The experimental work on testing the wide-band transmitters and receivers developed for Ka-band and Ku-band radar
systems, as well as the signal processing algorithms were introduced. A city light-railway train was selected as the
imaged target. The wide-band transmitters and receivers were designed based on the stepped-frequency chirp signal
(SFCS) with 2GHz bandwidth synthesized. The Super-SVA technique was used to deal with the case of transmitting
SFCS with band gaps between subchirps for purpose of achieving the same bandwidth using as less as possible subpulses.
Both Ka-band and Ku-band high-resolution radar images were obtained, which show that Ka-band images are much
clear than that of Ku-band as we expect. There are two reasons to explaining this, one reason is due to the
electromagnetic scattering of train itself are different for Ka-band and Ku-band frequencies, and the other reason is due
to the interactions, i.e. multi-reflection or multi-scattering between the train and the side metal fences or the lamp post
This paper introduces a simple method to obtain a much higher resolution than the designed resolution in both azimuthal
and rang directions for SAR by synthesizing the data taken by repeat passes without increasing any complexity in SAR
hardware and satellite platform. The basic idea of the method is to firstly establish the equivalence between the signal
models of repeat pass SAR signals in both azithumal and range directions and the signal model of stepped frequency
chirp signals (SFCSs) when some conditions are presumed, i.e. for range direction, interferometric condition is required
and for azimuthal direction, a small squint angle increase between repeat passes is required, and then using the already
proposed method for SFCSs compression to process the data of repeat passes. In the course of processing, each
observation in range direction or in azimuthal direction is treated as a subchirp in SFCSs. The major facts affecting the
final resolution one could get are investigated and found. They are the relative range measurement accuracy and the
absolute squint angle measurement accuracy between repeat passes. Detailed derivations and simulations are presented
to show the effectiveness of the method.
The design of the China Imaging ALTimeter (CIALT) and the flight experiment of its airborne model are presented in this paper. The system is aimed for providing observation measure for both oceanic applications and continental topographic mapping in the future. The motivation of this project is to develop a three dimensional imager fitted for small satellites with small volume, mass and power consumption. An experimental airborne model of the CIALT has been developed for verifying the design concept. The CIALT integrates three techniques together, i.e. the height measurement and tracking technique of traditional radar altimeter used for ocean applications, the synthetic aperture technique and the interferometric technique. A robust height tracker has been designed for meeting the requirements of both oceanic surfaces and continental surfaces (including surfaces of ice continent). The synthetic aperture technique is used for achieving a higher azimuthal resolution along the cross range direction compared with that of a traditional altimeter. The interferometric technique is used for retrieving the height information corresponding to each image pixel and for boresight angle correction of the antennas, which is crucial for accurate height measurement. The CIALT is different from other proposed imaging altimeters, such as SAR altimeter and scanning altimeter, in which no height tracker is involved. Some key technologies regarding the development of imaging altimeter are addressed, such as the antenna design, the transmitter, the receiver and the robust tracking algorithm.
We develop two methods of retrieving sea surface wind speed. One is a physical method using 19.35GHz brightness temperatures with vertical and horizontal polarization. The other is a semi-statistic method based on sea surface emissivity models. We compare the retrieved results with in-situ buoy data and with the existing wind retrieval model, namely Wentz'92 and Goodberlet'90.
The research of the X-Band High Spatial Resolution Radiometer (X- band HSRPR) is trying to enhance the spatial resolution by the synthetic aperture antenna. Its sensitive of the temperature measurement is 1.5K and the spatial resolution is 2°. The receiver includes 8 channels. Every channel compose 4 main parts: (1) high frequency components, (2) mid frequency amplifiers, (3) power dividers, (4) correlation detectors, and 2 supplementary parts: (1) local oscillator and (2) noise source. The article introduces the designing of the receiver and the characters designing of the components in the channels.
Echo tracking is always an important part in the design of radar altimeter, which is required in many ways. But above all, the essential requirement for the tracking is to avoid track losing, furthermore, the tracking precision and algorithm operation scale also are need to be optimized. So all the factors mentioned above have to be considered comprehensively. Till today, various tracking algorithms have been developed for different applications, but the common shortage of them is that they depend on some specific target modes strongly, which leads to poor adaptability to different targets and easily losing tracking. As to this problem, OCOG will be introduced in this paper, which is a good robust tracking algorithm and will be applied into a new type of satellite altimeter, tridimensional imaging radar altimeter, which will be applied in complex environments including sea, seaice and coast.
In this paper, the effects from mutual coupling and imbalance between channels on the interferometric correlation are analyzed. It is shown that the correlation error is mainly introduced by the phase imbalance. The phase balance of the central frequency can ensure the accuracy of the correlation phase, and the residual phase error will only reduce the coherency. Coherent/Incoherent noise calibration can correct the channel imbalance related interferometric correlation errors.
Microwave Remote Sensing has developed rapidly during the past period, becoming a leading method in remote sensing techniques, since its unique features, capability to penetrate clouds and some extent rain due to it independence from the sun as a source of illumination and other important properties different from visible and IR frequency bands, Microwave Remote Sensing becomes a key means for obtaining information from ocean, atmosphere, and land in global scale. The frequency range using for microwave remote sensing is extending to millimeter and submillimeter bands. To meet the wide requirements, China enhanced the microwave remote sensing research during the past 30 years and has got many achievements. In this paper, the microwave remote sensing activities and its achievement, the stage of the arts, the space program for microwave remote sensing are described, it also gives some strategic suggestions in future development, discusses some concepts of space borne system and gives the research areas suggested to be given priority to develop in national R&D plan. A new concept of remote sensing -- A comprehensive electromagnetic sensing system and a virtual space remote sensing are being suggested to improve remote sensing capability.
An airborne multi-function microwave remote sensing system has been developed in order to verify the design and performance of future Chinese spaceborne system. Future Chinese spaceborne microwave remote sensing system is for ocean research, atmosphere research and soil moisture content monitoring. Like spaceborne system, the airborne system also includes altimetry, scatterometry and radiometry functions. There are five operate modes: altimetry mode, scatterometry mode, radiometry mode, altimetry and radiometry mode, scatterometry and radiometry mode. The operate mode can be changed by program. There are five channels in radiometry mode. The altimetry mode, the scatterometry mode and the second channel of radiometry mode operate at the same Ku band. In the airborne system, the scatterometry mode uses two pyramidal horn antennae. One is for horizontal polarization. The other is for vertical polarization. The horizontal polarization antenna is also used in the altimetry mode. The radiometry mode uses five pyramidal horn antennae.
Flight experiments have been conducted on southern sea of China. The results verify the design and performance of the airborne multi-function microwave remote sensing system. They also show that the design of future Chinese spaceborne system is practicable. In this paper, the principle of airborne system is briefly introduced. Flight experiments and results are described.
Microwave radiometer is a kind of passive microwave remote sensor. Generally microwave radiometer is considered passively receiving radiation from the object and no energy radiate from the antenna to the outside. In the practical system, the components of radiometer really have thermal noise and radiate energy in the reverse direction. In another case, the reverse radiation comes for the mismatch of the components between the antenna to the receiver system. The energy radiates to the outside through antenna, and reflected back by the objects and received by antenna again. The value of reverse radiative temperature is related to the noise of the receiver and components of the receiver front-end. The reverse radiative temperature in the system will affect the accuracy of the calibration of microwave radiometer and the ground-based microwave radiative measurements near nadir angle.
In this paper, a scheme of microwave interferometric radiometer for earth observation is proposed. The movement of the interferometer will produce a u-v plane coverage of the visibility function, which can be used for imaging of the brightness temperature distribution. The coverage is analyzed and some comparisons of this interferometer with that for space observation are made. The inversion method is proposed and simulation results are presented to show the possibility. Some open problems are drawn out for further researchers.
In this paper a new real-time flood monitoring system using SAR is described. Flooding has been a puzzling problem to the Chinese government for a long time. During the last decade, China promoted a research program of flood monitoring and management using remote sensing techniques and established a quasi-real-time and real-time disaster monitoring system. The system has two functions: flood monitoring by SAR and an image transmitting system, and loss estimation of flooded area using an image processing GIS system. This system was used successfully in the 1991 flood in China and played an important role in reducing flood losses. To establish this system several key technical problems were solved, including the SAR system, SAR image processing, SAR image compression, and image long distance communication and information system.
A new microwave sensor in which active and passive mode sensors are working synergistically is designed for future China space projects. In the system the scatterometry, altimetry and radiometry functions are integrated technically. There are three operation modes and the mode combination can be selected in order of user requirement. The main modes are: ALT + RAD1, SCAT + RAD1, Multifrequency RAD, working at five frequency band (RAD2 - RAD6). Altimeter, Scatterometer and Radiometer RAD1, working at same ku band frequency and use a common antenna. The system design is based at operational airborne sensors which was in operation from early 1980. Main key problem of the system is solving during the design of this system is the mode combination technique, antenna technology, data management and system calibration.