Disk-Integrated Lunar Brightness Temperatures between 89 and 190 GHz

Abstract

Measurements of the disk-integrated brightness temperature of the Moon at 89, 157, 183, and 190 GHz are presented for phase angles between -80° and 50° relative to full Moon. They were obtained with the Microwave Humidity Sounder (MHS) on NOAA-18 from 39 instances when the Moon appeared in the deep space view of the instrument. Polynomials were fitted to the measured values and the maximum temperature and the phase angle of its occurrence were determined. A comparison of these results with the predictions from three different models or rather parametrical expressions by Keihm, Mo & Kigawa, and Yang et al. revealed significantly larger phase lags for the lower frequencies in the measurements with MHS. As the Moon has appeared thousands of times in the field of view of all microwave sounders combined, this investigation demonstrates the potential of weather satellites for fine tuning models and establishing the Moon as extremely accurate calibration reference.

A Study of Lunar Microwave Radiation Based on Satellite Observations

“…This instrument was operational from May 2005 through October 2018, so it is particularly well-suited to study the dependence of the lunar microwave radiation from phase angle (see Section 3). In [23], T b s of the Moon as a function of phase angle for each channel of the MHS onboard NOAA-18 were reported. Here, new measurements from other instruments were added to the plots to extend the range of phase angles and to determine the scatter among data from different instruments.…”

“…For most climate applications, the detection frequency needs to be extended to as high as 183 GHz, making the observations from Chang'E less useful. In recent years, Yang et al [20,21] and Burgdorf et al [22,23] have explored a method of retrieving lunar-disk-integrated microwave T b s from the space-view observations of microwave-sounding instruments onboard weather satellites. The basic idea is that during lunar intrusion (LI) events, when the Moon appears in the satellite observation field of view, the effective microwave radiance of the Moon's disk, R e f f moon , can be derived from the receiver output counts difference between the clean space view and the space view with LI [20]:…”

“…Unlike ground-based observations, spaceborne microwave radiometers can cover a wide range of frequencies and experience less contamination from their surroundings. In the most recent studies by Yang et al [20,21] and Burgdorf et al [22,23], well-calibrated satellite observations were used to derive the lunar microwave T b spectrum from 23 GHz to 183 GHz. Their results show that the maximum lunar disk-integrated T b varies from 270 K at 23 GHz to 300 K at 183 GHz.…”

“…The lunar solid angle term Ω moon slightly depends on the position of the satellite in the orbital plane, which is highly predictable. Burgdorf et al [23] showed that the Ω moon Ω p term could be determined by performing an analytical integration of the Gaussian function over the lunar disk when the Moon passes through the center of the antenna beam, i.e.,…”

An Uncertainty Quantified Fundamental Climate Data Record for Microwave Humidity Sounders

“…the sounding channels [40] or the full width at half maximum of the beams [42]. Both quantities were determined with innovative methods based on intrusions of the Moon in the DSV.…”