Developing Vicarious Calibration for Microwave Sounding Instruments Using Lunar Radiation

Abstract

Accurate global observations from space are critical for global climate change study. However, atmospheric temperature trend derived from spaceborne microwave instruments remains a subject of debate, due mainly to the uncertainty in characterizing the long-term drift of instrument calibration. Thus, a highly stable target with a well-known microwave radiation is required to evaluate the long-term calibration stability. This paper develops a new model to simulate the lunar emission at microwave frequencies, and the model is then used for monitoring the stability of the Advanced Technology Microwave Sounder (ATMS) onboard Suomi NPP satellite. It is shown that the ATMS cold space view of lunar radiation agrees well with the model simulation during the past five years and this instrument is capable of serving the reference instrument for atmospheric temperature trending studies, and connecting the previous generation of microwave sounders from NOAA-15 to the future Joint Polar Satellite System Microwave Sounder onboard NOAA-20 satellite.

A Study of Lunar Microwave Radiation Based on Satellite Observations

“…Together with the Microwave Humidity Sounder (MHS), it is the precursor of the ATMS onboard NOAA-20 and SNPP. AMSU-A LI samples can be identified from space-view observations by calculating the position of the Moon in the rotation-antenna coordinate system, taking into consideration the satellite attitude, earth rotation axis alignment, and instrument mounting matrix [20,21]. Since there is only one space-view sample available at each AMSU-A scan, searching for "clean" reference calibration counts is challenging because the calibration gain keeps changing during the LI process.…”

“…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.…”

A study of a two-dimensional scanned lunar image for Advanced Technology Microwave Sounder (ATMS) geometric calibration

“…Accordingly, the lunar scan data should appear the same shape in that frame except that the spread of the Gaussian function is widened by the integration over a solid angle and sampling time. More details about the lunar modeling can be found in Yang et al (2018).…”

“…As a distinctive target with stable microwave emission in the cold cosmic background, the Moon has already been proven to be very useful in evaluating ATMS long-term calibration stability. In doing so, a physical model is developed to simulate the lunar emission at microwave frequencies (Yang et al, 2018). However, the possibility of using the Moon for geolocation validation and correction of microwave sensors has not been widely discussed.…”