| Land surface temperature(LST)is an key parameter for measuring the global climate system changes,and it has great significance in scientific research fields such as climate,hydrology,and geobiochemistry.LST information has important applications in agricultural production and national economy,and it can be used to identify forest fires,detect crop water requirements,assess farmland drought,and monitor marine pollution.Remote sensing inversion has become an important means to quickly measure LST,and many research focus on LST retrievel from microwave remote sensing data due to the all-weather observation capability of microwave.At present,the existing passive microwave remote sensing data are obtained by artificial satellites,which have the limitations of orbital height,technical level,platform stability and design life,thus the satellite remote sensing cannot meet the needs of rapid acquisition of large-scale LST observation data.Arranging the Moon as an Earth observation platform with functions similar to artificial satellites,and deploying various thermal infrared or microwave sensors on the Moon to conduct long-term and continuous observation of the Earth,that is,Moon-based Earth observation.Compared with traditional polar orbiting and geostationary satellite Earth observation platforms,the Moon-based Earth observation platform has an unparalleled large observable range,high resolution,high surveying and mapping band width,reaching thousands of kilometers.Therefore,Moon-based Earth observation platform provides a new way to accurately obtain LST data on a large global scale.However,Moon-based Earth observation platform is still in the theoretical research stage with no actual Earth observation data.To understand the microwave radiation characteristics of ground objects for Moon-based Earth observation platform,the microwave radiation imaging simulation under the Moon-based earth observation is an essential work.Based on the characteristics of Moon-based Earth observation platform,this paper conducts study from three aspects: microwave remote sensing imaging simulation for Moon-based Earth observation platform,LST inversion for Moon-based Earth observation and parametric design of a microwave radiometer for Moon-based Earth observation platform.The main contents and conclusions are as follows:1)According to the imaging characteristics of the Moon-based Earth observation platform,a microwave imaging simulation model for Moon-based Earth observation is constructed,which considers the time zone effect,the relative motion of Earth and Moon,the atmosphere,the ionosphere,and the radiometer antenna system response.Then based on the global temperature data,the microwave radiation brightness temperature image from Moon-based Earth observation platform was simulated,and a space-borne microwave radiation data were selected to calculate the brightness temperature difference between the two Earth observation platforms and validate the accuracy of microwave radiation simulation result.Results show that the Moon-based Earth observation platform has lower brightness temperature than the satellite platform,and the brightness temperature of land surface has less change than of sea surface with the increasing frequency.Moreover,due to the complex nature of the land surface and the large daily temperature variation,the land surface has large simulation errors than sea surface for six frequencies.2)Based on the radiation transmission equation and the theory of microwave propagation in the ionosphere,using the correlation between the microwave horizontal and vertical polarization emissivity,a LST retrievel method under large-scale viewing zenith angle for Moon-based Earth observation was established.Then three microwave radiation brightness temperature data and simulated data from different Earth observation platforms with different viewing zenith angles were used to estimate LSTs,and verified them by the measured LST from USCRN observation station.The results show that the LST estimations from 23.8 GHz and 36.5 GHz microwave brightness temperature data has a high accuracy,and the accuracy decreases with the increase of the viewing zenith angle.Moreover,The Moon-based LST inversion method is applicable to the passive microwave remote sensing data from various Earth observation platforms,and data acquisition platform has little effect on the inversion results.3)Based on the Moon-based LST retrieval method from microwave remote sensing data,the Moon-based microwave radiation brightness temperature simulation data is used to obtain LST estimations under the Moon-based Earth observation platform.In order to verify the accuracy of the LST estimation results,the thermal infrared LST products obtained by the Fengyun-2 geostationary satellite were selected.The results show that the Moon-based Earth observation platform can continuously observe lowlatitude,mid-latitude and high-latitude areas for 10 h,13h or even longer time,thus Moon-based Earth observation platform provides a new perspective for accurately monitoring the global surface temperature.4)Based on the characteristics of the Moon-based Earth observation platform and the LST inversion application,antenna half-power beam width,antenna aperture size,spatial resolution,system integration time,polarization mode,scanning angle,and bands of Moon-based microwave radiometer are analyzed,and the optimal system parameters are determined.The results show that 18.7GHz,23.8GHz,36.5GHz,and89 GHz channels are suitable as the bands for microwave radiometer sensors of Moonbased Earth observation,120 m is the theoretical optimal antenna aperture size.With this size,the spatial resolution of the four frequencies is 10 m,32m,40 m,and 52 m,the antenna half-power beam width is 0.002°,0.004°,0.006°,and 0.007°,and the integration time is 0.01 ms,0.03 ms,0.12 ms,and 0.19 m. |
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