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.

The Chang’E-1 and E-2 (CE-1 and CE-2) orbital sounders provided high-resolution global maps of lunar microwave brightness temperatures (TBs) at wavelengths of 0.8, 1.55, 3.85, and 10 cm covering approximately two years of data over the 2007–2010 time frame. The four-channel microwave radiometers (MRMs) effectively sampled the upper ~2 m of the lunar regolith and are diagnostic of thermal and electrical properties, including mineralogy, rock abundance, and, potentially, interior heat flow. Early comparisons of colocated data between the two instruments revealed ~10–20 K offsets between the CE-1 and CE-2 measurements that required in- flight recalibration efforts. These have included comparisons with model predictions at Apollo sites as well as adjustments of the cold sky horn reference temperatures to include contamination from lunar surface emissions. This article proposes an in- flight recalibration methodology that focuses on correction of the preflight transfer coefficients that determine the relative importance of component losses along the radiometer hardware paths connecting the antennas to the detectors. It is shown that for each channel, a single parameter, representing the ratio of the cold sky and main antenna transfer coefficients, can be constrained by knowledge of the stable regolith physical temperatures below the diurnal-varying layer and is sufficient to establish values for the complete set of hardware transfer coefficients. The in- flight comparisons proposed for recalibration are based on backside highland models of regolith thermal properties. Potential remaining offsets of the recalibrated MRM data are evaluated in terms of parameter uncertainties of our chosen nominal thermal model.

Basic radiative transfer theory reveals that the physical temperature gradients related to heat flow (HF) within the lunar regolith below the diurnal varying layer can be constrained by measurements of brightness temperature (TB) variations over a selected wavelength range, coupled with knowledge of the regolith electrical loss properties. We present a methodology illustrating the processing using recalibrated data from the Chang’E-2 (CE2) 10 and 3.85 cm wavelength microwave radiometer (MRM) data (channels 1 and 2). The utilized data are contained in latitude bins of 1 degree width centered at latitudes of 0, 5,..., 60, north and south. Results, presented as retrieved HF gradients (dT/dz in K/m) vs longitude for each of the 25 latitude bins, provide useful constraints on the overall variability of the heat flow gradient within the 60S-60N latitude range. In particular, no evidence is found that HF variations exceeding twice the Apollo value occur widely in the extensive highland regions of low electrical loss. Limitations related primarily to signal-to-noise (SNR) issues in regions of elevated electrical loss severely reduce thermal gradient retrieval accuracy needed for correlation with enhanced thorium concentrations observed in the frontside mare. Analyses of the CE2 data reveals a noise uncertainty of ~ 0.5 K in the TB10-TB3.85 measurements, equivalent to ~ 0.7 - 1.4 (loss tangent dependent) times the Apollo measured mean HF value of 1.8e ^-6 w/cm ² . The limitations preclude meaningful identification of regional variations within a precision less than one Apollo heat flow unit. An analyses is presented demonstrating that a threefold increase in SNR would be attained by addition of a 30 cm wavelength channel to the CE2 MRM’s design, providing sufficient resolution to map regional HF variations to ~ 0.5e ^-6 w/cm ² precision, ~ 30% of the averaged Apollo sites’ measured HF value.

To determine the likelihood that the surface contamination effects can explain the offsets between Chang'E-1 (CE-1) and Chang'E-2 (CE-2) microwave radiometers' (MRMs) calibrated antenna temperatures (TAs), we quantitatively estimate the effects of the lunar contamination of the CE MRMs' cold sky horn antennas on TA. We calculated the lunar radiation contributions to the cold sky horn (Δ Tcosmic) values from the Apollo model brightness temperatures (TBs) convolved with the CE-1 and CE-2 cold sky horn antenna patterns for the circular orbit geometries of CE-1 and CE-2. The calculations were done for all four channels and estimated 20°-40° range of the full width half maximum (FWHM) Gaussian beam sizes over a latitude range of 0°-64°. Small differences between the predawn and noon results illustrate that the local time effects are negligible. Most noteworthy is the result that the largest plausible ``Δ Tcosmic'' are less than 10.8 K for CE-1 and less than 23.6 K for CE-2 at the largest assumed beam size. The latitude effect is small, although significant (~5-6 K difference), from the equator to 64°. Most importantly, the cold sky horn contamination effects are shown to produce target TA errors of only 2-5 K for CE-1 and 4-10 K for CE-2 with the largest errors occurring at the lowest TAs. These errors are inadequate to resolve much larger relative offsets reported in the CE-1 and CE-2 TA data. We thus propose an alternative recalibration scheme that focuses on the role of uncertainties in the preflight derivation of hardware loss coefficients.

The Chang’E-2 (CE-2) four-channel microwave radiometer (MRM) data with frequencies of 3 GHz, 7.8 GHz, 19.35 GHz, and 37 GHz have been used to investigate the properties of lunar surface such as regolith thickness, dielectric constant, and titanium abundance within a depth of several meters in middle and low latitudes. The purpose of this work is to take a close look at MRM data in the polar regions of the Moon and analyze the characteristics of the brightness temperature (TB) in permanently shadowed regions (PSRs), especially where evidence of water ice has been found. First, the comparisons of brightness temperature values in the polar region and in low latitudes show that (1) the periodic diurnal (day/night) variation of TB becomes weak in high latitudes since topography plays a dominant role in determining TB in polar region and (2) seasonal effects are more recognizable in polar region than in low latitudes due to the weak illumination condition. Second, even without direct sun illumination, significant seasonal variations of TBs are observed in PSRs, probably caused by the scattering flux from neighboring topography. TB Ratio (TBR) between channel 1 and channel 4, which indicates the differences of TB at different depths of lunar regolith, is higher and shows stronger seasonal variation in PSR than regions with direct illumination. Third, overall the distribution of high TBR values is in consistence with the water ice distributions obtained by the Moon Mineralogy Mapper instrument, the LAMP UV spectra, and the Lunar Prospector Neutron Spectrometer. The proportion of the summation over area with water ice proof in the regions of interest is 0.89 and 0.56 in south pole and north pole, respectively. The causes of the correlation of high TBR between different microwave frequencies and stability of water ice deposits still require further investigation, but MRM data shows unique characteristic in PSRs and could provide important information about the upper few meters of lunar regolith.

Lunar thermal conductivity is significantly important for understanding the geological processes of the Moon. The Apollo in-situ heat flow experiments and Diviner remote sensing data provide us with good constraints on the thermophysical properties of the lunar regolith fines layer. As the first farside in-situ experiments, Chang’E-4 (CE-4) temperature sensors will further extend our understanding. In this study, a one-dimensional thermal model with updated bulk densities by the CE-4 Lunar Penetrating Radar (LPR) data is used. Then, the nighttime surface temperatures from the sensors of the CE-4 lander are applied to retrieve the surface thermal conductivity at the CE-4 landing site. After minimizing the differences between the predicted temperature and CE-4 measurements, the range of surface layer contact conductivity ( k_s ) within the upper 1 cm is about (0.95 ~ 2.26) × 10 ^-3 Wm ^-1 K ^-1 for T1, (1.04 ~ 2.44) × 10 ^-3 Wm ^-1 K ^-1 for T2, (0.60 ~ 1.40) × 10 ^-3 Wm ^-1 K ^-1 for T3, and (0.60~1.39) × 10 ^-3 Wm ^-1 K ^-1 for T4, respectively. In addition, the factors that may affect the inversion or the measurements were discussed, such as the shadowing effect, the rock abundance, the lateral conduction from the rover transfer mechanism, and the densification effect during the measurements.