航天光学遥感器光学装调技术现状与展望

航天光学遥感器工作于太空中,长期恶劣的空间环境及短暂发射入轨时的状态对光学系统的设计与装调提出了苛刻的要求,确保光学系统在轨像质优异是航天光学遥感器研制的关键技术.文章结合国际上航天光学遥感器的发展需求对光学系统装调技术及发展现状进行了分析、总结,提出了中国后续航天光学遥感器装调与测试技术的突破方向.     

Detrend effect on the scalograms of GPS power scintillation

The study of amplitude scintillation on GPS radio links is usually done after detrending the time series of the transmitted power so to define scintillations as the chaotic fluctuation around a unitary value. In a sense, the choice of how to detrend the time series is part of the definition of scintillation.     

Distribution of chlorophyll and harmful algal blooms (HABs): A review on space based studies in the coastal environments of Chinese marginal seas

Monitoring of spatial and temporal distribution of chlorophyll (Chl-a) concentrations in the aquatic milieu is always challenging and often interesting. However, the recent advancements in satellite digital data play a significant role in providing outstanding results for the marine environmental investigations. The present paper is aimed to review ‘remote sensing research in Chinese seas’ within the period of 24 years from 1978 to 2002. Owing to generalized distributional pattern, the Chl-a concentrations are recognized high towards northern Chinese seas than the southern. Moreover, the coastal waters, estuaries, and upwelling zones always exhibit relatively high Chl-a concentrations compared with offshore waters. On the basis of marine Chl-a estimates obtained from satellite and other field measured environmental parameters, we have further discussed on the applications of satellite remote sensing in the fields of harmful algal blooms (HABs), primary production and physical oceanographic currents of the regional seas. Concerned with studies of HABs, satellite remote sensing proved more advantageous than any other conventional methods for large-scale applications. Probably, it may be the only source of authentic information responsible for the evaluation of new research methodologies to detect HABs. At present, studies using remote sensing methods are mostly confined to observe algal bloom occurrences, hence, it is essential to coordinate the mechanism of marine ecological and oceanographic dynamic processes of HABs using satellite remote sensing data with in situ measurements of marine environmental parameters. The satellite remote sensing on marine environment and HABs is believed to have a great improvement with popular application of technology.     

SPOT-5卫星系统性能概述

概要介绍SPOT - 5卫星的主要成像传感器 ,精确定位技术及数据格式。介绍分析卫星数据的应用前景     

The land remote sensing commercialization Act of 1984

This article examines the effect that private-sector remote sensing activities might have on the international community and on the future of international cooperation in space. It describes in detail The Land Remote Sensing Commercialization Act of 1984, recently passed by the US Congress and signed by President Reagan. The article concludes that it is possible to develop domestic regulations that balance the economic interests of the private sector with the legal and political concerns of the international community.     

一种孔径和频率二维稀疏的步进频SAR成像方法

 步进频率信号(SFWs)在不增加雷达系统瞬时带宽的情况下能够获得高的距离向分辨率的同时,也存在着抗干扰能力较差及其等效重复频率较低的问题,并且在方位向积累时间内由于雷达载机工作状态的变化,会导致方位向的数据录取不完整。针对上述问题,提出一种孔径和频率二维稀疏的步进频合成孔径雷达(SAR)成像方法。首先,分析了稀疏步进频率信号(SSFWs)的SAR成像模型,然后基于压缩感知理论完成距离向成像处理。其次,针对稀疏孔径的回波数据,通过构造成像算子和压缩感知重建模型的方法实现其距离徙动校正和方位压缩处理,进而获得二维成像结果。相比于传统的步进频率信号SAR成像,利用所提方法能够在少量的频率资源和雷达回波数据情况下实现准确的SAR成像。最后,通过对仿真和实测的步进频率雷达数据进行成像处理,验证了所提方法的有效性和可行性。     

Cost-driven design of small satellite remote sensing systems*

Earth remote sensing (alongside communications) is one of the key application of Earth-orbiting satellites. Civilian satellites in the LANDSAT and SPOT series provide Earth images which have been used for a vast spectrum of applications in agriculture, meteorology, hydrology, urban planning and geology, to name but a few. In the defence sector, satellite remote sensing systems are a critical tool in strategic and tactical planning – for the countries which can afford them. To date, remote sensing satellites have fallen into one of these two categories: military missions driven by the requirement for very high resolution and orbital agility; and multipurpose civil satellites using general purpose sensors to serve a diverse community of end users. For military-style missions, the drive to high resolution sets the requirements for optics, attitude control and downlink data bandwidth. For civil missions, the requirement to satisfy multiple, diverse user applications forces compromises on spectral band and orbit selection. Although there are exceptions, many small satellite remote sensing missions carry on in this tradition, concentrating on ultra high resolution products for multiple user communities. This results in satellites costing on the order of US $100 M, not optimised for any particular application. This paper explores an alternative path to satellite remote sensing, aiming simultaneously to reduce cost and to optimise imaging products for specific applications. By decreasing the cost of the remote sensing satellite system to a critical point, it becomes appropriate to optimise the sensor's spectral and temporal characteristics to fit the requirements of a small, specialised user base. The critical engineering trade-off faced in a cost driven mission is how to reduce mission cost while still delivering a useful product to the selected user. At the Surrey Space Centre, we have pursued an engineering path using two dimensional CCD array sensors, commercial off-the-shelf lenses and gravity-gradient stabilised microsatellites. In spite of the inherent limitations of such systems, recent successes with the Thai Microsatellite Company's Thai-Phutt satellite show that a system costing in the region of US $3 million, can approach the spectral and spatial characteristics of LANDSAT. Surrey's UoSAT-12 minisatellite (to be launched April, 1999) will further develop this cost-driven approach to provide 10 m panchromatic resolution and 30 m multi-spectral resolution. This paper describes the Thai-Phutt and UoSAT-12 imaging systems, explaining the engineering methods and trade-offs. Although Surrey is presently the only centre presently pursuing such implementations, our paper shows that they deserve wider consideration.     

A modern robust approach to remotely estimate chlorophyll in coastal and inland zones

The chlorophyll concentration of a water body is an important proxy for representing the phytoplankton biomass. Its estimation from multi or hyper-spectral remote sensing data in natural waters is generally achieved by using (i) the waveband ratioing in two or more bands in the blue-green or (ii) by using a combination of the radiance peak position and magnitude in the red-near-infrared (NIR) spectrum. The blue-green ratio algorithms have been extensively used with satellite ocean color data to investigate chlorophyll distributions in open ocean and clear waters and the application of red-NIR algorithms is often restricted to turbid productive water bodies. These issues present the greatest obstacles to our ability to formulate a modern robust method suitable for quantitative assessments of the chlorophyll concentration in a diverse range of water types. The present study is focused to investigate the normalized water-leaving radiance spectra in the visible and NIR region and propose a robust algorithm (Generalized ABI, GABI algorithm) for chlorophyll concentration retrieval based on Algal Bloom index (ABI) which separates phytoplankton signals from other constituents in the water column. The GABI algorithm is validated using independent in-situ data from various regional to global waters and its performance is further evaluated by comparison with the blue-green waveband ratios and red-NIR algorithms. The results revealed that GABI yields significantly more accurate chlorophyll concentrations (with uncertainties less than 13.5%) and remains more stable in different waters types when compared with the blue-green waveband ratios and red-NIR algorithms. The performance of GABI is further demonstrated using HICO images from nearshore turbid productive waters and MERIS and MODIS-Aqua images from coastal and offshore waters of the Arabian Sea, Bay of Bengal and East China Sea.     

TopPixelLoss:类别不均衡的遥感影像语义分割损失函数

针对遥感影像中类别不均衡的小目标分割效果不理想的问题，提出了一种类别不均衡小目标二分类分割的损失函数——TopPixelLoss损失函数。首先计算出每个像素的交叉熵，然后将所有像素的交叉熵按从大到小进行排序，随后确定一个K值作为阈值，筛选出前K个交叉熵最大的像素，最后对于筛选出的K个像素交叉熵取平均，做为损失值。在ISPRS 提供的 Vaihingen 数据集上，使用PSPNet网络与普通交叉熵、FocalLoss、TopPixelLoss三种损失函数分别对车辆进行二分类分割试验。结果表明，不同的K值，使用TopPixelLoss损失函数的平均交并比（MIoU）、F1-score、准确度（ACC）都最高;当K值为5×104时效果最佳，MIoU、F1-score、ACC分别比FocalLoss提高了3.0%、5.0%、0.1%。TopPixelLoss损失函数是一种针对类别不均衡分割非常有效的损失函数     

基于IMU/FADS/无线电的火星上升器组合导航方案

以火星采样返回任务中火星表面上升为背景，研究了基于惯性测量单元（Inertial Measurement Unit, IMU）、嵌入式大气数据传感系统（Flush Air Data Sensing System, FADS）和无线电信标的组合导航方法。首先，在传统的IMU导航框架中加入由无线电测量获得的相对距离、速度信息，以及由FADS获取的动压、温度数据，建立了基于IMU、无线电和FADS的导航观测模型；然后，基于无迹卡尔曼滤波（Unscented Kalman Filter, UKF）技术对测量信息进行了融合，并压制了过程噪声和测量噪声，从而对上升器的状态进行了联合估计；最后，在数值仿真中，将UKF与自适应无迹卡尔曼滤波（Adaptive Unscented Kalman Filter, AUKF）技术进行了对比，在比较不同滤波器性能的同时，验证了组合导航方法的有效性。