Laboratory of Radiophysical Problems of Remote Sensing

The main direction of our laboratory is to work out remote microwave measurement data processing techniques for definition of the relationships between the observed radio brightness temperature and the surface conditions. We pay the main attention to microwave radiometric methods. The creation of the high sensitive and accurate microwave equipment for remote sensing also is an important problem. During the last 15 years the series of microwave radiometers for 21 cm, 7.6 cm, 2.1 cm, 1.35 cm and 0.8 cm wavelenght; multi-channel (wavelenght 0.8 cm, 1.35 cm, 2.1 cm ) polarimetric microwave radiometer system; 2.1 cm and 21 cm wavelength ranges microwave scanning systems; various antenna types were elaborated. A special system for calibration of radiometric devices was created. That consists of the microwave space load which temperature may vary from 20 to 80 degrees Celsius. The load temperature is controlled with a special electronic system. The temperature support accuracy is 0.2 degree Celsius. The emission coefficient of the space load is more than 0.995 in the wavelenght range 8 mm - 30 cm. Therefore the absolute accuracy of the radio-brightness temperature is 1.5 K. This special system let calibrate the radiometric receiver with the antenna. Maximum cross-dimension of the tested antenna may be 0.7 m. Created microwave apparatus was exploited on the research ships "Limneja", "Academic Korolev", "Academic Shirshov", "Academic Nesmejanov", laboratory-aircraft IL-18. Ships measurements were made on aquatories of the Pacific Ocean, Okhotsk Sea, Onega and Ladoga Lakes. The laboratory-aircraft measurements were made on aquatories of Arctic Ocean and Ladoga Lake, at Kazakhstan, Middle Asia, in Herson region.

The aircraft microwave scanning radiometric system carried by a flying laboratory measures the emissivity of soils and soil covers, sea surface,ice in the 2-cm wavelenght interval. The system includes an electric-scanning antenna (phase array), radiometric high-sensitivity radiation receiver (0.05 K/s), as well as an airborne automated complex to control the scanning antenna and to preliminarily process the obtained information; video-control arrangement to record the distribution of radiation (radio-brightness map of the surface under investigation) in false colours. The thermal microwave radiation parameters - intensity, spectrum composition, polarization degree - depend on the physical parameters of the investigated obiect. This dependence is the basis of the data processing procedure. It is necessary to construct mathematical models of objects under investigation to interpret radiometric measurements data and to determine objects physical parameters. One of the possible models is the model of the stratified structure. We have developed software for microwave measurement data processing. Collection of the program may be used for construction of various applied program complexes. For example, the program complex for the calculation of backscattering coefficient and radiobrightness temperature of ice fields was created that way. This complex transforms experimental data (microwave radiometer output voltages) to radiobrightness temperature data and makes theoretical brightness temperature and backscattering coefficient calculation using a mathematical model of the stratified structure. The complex gives output results in a convenient form of graphics (in coordinates "observation angle - brightness temperature") and tables with experimental and calculated data.

An important direction of the laboratory works is the determination of antenna parameters influence on obtained microwave measurement results. Reconstruction technique of radio-brightness temperature based on the antenna temperature values and antenna parameters has been worked out. Prospective direction of the laboratory activities is application of passive and active locations at the same time in one remote sensing system. Passive location gives average signal from a large area. Active one gives a possibility to display small details. Thus, passive and active remote sensing data complement each other. These results are the base for forming maps of condition and property modification of land and water surfaces.

Long experience in the field of remote sensing data processing and interpretation, in the sphere of investigation of the correlation between radiation characteristics and objects physical parameters, as well as created microwave equipment gives the possibility both to make applied measurements and to develop microwave remote sensing theory. The major task of the laboratory is to improve microwave equipment and processing techniques of remote sensing data.