Comparison and Analysis of Geometric Correction Models of Spaceborne SAR.

Weihao Jiang,Anxi Yu,Qingsong Wang,Zhen Dong

doi:10.3390/s16070973

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.

Highlights

With the development of synthetic aperture radar (SAR), SAR images play an increasingly important role in military reconnaissance and national economies
An error of only 0.03 pixels was produced on the flat terrain image, its maximum geolocation error reached 5.65 pixels on the mountain terrain image; the plane location error was more than 29 pixels, especially on the large scene image, which cannot meet the precision required for conventional applications
The RD model is the standardized method of geometric correction but is not suitable for real time applications because of large computing times

Summary

Introduction

With the development of synthetic aperture radar (SAR), SAR images play an increasingly important role in military reconnaissance and national economies. Because a SAR image records the back-scattering performance of surface features influenced by system survey precision and terrain undulations, SAR imagery contains several types of geometric distortion that seriously restrict their application. To effectively use a SAR image, precise geolocation of image pixels is required and is necessary for precise geometric correction during later image processing. In 1982, Curlander first proposed the use of satellite ephemeris, echo time delay and Doppler data to derive the absolute location of a target, a method called the Range-Doppler (RD) algorithm [1,2]. Some researchers made improvements to the RD algorithm and analyzed the sources of location errors. In 2006, Wang et al used polynomial fitting of the Doppler center frequency to adjust the Sensors 2016, 16, 973; doi:10.3390/s16070973 www.mdpi.com/journal/sensors

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