| Microwave radiometer is an instrument that uses passive microwave principle to realize detection.The spaceborne microwave radiometer is a high sensitivity receiver for quantitative measurement of microwave radiation of targets(such as ground objects and atmospheric components)by using passive detection to obtain the radiation of each layer of atmosphere to the surface microwave signal to reverse the large temperature and humidity profile.In the application scenario of atmospheric remote sensing,the absorption characteristics of different atmospheric components on the surface microwave radiation are used to obtain and inverse the motion characteristics of each layer of the atmosphere,which has been widely used in weather forecasting,climate forecasting and numerical weather forecasting.The calibration of microwave radiometer is a process to quantitatively determine the response of the system to known and controllable input signals,so as to realize the quantification of atmospheric detection and lay a foundation for improving the accuracy of weather forecast.The solar synchronous orbit meteorological satellite has been loaded with passive microwave payload to realize on orbit application.The microwave detection data obtained has achieved very good results in the field of meteorological application.Limited by the orbit characteristics,the sun synchronous orbit satellite can not realize the fixed area,realtime,high-frequency microwave detection.At present,there is no engineering application of microwave radiometer on geostationary satellite to realize atmospheric sounding in the world.The space agencies of the United States,Europe and China have carried out research on the geostationary microwave radiometer.The geostationary orbit microwave radiometer adopts the large aperture antenna scheme.When the large aperture antenna works in orbit,it is affected by the antenna material characteristics,orbit environment,external heat flow,etc.,resulting in errors in the radiation signals received by the antenna,which affects the calibration accuracy of the large aperture microwave radiometer.In this study,the calibration model and model parameters are analyzed from many factors that affect the deformation of large aperture antenna,such as antenna material selection,reflector surface material,in orbit thermal deformation,etc.The purpose of this study is to study and propose solutions to the new problems that affect the calibration of the geostationary microwave radiometer by using the large aperture antenna scheme,so as to provide technical support for the on orbit calibration and application of the geostationary microwave radiometer.Firstly,the development status of passive microwave remote sensing technology at home and abroad is investigated,and the calibration model is established according to the scheme that the large aperture reflector antenna is used for the first time in the engineering of the geostationary microwave radiometer;Then,according to the electromagnetic wave propagation theory and the atmospheric radiation formula,the factors affecting the on orbit calibration accuracy introduced by the large aperture scheme are derived.Since the engineering realization of the antenna aperture,shape accuracy,thermal deformation and other indicators is the first time in China,the impact of the geostationary orbit environment on the large aperture antenna is studied.Combined with the development of the engineering prototype,the test verification of the reflector accuracy in the orbit environment is carried out;The scheme of full aperture calibration in orbit is studied.The main work and results of this study are as follows:(1)The mathematical model of on orbit calibration of large aperture microwave radiometer is established,the factors affecting the calibration accuracy of microwave radiometer are analyzed,and the allocation scheme of calibration error of microwave radiometer is determined for the first time.The calibration error of 183 ghz system is less than 1K,and that of 425 ghz system is less than 2K,which meets the needs of meteorological inversion,and points out the direction for the engineering of on orbit calibration of large aperture microwave radiometer.(2)A high thermal stability and high precision coating method for large aperture antenna is proposed.The surface coating parameters are optimized by electromagnetic simulation to balance the absorption and emission of solar radiation energy from the reflecting surface;An engineering prototype of antenna reflector coating is developed.The coated reflector has been tested and the electrical and thermal performance indexes of the reflector meet the engineering requirements,which lays a technical foundation for the on orbit application of large aperture microwave radiometer.(3)A thermal deformation evaluation method for large aperture antenna is proposed.The temperature field of large aperture antenna is obtained according to the change of heat flux outside the geostationary orbit;Through the temperature field and the antenna model,the shape accuracy of the thermal deformation of the large aperture antenna during its life cycle is obtained;According to the shape accuracy of large aperture antenna after thermal deformation,the main beam efficiency index of large aperture antenna under the influence of external heat flow in orbit is obtained.The theoretical analysis shows that the main beam efficiency of antenna under all working conditions is greater than 90%,which meets the requirements of satellite application,and provides an important means for the control of thermal deformation of microwave loaded antenna of geostationary satellite. |
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