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IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 55, NO. 11, NOVEMBER 2017
Three-Dimensional Deformation Retrieval in Geosynchronous SAR by Multiple-Aperture Interferometry Processing: Theory and Performance Analysis Cheng Hu, Senior Member, IEEE, Yuanhao Li, Xichao Dong, Rui Wang, Chang Cui, and Bin Zhang Abstract— The 3-D deformation retrieval is significant for the accurate evaluation of geologic disasters (e.g., earthquakes and landslides). Multiple-aperture interferometry (MAI) is an effective method to obtain 3-D deformation, combined with the cross-heading tracks synthetic aperture radar (SAR) data. However, because of the limitations of the low earth orbit SAR, a long satellite revisit time, small common areas of the crossheading tracks data, and the unsatisfied along-track deformation measurement accuracy usually exist in the traditional MAI 3-D deformation retrieval. Geosynchronous SAR (GEO SAR) runs in the geosynchronous orbit, which has the advantages of a large observation area and a short revisit time. This paper focuses on 3-D deformation retrieval by GEO SAR MAI processing. Aiming at the high orbit and the squint looking of GEO SAR, the accurate expressions of the along-track deformation, 3-D deformation, and the errors in GEO SAR MAI processing are given. The distortions and their correction in the MAI interferogram brought by the geometrical difference between the forward- and backward-looking interferograms and the multicycles flat-earth and topographic phases are given. Moreover, an optimal subaperture selection method based on minimum position dilution of precision is proposed. Finally, the effectiveness of the proposed method is validated by simulations and the experiment of BeiDou-2 inclined geosynchronous orbit navigation satellite. The theoretical analysis and the experimental results suggest centimeter-level and even millimeter-level deformation measurement accuracy could be obtained in 3-D by GEO SAR MAI processing. Index Terms— 3-D deformation measurement, differential interferometric SAR (D-InSAR), geosynchronous synthetic aperture radar (GEO SAR), Multiple-aperture interferometry (MAI). Manuscript received November 29, 2016; revised April 10, 2017 and June 9, 2017; accepted June 24, 2017. Date of publication July 31, 2017; date of current version October 25, 2017. This work was supported in part by the National Natural Science Foundation of China under Grant 61427802, Grant 61471038, and Grant 61501032, in part by the Beijing Natural Science Foundation under Grant 4162052, in part by the Chang Jiang Scholars Program under Grant T2012122, and in part by the China Scholarship Council. (Corresponding author: Yuanhao Li.) C. Hu is with the School of Information and Electronics, Beijing Institute of Technology, Beijing 100081, China, and also with the Key Laboratory of Electronic and Information Technology in Satellite Navigation, Ministry of Education, Beijing Institute of Technology, Beijing 100081, China (e-mail:
[email protected]). Y. Li, X. Dong, C. Cui, and B. Zhang are with the School of Information and Electronics, Beijing Institute of Technology, Beijing 100081, China (e-mail:
[email protected];
[email protected];
[email protected];
[email protected]). R. Wang is with the Department of Electronic Engineering, Tsinghua University, Beijing 100084, China (e-mail:
[email protected]). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TGRS.2017.2721554
I. I NTRODUCTION IFFERENTIAL interferometric synthetic aperture radar (D-InSAR) can realize accurate measurements of the surface deformations induced by geologic activities, such as earthquakes and landslides, which plays an important role in geological applications [1]–[6]. However, D-InSAR measurement is only sensitive to the 1-D deformation in line of sight (LOS). Thus, it is hard to obtain deformations in other directions. Since deformations usually occur in multidirection when natural disasters happen, 1-D deformation measurement cannot give out a real deformation evaluation if only the deformation in LOS can be obtained. Huang and Fan [7] pointed that earthquake faults included both vertical and horizontal deformations based on the research of obviously moved Longmen Shan fault in 2008 Mw 7.9 China Wenchuan earthquake. The lack of the 3-D deformation information will not only impede the accurately modeling and evaluating toward the disaster area (e.g., faults), but even any deformation cannot be detected when the deformation occurs along the flying direction. To address the issue, Michel et al. [8] proposed a 3-D deformation retrieval method based on the combination of the azimuthal offsets (AZO) and the cross-heading tracks D-InSAR data. Nevertheless, because the along-track deformation measurement accuracy in AZO is only 1/10 ∼ 1/30 of the spatial resolution, it only has the advantages in detecting large deformations (e.g., glacier movements). Wright et al. [9] demonstrated a 3-D deformation retrieval method based on multiangle SAR data (more than three angles). However, restricted by the geometry configuration (e.g., only running in the polar orbit), the current running SAR satellites are hard to provide the effective multiangle data [10]. Gudmundsson and Sigmundsson [11] and Samsonov and Tiampo [12] proposed the 3-D deformation retrieval methods by fusing the global positioning system (GPS) data and the D-InSAR data, and the processing accuracy could be improved to the millimeter level. However, the method is restrained by the numbers of GPS stations and the accuracy of the GPS data, which cannot improve the 3-D deformation retrieval accuracy essentially. In order to improve the along-track deformation retrieval accuracy, Bechor and Zebker [13] utilized multiple-aperture interferometry (MAI) to obtain the more accurate along-track deformation by separating the full aperture of the SAR data into the forward- and backward-looking
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0196-2892 © 2017 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
HU et al.: THREE-DIMENSIONAL DEFORMATION RETRIEVAL IN GEO SAR BY MULTIPLE-APERTURE INTERFEROMETRY PROCESSING
TABLE I E XAMPLES OF THE R EVISIT T IMES OF THE LEO SAR S YSTEMS
Fig. 1. Sketch map of the positions of the cross-heading tracks data (Sentinel-1 A data of January 14, 2016 in the Huabei area, China. Frames 1 and 2 are the ascending data and descending data, respectively).
subapertures and differentiating the corresponding interferograms. MAI processing realizes the 2-D (LOS and alongtrack) deformation retrieval rather than the simple 1-D (LOS) deformation retrieval. The 3-D deformation can be obtained by combining the cross-heading tracks data after MAI processing based on the weighted least squares solution [14]. Since the phase information is utilized, the deformation retrieval standard deviation error is improved by a factor of 2 in the along-track by MAI compared with AZO [15]–[19]. Although MAI combined with the cross-heading tracks data can realized 3-D deformation retrieval, lots of problems exist in the real measurements for disaster evaluations. First, a conventional low earth orbit (LEO) SAR has a long revisit time, from several days to dozens of days (shown in Table I), which cannot satisfy the high temporal sampling rate requirement for disaster area observations. Second, because of the short coverage time of the LEO SAR systems, common areas of the cross-heading tracks SAR images used for 3-D deformation retrieval are small. Shown in Fig. 1, the frames marked as 1 and 2 are the cross-heading tracks obtained by the Sentinel-1 A interferometric wide swath mode (250 km × 50 km coverage) in a single day, and the common area of the frames is only about 1/6. Third, along-track deformation retrieval accuracy of the LEO SAR MAI is still unsatisfactory, which is only about dozens of centimeters [13], [15]. The accuracy could be improved to several centimeters only under the processing of large-look multilooking processing (above 40 looks) and intense phase filtering [15], [19]. Because of the aforementioned issues, the employment of MAI in LEO SAR is restricted in the practical applications of the 3-D deformation retrieval.
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An effective method to address the shortcomings of the LEO SAR MAI is to realize 3-D deformation retrieval based on geosynchronous SAR (GEO SAR) data. A GEO SAR runs in a geosynchronous orbit of 36 000-km height [20]. It has a short revisit time (
