LASER ALTIMETRY FOR LOW-FLYING AGRICULTURAL AIRCRAFT

A laser-based altimetry system was developed to measure the low above- ground-level (AGL) altitudes that agricultural aircraft typically enco unter during aerial applications. The laser altimetry system was evalu ated on-board an aircraft under various conditions. Distance signals of a range-finder, determined based on the time of flight of laser pul ses reflected by a target were corrected for varying pitch angle of th e aircraft to indicate AGL altitudes dagger using an angle sensor. Eff ects of ground speed (193 to 241 km/h), AGL altitude (1.8 to 7.9 m), g round surface condition (hard surface, bare soil, cotton field, peanut field, wheat field), and other operating conditions (boom, hopper loa d) were investigated Ground surface condition was the only variable th at significantly affected the difference between the true and laser-me asured AGL altitudes. Percent errors of the measured AGL altitudes ove r hard surfaces ranged from -0.8 to 2.1% with standard deviations vary ing from 2.9 to 5.2%. The laser altimetry system sensed part of the cr op canopy height, resulting in an offset of AGL altitude. The altimetr y system provided repeatable measurements of AGL altitudes with consis tent off sets over crop canopies.