| The microwave radiometer occupies on the important status in the microwave remote sensing instruments,it is used widely ,such as remote sensing, guidance, target characteristic detect and so on . SMOS(Soil Moisture and Ocean Salinity)is the second Earth Explorer Opportunity mission to be implemented as part of ESA's Living Planet Programmer. It will provide global maps of soil moisture and ocean salinity. The biggest challenge the SMOS mission faces is to fly and demonstrate a completely new type of instrument– a radiometer that operates between 1400-1427 MHz (L-band). In order to achieve the required spatial resolution with reasonable antenna size, the antenna aperture has been cleverly synthesized through a multitude of small antennae. The ground calibration experiment for SMOS Mission will use an L-band radiometry to measure soil brightness temperature of Taklimakan Desert. This experiment will have a great effect on calibration and validation of SMOS.This paper presents the basic principle of microwave measure, system structure of L-band microwave radiometry and its digital control system. Furthermore, because of the antenna aperture, the paper gives a reasonable calibration method: using cold sky as the"cold"target and obtaining the"warm"target in an anechoic chamber. For the complex condition, in L-band, many factors have effect on brightness temperature of cold sky. This paper establishes a sun radiation model to calculate brightness temperature at any time according affected by sun when it crosses the view field of antenna to the position relationship between sun and earth also sun and antenna. It analyzes briefly the radiometric temperature under the influences of moon, planets in our solar system and galactic radio emission. At last, this paper analyzes the detrimental effects radio frequency interference have on microwave measuring and presents a test method based on KURTOSIS theory. |
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