Comparison and evaluation of the Chang'E microwave radiometer data based on theoretical computation of brightness temperatures at the Apollo 15 and 17 sites

A New Method for Simulation of Lunar Microwave Brightness Temperatures and Evaluation of Chang'E‐2 MRM Data Using Thermal Constraints From Diviner

“…Lunar regolith is highly insulating due to its low density and thermal conductivity (Keihm & Langseth, ), and therefore, internal heat flux into the surface during the day is small compared to the incident solar flux (Vasavada et al, ). The absorbed heat and conduction at the surface are balanced against infrared emission to space which can be expressed as (Hu et al, ) where ε IR is infrared emissivity, A is surface albedo, σ B is Stefan‐Boltzmann constant. I ( t ) and E ( t ) are solar irradiance and earthshine, respectively.…”

“…However, it is more likely that the difference between the CE‐1 and CE‐2 observations is caused by calibration uncertainties in the CE‐2 37‐GHz channel data. The uncertainties in T B37 are likely larger than those at T B19 because of lunar surface heat contaminations (Hu et al, ) because the 37‐GHz channel is more sensitive to surface temperatures. The better agreement of CE‐1 observations with our simulation results suggests that CE‐1 T B37 data are of better data quality than that of CE‐2.…”

“…For the CE‐2 observations, however, both the 19.35‐ and 37‐GHz channels worked under the same conditions and used the same calibration method, yet there exists a larger departure from the model results in the 37‐GHz data than in 19.35 GHz. Here we note that the lower altitude of the CE‐2 orbit (half of CE‐1's) allowed a larger area of the warm lunar surface to intrude into the field of view of the cold‐reference antennas at certain times during in‐orbit calibration (Hu et al, ; Siegler & Feng, ). In addition, due to the relatively short wavelength of the 37‐GHz channel, it is more sensitive to surface temperature compared to 19.35 GHz (Hu et al, ).…”

“…Here we note that the lower altitude of the CE‐2 orbit (half of CE‐1's) allowed a larger area of the warm lunar surface to intrude into the field of view of the cold‐reference antennas at certain times during in‐orbit calibration (Hu et al, ; Siegler & Feng, ). In addition, due to the relatively short wavelength of the 37‐GHz channel, it is more sensitive to surface temperature compared to 19.35 GHz (Hu et al, ). As a result, greater error from this surface heat contamination might be present in the calibrated CE‐2 MRM data, especially for the 37‐GHz data.…”

“…Future lunar mission or ground‐based observations at the MRM frequencies could provide more data for comparing with CE‐1/2 observations and further verifying our simulation results. Here we assume that the uncertainties in the CE‐2 observations were caused by thermal contamination of the cold‐reference antennas (Hu et al, ; Siegler & Feng, ) and propose a simple empirical normalization to modify the midnight data. We apply an approach following the work of Hu et al () to modify the CE‐2 observations: where is the modified value of T B , and ⟨ΔT B ⟩ is the averaged biases between simulation results and CE‐2 MRM observations.…”