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Wan W.,Peking University | Chen X.,Peking University | Zhao L.,University of Chinese Academy of Sciences | Zhao L.,Center for National Spaceborne Demonstration | And 2 more authors.
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2012

The microwave signal of GNSS L band is very sensitive to the electromagnetic property of soil surface, through measuring the reflected electromagnetic energy from soil, the relationship between power of GNSS reflected signals and soil dielectric constant can be built, and then soil moisture can be estimated. In order to improve estimation accuracy, both the direct and reflected GNSS signals need to be calibrated to eliminate the signal error. A soil moisture estimation model utilizing calibrated GNSS L band reflected signals is proposed in this paper, and the estimation accuracy is validated using SMEX02 data. The error of areas with different NDVI is calculated. The error of soil moisture estimation is 7.04% for bare soil condition of the verify areas. It is shown that this model is suitable for bare soil condition or areas with low vegetation coverage. For further research, in the case of soil with high vegetation coverage, the model should be modified through adding the vegetation effect into it. © 2012 IEEE. Source

Hu X.,University of Chinese Academy of Sciences | Hu X.,CAS Institute of Remote Sensing | Hu X.,National Satellite Meteorological Center | Hu X.,Center for National Spaceborne Demonstration | And 10 more authors.
Canadian Journal of Remote Sensing | Year: 2010

The Dunhuang test site, one of the China Radiometric Calibration Sites (CRCS) for the vicarious calibration (VC) of Chinese spaceborne sensors, was selected in 2008 by the Working Group on Calibration and Validation (WGCV) of the Committee on Earth Observation Satellites (CEOS) as one of the instrumented reference sites. The site is spatially uniform with a coefficient of variation (CV) (standard deviation / mean) less than 2% of spectral reflectance over the 10 km × 10 km central region, based on the imagery of the Medium Resolution Spectral Imager (MERSI) onboard the Fengyun 3A (FY-3A) satellite. This result is also proven by several ground truth measurements. The surface spectral reflectance is temporally stable with a CV of about 3% from 7-year Moderate Resolution Imaging Spectroradiometer (MODIS) surface albedo product and has been validated using the ground-based measurement eight times in 10 years. Several calibration/validation (Cal/Val) field campaigns for the site evaluation and VC have been conducted since 1999, and a database including atmospheric and surface characteristics has been established. The aerosol optical depth (AOD) at the Dunhuang site is low (τ550 is about 0.2), except for the dusty spring season from March to May. The surface reflectance of this site is about 15%-30% from the visible to near-infrared spectral region. The site surface is not Lambertian, with clearly direction-dependent reflectance variation especially at the large solar or observation zenith angles. The CRCS VC was the baseline operational calibration approach from 2002 for the Multichannel Visible and Infrared Scanning Radiometer (MVISR) onboard the FY-1C and FY-1D satellites. The approach is inherited by the optical imaging sensors (Visible and Infrared Radiometer (VIRR) and MERSI) of the Chinese second-generation polar-orbiting satellite FY-3A. The CRCS VC is used not only to correct the significant bias of preflight calibration in some bands of these sensors but also to monitor the sensor radiometric degradation. The Dunhuang site can also be used as the earth target in the cross-calibration for the FY satellite sensors. © 2010 CASI. Source

Xu J.,CAS Institute of Remote Sensing Applications | Xu J.,Center for National Spaceborne Demonstration | Gu X.,CAS Institute of Remote Sensing Applications | Gu X.,Center for National Spaceborne Demonstration | And 6 more authors.
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2010

In remote chlorophyll-a (Chla) retrieval in Case-II waters, the uncertainties from Chla specific absorption coefficient a * ph has a significant effect on the retrieving accuracy. In this paper, we presented newly improved three-band model and four-band model by a case study in Shitoukoumen Reservoir. The proposed three-band model can be expressed as [R rs -1(λ 1-R rs -1(λ 2)]×R rs(λ 3)×a * ph -1(λ 1), while the improved four-band model is [R rs -1(λ 1-R rs -1(λ 2)]×[R rs -1(λ 4)-R rs -1(λ 3)] -1×a * ph -1(λ 1) Results showed that the latter one was slightly superior to the former one. Comparison with original models without correction of a * ph, the improved models achieved higher precision and stability. The findings underlined the rationale behind the proposed models and demonstrated a potentially use for assessing Chla in Case-II waters. © 2010 IEEE. Source

Xu H.,CAS Institute of Remote Sensing Applications | Xu H.,University of Chinese Academy of Sciences | Xu H.,Center for National Spaceborne Demonstration | Yu T.,CAS Institute of Remote Sensing Applications | And 7 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

April 8, 2012, the east region of Inner Mongolia out broke a strong sandstorm. Based on the analysis of the spectral characteristics of dust, cloud and surface, this paper propose a duststorm mask algorithm for the identification of dust coverage region by using three infrared channels of FY-3B. By utilizing diurnal variation of brightness temperature of dust aerosol, the bi-temporal thermal dust index was established to represent the intensity of duststorm. Through the analysis we found that BTDI has a high negative correlation with aerosol optical depth which can be used as an effective means to monitor the duststorm. © 2012 SPIE. Downloading of the abstract is permitted for personal use only. Source

Xiong P.,Beijing Normal University | Xiong P.,University of Chinese Academy of Sciences | Xiong P.,Center for National Spaceborne Demonstration | Xiong P.,China Earthquake Administration | And 7 more authors.
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2011

In this paper we present an analysis of DEMETER (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions) satellite data by using the wavelet-based data mining techniques. The analyzed results reveal that the possible anomalous variations exist around the earthquakes. The methods studied in this work include wavelet transformations and spatial/temporal continuity analysis of wavelet maxima. These methods have been used to analyze the singularities of seismic precursors in DEMETER satellite data, which are associated with the two earthquakes of Wenchuan and Pure recently occurred in China. © 2011 Springer-Verlag. Source

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