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31.
《International Journal of Digital Earth》2013,6(10):840-860
The permafrost in Qinghai-Tibet Plateau (QTP) has long been the focus of many researchers. In this study, we first use the method that integrates synthetic aperture radar (SAR) intensity and phase information to monitor permafrost environment in the Beiluhe Region, using time series advanced SAR images. The backscattering coefficients (σ0) and deformation were extracted for the main features, and the influences of meteorological conditions to them were also quantified. The results show that both the change in σ0 and surface deformation are closely related to the active layer, and the deformation is also affected by the permafrost table. First, over meadow and sparse vegetation regions, σ0 rose about 6.9 and 4 dB from the freezing to thawing period, respectively, which can be mainly attributed to the thaw of the active layer and increased precipitation. Second, seasonal deformation, derived from the freeze-thaw cycle of the active layer, was characteristic of frost heave and thaw settlement and exhibited a negative correlation with air temperature. Its magnitude was larger than 1 cm in a seasonal cycle. Last, significant secular settlement was observed, with rates ranging from –16 to 2 mm/a, and it was primarily due to the thaw of the permafrost table caused by climate warming. 相似文献
32.
The information content of flood extent maps can be increased considerably by including information on the uncertainty of the flood area delineation. This additional information can be of benefit in flood forecasting and monitoring. Furthermore, flood probability maps can be converted to binary maps showing flooded and non-flooded areas by applying a threshold probability value pF = 0.5. In this study, a probabilistic change detection approach for flood mapping based on synthetic aperture radar (SAR) time series is proposed. For this purpose, conditional probability density functions (PDFs) for land and open water surfaces were estimated from ENVISAT ASAR Wide Swath (WS) time series containing >600 images using a reference mask of permanent water bodies. A pixel-wise harmonic model was used to account for seasonality in backscatter from land areas caused by soil moisture and vegetation dynamics. The approach was evaluated for a large-scale flood event along the River Severn, United Kingdom. The retrieved flood probability maps were compared to a reference flood mask derived from high-resolution aerial imagery by means of reliability diagrams. The obtained performance measures indicate both high reliability and confidence although there was a slight under-estimation of the flood extent, which may in part be attributed to topographically induced radar shadows along the edges of the floodplain. Furthermore, the results highlight the importance of local incidence angle for the separability between flooded and non-flooded areas as specular reflection properties of open water surfaces increase with a more oblique viewing geometry. 相似文献
33.
Envisat-1双极化雷达数据建模及应用 总被引:1,自引:0,他引:1
根据欧空局Envisat-1卫星上ASAR传感器的系统参数和双极化特点,利用AIEM模型模拟,建立了裸露地表同极化后向散射模型和粗糙度参数计算模型。前者把同极化总后向散射系数表达成人射角和两个地表参数(土壤水分和粗糙度)的函数;后者给出了用双极化雷达数据计算粗糙度的方法。把这两个模型结合,用于土壤水分反演,分别用模拟数据和实测数据验证,良好的结果证明了这两个模型的可靠性和实用性。双极化后向散射模型的建立,将为以后PALSAR(日本)和RADARSAT-2(加拿大)多极化雷达数据的应用打下基础。 相似文献
34.
��L���κ�C����SAR�����о��봨�����ͬ���α� 总被引:2,自引:3,他引:2
???ALOS PALSAR??Envisat ASAR?????????????α?????????L???κ?C????SAR?????????????????????L?????????????????????????????????????????α??????????α???????????PALSAR??????????????е?????????????????λ???????????????? 相似文献
35.
Active microwave remote sensing data were used to calculate the near-surface soil moisture in the vegetated areas. In this study, Advanced Synthetic Aperture Radar (ASAR) observations of surface soil moisture content were used in a data assimilation framework to improve the estimation of the soil moisture profile at the middle reaches of the Heihe River Basin, Northwest China. A one-dimensional soil moisture assimilation system based on the ensemble Kalman filter (EnKF), the forward radiative transfer model, crop model, and the Distributed Hydrology-Soil-Vegetation Model (DHSVM) was developed. The crop model, as a semi-empirical model, was used to estimate the surface backscattering of vegetated areas. The DHSVM is a distributed hydrology-vegetation model that explicitly represents the effects of topography and vegetation on water fluxes through the landscape. Numerical experiments were con- ducted to assimilate the ASAR data into the DHSVM and in situ soil moisture at the middle reaches of the Heihe River Basin from June 20 to July 15, 2008. The results indicated that EnKF is effective for assimilating ASAR observations into the hydrological model. Compared with the simulation and in situ observations, the assimilated results were significantly improved in the surface layer and root layer, and the soil moisture varied slightly in the deep layer. Additionally, EnKF is an efficient approach to handle the strongly nonlinear problem which is practical and effective for soil moisture estimation by assimilation of remote sensing data. Moreover, to improve the assimilation results, further studies on obtaining more reliable forcing data and model parameters and increasing the efficiency and accuracy of the remote sensing observations are needed, also improving estimation accuracy of model operator is important. 相似文献
36.
基于MERIS数据的永久散射体处理中大气改正方法研究 总被引:1,自引:0,他引:1
分析了永久散射体PS(Permanent Scatlerers)处理中进行大气改正的必要性,介绍了大气改正的方法,指出现有方法存在的不足; 结合利用MERIS数据进行大气改正的优势,提出了基于MERIS数据的PS处理中大气改正的模型.采用青藏高原北麓河实验区ASAR数据对该模型进行验证的结果表明,该方法能够有效提高永久散射体处理中大气改正的可信性,从而使得利用相对较少的ASAR数据进行PS分析成为可能. 相似文献
37.
基于ENVISAT ASAR数据的森林蓄积量估测研究 总被引:5,自引:0,他引:5
以东北大兴安岭地区的图强林业局作为试验区,基于统计方法对多时相ENVISAT ASAR数据进行森林蓄积量估测研究,分别选取HH、HV及HV/HH值分析森林蓄积量与SAR后向散射系数之间的关系;根据其散点图形状进行方程拟合及优选,完成蓄积量的估测。利用独立的检验样本对估测结果进行评价,均方根误差(RMSE)为16.526 m3/hm2,与实际情况基本相符。 相似文献
38.
由于可以探测到视线向的微小形变量,重复轨道雷达干涉测量(INSAR)成为探测极地冰流的有效手段。基于ERS-1/2SAR影像的INSAR已经成功获取了南北极许多地区的冰流信息。采用最新的ENVISAT ASAR影像,利用干涉方法获得了东南极内陆格罗夫山地区的首幅ASAR干涉条纹图(其中包括地形信息和冰流信息)。其与利用该地区1996年ERS-1和JERS-1数据所获得的干涉条纹进行对比表明,在格罗夫山角峰群内分布有两个冰流子系统,且状态较为稳定,ENVISAT ASAR数据在冰盖干涉测量方面具有良好的性能和应用潜力。 相似文献
39.
This paper is focused on the method for extracting glacier area based on ENVISAT ASAR Wide Swath Modes (WSM) data and digital elevation model (DEM) data, using support vector machines (SVM) classification method. The digitized result of the glacier coverage area in the western Qilian Mountains was extracted based on Enhanced LandSat Thematic Mapper (ETM+) imagery, which was used to validate the precision of glacier extraction result. Because of similar backscattering of glacier, shadow and water, precision of the glacier coverage area extracted from single-polarization WSM data using SVM was only 35.4%. Then, texture features were extracted by the grey level co-occurrence matrix (GLCM), with extracted glacier coverage area based on WSM data and texture feature information. Compared with the result extracted from WSM data, the precision improved 13.2%. However, the glacier was still seriously confused with shadow and water. Finally, DEM data was introduced to extract the glacier coverage area. Water and glacier can be differentiated because their distribution area has different elevations; shadow can be removed from the classification result based on simulated shadow imagery created by DEM data and SAR imaging parameters; finally, the glacier coverage area was extracted and the precision reached to 90.2%. Thus, it can be demonstrated that the glacier can be accurately semi-automatically extracted from SAR with this method. The method is suitable not only for ENVISAT ASAR WSM imagery, but also for other satellite SAR imagery, especially for SAR imagery covering mountainous areas. 相似文献
40.