基于星载旋转扫描雷达的高分辨率实现

为了提高传统星载真实孔径雷达(微波散射计)空间分辨率、满足地球物理参数(雪水当量、冰雪冻融等)的观测需求,开展了扫描体制散射计的高分辨率分析和研究。基于距离向脉冲压缩处理和方位向多普勒处理技术,提出了一种旋转扫描体制下的分辨率提高方法。针对笔形波束圆锥扫描散射计的观测方位角在天线扫描过程中不断变化的特点,在正侧视和斜侧视时对模型分别进行了仿真验证。验证表明利用散射计旋转扫描多普勒信息能够建立与方位向分辨率的关系,可以有效提高微波散射计的空间分辨率。当正侧视时,方位向分辨率可以达到2km,斜前视或者斜后视时,方位向分辨率能够达到2~5km。针对雪水当量模型数据进行分析验证,设计的系统传递误差Kpc在5km分辨率下可以达到0.3,在2km分辨率下达到0.3~0.5。     

基于回波模拟器的CFOSAT散射计校飞模式定标研究

航空校飞是中法海洋卫星(Chinese-French Oceanic SATellite,CFOSAT)散射计发射前需要完成的一项重要实验内容,它可以检验星载散射计的各项功能和性能,获取有效数据,是保障散射计在轨正常工作的重要环节。在本次校飞实验中,利用了回波模拟器对散射计进行地面系统测试及定标验证,探索了一种利用回波模拟器对星载散射计进行系统测试定标的方法。运用该方法对CFOSAT星载散射计进行全系统地面测试以及定标实验。回波模拟器提供给散射计标准的、已知的回波信号,散射计处理该信号后,获取系统参数并得到定标常数。校飞的实验结果验证回波模拟器对星载散射计地面测试和定标方法的可行性和准确性。     

神舟4号（SZ-4）多模态遥感器散射计数据预处理及Sigma-0数据显示

神舟4号多模态遥感器散射计（CN/SCAT）是我国星载散射计系统的前驱,对其进行深入研究有利于进一步掌握散射计系统的相关技术,为海洋卫星2号（HY-2）工作的顺利开展打下坚实基础。详细描述了CN/SCAT数据预处理所涉及的主要内容：地理定位、物理量转换、面元配准等,这些处理过程可以为HY-2提供参考,同时文中对Sigma-0数据进行科学显示,用户可以快速浏览散射计获取的数据,并找到感兴趣的区域,为HY-2提供业务化服务做准备。
     

星载微波散射计高分辨率σ~0图像重构方法研究

针对我国海洋二号卫星微波散射计(HaiYang-2Scatterometer,HY2-SCAT)数据存在的空间分辨率较低、无法满足对于地球冰冻圈、生物圈探测需求的问题,以其数据拓展应用为目标,开展了微波散射计高分辨率后向散射系数(σ0)图像重构技术仿真研究。采用仿真的方法实现并对比了AART(Additive Algebraic Reconstruction Technique)、MART(Multiplicative Algebraic Reconstruction Technique)、SIR(Scatterometer Image Reconstruction)3种分辨率增强的图像重构算法,得出了AART算法没有噪声抑制能力、MART算法噪声抑制能力较弱、SIR算法具有较强的噪声抑制能力,能更好地重构图像,达到分辨率增强效果的结论。然后采用HY2-SCAT测量L1B数据对结论进行了验证,重构了岛屿的地貌特征,得到了分辨率增强、细节丰富、边界清晰的重构图像;重构后的图像还可以应用于植被、冰盖和台风观测等地球地理学研究领域。     

星载微波辐射计数控单元系统设计与实现

星载微波辐射计是一种测量大气的液态水和水汽含量的被动式星载遥感器,在海洋和大气环境探测中有重要的应用,在神舟飞船（神舟四号）、嫦娥卫星（嫦娥一号）等航天项目中均有成功的应用经历。数控单元作为星载微波辐射计的核心单元,承担着系统控制、数据处理及与卫星的数据通讯等重要功能。着重介绍了星载微波辐射计的数控单元的系统设计以及一些关键技术。     

星载雷达高度计沙漠散射特性及定标方法研究

为了提高星载雷达高度计海面风速产品的精度并更好地修正海况偏差的影响,有必要对高度计测量的后向散射系数进行定标。分布目标是星载雷达散射系数定标的有效手段,而沙漠的散射特性特别适于高度计的散射系数定标。检验了Jason-2卫星高度计的沙漠回波波形,在澳大利亚辛普森沙漠和我国的塔克拉玛干沙漠选取了适当的区域,收集了在这些区域长达7a的Jason-2高度计数据。基于这些数据,研究了Jason-2卫星雷达高度计在沙漠上的散射系数特性,并提出了基于沙漠的散射系数定标方法,分析了其原理、可行性和试验方案,探讨了高度计和现场定标散射计足迹匹配等关键技术,并对其定标误差进行了分析,论证了沙漠定标场可实现优于0.5dB的定标精度。该方法有助于进一步提升海洋2号(HY-2A)卫星风速和海况偏差产品的质量和应用前景。     

建筑物目标高分辨率SAR图像模拟方法

随着TerraSAR-X,Cosmo-SkyMed和Radarsat-2等高分辨率合成孔径雷达(SAR)卫星系统的升空,星载SAR图像空间分辨率达到了米级。在这些高空间分辨率SAR图像中,单个建筑物结构的散射特征能够得到明显的展现,推动了SAR在城市监测中的应用。而城市环境的复杂性给SAR图像的解译和应用带来了巨大的挑战,由于SAR图像模拟有助于图像的解译和应用,因此城市目标高分辨率SAR图像模拟成为一个研究热点。提出了一种基于射线追踪法的图像模拟方法,它能够模拟城市目标SAR图像上叠掩、阴影和多次散射等主要特征,非常有利于SAR图像的解译。该模拟方法首先构建虚拟SAR传感器,发射电磁波射线与场景中三维模型相互作用,并接收回波信号成像,电磁波的传播以及与场景的多次散射在整个过程中都能够被追踪。为了评价该模拟方法的有效性,首先通过模拟平顶屋、尖顶屋模型的SAR图像,然后选择国家体育馆和大场景小区三维模型作为输入,将生成的模拟图像与真实TerraSAR-X聚束模式图像进行比较。结果表明:该模拟器能够模拟城市目标的散射特征并应用于图像的理解和变化检测。     

微波散射计反演海面风场的神经网络方法研究

研究利用神经网络方法处理微波散射计数据,反演海面风场。重点研究海洋二号(HY-2)卫星微波散射计数据反演,特别是中高风速条件下的风场反演。其中风速的反演基于后向传播(Back Propagation,BP)神经网络;多解风向的反演基于混合密度(Mixture Density Network,MDN)神经网络,求解过程中的核函数采用高斯分布;网络训练的目标风场采用欧洲中期天气预报中心(European Centre for Medium-range Weather Foresting,ECMWF)模式风场。通过与ECMWF风场的比较,利用神经网络方法反演的风场可以满足HY-2微波散射计风场反演的精度要求。同时通过与国家卫星海洋应用中心发布的HY-2微波散射计L2B级风场产品相比较,表明该方法反演的风场更接近ECMWF模式风场。     

RFSCAT散射计数据地理定位与误差分析

星载微波散射计是目前唯一能够同时测量海面风速和风向的传感器,在海洋科学研究中发挥着重要作用。散射计获取的地物后向散射只有经过地理定位才能得到包含地物位置信息的有效物理量。因此,散射计地理定位是数据预处理的重要组成部分,与遥感数据的质量密切相关。扇形波束旋转扫描散射计具备扇形固定波束散射计和笔形波束旋转扫描散射计的优势,目前还没有实现在轨运行。基于其工作方式的特殊性,详细分析了该散射计的扫描方式,给出了一种适用于该散射计的地理定位方法,得到了最终的定位结果。然后分析了影响定位结果的误差源,讨论了卫星姿态对于定位结果的影响情况,最终利用HY\|2卫星产品评价了该地理定位算法的相对精度指标。     

星载高分辨率红外触摸屏的设计与实现

针对航天电子产品特殊的应用环境,为优化航天仪表产品人机交互方式,研究了基于现场可编程门阵列(FPGA)+数字信号处理(DSP)架构的星载高分辨率红外触摸屏的设计与实现方法。在介绍了星载红外触摸屏系统整体架构的基础上,详细阐述了星载红外触摸屏的硬件设计、FPGA设计、图形用户界面(GUI)设计以及基于拉格朗日插值的DSP算法设计。针对星载红外触摸屏的特殊用途,分析了星载红外触摸屏的可靠性设计;对装配完成后的星载红外触摸屏进行了系统性能测试。测试结果表明,该系统简单可靠、工作稳定、屏幕分辨率高,可以满足航天仪表产品的特殊需求。     

Removal of clutter background limitations in dual-frequency scattering from the ocean

Frequency agility is applied to dual-frequency scattering from the ocean using an L-band microwave system in order to reduce the clutter background which has previously limited signal detectability in such scatterometers. Doppler spectra of the return show improvements of up to 13 dB in signal-to-clutter ratio using this technique compared with the standard non-frequency-agile technique. This improvement greatly enhances the ability of a dual-frequency scatterometer to measure ocean surface currents. Composite surface scattering theory is applied to explain the signal improvement. The clutter background is shown to be proportional to the ocean surface wave spectrum evaluated at a wavenumber corresponding to the wavenumber separation between the carrier frequencies of two transmitted pairs of frequencies. Thus, if the frequency separation between these carriers is equal to the frequency separation between the lines of each pair, the entire signal received by the system is proportional to the ocean surface wave spectrum evaluated at the common wavenumber difference. This three-frequency technique completely removes previous limitations on the measurement of ocean wave spectra by dual-frequency scatterometers by converting the clutter background into part of the desired signal. Signal detectability is then limited only by thermal noise.     

非降水条件下微波辐射计海面风遥感产品性能分析

通过对5种微波辐射计SSM/I、SSM/IS、TMI、AMSR\|E和WINDSAT以及2种微波散射计ASCAT和QUIKSCAT多年的海面风产品同浮标同步的实测资料进行数据匹配处理,再对匹配后的数据进行数据分析和统计。研究结果表明:微波辐射计遥感海面风的性能在1 m/s左右,可以满足绝大多数应用的需求。微波辐射计的低频海面风产品性能优于中频产品,但是中频数据地面分辨率高,建议在近海应用中使用中频产品,在大洋应用中使用低频产品。就不同微波辐射计而言,AMSR\|E和WINDSAT性能较优,SSM/I和SSM/IS性能较差,TMI则处于中等水平。微波辐射计测量风速的性能与微波散射计相比处于同一水平,但在高风速段微波辐射计有一定优势。微波辐射计中仅全极化微波辐射计WINDSAT具有测量海面风向的能力,在低风速段,WINDSAT测量海面风向的性能远远不及微波散射计,只有风速超过6 m/s时,WINDSAT提供的海面风向数据才能符合应用的需求。当风速超过8 m/s后,WINDSAT遥感海面风向的能力就和微波散射计基本一致。在此基础上,提出了强风条件下深入研究的必要性,并对浮标测风存在的问题做出了初步的分析并指出了改进的方向。
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Retrieval of bare soil and vegetation parameters from wind scatterometer measurements over three different climatic regions

Medium to low resolution (1-50 km) active microwave sensors such as spaceborne scatterometers and wide-swath mode synthetic aperture radars have great potential as tools for long term monitoring over land and ice. To optimise the use of this kind of data, the heterogeneity of the target and its effects on the radar measurements need to be investigated and modelled, particularly in the view of retrieving geophysical parameters. In this paper, wind scatterometer measurements over three different test sites, the NOPEX region in Sweden, the HAPEX-Sahel site in Niger and the Niger delta area in Nigeria, are analysed. For these regions, a forward model is developed by considering the backscatter contributions of the bare surface, the seasonal and evergreen vegetation and the open water areas. Colocated high spatial resolution SAR data and ground information are used to characterise the target scene. The model is then inverted to retrieve monthly soil roughness, dielectric properties and vegetation parameters. It is shown that the measurements contain enough information to characterise these three different regions and to monitor their temporal evolution. The retrieved values obtained for the bare surface and the vegetation parameters are consistent with ground measurements collected in these areas. Further improvements are achieved by incorporating the time scale variability of the variables investigated into the retrieval scheme.     

海洋二号有效载荷微波散射计数据处理系统的设计

海洋二号有效载荷微波散射计是由中科院空间中心研制的一种星载微波遥感器。它采用笔型波束圆锥扫描脉冲体制,主要用来测量海面风矢量,具有广泛的应用需求。着重介绍了散射计的数据处理系统的功能、结构及部分实验结果。     

Fusion of sea surface wind vector data acquired by multi-source active and passive sensors in China sea

This work is the first to analyse the sea surface wind vector (SSWV) data acquisition capabilities of eight satellites carrying microwave scatterometer (scanning scatterometer carried by Haiyang satellite 2A, advanced scatterometer carried by Metop satellite A, advanced scatterometer carried by Metop satellite B and scanning scatterometer carried by Oceansat satellite 2) or radiometers (Special Sensor Microwave Imager carried by Meteorological Satellite Program satellites F15 and F17, advanced microwave scanning radiometer 2 carried by GCOM-W1 satellite, and windsat polarimetric radiometer carried by Coriolis satellite) and investigate a SSWV fusion algorithm for active and passive remote-sensing data. We found that combining observations of the eight satellites can provide an SSWV data product with spatial resolution of 25 km × 25 km and temporal resolution of 3 h. Sea surface wind speed and direction data were obtained from multi-source active and passive sensors using a spatiotemporally weighted fusion algorithm. An adaptive sliding window was introduced for calculating effective observation data within spatial/temporal radii, which can effectively improve calculation efficiency for wind field fusion. Comparing the fused and buoy observation results, the root-mean-square errors of the wind direction and speed were 20.6° and 1.2 m s^–1, respectively, indicating that the fusion results can meet most application requirements for wind vector. Meanwhile, the space coverage, accuracy of merged wind speed and wind direction can be improved comparing to a single sensor.     

Impact of sub-daily wind forcing on mixed-layer depth and sea surface temperature: study using observations and a one-dimensional upper ocean model

The impact of sub-daily wind sampling on the diurnal cycle of oceanic mixed-layer depth (MLD) and sea surface temperature (SST) is investigated using a one-dimensional upper ocean model and observations at two locations: the Central Arabian Sea (CAS) and Eastern Equatorial Indian Ocean (EEIO). Motivation to carry out this study is twofold: first, it will help in understanding the possible error in model-simulated MLD and SST due to the non-inclusion of high-temporal wind sampling; and second, it will also emphasize the requirements of temporal sampling from space-based measurements of surface winds. Temporal decorrelation analysis suggests that over a 24-hour period, auto-correlation falls rapidly in the EEIO region, whereas the fall is less even at a lag of 24 hours in CAS. Time series analysis with different sub-daily sampling rates suggests that the optimum sampling rate is three hours for MLD and SST. A suite of one-dimensional model simulations performed at the CAS and EEIO locations with sub-daily wind suggests that once-daily synoptic measurements of wind, which is the most likely scenario with one scatterometer, results in small biases but large standard deviations in MLD. In the case of SST, there is a small positive bias in the order of 0.1°C at the CAS buoy location while at the EEIO location, no such bias is observed. With two scatterometers in a constellation resulting in two observations per day, one can obtain a small standard deviation in MLD, but the bias is greater in this case. For SST, except for a small bias (about 0.1°C) at the CAS location, the distribution is mostly well-behaved Gaussian in all cases. The present study suggests the advisability of acquiring more frequent wind measurements from space-borne scatterometers. A well-coordinated satellite scatterometer constellation will help in resolving the diurnal variability and associated feedback mechanism of air–sea exchange processes, enhancing the understanding of large-scale phenomena such as the Indian summer monsoon, El Niño-southern oscillations, and the Madden–Julian oscillation.     

Empirical transfer function determination by the use of multilayer perceptron

Neural Networks are relevant statistical methods to extract information from data when physical phenomena are very complicated and cannot be described in terms of theoretical analysis. Scatterometers are active microwave radar which accurately measure the power of the backscatter signal versus incident signal in order to calculate the normalized radar cross section (σ₀) of the ocean surface. We use multilayer perceptrons in order to determine the Geophysical Model Function and to estimate the variability of the signal of ERS-1, ERS-2 and NSCAT scatterometers.     

Mapping of Sahelian vegetation parameters from ERS scatterometer data with an evolution strategies algorithm

The West African Sahel rainfall regime is known for its spatio-temporal variability at different scales which has a strong impact on vegetation development. This study presents results of the combined use of a simple water balance model, a radiative transfer model and ERS scatterometer data to produce map of vegetation biomass and thus vegetation cover at a spatial resolution of 25 km. The backscattering coefficient measured by spaceborne wind scatterometers over Sahel shows a marked seasonality linked to the drastic changes of both soil and vegetation dielectric properties associated to the alternating dry and wet seasons. For lack of a direct observation, METEOSAT rainfall estimates are used to calculate temporal series of soil moisture with the help of a water balance model. This a priori information is used as input of the radiative transfer model that simulates the interaction between the radar wave and the surface components (soil and vegetation). Then, an inversion algorithm is applied to retrieve vegetation aerial mass from the ERS scatterometer data. Because of the nonlinear feature of the inverse problem to be solved, the inversion is performed using a global stochastic nonlinear inversion method. A good agreement is obtained between the inverse solutions and independent field measurements with mean and standard deviation of −54 and 130 kg of dry matter by hectare (kg DM/ha), respectively. The algorithm is then applied to a 350,000 km² area including the Malian Gourma and Seno region and a Sahelian part of Burkina Faso during two contrasted seasons (1999 and 2000). At the considered resolution, the obtained herbaceous mass maps show a global qualitative consistency (r²=0.71) with NDVI images acquired by the VEGETATION instrument.     

High Resolution Implementation based on Scanning Spaceborne Radar

In order to improve a relatively high spatial resolution for spaceborne scatterometer and satisfy the observation requirements of geophysical parameters (such as,snow water equivalent,snow/ice freezing and thawing),the analysis and research is carried on based on the scanning spaceborne microwave radar.Based on the pulse compression processing and Doppler technology,a scanning resolution improvement method is established.For the characteristic that the azimuth is changing with the rotating antenna,a model of different azimuth angles is established.The results show that the azimuth resolution is related to radar Doppler information,and using this relationship can improve the azimuth resolution.The spatial resolution can reach 2km at side\|looking and 2~5 km at inclined front and rear.In view of the snow water equivalent observations,the system Kpc can reach 0.3 when the spatial resolution is 5km,and can reach 0.3~0.5 when the spatial resolution is 2 km.     

基于SWIM、SCAT联合观测小卫星的总体设计要点

海洋对全球气候、气象、环境和经济发挥着重要作用,因此,有必要对其进行监测、研究及预测发生在海洋内部和海洋表面的运动过程。海面风场信息、海面波浪谱信息能够体现并反演海洋气象、海洋动力学特性、海洋资源、海洋污染情况、海洋经济性和海岸环境。波谱仪(SWIM,Surface Wind Investigation and Monitoring)和微波散射计(SCAT,Scatterometer )可以用于获取海面波浪谱信息和海面风场信息。首先对这两套载荷系统进行了介绍,并简要对基于这类主动微波遥感载荷配置的卫星设计进行了任务分析,最后给出了基于波谱仪、微波散射计联合使用在小卫星平台应用背景下卫星系统级设计的几个主要方面进行了研究和分析。