一种基于压缩感知的信道估计算法

信道估计是无线通信系统的关键技术之一。文章提出一种基于压缩感知（Compressed Sensing）的信道估计方法,这种方法通过分析信道时延和多普勒域的稀疏度,可以有效降低导频的数量,从而提高系统的频谱利用率。通过与最小均方（Least Square,LS）信道估计方法的对比,可以明显看到导频数量的降低。     

出口封闭的冲压发动机进气道激波振荡现象

采用计算流体力学和风洞试验两种手段,对冲压发动机出口封闭的多种超声速进气道内通道气流振荡现象进行了研究。结果表明,在一定的超声速范围内,封闭的进气道内通道发生了较强气流振荡现象,振荡频率、幅值和内通道长度、飞行马赫数有关,该振荡现象是一种自激振荡现象。利用亥姆霍兹共振器频率公式可以对封闭的进气道内通道振荡频率进行预估,并对其归纳出一种修正方法,可以结合模型试验结果对进气道和燃烧室内流振荡频率和幅值进行分析,为飞行试验提供预估和参考。     

Improved rainfall estimation over the Indian region using satellite infrared technique

The GOES Precipitation Index (GPI) technique (Arkin, 1979) for rainfall estimation has been in operation for the last three decades. However, its applications are limited to the larger temporal and spatial scales. The present study focuses on the augmentation on GPI technique by incorporating a moisture factor for the environmental correction developed by Vicente et al. (1998). It consists of two steps; in the first step the GPI technique is applied to the Kalpana-IR data for rainfall estimation over the Indian land and oceanic region and in the second step an environmental moisture correction factor is applied to the GPI-based rainfall to estimate the final rainfall. Detailed validation with rain gauges and comparison with Tropical Rainfall Measuring Mission (TRMM) merged data product (3B42) are performed and it is found that the present technique is able to estimate the rainfall with better accuracy than the GPI technique over higher temporal and spatial domains for many operational applications in and around the Indian regions using Indian geostationary satellite data. Further comparison with the Doppler Weather Radar shows that the present technique is able to retrieve the rainfall with reasonably good accuracy.     

Changes in hyperspectral reflectance signatures of lettuce leaves in response to macronutrient deficiencies

The adaptation of specific remote sensing and hyperspectral analysis techniques for the determination of incipient nutrient stress in plants could allow early detection and precision supplementation for remediation, important considerations for minimizing mass of advanced life support systems on space station and long term missions. This experiment was conducted to determine if hyperspectral reflectance could be used to detect nutrient stress in Lactuca sativa L. cv. Black Seeded Simpson. Lettuce seedlings were grown for 90 days in a greenhouse or growth chamber in vermiculite containing modified Hoagland’s nutrient solution with key macronutrient elements removed in order to induce a range of nutrient stresses, including nitrogen, phosphorus, potassium, calcium, and magnesium. Leaf tissue nutrient concentrations were compared with corresponding spectral reflectances taken at the end of 90 days. Spectral reflectances varied with growing location, position on the leaf, and nutrient deficiency treatment. Spectral responses of lettuce leaves under macronutrient deficiency conditions showed an increase in reflectance in the red, near red, and infrared wavelength ranges. The data obtained suggest that spectral reflectance shows the potential as a diagnostic tool in predicting nutrient deficiencies in general. Overlapping of spectral signatures makes the use of wavelengths of narrow bandwidths or individual bands for the discrimination of specific nutrient stresses difficult without further data processing.     

TOPSAR data focusing based on azimuth scaling preprocessing

Both Doppler spectral aliasing and azimuth output time folding simultaneously exist in TOPSAR (Terrain Observation by Progressive Scans) raw data. Resampling in both Doppler frequency and azimuth time domain can resolve the azimuth aliasing problem but with the seriously increased computational complexity and memory consumption. According to the special characteristics of TOPSAR raw data support in the slow time/frequency domain (TFD), the presented azimuth scaling preprocessing step is introduced to not only resolve the Doppler spectral aliasing problem but also reduce the increased azimuth samples. Furthermore, the correction of sawtoothed azimuth antenna pattern (AAP) becomes easy to be implemented. The following conventional stripmap processor can be adopted to focus the residual TOPSAR raw data but with the result of azimuth aliased TOPSAR image. The mosaic approach, which has been presented to unfold azimuth aliased ScanSAR image, is exploited to resolve the problem of azimuth output folding in TOPSAR mode. Simulation results and pulse response parameters are given to validate the presented imaging approach.     

The possibilities of polar meteorology,environmental remote sensing,communications and space weather applications from Artificial Lagrange Orbit

The ability to observe meteorological events in the polar regions of the Earth from satellite celebrated an anniversary, with the launch of TIROS-I in a pseudo-polar orbit on 1 April 1960. Yet, after 50 years, polar orbiting satellites are still the best view of the polar regions of the Earth. The luxuries of geostationary satellite orbit including rapid scan operations, feature tracking, and atmospheric motion vectors (or cloud drift winds), are enjoyed only by the middle and tropical latitudes or perhaps only cover the deep polar regions in the case of satellite derived winds from polar orbit. The prospect of a solar sailing satellite system in an Artificial Lagrange Orbit (ALO, also known as “pole sitters”) offers the opportunity for polar environmental remote sensing, communications, forecasting and space weather monitoring. While there are other orbital possibilities to achieve this goal, an ALO satellite system offers one of the best analogs to the geostationary satellite system for routine polar latitude observations.     

卫星遥感影像外方位元素的误差传播研究

高分辨率卫星遥感影像的几何定位精度与影像外方位元素精度密切相关.文章针对单景影像直接对地定位和立体影像前方交会定位两种典型情况,对影像各外方位元素在目标几何定位中的误差传播规律进行分析比较,相关结论可供卫星姿控及相机载荷设计方参考.     

基于刃边法的星载相机在轨MTF测量精度分析

调制传递函数(MTF)反映可见光对地遥感系统在对地物成像过程中信号的扩散与削弱程度,是表达系统辐射性能的重要指标.文章对星载可见光CCD相机在轨MTF主要测量方法进行比对分析,通过数据仿真,重点对随机噪声、边缘探测与拟合等主要影响刃边法精度的因素进行了分析.分析结果表明,计算所用刃边法能够较准确地计算可见光遥感系统的M...     

InGaAs探测器热电制冷方法研究

InGaAs探测器在短波红外领域具有良好的探测率,对空间遥感和探测有重要的价值。为了实现空间红外仪器的高灵敏度要求,使用热电制冷技术设计了探测器制冷系统,使探测器稳定地工作在合适的温度,以相对较小的体积和功耗代价显著地提高红外仪器的探测灵敏度。     

强度关联遥感成像技术

过去十多年中,利用光场的量子（或经典）涨落及其关联获取目标图像信息的量子（强度）关联成像技术和基于自适应稀疏结构表象的信号处理技术的不断发展,为图像信息的获取提供了一条可突破传统光学成像技术图像分辨率和图像获取效率理论极限的全新技术途径。文章将概括地介绍这一研究方向,并简要讨论其在遥感领域中的应用前景和需要进一步研究的...