Calibration and validation (CAL/VAL) is a key expertise for quantitative utility of space-borne distant sensing knowledge. Nevertheless, the advanced house surroundings could cause many uncertainties and degrade the calibration accuracy. In-flight calibration is at all times wanted. The thermal emission of the Moon is steady over lots of of years as a result of there isn’t any ambiance and no important bodily or chemical change on its floor. The deep house view of the Microwave Humidity Sounder onboard NOAA-18 has considered the Moon many occasions yearly. Below photo voltaic illumination, the lunar floor reveals steady and periodical variation in microwave brightness temperature (TB). The Moon is a possible calibration supply for thermal calibration
The associated work was revealed in Science China Earth Sciences with the title of “Calibration of the space-borne microwave humidity sounder based mostly on real-time thermal emission from lunar floor”. Primarily based on the warmth conductive equation, the temperature profiles of lunar regolith at totally different areas and native time are simulated numerically with the real-time photo voltaic radiance and angle of incidence. The simulated temperatures are validated with the infrared TBs measured by the Diviner infrared sounder onboard the Lunar Reconnaissance Orbiter. The microwave TBs measured by China’s “Chang’e 2” satellite tv for pc had been used to invert the loss tangents of lunar floor. The inverted loss tangents had been utilized to modelling the microwave TBs of lunar close to facet at microwave humidity sounder’s channels. The simulated common microwave TBs are in line with the commentary of NOAA-18 microwave humidity sounder (Determine 1).
The evaluation reveals that microwave TB of lunar floor is said with the frequency. The microwave can penetrate the lunar regolith. Microwave TB is the cumulative contribution of the regolith thermal emission. The superficial temperature performs a dominate function in microwave TB at excessive frequency channels due to the small penetration depth. The superficial temperature of regolith drops considerably with depth at daytime, leading to a excessive microwave TB at excessive frequency. Whereas at night time, the noticed TB is low at excessive frequency as a result of the superficial temperature of regolith will increase with depth.
The digital counts of microwave humidity sounder had been used to suit the complete width at half maxima of the sounder when the deep house view scans throughout the Moon. The fitted full width at half maxima was utilized in deriving the typical lunar TB from the noticed digital counts. The simulation evaluation reveals that the gap between the satellite tv for pc and the lunar section angle will affect the inverted full width at half maxima. In line with the research of “Chang’e 2” microwave commentary of the Moon, the typical microwave TBs of the lunar close to facet at totally different frequencies and section angles are modelled. The simulation could be taken as a supplemental reference for the calibration of microwave humidity sounder onboard NOAA-18. It may be taken because the calibration supply of the microwave sounders onboard Geosynchronous satellites and CubeSats as effectively.
Nevertheless, the microwave TB are measured by “Chang’e 2” satellites at nadir commentary. The very best frequency is 37GHz. Particular commentary of lunar floor at larger frequencies and enormous angles are wanted for bettering the modeling.
See the article:
Liu N, Jin Y. 2021. Calibration of the space-borne microwave humidity sounder based mostly on real-time thermal emission from lunar floor. Science China Earth Sciences, 64(3): 494-502, https:/
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