Weiying Sun

Imaging Analysis and First Results of the Geostationary Interferometric Microwave Sounder Demonstrator

The Geostationary Interferometric Microwave Sounder (GIMS) is a new concept of atmospheric microwave sounder for Chinas future geostationary Earth orbit meteorological satellite (FY-4). It is a microwave interferometric radiometer (MIR) using aperture synthesis and working in rotating time-sharing mode with a circular antenna array. A GIMS proof-of-concept demonstrator operating in the temperature sounding bands of 50-56 GHz has been successfully developed. The instrument uses a circular array with 28 elements (including one in the center of the array). It is capable of imaging a scene with an angular resolution of about 0.08° and a radiometric resolution of less than 1 K with 5-m integration time within a 5° field of view (FOV). Some theoretical aspects of the imaging characteristics of GIMS are discussed, such as the alias-free FOV, angular resolution, radiometric resolution, and imaging algorithm. Some early tests and preliminary imaging experiments of the GIMS demonstrator are also presented.

The Geostationary Interferometric Microwave Sounder (GIMS): Instrument overview and recent progress

The concept of Geostationary Interferometric Microwave Sounder (GIMS) has been proposed based on the rotating circular thinned array, aiming for Chinas next generation geostationary meteorological satellite (FY-4M). The spaceborne system design has been investigated. The tradeoff analysis between the system performance and system complexity has been studied. A full-scale ground-based 50∼56GHz GIMS demonstrator with 28 elements has been defined and developed. Preliminary test results of the demonstrator will also be presented in this paper.

Applications of Pseudo-polar FFT in Synthetic Aperture Radiometer Imaging

In this study we analyzed the potential use of Pseudo-Polar FFT algorithm for image reconstruction of synthetic aperture radiometer, and developed an effective method to improve the image reconstruction accuracy and computational efficiency simultaneously. The advantage of the new algorithm is that it takes pseudo-polar grid instead of Cartesian grid to perform the inverse Fourier transform, and it involves only 1-D interpolation, which leading to a more fast.and accurate performance. As a critical stage, the interpolation algorithms that perform the changing from polar grid to pseudo-polar grid are present. At last, the superiority of the new algorithm is validated by numerical simulation. It is believed that the new approach may have wide-spread application in science and practice for synthetic aperture radiometer system.

Conceptual design and breadboarding activities of Geostationary Interferometric Microwave Sounder (GIMS)

In this paper, the authors will report some basic considerations on the synthetic aperture imaging radiometer for mm-wave sounding from GEO, especially for the Chinas next generation geostationary meteorological satellite (FY-4M).

Clock scan of imaging interferometric radiometer and its applications

High spatial resolution image of passive microwave brightness temperature can be taken by so called synthetic aperture radiometer or imaging interferometric radiometer. However the future application of this new technology is limited by its large number of element antennas and receiving channels. To overcome this difficulty, a novel time shared scan scheme is presented using the concept of clock arms. Potential applications of this new scan scheme are also presented in this paper.

Flame acceleration and overpressure development in a semiopen tube with repeated obstacles

An investigation of the dependence of turbulent flame acceleration and overpressure in a semiopen tube on the configuration of obstacles has been performed in a flame propagation tube with one end closed and the other open, having an 80 mm inner diameter, a 5 in length, and repeated obstacles. Three kinds of obstacle shapes have been used for various blockage ratios and spacing of obstacles. There is evidence that the influence of the obstruction characteristics on the flame speed and overpressure is different in the various flame regimes. In the low-speed combustion regime, the highest terminal flame speed is obtained with the blockage ratio of BR = 0.3-0.4. In the choking regime, the maximum flame speed is insensitive to the blockage ratio, and a blockage ratio of about 0.5 generates the highest peak overpressure. In the detonation regime, the maximum flame speed and overpressure decrease with increasing blockage ratio due to the severe momentum losses induced by the blockage effect of the obstacles, and at the same time, the detonative range is observed to become narrower. The steady flame speed is, independent of the shape of obstacles when the blockage ratio is the same, and the spacing of obstacles plays a role only in determining the flame acceleration rate rather than the steady flame speed; the highest mean flame speed and peak overpressure are obtained when the spacing of obstacles is about equal to the inner diameter of the flame tube. In addition, the unsteady compressible flow model with correction for the influence of turbulence Mach number on viscosity dissipation and pressure dilatation was formulated, and numerical studies using the eddy-break-up combustion model were made to predict the flame acceleration and the development of overpressure in the tube. The comparison of calculated overpressure and flame speeds with experimental data shows good agreement.

Applications of Synthetic Aperture Radiometer Technology in Solar Wind Remote Sensing

Synthetic aperture radiometer technology used nowadays in earth remote sensing is an extended development from ground-based radio astronomy used for stellar observation. However, once the technology is further developed in the Earth remote sensing area, it can certainly be applied back in its original field or other fields. In this paper, we discuss a rotational phased array of time-shared synthetic aperture technology application in solar wind remote sensing. The main idea is to send a spacecraft into solar polar orbit. From this orbit, one can look down to the ecliptic plane. In and around the ecliptic plane, the most interested and useful information of the interplanetary solar wind is the Corona Material Ejection (CME) of the Sun since it can cause sever geo-space storms and result man made technical system failure such as navigation positioning errors and communication break down or even satellite failures. The main scientific initiatives and technical system conceptual design of this application will be presented in this paper.

Design and analysis of time shared imaging interferometric radiometer with asynchronous rotating scan

The synthetic aperture interferometric radiometry (SAIR) is a promising technique for microwave remote sensing. Various system configurations have been built. In this article, a new concept of time sharing sampling system with asynchronous rotating scan is proposed, which can greatly simplify the system hardware, and to a large extent overcome the technical barriers of applying high spatial resolution imaging systems in space borne earth observation. Asynchronous rotating scan (ARS) employs two groups of antenna elements, which have different arm length and separately rotating around a same central axis at different speed during the sampling scan process. It can achieve a full u-v sampling coverage even with only two antenna elements, whereas a longer imaging refresh time would be taken. More explicitly, ARS-SAIR can effectively adjust the tradeoff between the system complexity and time resolution.

Recent progress on rotational time shared scanning synthetic aperture imaging radiometer

Up to the present, most earth observation applications of synthetic aperture imaging radiometers (SAIR) are air-born and low earth orbit (LEO) space-born, where snap shot system with high imaging frame rate is necessary. With the increasing demands of microwave Geostationary Earth Orbit (GEO) earth observation for weather forecast, non snap shot type of imaging technology can be considered. While an image can be taken within a certain period of time, the hardware complexity can be dramatically reduced by scanning the sampling system during this period of time. In this paper, two kinds of rotational time shared scan scheme are analyzed, which are single rotation scan and double rotation scan. The recent progress on polarimetric correction methods developed for the two rotation schemes are present.

Imaging algorithm and experimental demonstration of rotating scanning interferometric radiometer

Recently, a new concept of rotation scanning synthetic aperture interferometric radiometer (RS-SAIR) has been receiving more and more attentions for its advantage of much simpler configuration with looser requirements of antenna elements. In this article, we investigate the imaging theory of RS-SAIR, and introduce the pseudo-polar FFT algorithm to deal with the polar u-v samples. It only involves 1D interpolation and 1D FFT routine that guarantee a high accuracy and computation efficiency. The sampling strategy and aliasing effect of RS-SAIR are studied with this imaging algorithm. Numerical simulations are provided to validate the associate theory. Finally we develop a 5-elements RS-SAIR instrument and carry out rotating scanning imaging experiment successfully. The first imaging results consist with the expectation.