Remote Probing of the Moon by Infrared and Microwave Emissions and by Radar

Abstract

The results of the remote probing of the moon by means of infrared and microwave emissions and by radar are reviewed. Also, we discuss how the various observational results can help to explain physical parameters of the lunar surface, such as thermal and electrical conductivities, dielectric constant, density, particle sizes in the lunar regolith, depth of the surface layer, roughness of the surface, variation of these parameters from point to point on the surface, and amount of heat generated in the lunar interior. 190 T. HAGFORS ' at several different phase angles in order to obtain maps of isotherms on the moon. The resolution used was 25 seconds of arc as compared with the diameter of the moon which is about 30 minutes of arc. The data in the figure were obtained from the thermal contours at a few different phase angles. The data ascribed to Saari and Shorthill [1967] were obtained in a wavelength interval from 10 to 12t• with an instrument having an angular resolution of 8 seconds of arc. The post-sunset data were obtained by Murray and Wildey [1964] at 8-13t• with a resolution of 26 seconds of arc and by Shorthill and Saari [1965] at 10-12tz with their higher resolution instrument. The pre-sunrise observations are particularly difficult to make because of the high sensitivity required. Having special instrumentation Low [ 1965] was able to determine the pre-sunrise temperature by scanning over the cold limb of the moon at a wavelength of 20t•. He found an average pre-dawn temperature of 90øK and also observed colder localized areas with temperatures down to 70øK.

Ground-based radar observations of Titan: 2000–2008

“…The RMS slopes obtained from these spectra are significantly smaller than those measured at 2.2 cm wavelength by the Cassini RADAR (Wye et al, 2007). The larger RMS slopes at shorter wavelengths is consistent with the behavior of other surfaces such as the Moon (Hagfors, 1970) or Mars .…”

Regolith composition and structure in the lunar maria: Results of long‐wavelength radar studies

“…To compare these data to the results of theoretical models, we first calibrated the radar images to values of backscatter cross section per unit area ((•"). This was done by letting the mean polarized (LR: left-circular transmit, right circular receive; also called opposite-sense circular or OC) echo behavior at 70 cm be characterized by the 68-cm lunar average compiled by Hagfors [1970]. The alepolarized (LL: left-circular transmit, letl-circular receive; also called same-sense circular or SC)returns were calibrated by letting the average echoes near the limb be 1/2 (-3 dB)the strength of the polarized component, again as indicated by earlier disk-integrated measurements [Hagfors, 1970].…”

“…This was done by letting the mean polarized (LR: left-circular transmit, right circular receive; also called opposite-sense circular or OC) echo behavior at 70 cm be characterized by the 68-cm lunar average compiled by Hagfors [1970]. The alepolarized (LL: left-circular transmit, letl-circular receive; also called same-sense circular or SC)returns were calibrated by letting the average echoes near the limb be 1/2 (-3 dB)the strength of the polarized component, again as indicated by earlier disk-integrated measurements [Hagfors, 1970]. The systematic error in these calibrations is difficult to define, but mosaicking offsets probably produce error bounds of about 1-2 dB between sites in widely separated locales.…”

Modeling radar scattering from icy lunar regoliths at 13 cm and 4 cm wavelengths

“…These radar cross sections were obtained using the conventional Earth-based radar configuration, where circularly polarized waves are transmitted and received to obviate the adverse affects of Faraday rotation in the Earth's ionosphere. The values of s() given by Hagfors [1970] are for OC echoes, the polarization for mirror reflections from large, flat surfaces that are oriented perpendicular to the radar's line-of-sight. Average radar echoes in the SC polarization are assumed to be proportional to cos() with values such that the ratio of stronger OC to weaker SC echoes is 2 at the limb (where = 90°), as observed in the 1960s lunar radar observations reported igure 1.…”

“…Here = 0°at the center of the lunar disk and = 90°at the limb as viewed from Earth. Hagfors [1970] tabulates s() for wavelengths of 3.8, 23, and 68 cm based on the earlier measurements by Evans and Pettengill [1963]. These radar cross sections were obtained using the conventional Earth-based radar configuration, where circularly polarized waves are transmitted and received to obviate the adverse affects of Faraday rotation in the Earth's ionosphere.…”