence of subsurface scattering but do not provide strong constraints on e' (e.g., [54]). There is also evidence that multiple scattering is a significant component of echoes in settings where smooth-sided rocks or other objects are closely spaced at the surface or suspended in a low-loss matrix [55] or where a very low-loss medium (particularly ice) with included voids permits coherent superposition of signals traveling along time-reversed paths back to the observer (e.g., 156] and [57]). New studies are needed to understand single and multiple scatterings among arbitrary-shaped rocks [58] on a surface or suspended in a low-loss medium, in order to capture the range of properties exhibited by the lunar or martian regolith.…”

Section: B Empirical Models Based On Scale-dependent Roughness Parammentioning

confidence: 99%

Scale-Dependent Surface Roughness Behavior and Its Impact on Empirical Models for Radar Backscatter

Campbell

2009

IEEE Trans. Geosci. Remote Sensing

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Abstract-One goal of radar remote sensing is the extraction of terrain statistics and surface dielectric properties from backscatter data for some range of wavelengths, incidence angles, and polarizations. This paper addresses empirical approaches used to estimate terrain properties from radar data over a wider range of roughness than permitted by analytical models. Many empirical models assume, at least implicitly, that roughness parameters like rms height or correlation length are independent of the horizontal length scale over which they are measured, in contrast to recent surveys of natural terrain, which show that self-affine, or powerlaw scaling, between horizontal scale and roughness statistics is very common. The rms slope at the horizontal scale of the illuminating wavelength s(A) is directly related to the variogram or structure function of a self-affine surface, can be readily obtained from field-measured topography, and, when used in an empirical model, avoids the need for arbitrary wavelength-dependent terms. To facilitate comparison with earlier approaches, an expression that links the rms height at some profile length with the rms (Allan) deviation at an equivalent horizontal sampling interval is obtained from numerical simulations. An empirical model for polarimetric scattering as a function of 6'(A) at 35°-60° incidence from smooth to rugged lava surfaces is derived and compared with earlier models for backscatter from modestly rough soil surfaces. The asymptotic behavior of polarization ratios for the lava flows suggests that the depolarization of linear-polarized illuminating signals occurs as a first-order process, likely through single scattering by rock edges or other discontinuities, rather than as the solely multiple-scattering effect predicted by some analytical models. Efforts to fully understand radar scattering from geological surfaces need to incorporate wavelength-scale roughness, perhaps through computational simulations.

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Icy Galilean Satellites: Modeling Radar Reflectivities as a Coherent Backscatter Effect

Cited by 81 publications

References 36 publications

Arecibo radar observations of Rhea, Dione, Tethys, and Enceladus

Arecibo radar observations of Rhea, Dione, Tethys, and Enceladus

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

Scale-Dependent Surface Roughness Behavior and Its Impact on Empirical Models for Radar Backscatter

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