The Moon as a Microwave Calibration Reference

We present new model predictions of the earth-directed microwave brightness temperatures (TB) of the moon with dependence on phase angle over the wavelength range of 1 mm – 10 cm. Both disk average and global maps are included. The models are based on detailed thermophysical property retrievals provided by Apollo in situ measurements, Diviner and Chang E’2 (CE2) global measurements, and high quality pre-Apollo earth-based observations. Of particular importance are the advances in electrical property (loss tangent) determinations provided by the CE2 lunation amplitude data. A detailed error analyses is included to provide estimates of the TB model error bounds due to realistic assessments of the uncertainties of the contributing thermophysical properties. Disk average TB uncertainty levels of ~ +/- 4 K are found for wavelengths in the 1-10 cm range and ~ +/-8 K for ~ 1-5 mm wavelengths. Analyses are presented indicating that neither surface roughness nor potential correlation of the thermal parameter uncertainties significantly impact the model total error budget. The new models are proposed as stable absolute calibration references for earth-based microwave radiometers, in particular the vast array of earth-orbiting instruments now monitoring weather and climate properties globally.