Remote sensing of forest structure using LiDAR and SAR

Forests play an important role in the global climate system because they take up and store large amounts of carbon in the form of biomass. This paper examines techniques of retrieving structural forest information using the remote sensing techniques of LiDAR and SAR. Both sensing methods can provide information on the vertical structure of forests. Certain LiDAR instruments can record a vertical waveform of reflected radiation from the forest which can be related to vertical biomass distribution. Forest height is a biophysical parameter that can be used to estimate aboveground forest biomass using allometric equations. Interferometric and polarimetric SAR instruments at different wavelengths can deliver information on terrain elevation under forest, tree canopy height and biomass. Examples of airborne imaging LiDAR (Optech), spaceborne profiling LiDAR (ICESAT-GLAS), airborne interferometric SAR (ESAR) and spaceborne interferometric SAR (ALOS-PALSAR) are presented. In particular, L-band and X-band SAR have been investigated for use to generate a forest height and biomass map without the need for an external Digital Terrain Model. For denser forests a longer wavelength such as P-band would be required.