Simplified Normalization of C-Band Synthetic Aperture Radar Data for Terrestrial Applications in High Latitude Environments

Barbara Widhalm,Annett Bartsch,Robert Goler

doi:10.3390/rs10040551

Abstract

Synthetic aperture radar (SAR) applications often require normalization to a common incidence angle. Angular signatures of radar backscatter depend on surface roughness and vegetation cover, and thus differ, from location to location. Comprehensive reference datasets are therefore required in heterogeneous landscapes. Multiple acquisitions from overlapping orbits with sufficient incidence angle range are processed in order to obtain parameters of the location specific normalization function. We propose a simpler method for C-band data, using single scenes only. It requires stable dielectric properties (no variations of liquid water content). This method is therefore applicable for frozen conditions. Winter C-band data have been shown of high value for a number of applications in high latitudes before. In this paper we explore the relationship of incidence angle and Sentinel-1 backscatter across the tundra to boreal transition zone. A linear relationship (coefficient of determination R 2 = 0.64) can be found between backscatter and incidence angle dependence (slope of normalization function) as determined by multiple acquisitions on a pixel by pixel basis for typical land cover classes in these regions. This allows a simplified normalization and thus reduced processing effort for applications over larger areas.

Highlights

Radar backscatter intensity depends on sensor parameters like incidence angle, polarisation and wavelength, as well as on target parameters such as surface roughness, vegetation structure and dielectric properties [1]
Normalization of Synthetic aperture radar (SAR) data to a common incidence angle is required for many applications, but this is challenging in heterogeneous landscapes with varying angular dependencies
The analyses of angular signatures of winter C-band backscatter of Arctic land cover types revealed a linear relationship between the incidence angle dependencies of σ0 and σ0 itself, which can be exploited for normalization

Summary

Introduction

Radar backscatter intensity depends on sensor parameters like incidence angle, polarisation and wavelength, as well as on target parameters such as surface roughness, vegetation structure and dielectric properties [1]. The incidence angle has a major effect on backscatter values of Synthetic Aperture Radar (SAR) acquisitions. A terrain slope of 20◦ may increase an incidence angle range of 20–40◦ to 0–60◦ for which the linear approximation is not necessarily valid [7]. Van Doninck et al [7] further showed that the mean values of difference in R2 (coefficient of determination) of quadratic and linear fits increase with terrain slope. The parameters of a fitted linear model vary with land cover type, and over time during unfrozen conditions. In order to establish a location specific model, a sufficient set of acquisitions with varying incidence angles (as available usually from overlapping orbits) are required. A simpler method for the determination of the parameters of the linear model is required for applications over large regions

Methods

Results

Discussion

Conclusion