3. Doktoritööd
Selle kollektsiooni püsiv URIhttp://hdl.handle.net/10492/7081
Sirvi
Sirvi 3. Doktoritööd Autor "Bunce, Robert G. H." järgi
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Kirje Correcting and Calibrating Airbone Laser Scanning Intensity Data Using Naturally Available Targets(Eesti Maaülikool, 2012) Vain, Ants; Liba, Natalja; Sepp, Kalev; Bunce, Robert G. H.; Mücher, SanderAirborne laser scanning (ALS) has been used widely due to its three dimensional information. Additionally to coordinates, ALS systems record also intensity values that describe the objects backscattering properties. The usage of ALS intensity data has been problematic due to the lack of information for correcting itnensity values for different affects, and also how to calibrate intensity data. Doctoral thesis of Ants Vain focuses on the usage of naturally availabel targets (e.g. asphalt, concrete etc.) of the measured area to use them as calibration targets. The tests carried out for this Thesis showed that the asphalt proved to be the most stable target and produced quite good results when used as calibration target. A near infrared camera was also tested to obtain objects backscattering properties. The camera solution proved to be an useful tool since it can be used simultaneously when the flights take place, therefore it provides results that are closer to actual ones than those measured in the laboratory. The samples will dry in the laboratory, therefore their backscattering properties will change also. Previous tests showed that naturally available targets can be used as calibrators. Since the ALS measurements are one of the remote sensing techiques, the intensity data has to be corrected for several factors before the calibration procedure. This Thesis also studied the range and topography influence on the ALS intensity data. Since the targets are assumed to have a Lambertian backscattering properties, the backscattered energy will reduce with the growth of incidence angel (the angle between incoming laser bean and surface normal). The tests showed the the 20 degree incidence angle will reduce the intnesity values up to 8%. The moisture level in the surface will reduce the intensity values. The study conducted within this Thesis showed that the moisture can reduce the intensity up to 30%. To obtain the moisture level in the surface the near infrared camera was used. The results were similar as in the test that was carried out in the laboratory. The Leica ALS50-II uses Automatic Gain Control (AGC), that is used to ramp up the weak returns or ramp the too strong signals down. In other words, the AGC will keep the received signal in the sensitive area of the receiver. The study conducted within this Thesis showed that the ALS intensity follows the AGC trend. The result of this study was a linear correction model that minimizes the effect of AGC on the intensity values. The doctoral thesis of Ants Vain is one of the few in the world and the first in Estonia that studies the correction and calibration of ALS intensity data. The knowledge that was collected thorughout the studies that were carried out in this Thesis can be used in further studies were ALS intensity data plays a relevant part.