One of the most challenging aspects of monitoring forest change in Guyana is the persistent cloud cover. Before forest loss can be identified, the operator must first search for cloud-free imagery over the target area. Changes occurring under persistent-cloud, are not detected. To this end, Indufor has developed a complementary approach that takes advantage of Sentinel-1. Sentinel-1 is a synthetic aperture radar (SAR) sensor – it captures information using microwaves rather than visible and infrared light. The sensor penetrates cloud, allowing clear imagery to be captured regardless of atmospheric conditions. An additional benefit to using SAR data is that daylight is not required – Sentinel-1 works equally as well at night.
The example presented here compares the quarterly Sentinel-1 composites generated for 2018 Q3 and 2018 Q4 (coinciding with 2018 forest change map produced by Guyana Forestry Commission). Sentinel-1 detected changes are shown in the form of an alerts layer, which highlights pixels of probable change.
The non-optical nature of SAR data makes processing and interpretation more difficult: Thus, Sentinel-1 is most valuable when combined with GFC’s existing forest monitoring system, which uses Sentinel-2.
The monitoring solution presents a compelling example of how Guyana Forestry Commission uses Sentinel-2 to detect and characterise forest change and Sentinel-1 Radar imagery to provide ‘Alerts’. The two data streams combining to ensure accurate countrywide deforestation monitoring – increasing progress towards a near real-time solution.