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Abstract The microwave radiation passively emitted from the Moon is valuable for investigating the physical properties of the lunar regolith. Microwave maps, which can reveal subsurface characteristics at depths of centimeters to meters, give clues to understanding the evolution of the lunar surface. China's Chang'E-2 (CE-2) spacecraft carried a microwave radiometer (MRM) and conducted passive microwave remote sensing of the Moon at 3, 7.8, 19.35 and 37 GHz (10, 3.84, 1.55 and 0.81 cm wavelengths) during 2010–2011. Brightness temperature (TB) data derived from the MRM orbital observations cover the entire Moon, and the time coverage is over a complete lunation. In this paper, we use spherical harmonic fits to model the TB variation as functions of local time and latitude. Using these fits, we normalized the day- and nighttime TB data measured at various local times into noon-time and midnight conditions. The spatial sampling of the normalized TB maps is ∼6 km/pixel, much higher than ground-based observations and higher resolution than the MRM maps derived from Chang'E-1. By removing the variation in TB related to local time and latitude, we produced a series of microwave maps that reveal differences in the properties of the regolith across the lunar surface. The microwave behavior of various lunar surface features can be explained primarily by differences in the microwave loss tangent of the materials. For example, we find that the high-Ti maria have high daytime TB and exhibit lower nighttime TB than the other maria as a result of the high dielectric loss tangent of ilmenite. The ilmenite-rich materials are less transparent to microwaves, and hence emissions emerge from closer to the surface, which is heated strongly in the day and cools quickly at night. Most fresh craters correspond to low-TB spots in the nighttime microwave maps, in contrast to their behavior as hot spots in nighttime infrared data, suggesting that the higher loss tangent of rocks (compared to soils) suppresses microwave emission at night. The Aristarchus plateau has a lower loss tangent relative to its surroundings because it is blanketed by fine-grained, rock-poor pyroclastic material. The pyroclastic blanket is more transparent to microwaves than the nearby maria, causing the plateau to have relatively cool daytime TB and warm nighttime TB as a consequence of microwave emissions that originate at greater depths The Orientale basin is another prominent anomaly in the microwave maps, indicating that Orientale materials differ in thermophysical and/or dielectric properties from typical highland lithologies. Brightness temperature differences among prominent rayed craters indicate that the very youngest crater rays (e.g., Giordano Bruno) have lower thermal inertia than older but still optically immature rays (e.g., Tycho). [ABSTRACT FROM AUTHOR]

Thermal anomaly spots (both hot and cold) have been found in the global 37-GHz brightness temperature (TB) map of the moon based on the Chang’E (CE) microwave radiometer measurements. To explain their origin, a rock model is proposed to simulate the TB variation against latitude along the profile of a fresh crater in a single track way, which is selected to highlight the topographic effect and avoid any modification to the data. A mixed upper layer made up of rock and soil (regolith and dust) was employed into our previous multilayer model. The thermal properties (thermal conductivity and heat capacity) of the mixture layer are presumed to be linear with the fraction of rocks. Given that high-frequency (37 GHz) measurements are chosen, only the meter size and larger rocks of the upper mixed layer are considered to avoid scattering effects. Several fresh craters poor/rich in ilmenite are selected as testing sites. Despite uncertainties in parameters such as rock abundance (RA), and iron and titanium abundances, three conclusions can be reached from these cases: 1) RA has a significant effect on both the TB value and TB variation trend against latitude; its contribution over some craters may be as high as 15 K; 2) the simulations based on our rock model fit the CE observations better than those when rocks are not included; and 3) the rock and ilmenite contributions could be the main cause for the cold and hot spots found in the CE microwave map. [ABSTRACT FROM AUTHOR]

The calibration quality of the Chang'E-2 (CE-2) microwave radiometer (MRM) and the accuracy of brightness temperature (TB) data should be adequately addressed. The quality of CE-2 MRM data can be demonstrated by the analysis and simulation of TB data with the microwave transfer model and by the relative comparison between the TB and other data sets. To calibrate the TB data in a relative way, we calculated the variation of TB with respect to the latitude over certain typical regions theoretically. Three types of areas in the Moon, including the old crater, the fresh crater, and the Apollo region, are chosen as examples. A detailed method incorporating the topographic effect is employed to compute the TB. The Lunar Reconnaissance Orbiter's Diviner infrared measurement is used to ensure the accuracy of the simulated physical temperature. The consistency of the TB undulation between simulations and observations along the profile of these regions verifies the reasonability of CE-2's TB data partly. Our simulation also confirms the topographic effect of sloping walls at the crater rims on the solar heat flux received per unit surface area and reproduces the TB undulation observed by CE-2. Rock abundance and topography data are used for qualitative comparison with the CE-2 TB data. General similarity between the diurnal TB difference and the altitude profile over most craters and the similarity between the diurnal TB difference and the rock abundance profile over fresh craters can prove the relative qualification of CE-2 MRM data to a certain degree. [ABSTRACT FROM PUBLISHER]

To improve the retrieval accuracy of the lunar properties from microwave brightness temperature (TB) data sets of the lunar surface, TB measurements of the global moon need a calibration source to better estimate. In this letter, the standard for the calibration source is defined, and two possible calibration sources (the lunar center and Apollo 15) are proposed, which are based on a theoretical TB model. There is a difference of about 4 (3/37 GHz) and 11 K (7.8/19.35 GHz) between the simulated calibration source and Chang'E observation at the lunar center, and of about 7 K (3/7.8/19.35/37 GHz) at Apollo 15. The simulated calibration source (7.8/37 GHz) of the lunar center is within the range of the ground-based measurement. Note that the lunar center has been measured frequently by both ground-based and in-orbiter instruments, and the calibration source of the lunar center is the most possible and credible for the lunar surface. The uncertainty of the calibration source has been also analyzed. [ABSTRACT FROM PUBLISHER]

Abstract: Microwave brightness temperature data obtained by the Chinese Chang''E-1 lunar orbiter are analyzed with the lunar diurnal variations filtered. Resulting maps from the high frequency microwave channel show lunar topographic signatures with close similarity to those seen in Clementine''s lunar topography maps, while the low frequency channels reveal intriguing lunar surface properties not previously observed. Here we focus on two characteristics displayed by the filtered brightness temperature maps: in the high frequency maps the existence of an anti-correlation between daytime and nighttime brightness temperature deviations in certain regions (especially in the lunar maria), and in the low frequency maps the appearance of cold spots which correspond with the hot spots observed in the infrared during lunar eclipses. [Copyright &y& Elsevier]