Detection of land cover change in the Brazilian Cerrado using radar data (Sentinel-1A)

Abstract

The detection of changes in the natural vegetation of the Cerrado (Brazilian tropical savanna) has been conducted based on optical satellite images. With the open availability of Sentinel-1A satellite radar images, continuous, near-real-time monitoring of land-use changes has become a reality. The objective of this study was to analyze the potential of Sentinel-1A satellite radar images to detect changes in the natural vegetation cover of the Cerrado for the purpose of law enforcement procedures to control illegal deforestation. The test site was western Bahia State, northeast Brazil. We selected two Sentinel-1A scenes obtained on October 3, 2016 (T0) and October 27, 2017 (T1) (C-band, 20-meter spatial resolution, VV and VH polarizations). A set of 159 deforestation polygons identified in the Landsat-8 Operational Land Imager (OLI) satellite images from 2016 and 2017 (eight scenes) were used as training samples to define the typical radar backscattering coefficients ((°) from the areas corresponding to the changes in the natural vegetation cover. The potential of the change detection technique was analyzed based on the boxplots involving the (° values derived from the ratio T1/T0 (both without filtering and processed by the refined Lee and Quegan & Yu filters). Three thresholds were considered for each polarization. All radar image processing was conducted on the Google Earth Engine platform. The best result was obtained for the combination of VH, refined Lee, and a threshold of 0.60, which presented 95% overall accuracy and a 39% omission error.

Keywords:
Savanna; Western Bahia State; Remote sensing; Backscattering