Design and Development of a Ground-based Microwave Radiometer System

This paper presents the design and development of a ground-based microwave radiometer system (MWR) for the offshore oil platform. It will be used to provide long time series of geophysical parameters such as the sea-surface temperature, the near-surface wind speed and the sea ice type. The ground-based MWR is a five-frequency, dual-polarized microwave radiometer which is a total power type microwave radiometer based on a heterodyne receiver. It operates at 6.8 GHz, 10.7 GHz, 18.7 GHz, 23.8 GHz and 37 GHz, respectively. The scanning mode adopts circular scan in a vertical plane. During each period, two-point calibration is performed to calibrate the receiver gain and noise. The antenna beam directs different angles and the blackbody used in calibration to obtain measurement data and calibration data. The ground-based MWR consists of three units: antenna and receiver unit, electronic unit and power supply unit. Antenna and receiver unit collects emission from the atmosphere. It is constructed with several RF components, which include voltage-controlled oscillator, high power amplifier, directional coupler, RF switch, band-pass filter, isolators, detectors and mixers. The received signal is down-converted by the double side band mixer to Intermediate Frequency, and then the IF signals are down-converted to Low Frequency by the detector and integrator. The electronic unit digitizes the LF signal, controls the scanning mechanism and measures physical temperature of the hot target for calibration, and takes charge of communication with a remote computer. The power supply unit performs DC/DC conversion, distributes the DC lines to various sub assemblies and switches. In paper, the basic principle and technical specifications of microwave radiometer will be briefly introduced, and the block diagram and detail design parameters of the proposed system will be described. The system followed radiometer electronics design and achieved exacting stability and high accuracy requirements.