Comparison and Analysis of Geometric Correction Models of Spaceborne SAR

Abstract

Following the development of synthetic aperture radar (SAR), SAR images have become increasingly common. Many researchers have conducted large studies on geolocation models, but little work has been conducted on the available models for the geometric correction of SAR images of different terrain. To address the terrain issue, four different models were compared and are described in this paper: a rigorous range-doppler (RD) model, a rational polynomial coefficients (RPC) model, a revised polynomial (PM) model and an elevation derivation (EDM) model. The results of comparisons of the geolocation capabilities of the models show that a proper model for a SAR image of a specific terrain can be determined. A solution table was obtained to recommend a suitable model for users. Three TerraSAR-X images, two ALOS-PALSAR images and one Envisat-ASAR image were used for the experiment, including flat terrain and mountain terrain SAR images as well as two large area images. Geolocation accuracies of the models for different terrain SAR images were computed and analyzed. The comparisons of the models show that the RD model was accurate but was the least efficient; therefore, it is not the ideal model for real-time implementations. The RPC model is sufficiently accurate and efficient for the geometric correction of SAR images of flat terrain, whose precision is below 0.001 pixels. The EDM model is suitable for the geolocation of SAR images of mountainous terrain, and its precision can reach 0.007 pixels. Although the PM model does not produce results as precise as the other models, its efficiency is excellent and its potential should not be underestimated. With respect to the geometric correction of SAR images over large areas, the EDM model has higher accuracy under one pixel, whereas the RPC model consumes one third of the time of the EDM model.

Geo-Positioning Accuracy Improvement of Multi-Mode GF-3 Satellite SAR Imagery Based on Error Sources Analysis

“…In addition, three equations are applied to represent the relationships [ 26 ]: the SAR range equation, the SAR Doppler equation and the earth model equation. All three equations are shown as Equation ( 1 ): where R is the distance between the target and satellite platform, and are the position vector of the satellite platform and target, c is the light speed and represents the time delay; is the Doppler centroid frequency, and are the velocity vector of the satellite platform and target; is the target position vector, h is the target height relative to the earth model, and are the equatorial radius and the polar radius of the earth with , and f is a flattening factor [ 27 ].…”

A New RD-RFM Stereo Geolocation Model for 3D Geo-Information Reconstruction of SAR-Optical Satellite Image Pairs

“…The Range Doppler model is the rigorous sensor model according to the imaging principle of SAR sensors [13]. For a single SAR image, the geometric relationship of an image space coordinate and the corresponding object space coordinate can be established as:…”

“…Therefore, the production of RPCs increases the workload of users for the application of this model. Moreover, the suitability of the RFM for SAR images in mountainous areas is relatively poor, which will introduce extra fitting errors during the reconstruction for 3D geo-information [13]. Therefore, we proposed a new RD-RFM model for SAR-optical stereogrammetry which is suitable and applicable both in mountainous and urban areas.…”

A New Combined Adjustment Model for Geolocation Accuracy Improvement of Multiple Sources Optical and SAR Imagery

“…A set of virtual GCPs are arranged in a grid-shape format on planes located at different heights. Usually the fitting accuracy of approximated RPCs is better than 5% pixels, whereas errors increased to pixel-level in areas with undulating terrain [32].…”