Environmental Science
Monitoring Deforestation with Satellite Remote Sensing
Quick fact
A single satellite can generate a deforestation map of an entire country in days, a task that would take ground teams many years. Global forests have been monitored consistently from space since the 1970s.
Why this is interesting
Have you ever wondered how we know so precisely that the Amazon lost an area the size of a football pitch every minute? The answer lies hundreds of kilometres above our heads, watching the forests day and night.
Read the full explanation
Understanding Monitoring Deforestation with Satellite Remote Sensing
Imagine flying over a forest in an airplane: you can easily see a clear-cut area as a brown patch among the green. Satellites do this on a global scale, using sensors that measure the light reflected from Earth's surface. Forest is very dark in the red part of the spectrum and very bright in the near-infrared, because healthy leaves absorb red light for photosynthesis and reflect near-infrared strongly. When forest is cleared, the red reflectance increases and the near-infrared drops. By comparing these reflectance patterns from images taken at different times, we can detect exactly where and when deforestation occurred, and measure the area lost.
A deeper explanation
At the heart of satellite deforestation monitoring is change detection. Satellite instruments record a continuous stream of spectral data, which can be transformed into vegetation indices like NDVI. NDVI is calculated as (NIR - Red) / (NIR + Red) and serves as a proxy for greenness. When forest is cleared, NDVI falls sharply. Algorithms classify each pixel as forest, non-forest, or deforested, and by comparing classifications over time, we compute the rate of loss per year. With frequent revisits and high-resolution imagery, even small-scale clearing is captured. This data is crucial for enforcing environmental laws, reporting greenhouse gas emissions, and understanding global forest trends.