Radar using satellites as a platform can be used for mapping forests across large areas. The technology is similar to lidar (laser scanning) using electromagnetic waves but is less affected by e.g. cloud coverage.
Over the last 5-10 years, satellite missions like COSMO-SkyMed and TandDEM-X have been launched with significantly higher resolution (in the range ~ 1m), which allows them to be used for mapping smaller areas. Unlike sufferers, the radar has a side-by-side configuration and longer wavelengths. The wavelengths are divided into "bands" and currently the most common bands in forestry are X- (~ 3 cm resolution), C- (~ 5.5 cm), and L-bands (~ 15-30 cm). There are different ways to process the radar signal, and today, radargrammetry (using amplitude), interferometric SAR (InSAR, phase use) and polarimetric InSAR (PolInSAR, using coherence and phase, and considers also the polarization) use the most developed methods.
Radar can be used for calculations of forest variables such as biomass, volume, tree height and crown height. The goal of the TanDEM-X mission is to create a world-wide digital elevation model with a relative accuracy of less than 2 meters in height.
TanDEM-X, credit EADS Astrium.
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TanDemX, Remningstorp.
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