Active microwave remote sensing for soil moisture measurement: a field evaluation using ERS‐2     

Jeffrey P. Walker  Paul R. Houser  Garry R. Willgoose 《水文研究》2004,18(11):1975-1997

Active microwave remote sensing observations of backscattering, such as C‐band vertically polarized synthetic aperture radar (SAR) observations from the second European remote sensing (ERS‐2) satellite, have the potential to measure moisture content in a near‐surface layer of soil. However, SAR backscattering observations are highly dependent on topography, soil texture, surface roughness and soil moisture, meaning that soil moisture inversion from single frequency and polarization SAR observations is difficult. In this paper, the potential for measuring near‐surface soil moisture with the ERS‐2 satellite is explored by comparing model estimates of backscattering with ERS‐2 SAR observations. This comparison was made for two ERS‐2 overpasses coincident with near‐surface soil moisture measurements in a 6 ha catchment using 15‐cm time domain reflectometry probes on a 20 m grid. In addition, 1‐cm soil moisture data were obtained from a calibrated soil moisture model. Using state‐of‐the‐art theoretical, semi‐empirical and empirical backscattering models, it was found that using measured soil moisture and roughness data there were root mean square (RMS) errors from 3·5 to 8·5 dB and r² values from 0·00 to 0·25, depending on the backscattering model and degree of filtering. Using model soil moisture in place of measured soil moisture reduced RMS errors slightly (0·5 to 2 dB) but did not improve r² values. Likewise, using the first day of ERS‐2 backscattering and soil moisture data to solve for RMS surface roughness reduced RMS errors in backscattering for the second day to between 0·9 and 2·8 dB, but did not improve r² values. Moreover, RMS differences were as large as 3·7 dB and r² values as low as 0·53 between the various backscattering models, even when using the same data as input. These results suggest that more research is required to improve the agreement between backscattering models, and that ERS‐2 SAR data may be useful for estimating fields‐scale average soil moisture but not variations at the hillslope scale. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

全极化合成孔径雷达近岸风场反演研究   总被引：2，自引：2，他引：0  

ZHANG Yi  JIANG Xingwei  SONG Qingtao  LIN Mingsen  XIE Xuetong 《海洋学报(英文版)》2014,33(5):54-61

Coastal winds are strongly influenced by topology and discontinuity between land and sea surfaces. Wind assessment from remote sensing in such a complex area remains a challenge. Space-borne scatterometer does not provide any information about the coastal wind field, as the coarse spatial resolution hampers the radar backscattering. Synthetic aperture radar （SAR） with a high spatial resolution and all-weather observation abilities has become one of the most important tools for ocean wind retrieval, especially in the coastal area. Conventional methods of wind field retrieval from SAR, however, require wind direction as initial information, such as the wind direction from numerical weather prediction models （NWP）, which may not match the time of SAR image acquiring. Fortunately, the polarimetric observations of SAR enable independent wind retrieval from SAR images alone. In order to accurately measure coastal wind fields, this paper proposes a new method of using co-polarization backscattering coefficients from polarimetric SAR observations up to polarimetric correlation backscattering coefficients, which are acquired from the conjugate product of co-polarization backscatter and cross-polarization backscatter. Co-polarization backscattering coefficients and polarimetric correlation backscattering coefficients are obtained form Radarsat-2 single-look complex （SLC） data.The maximum likelihood estimation is used to gain the initial results followed by the coarse spatial filtering and fine spatial filtering. Wind direction accuracy of the final inversion results is 10.67 with a wind speed accuracy of 0.32 m/s. Unlike previous methods, the methods described in this article utilize the SAR data itself to obtain the wind vectors and do not need external wind directional information. High spatial resolution and high accuracy are the most important features of the method described herein since the use of full polarimetric observations contains more information about the space measured.This article is a useful addition to the work of independent SAR wind retrieval. The experimental results herein show that it is feasible to employ the co-polarimetric backscattering coefficients and the polarimetric correlation backscattering coefficients for coastal wind field retrieval.  相似文献   

Snow permittivity retrieval inversion algorithm for estimating snow wetness     

Gulab Singh  G. Venkataraman 《国际地球制图》2013,28(3):187-212

The environmental satellite (ENVISAT) advanced synthetic aperture radar (ASAR) offers the opportunity for monitoring snow parameters with dual polarization and multi-incidence angle. Snow wetness is an important index for indicating snow avalanche, snowmelt runoff modelling, water supply for irrigation and hydropower stations, weather forecasts and understanding climate change. We used a first-order scattering model that includes both volume and air/snow surface scattering based on a developed inversion model to estimate snow dielectric constant, which can be further related for estimating snow wetness. Comparison with field measurement showed that the correlation coefficient for snow permittivity estimated from ASAR data was observed to be 0.8 at 95% confidence interval and model bias was observed as 2.42% by volume at 95% confidence interval. The comparison of ASAR-derived snow permittivity with ground measurements shows the average absolute error 2.5%. The snow wetness range varies from 0 to 15% by volume.  相似文献   

复合雷达后向散射模型与合成孔径雷达、散射计和高度计海面雷达后向散射观测的比较分析     

叶小敏  林明森  宋清涛  廖菲  梁超  周旋 《海洋学报》2019,41(7):123-135

海洋微波散射模型相比于以经验统计建立的地球物理模式函数具有不受特定微波频率限制的优势。组合布拉格散射模型和几何光学模型形成了复合雷达后向散射模型。利用南海北部气象浮标2014年海面风速风向实测值作为散射模型输入，分别比较了复合雷达后向散射模型与RADARSAT-2卫星C波段SAR、HY-2A卫星Ku波段微波散射计的海面后向散射系数，偏差分别为(?0.22±1.88) dB (SAR)、(0.33±2.71) dB (散射计VV极化）和(?1.35±2.88) dB (散射计HH极化)；以美国浮标数据中心(NDBC)浮标2011年10月1日至2014年9月30日共3年的海面风速、风向实测值作为散射模型输入，分别比较了复合雷达后向散射模型与Jason-2、HY-2A卫星Ku波段高度计海面后向散射系数，偏差分别为(1.01±1.15) dB和(1.12±1.29) dB。中等入射角和垂直入射下的卫星传感器后向散射系数观测值与复合雷达后向散射模型模拟值比较，具有不同的偏差，但具有相同的海面风速检验精度，均方根误差小于1.71 m/s。结果表明，复合雷达后向散射模型可模拟计算星载SAR、散射计和高度计观测条件下的海面雷达后向散射系数，且与CMOD5、NSCAT-2、高度计业务化海面风速反演的地球物理模式函数的计算结果具有一致性；复合雷达后向散射模型可用于微波遥感器的定标与检验、海面雷达后向散射的模拟。  相似文献   

基于Landsat TM和ENVISAT ASAR数据的鄱阳湖湿地植被生物量的反演   总被引：2，自引：0，他引：2  

王庆  廖静娟 《地球信息科学学报》2010,12(2):282-291

作为湿地生态系统的重要组成部分,湿地生物量是衡量生态系统健康状况的关键指标。由于光学遥感对植被垂直分布探测的局限,使得植被指数反映生物量变化的灵敏度下降。利用C波段SAR反演生物量时,对于低中等生物量,含水量高的湿地地表的后向散射对总雷达后向散射的影响会在雷达图像上出现类似光学遥感中"异物同谱"的现象。本文用光学遥感中NDVI、RVI和DVI三种植被指数对生物量变化的敏感性,利用改进的MIM-ICS模型,对湿地植被各散射分量进行模拟分析,建立符合湿地植被类型的各散射分量模拟数据库,以LandsatTM和Envisat ASAR交替极化数据为基础,选择植被指数DVI=0.45为阈值,将湿地植被分割为低叶片密度植被区和高叶片密度植被区,分别应用统计回归模型和半经验微波散射模型,对两个区域植被生物量进行反演。最后,得到整个鄱阳湖湿地生物量为2.1×10⁹kg。研究表明,对于生物量动态范围较大的地区,采用光学和雷达遥感相结合可以有效地提高湿地植被生物量反演的精度,克服光学遥感探测植被垂直分布能力有限和雷达遥感受背景影响大的不足。  相似文献   

Minimising errors in estimating fish population and biomass densities using the ‘acoustic volume backscattering strength’ method     

M. A. Do 《新西兰海洋与淡水研究杂志》2013,47(1):99-108

The basic acoustical methods for estimating the volume backscattering strength and the absolute biomass density are commonly known. However, the detailed techniques for minimising errors in fitting the calibrated parameters of an echo sounding system in these computations are still not adequately examined and discussed. This paper describes and discusses the following computing techniques involved in the absolute biomass estimation: (i) the fitting of the calibrated time varied gain (TVG) curve, the selection of its operating interval, and the correction of its response; (ii) the compensation for the limitation of the signal bandwidth; (iii) the computation of the equivalent beam width of a transducer using its calibrated beam patterns; and (iv) the accuracy in the conversion from the volume backscattering to the absolute fish density using individual fish target strength measurements.  相似文献   

基于粗糙海面高度频谱函数的雷达后向散射系数计算   总被引：2，自引：0，他引：2  

董庆  郭华东  王长林 《遥感学报》2001,5(3):171-176

海面雷达后向散射系数是主动微波遥感定量化研究海洋的基础，基于各种海浪谱模式的后向散射系数计算可比性差，鉴于风成粗糙海面的波面斜率呈非Guassian分布的特点，本文给出了依据自由海面的二维高度谱计算海面的雷达后向散射系，并与实际SIR－C／X－SAR数据进行对比。  相似文献   

基于激光云高仪的雾霾光学特性研究     

乔晓燕 《沙漠与绿洲气象(新疆气象)》2020,14(3):137-143

利用2016年10月~2017年2月激光云高仪资料，分析了霾、雾、轻霾、轻雾、晴空等天气后向散射强度廓线特征，通过统计各高度层后向散射强度、后向散射强度垂直梯度的概率分布，分析了多种天气的气溶胶光学特性。结果表明：雾天气后向散射强度较霾天气大，雾厚度一般不超过300m。霾天气后向散射强度随着高度的增加减小缓慢，霾的厚度大于500m。与雾和轻雾相比，霾和轻霾天气垂直梯度绝对值取小值的概率较大。雾和轻雾天气400m高度以上垂直梯度绝对值较小，400m高度以下数值较大。由于霾区内粒子分布较均匀，雾区粒子分布起伏明显，雾区内后向散射强度忽大忽小，所以雾天气垂直梯度绝对值出现大值的概率较霾天气高。  相似文献   

ERS-1散射计数据用于全球陆地监测   总被引：6，自引：0，他引：6  

郭华东  王超  王湘云  施央申 《遥感学报》1997,1(4):277-281

该文介绍了ＥＲＳ－１（欧洲资源卫星１号）ＷＳＣ（风散射计）数据结构。描述了全球雷达后向散射系数（σ°）图的成图方法。展示池中国第一幅全球雷达后向散射系数分布图。重点分析了ＷＳＣ数据用于全球陆地监测的能力，并对全球典型地物地雷达后向散射系数进行了统计。研究结果表明：１．全球雷达后向散射系数侧重反映了全球值被图和地形图的叠合信息；２．ＷＳＣ数据能够以区域和全球尺度分区分６类主要的地表覆盖类型。它们是：  相似文献   

基于等相位体概念的水下激光背向散射强度的估算方法          下载免费PDF全文

温强  温文  智国宁 《海洋学报》2007,29(1):26-30

详细讨论了海水作为激光传输信道的基本特点,在此基础上提出了等相位体的概念,分析了等相位体的形状,并且研究了等相位体背向散射强度的估算方法,为利用伪随机序列进行水下测量或通讯获得的资料估算散射强度提供一种方法.  相似文献