LiDAR
The most serious limitation to accurate mapping is the terrain vegetation cover. It obscures the terrain surface and hides planimetric detail making it difficult and sometimes impossible to generate a complete map or accurate topo. Hence the importance of obtaining the aerial photography during the leaf free season if at all possible. In situations when photography can not be flown at the ideal time or evergreen vegetation is present, a new technology is available that can assist in generating topos meeting contract specifications. This is LiDAR or Light Detection And Range. It uses a high frequency laser light pulse generated by a sensor on board the aircraft, that blankets the terrain surface with a dense “point cloud” during flight. Many of the laser light pulses will find gaps on the vegetation cover and reach the terrain surface. The sensor will detect the pulse return and compute the distance between sensor and reflective surface. Because the spatial location and altitude of the sensor above the terrain is being recorded by GPS, it is possible to extract the terrain surface from the data collected. This is of course a very simplistic description of the technique and is intended to convey a general idea of the process.
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