Analysis Of Calibration Standard Of Microwave Radiometer For Amazon Rainforest

The calibration accuracy of statellite microwave radiometer plays an important role in the quantitative application of its products.The external calibration of the radiometer can monitor the systematic errors caused by environmental factors,at the same time,the characteristics of the on-board internal calibration system can be monitored.The calibration characteristics of the spaceborne microwave radiometer can be monitored at any time by using the external calibration of natural objects.In this paper,the amazon rainforest is taken as the target,the target field,that is optimized through the consistency analysis of space and time dimensions,and the calibration reference of spaceborne microwave radiometer is proposed.The important optimum condition of the target field is that the field has the performance of high isotropy and uniformity of microwave radiation,and the range should cover multiple antenna beam field of view.In this paper,the AMSR2 L1 R bright temperature data(with horizontal and vertical polarization of 6.93 GHz,10.65 GHz,18.7 GHz,23.8 GHz and 36.5 GHz channels)with high product quality recognized by the academia was used to evaluate the performance of the target field area.For this reason,the quality of the data was firstly evaluated in the open target area of the south Pacific with stable environmental field.The analysis of the data from 2015 to 2017 shows that the total deviation and standard deviation of all channels of AMSR2 L1 R are 1.466 K-6.352 K and 0.270 K-1.693 K respectively compared with the theoretical calculation results,and the fluctuation of all channels' bright temperature deviation over time is within ± 0.5 K.This shows that AMSR2 L1 R bright temperature data has high precision and stability,and can be used to evaluate the radiation performance changes in the target field.The amazon rainforest has been widely used for external calibration of spaceborne microwave radiometer as a stable object target.In this paper,5°×5° was used as a unit to initially select areas with dense vegetation coverage.In this paper,AMSR2 L1 R bright temperature data from 2013 to 2018(transit at 6:00 and 18:00 UTC time)are used to statistically analyze the target region: 1)the bright temperature difference between different polarization channels of the same frequency is 0.68 K-1.88 K,indicating the isotropy of microwave radiation characteristics in the primary target region;2)the standard deviation of the bright temperature of each channel in the spatial dimension is 0.48 K-1.24 K,and the standard deviation of the bright temperature of each channel in the time dimension is 0.03 K-0.88 K,indicating that the microwave radiation characteristics of the primary target region are uniform.To sum up,the target area match the above optimal conditions and can be used as the external calibration target field area(10° S-5 °S,74° S-69 °W).In addition to the above analysis,this paper also analyzes the variation trend of the brightness temperature in the target region,and obtains the brightness temperature benchmark and the fluctuation range of the corresponding channel.GMI L1 B bright temperature data are used to compare and verify the benchmark,and the results show that the two are in good agreement.It can be seen that the optimized calibration target area and its calibration benchmark proposed in this paper can be used for external calibration of spaceborne microwave radiometer to monitor the change of its radiation performance.