Single Photon LIDAR
Single photon LIDAR offers particularly fast data acquisition and a particularly high data density, because this technique detects multiple laser pulses simultaneously and analyzes them separately. The Single Photon Lidar (SPL) technique uses collimated laser radiation in the visible green region of the spectrum (λ=532 nm). The collimation of the laser pulse is achieved by using a diffractive optical element (DOE) to split the laser into several partial beams, called "beamlets". In this way, the density of the measurement points is significantly increased. In contrast to GmLidar, not the entire FOW of the receiver is illuminated in full, but each beamlet is aligned in its spatial direction in such a way that it hits a single-photon-sensitive detector array assigned to it on the detector side, the so-called "sub-array". Each individual sub-array consists of numerous light-sensitive detector elements and virtually splits the FOW into sub-areas that can be included in the analysis in parallel. In this way, the light-sensitive sub-arrays are efficiently illuminated and optical crosstalk is avoided. Provided that the dynamic range is properly adjusted, the strength of the output signal from the sub-arrays is linear with respect to the optical power. In this way, each laser beamlet can deliver multiple echoes, the analysis of which also makes it possible to pass through vegetation, for example. Compared to conventional LIDAR, SPL provides higher area performance at comparable point cloud densities, although the height accuracy for non-planar surfaces is somewhat lower than with full-waveform LIDAR. Single-photon LIDAR is more sensitive to multiple reflections than Geiger-mode LIDAR. As it currently stands, SPL does not achieve the precision of full-waveform LIDAR.
The wavelength used in SPL makes it possible to perform bathymetric measurements and combine them with topographic surveys.
A typical use case for SPL would be the detection of objects under foliage in a forest from above. In this case, individual beamlets might detect treetops, others might hit and be reflected by some branches along the way, and other beamlets might hit the ground and provide corresponding data.