Abstract
To determine the geolocation of a pixel for spaceborne synthetic aperture radar (SAR) images, traditional indirect geolocation methods can cause great computational complexity. In this paper, a fast, three-dimensional, indirect geolocation method without ground control points (GCPs) is presented. First, the Range-Doppler (RD) geolocation model with all the equations in the Earth-centered rotating (ECR) coordinate system is introduced. By using an iterative analytical geolocation method (IAGM), the corner point locations of a quadrangle SAR image on the Earth’s surface are obtained. Then, a three-dimensional (3D) grid can be built by utilizing the digital surface model (DSM) data in this quadrangle. Through the proportional relationship for every pixel in the 3D grid, the azimuth time can be estimated, which is the key to decreasing the calculation time of the Doppler centroid. The results show that the proposed method is about 12 times faster than the traditional method, and that it maintains geolocation accuracy. After acquiring the precise azimuth time, it is easy to obtain the range location. Therefore, the spaceborne SAR image can be geolocated to the Earth surface precisely based on the high-resolution DSM data.
Highlights
IntroductionSpaceborne synthetic aperture radar (SAR) images are widely used in a variety of fields [1].With the paramount need to target surveillance and state security, i.e., target geolocation, the accuracy of the absolute locations of sensitive targets on the ground in spaceborne SAR images is very critical.The absolute accuracy of SAR geolocation depends on multiple factors, such as the orbital precision of the satellite, sensor stability, radar accuracy, knowledge of the propagation medium, SAR processing accuracy, timing accuracy, target detection accuracy, coordinate transformation accuracy, etc. [2,3,4,5,6,7].The traditional indirect geolocation method establishes the mapping association between image coordinates and geodetic coordinates by repetitively calculating the relation between the digital elevation model (DEM) grid and the satellite position, which requires several processing iterations [8,9,10].A good deal of work has been done using the traditional indirect geolocation method to achieve good accuracy
Geolocation accuracy can be effectively improved by using the precise latitude, longitude, and elevation provided by ground control points (GCPs), such as Wettzell corner reflector experiment
This paper proposes a fast, three-dimensional, indirect geolocation method using iterative analytical geolocation method (IAGM) and digital surface model (DSM)
Summary
Spaceborne synthetic aperture radar (SAR) images are widely used in a variety of fields [1].With the paramount need to target surveillance and state security, i.e., target geolocation, the accuracy of the absolute locations of sensitive targets on the ground in spaceborne SAR images is very critical.The absolute accuracy of SAR geolocation depends on multiple factors, such as the orbital precision of the satellite, sensor stability, radar accuracy, knowledge of the propagation medium, SAR processing accuracy, timing accuracy, target detection accuracy, coordinate transformation accuracy, etc. [2,3,4,5,6,7].The traditional indirect geolocation method establishes the mapping association between image coordinates and geodetic coordinates by repetitively calculating the relation between the digital elevation model (DEM) grid and the satellite position, which requires several processing iterations [8,9,10].A good deal of work has been done using the traditional indirect geolocation method to achieve good accuracy. With the paramount need to target surveillance and state security, i.e., target geolocation, the accuracy of the absolute locations of sensitive targets on the ground in spaceborne SAR images is very critical. The absolute accuracy of SAR geolocation depends on multiple factors, such as the orbital precision of the satellite, sensor stability, radar accuracy, knowledge of the propagation medium, SAR processing accuracy, timing accuracy, target detection accuracy, coordinate transformation accuracy, etc. The traditional indirect geolocation method establishes the mapping association between image coordinates and geodetic coordinates by repetitively calculating the relation between the digital elevation model (DEM) grid and the satellite position, which requires several processing iterations [8,9,10]. Geolocation accuracy can be effectively improved by using the precise latitude, longitude, and elevation provided by ground control points (GCPs), such as Wettzell corner reflector experiment
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