A Quality Assessment of Airborne Laser Scanner Data

A Toposys-1 airborne laser scanner (ALS or LIDAR) measurement campaign was arranged in June 2000 (Kalkkinen) and another campaign with helicopter-borne TopEye laser scanner was arranged in September 2002 in southern Finland (Masala, Otaniemi). The Toposys flying altitudes were about 400 and 800 m above ground and for the TopEye, 100, 200, 400 and 550 m flying altitudes were used. Reference measurements on the ground were made with a RTK GPS and a tachymeter. Points on asphalt, grass, gravel and forest ground were measured. Height errors for different surfaces were calculated. The higher the flying altitude, the larger is the height error. All the three comparison methods (ALS mean height in the test circle, height of the nearest laser point and interpolated height) seem to give the similar results for the mean of differences (reference height – ALS height) in the same flight line. There were also quality differences between flight lines. Also height errors as a function of observation angle were determined. Observation angle had an effect on the height accuracy. A systematic error of typically 10 cm was observed due to observation angle changes. Different R-squared values (coefficient of determination in the regression analysis) were obtained for the same surface material at different flying altitudes.