Deforestation changelooks SAR evidence raster

For each processed sub-area ("stack") within an observation, customers receive a two-band SAR evidence raster to support visual validation of detected change. These rasters provide the underlying SAR imagery paired to each incremental detection. For regions with multiple sub-areas processed for a given delivery cycle, the customer will receive the requisite number of changelooks.

Unlike traditional SAR imagery, changelooks are delivered in a multilooked, coregistered format optimised for change comparison rather than single-scene interpretation. Multilooking reduces the inherent graininess (speckle) of raw radar data by averaging across multiple measurements, producing a cleaner image at a modest cost to spatial resolution. Coregistration ensures that images from different acquisition dates are aligned to sub-pixel precision, so that any differences between them reflect true on-the-ground change rather than geometric misalignment. The resulting images are orthorectified for viewing in traditional GIS platforms.

Certain terrain areas visible within the changelook should be disregarded during visual review. These appear as bright white regions on the greyscale imagery, and typically correspond to areas where the radar geometry produces unreliable returns — such as steep slopes, or other surfaces that cause signal distortion. These areas are not masked out of the imagery, but any detections coinciding with or adjacent to them should be treated with caution, as the underlying SAR signal in these zones is not suitable for reliable change analysis.

Changelooks can be loaded in any standard GIS tool and compared visually against the vector detection polygons. They are suitable for use in audit trails, regulatory submissions, and field verification workflows.

Parameter Specification

Bands are named using their respective acquisition timestamps, allowing customers to identify exactly which SAR acquisitions underlie each detection.