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Chen W.,China University of Mining and Technology | Tang H.,Satellite Surveying and Mapping Application Center | Zhao H.,Peking University
Atmospheric Environment | Year: 2015

Under the National Ambient Air Quality Standard released in 2012 (NAAQS-2012), Beijing began to publicize hourly Air Quality Index as well as real time concentrations of 6 pollutants in its web platform to provide detailed information for air quality assessment from 2013. In this study, hourly air quality monitoring data from May 2014 to April 2015 were collected for all 35 monitoring stations in Beijing to analyze the temporal and spatial variations of air pollutants and air quality. It is found that in spatial pattern, the air qualities in southern and northern Beijing are totally different. The association between heavy pollution concentrations and wind situations suggested that neighboring area's air quality has an important role in the air quality of Beijing combining with air quality attainment rates in all 35 monitoring stations and northern China. For temporal variations, late night and early morning are the most polluted time while afternoon is the least polluted time for all pollutants except O3 with most polluted time in afternoon. Summer time in Beijing has the best air quality while winter time has the worst air quality coinciding with the heating season in the winter. © 2015 Elsevier Ltd.

Wang M.,Hubei University | Hu F.,Satellite Surveying and Mapping Application Center | Li J.,University of Waterloo
ISPRS Journal of Photogrammetry and Remote Sensing | Year: 2011

This paper presents a practical epipolarity model for high-resolution linear pushbroom satellite images acquired in either along-track or cross-track mode, based on the projection reference plane in object space. A new method for epipolar resampling of satellite stereo imagery based on this model is then developed. In this method, the pixel-to-pixel relationship between the original image and the generated epipolar image is established directly by the geometric sensor model. The approximate epipolar images are generated in a manner similar to digital image rectification. In addition, by arranging the approximate epipolar lines on the defined projection reference plane, a stereoscopic model with consistent ground sampling distance and parallel to the object space is thus available, which is more convenient for three-dimensional measurement and interpretation. The results obtained from SPOT5, IKONOS, IRS-P5, and QuickBird stereo images indicate that the generated epipolar images all achieve high accuracy. Moreover, the vertical parallaxes at check points are at sub-pixel level, thus proving the feasibility, correctness, and applicability of the method. © 2011 International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS).

Jiang Y.-H.,Wuhan University | Zhang G.,Wuhan University | Tang X.,Satellite Surveying and Mapping Application Center | Li D.,Wuhan University | Huang W.-C.,Wuhan University
IEEE Transactions on Geoscience and Remote Sensing | Year: 2014

Ziyuan1-02C (ZY1-02C) was launched on December 22, 2011, and it is the first civilian high-resolution remote sensing satellite in China. However, the limited precision of the onboard attitude measurement system causes many errors during attitude transfer by ZY1-02C. Thus, there are complex distortions in the images obtained by ZY1-02C, which restricts its application greatly. In this paper, we consider the feasibility of attitude error correction based on parallel observations with high-resolution cameras, and the method is described in detail. To validate the efficiency of the proposed method, several images and corresponding control data were collected from the Henan, Taihang Mountain, Neimeng, and Taiyuan areas in China. The experimental results indicate that seamless mosaic images without distortion can be obtained using our method. Furthermore, the positioning accuracy with a few ground control points (GCPs) was shown to be better than 1.5 pixels and equivalent to the accuracy of the GCPs. © 2014 IEEE.

Tang X.,Satellite Surveying and Mapping Application Center | Zhang G.,Satellite Surveying and Mapping Application Center | Zhang G.,Wuhan University | Zhu X.,Satellite Surveying and Mapping Application Center | And 4 more authors.
International Journal of Image and Data Fusion | Year: 2013

ZiYuan-3 (ZY-3) surveying satellite is China's first civilian high-resolution stereo mapping satellite. The satellite's objective is oriented towards plotting 1:50,000 and 1:25,000 topographic maps. Compared with plotting using foreign commercial mapping satellite imagery, establishment of the image geometry model is the core technical problem for different products and various applications of ZY-3 surveying satellite. This article analyses key problems of high-precision geometry processing based on the overall design, and proposes ZY-3 surveying satellite image geometry model with the technology of virtual CCD line-array imaging. In addition, this article utilises the first orbit imagery of ZY-3 satellite with coverage of Dalian region in Liaoning Province, and produces forward, backward and nadir camera calibrated products. Different ground control points are selected for the block adjustment experiment and the digital surface model (DSM), digital ortho-map (DOM) are generated. The accuracy is validated by check points. The experiment reveals that the planar accuracy of DOM and vertical accuracy of DSM are better than 3 m and 2 m, respectively. The experiment demonstrates the effectiveness of ZY-3 surveying satellite image geometry model. © 2013 Copyright Taylor and Francis Group, LLC.

Zhang G.,Wuhan University | Zhang G.,Satellite Surveying and Mapping Application Center | Li Z.,Wuhan University | Zhu X.,Satellite Surveying and Mapping Application Center | Fei W.,Wuhan University
International Journal of Image and Data Fusion | Year: 2013

SAR Geocoded Ellipsoid Corrected (GEC) imagery is often taken as a post product processed from slant or ground range radar images. However, its geometric specific, being corrected to a constant ellipsoid height, makes it a coarse geocoded reference for users who are interested in accurate absolute localisation in applications, such as 'ortho-image' generation and digital elevation model (DEM) production. In order to improve the usefulness of SAR GEC imagery, the specific geometric distortions induced by the terrain require corresponding geometric models to perform geometric corrections to the imagery. In this article, both the rigorous physical model and the Rational Polynomial Coefficient (RPC) model for SAR GEC imagery are studied. First, the specific geometry of GEC imagery is illustrated. Then the procedure of reconstructing the rigorous physical model of GECs, which actually is mathematically combined with the normal range-Doppler model, is described in detail. The RPC estimator for replacing this rigorous physical model is then derived. Finally, based on numerous tests with the rigorous physical model available, the modelling error of the RPC is analysed. Four different kinds of high resolution SAR GEC images, i.e. TerraSAR-X, COSMO-SkyMed, RADARSAT-2 and ALOS-PALSAR, are used as experimental data. The experimental results show that using the third-order RPC model with unequal denominators as a substitute for the GEC imaging rigorous physical model, delivers accuracies for different high-resolution SAR GEC images that are all better than 0.01 pixels. The RPC model can be a robust and efficient substitute for the GEC imaging rigorous physical model to perform geometrical processing. © 2013 Copyright Taylor and Francis Group, LLC.

Pan H.,Wuhan University | Zhang G.,Wuhan University | Tang X.,Satellite Surveying and Mapping Application Center | Li D.,Wuhan University | And 3 more authors.
Photogrammetric Engineering and Remote Sensing | Year: 2013

The ZiYuan-3 satellite allows users to obtain triplet along-track stereo and four-band multispectral images within a single pass. Its basic sensor-corrected products are generated by reimaging with a virtual CCD array in which inner and exterior distortions are resolved and the introduced errors are negligible. In this study, three Z Y- 3 datasets (Dengfeng, Anping, and Taihang) were used to evaluate the accuracy of bundle adjustment using triplet stereo images. For both standard and long-strip scenes, the RMS errors of plane and elevation were 2.6 m and 1.6 m, respectively, when ground control points (GCPS) were deployed around the corners. The digital surface model (DSM) of the Dengfeng dataset was compared with a reference DEM (1:2000); the RMS errors produced varied with topography, with values of 3.9 m, 6.4 m, and 6.8 m for plain, hilly, and steep mountainous areas, respectively. © 2013 American Society for Photogrammetry and Remote Sensing.

Huang X.,Wuhan University | Wen D.,Wuhan University | Xie J.,Satellite Surveying and Mapping Application Center | Zhang L.,Wuhan University
IEEE Geoscience and Remote Sensing Letters | Year: 2014

The first results of multispectral (MS) and panchromatic (PAN) image fusion for the ZiYuan-3 (ZY-3) satellite, which is China's first civilian high-resolution satellite, are announced in this study. To this end, the various commonly used image fusion (pan-sharpening) techniques are tested. However, traditionally, image fusion quality is assessed by measuring the spectral distortion between the original and the fused MS images. The traditional methods focus on the spectral information at the data level but fail to indicate the image content at the information level, which is more important for specific remote sensing applications. In this context, we propose an information-based approach for assessing the fused image quality by the use of a set of primitive indices which can be calculated automatically without a requirement for training samples or machine learning. Experiments are conducted using ZY-3 PAN and MS images from Wuhan, central China. One of the objectives of the experiments is to investigate the appropriate image fusion strategies for the ZY-3 satellite at both the data and information levels. On the other hand, the experiments also aim to reveal the inadequacy of the traditional image quality indices and the advantages of the proposed information indices for describing image content. It is suggested that an appropriate image quality index should take into account the global and local image features at both the data and information levels. © 2013 IEEE.

Jiang Y.-H.,Wuhan University | Zhang G.,Wuhan University | Tang X.-M.,Satellite Surveying and Mapping Application Center | Li D.,Wuhan University | And 2 more authors.
IEEE Transactions on Geoscience and Remote Sensing | Year: 2014

The ZiYuan-3 (ZY-3) remote sensing satellite is China's first civilian high-resolution stereo mapping satellite. Because the interior orientation parameters measured before launch are biased, the multispectral (four-band) images collected by ZY-3 exhibit low-accuracy band-to-band registration, which affects their subsequent applications. This paper presents a valid method for interior orientation determination of the ZY-3 multispectral sensor by determining the look angles of the charge-coupled device arrays for all bands. One band is chosen as the benchmark band, and its interior orientation is determined using the relevant ZY-3 image collected over the calibration field and the corresponding digital orthoimage map and digital elevation model. The remaining bands are then calibrated using the benchmark band as control data. The quality of the calibration is further enhanced by shortening the calibration period and by combining images collected over different calibration fields, which decreases the negative effects of errors in the satellite's attitude and position data. The interior orientation of the multispectral sensor in ZY-3 was determined using data sets taken over two calibration fields, namely, Dengfeng (Henan Province) and Tianjin. Evaluation experiments were performed using ZY-3 multispectral images and ground control points (GCPs) collected over several different periods and areas. The positioning accuracy of the ZY-3 multispectral images with a limited number of GCPs after calibration of the interior orientation was better than 0.3 pixels, and the band-to-band registration accuracy was up to 0.15 pixels. © 1980-2012 IEEE.

Wang M.,Wuhan University | Yang B.,Wuhan University | Hu F.,Satellite Surveying and Mapping Application Center | Zang X.,Wuhan University
Remote Sensing | Year: 2014

On-orbit geometric calibration is a key technology to guarantee the geometric quality of high-resolution optical satellite imagery. In this paper, we present an approach for the on-orbit geometric calibration of high-resolution optical satellite imagery, focusing on two core problems: constructing an on-orbit geometric calibration model and proposing a robust calculation method. First, a rigorous geometric imaging model is constructed based on the analysis of the major error sources. Second, we construct an on-orbit geometric calibration model through performing reasonable optimizing and parameter selection of the rigorous geometric imaging model. On this basis, the calibration parameters are partially calculated with a stepwise iterative method by dividing them into two groups: external and internal calibration parameters. Furthermore, to verify the effectiveness of the proposed calibration model and methodology, on-orbit geometric calibration experiments for ZY1-02C panchromatic camera and ZY-3 three-line array camera are conducted using the reference data of the Songshan calibration test site located in the Henan Province, China. The experimental results demonstrate a certain deviation of the on-orbit calibration result from the initial design values of the calibration parameters. Therefore, on-orbit geometric calibration is necessary for optical satellite imagery. On the other hand, by choosing multiple images, which cover different areas and are acquired at different points in time to verify their geometric accuracy before and after calibration, we find that after on-orbit geometric calibration, the geometric accuracy of these images without ground control points is significantly improved. Additionally, due to the effective elimination of the internal distortion of the camera, greater geometric accuracy was achieved with less ground control points than before calibration. © 2014 by the authors.

Tang X.,Satellite Surveying and Mapping Application Center | Xie J.,Satellite Surveying and Mapping Application Center
International Journal of Digital Earth | Year: 2012

As the important infrastructures for land mapping and resource monitoring, high-resolution remote sensing satellites (HRSS) are urgently demanded for the development of China. In this article, the key technologies of the main HRSS are summarized, and these technologies include sensor design, attitude and orbit determination, geometric calibration, imaging model construction, and block adjustment, etc., which involve the mapping accuracy of HRSS. Finally, the system design of the ZY-3 Satellite (China's first civil stereoscopic surveying and mapping satellite, to be launched in 2012) is introduced, which mainly include satellite technical specifications and strategies design based on these key technologies research. © 2012 Taylor and Francis Group, LLC.

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