GEDI has been optimized to provide global measures of vegetation structure. The footprint is large enough to measure whole trees while being small enough to accurately detect the ground on steep terrain. GEDI measurements penetrate dense canopies and provide comprehensive sampling.
GEDI contains three Nd:YAG lasers, emitting 1064 nm light. These pulse 242 times per second with a power of 10 mJ, firing short pulses of light (14 ns long) down towards the Earth’s surface with a beam divergence of 56 mrad, resulting in footprints averaging 25 m in diameter.
Two of the lasers are full power, and one is split into two beams, producing a total of four beams. Beam Dithering Units (BDUs) rapidly change the deflection of the outgoing laser beams by 1.5 mrad, shifting them by 600 m on the ground. This produces eight ground tracks; four power and four cover tracks. Footprints are separated by 60 m along-track and 600 m across track.
GEDI’s ground sampling pattern
GEDI measurements are made over the Earth’s surface between 51.6° N and 51.6° S. GEDI can be rotated on the JEM by up to 6°, allowing the lasers to be pointed up to 40 km on either side of the ISS ground track. This capability is used to sample the Earth’s land surface as completely as possible, filling in gaps due to clouds. During GEDI’s two year mission life, about 10 billion cloud-free observations of the Earth’s surface will be acquired. These observations can then be gridded into regular coverages of varying resolution, such as 1 km grid cells.
