System Study On The High Stability Interferometric Synthetic Aperture Microwave Radiometer

With the development of microwave remote sensing technology,the various applications propose more comprehensive requirements on the space-borne microwave radiometer performances.The space-borne microwave radiometer needs to realize high sensitivity,high stability,high spatial resolution and wide swath at the same time.Therefore,a new structure radiomer: interferometric synthetic aperture radiometer has become a research hotspot in the field of passive microwave remote sensing in recent years for it has obvious advantages in spatial resolution and swath compared to the traditional real aperture radiometer.The disadvantage of the interferometric synthetic aperture radiometer is that the system is very complex,so it needs to use complex calibration methods to reduce the error.The system should have good stability to ensure the validity of these calibration methods.At present,there is still a certain distance between the technical level and the needs of the people.Microwave Imager Combined Active and Passive,MICAP is a new ocean salinity mission concept proposed in MIRSlab,CAS.The imager is composed of an L band radiometers and an L band scattermeter.Two instruments share one parabolic cylinder reflector.The L band one dimensional synthetic aperture radiometer is used to realize the high precision measurement of the ocean salinity,while L band digital beamforming scatterometer is used to detect sea surface roughness and improve the accuracy of salinity measurement.The system ensures high spatial resolution and wide swath,and avoid the system is too complex.In addition,it can also integrate more band radiometer to realize the synchronous acquisition of auxiliary data such as sea surface temperature.The L band one dimensional synthetic aperture radiometer is a key part of MICAP,which use a high stability real-time calibration synthetic aperture radiometer architecture.The architecture is able to combine the high stability radiometer receiver technology with the real-time calibration synthetic aperture radiometer technology.Therefore,the L band synthetic aperture radiometerc can achieve high sensitivity,high stability,high spatial resolution and wide swath at the same time.In this paper,based on the L band one dimensional synthetic aperture radiometer prototype,the high stability synthetic aperture radiometer system is studied.First of all,a radiometer receiver with high sensitivity and high stability is researched.The receiver is suitable to be used as a radiometer unit of the high stability synthetic aperture radiometer.High stability is realized by the real-time calibration method,and the sensitivity is effectively improved by the calibration data average technology.The optimal average time is obtained by the frequency domain analysis for the first time.A high stability L-band radiometer using these techniques is developed,and long time stability experiments are completed to demonstrate its performance.Experimental results show that the radiometer receiver can achieve high sensitivity and high stability simultaneously.Then,the real-time calibration technique is applied to the interferometric synthetic aperture radiometer.The technology of real-time calibration of synthetic aperture radiometer is studied,and the synthetic aperture radiometer imaging technique is studied.For the first time,a method is proposed to correct the AD offset error of digital to analog correlation conversion by using the three level quantization means.A method of measuring the zero baseline visibility function by using the direct sampling digital correlation technique is presented,which can simplify synthetic aperture radiometer system architecture.Thirdly,the method for analyzing the sensitivity and stability index of real-time calibration synthetic aperture radiometer is studied.The application of the calibration data averaging technique in the real-time calibration synthetic aperture radiometer is studied.Finally,the development and experimental results of the L band synthetic aperture radiometer prototype is introduced.The prototype uses a parabolic cylindrical reflector antenna,a high stability radiometer receiver,three order quantization digital correlation,high-precision temperature control,synthetic aperture radiometer real-time calibration technology,G matrix imaging technology,etc.The test results verify the correctness of the real time calibration technology and the data average technology in synthetic aperture radiometer.The imaging capability,sensitivity and stability of the prototype is verified.