Lidar can also be used to penetrate water to measure the morphology of coastal water, detect oil forms, fluorescent dye traces, water clarity, and organic pigments including chlorophyll. In this case, part of the pulse is reflected off the water surface, while the rest travels to the water bottom and is reflected. The time elapsed between the received impulses allows for a determination of water depth and subsurface topography. SAR beams energy waves to the ground and records the energy reflected. Radar is sensitive to linear and geometric features on the ground, particularly when different radar wavelengths and different combinations of the horizontal and vertical data are employed.
Different wavelengths are sensitive to vegetation or to ground surface phenomena.
In dry, porous soils, radar can penetrate the surface. In 1982, radar from the space shuttle penetrated the sand of the Sudanese desert and revealed ancient watercourses. Using airborne radar in Costa Rica, prehistoric footpaths have been found. Cultural and Ecological Applications of Remote Sensing. Final Report of a Conference Sponsored by the National Science Foundation.