Heguang Liu, Jingshan Jiang, Xiaolong Dong, Jing Li, Ke Xu
Center for Space Science and Applied Research, Chinese Academy of Science
P.O.Box 8701, Beijing 100080, P. R. China
Tel: 86-10-62582846, Fax: 86-10-62576921,
Tel: 86-10-62559575, Fax: 86-10-62559575,
This paper deals with the aim and the application of the spaceborne China Advanced Microwave Remote Sensor (CAMRS). The aim of this project is to develop the second generation China Multimode Microwave Remote Sensor (M3RS) in which the dual frequency altimeter, scanning scatterometer and multi-channel millimetre-wave radiometers are integrated together. Altimeter (ALT), scatterometer (SCAT) and radiometer (RAD) are all designed in module so they can be combined or decomposed arbitrarily according to different mission. This new sensor can be used to sea surface, atmosphere and land applications.
Over the three decades, microwave remote sensing has evolved into an important tool for monitoring the atmospheres and surfaces of planetary objects, with special emphasis on observations of the planet earth. Sensors are very important part of microwave remote sensing and usually are divided into two groups according to their modes of operation: active and passive. Active modes are those that provide their own source of illumination and therefore contain a transmitter and a receiver, while Passive modes are simply receivers that measure the radiation emanating from the scene under observation. Active modes include imaging radar, SCAT and ALT, and passive modes are often referred to as microwave RAD. Active sensors have been used extensively for mapping geological structures and features. Particularly in those parts of the world where cloud cover presents a serious problem to optical sensors. Active modes also can used for other application areas, including vegetation mapping, discrimination of sea-ice types, measuring ocean wind speed and direction, mapping soil moisture content and snow water content, and land-use evaluation.
The CAMRS is a second generation M3RS, including scanning SCAT, the dual frequency ALT and multi-channel millimetre-wave RAD, in which active and passive modes are working synergistically. The primary goal of the sensor is to ocean and atmospheric research. The ALT mode can provide geoid, significant wave high and wind speed with precision satisfying to user requirement. SCAT mode will provide ocean wind field data and the RAD can provide on atmospheric data.
2.0 A brief description and key specification of the system
The CAMRS consists of seven operation modes and the mode combination can be selected in order of user requirements. The main modes are: ALT, SCAT, RAD, ALT+SCAT, ALT+RAD, SCAT+RAD and ALT+SCAT+RAD. The functional block diagram has shown in fig-1.
2.1 The dual frequency altimeter unit
Satellite altimetry is devoted to the active remote sensing of the ocean surface and thereby represents an important new source of measurements. These measurements are sufficient to provide all-weather independent observations of global topographic features, thus contributing to the accurate mapping of underwater features and the detection and measurement of ocean current, tides, and storm surges, as well as the monitoring of wave height on a global basis. The radar ALT is therefore an unique tool for studying the role that oceans play in the Earth’s climate system and for understanding climatic change on a global scale.
The radar ALT operates in the pulse-width limited mode, and use the full deramp system of pulse compression. The basic altimeter operation principle can be found in (Chelton, 1989).
The radar ALT operates at C-band and Ku-band respectively. The dual frequency design allows for height measurement corrections due to the ionospheric effects on the signal. This system was designed to operate from a space platform over the ocean with sea conditions ranging from 0.5 to 20 meters in significant wave height. The altitude resolution is 4.5cm. The significant wave height is 0.25m or