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The Optech Airborne Laser Terrain Mapper 3033

The Optech ALTM instrument setup

The Optech ALTM instrument setup

This equipment is no longer available for use. The following details are retained for reference.

A collaborative agreement with the Unit for Landscape Modellingexternal link at Cambridge has enabled the ARSF access to their Optechexternal link ALTM3033 for the past 3 flying seasons. During this time, the instrument has been used extensively as demand continues to increase. However, please note that ARSF access to the ALTM is limited and support cannot be guaranteed. Please contact the Science & Operations Coordinator for details.

LiDAR basics (from link)

A high-accuracy laser rangefinder is mounted over an opening in the aircraft floor. The rangefinder scans beneath the aircraft, producing a wide swath over which the distance to the ground is measured. The angle at which the laser is scanned is also measured. A GPS receiver in the aircraft records the aircraft's position at fixed intervals. To correct for the aircraft's movements, the motions of the aircraft are recorded by an Inertial Navigation System (INS) for later post-processing. A second, ground-based GPS receiver provides differential correction for a more accurate position estimate. In post-flight processing, the laser range, scan angle, GPS data and INS data are combined to determine the accurate position of a point on the earth's surface.

The device collects 33,000 laser observations per second and in standard operating mode it collects first pulse, last pulse and intensity data. From an operating altitude of 1000 metres the resulting height data has an absolute RMS accuracy of better than plus or minus 15cms. LiDAR data are processed by ULM and provided as point clouds, which can be gridded upon receipt, if required. Furthermore, data are provided as time-of-flight order swaths, rather than 2km2 tiles.