Calibration and Signal Processing of Airborne Stand Profile Radar used in forest inventory

摘要

TomoRadar is a helicopter/UAV (Unmanned Aerial Vehicle) based FM-CW microwave ranging radar designed for the forest inventory. Developed by FGI (Finnish Geospatial Research Institute), TomoRadar can scan forest with Ku-band signals and then receive the backscatter signal from targets. The target distance can be figured out from the backscattered signal. Furthermore, various information around forest can be evaluated. As a ranging scatterometer the system calibration and signal processing are necessary and critical tasks. In This thesis, these two major problems are researched and solved.The system calibration is limited to complete on ground and restricted in a particular range despite TomoRadar works on helicopter. Thus the range calibration experiment is conducted on the ground test field with a Luneburg lens. Besides, power calibration of system backscatter signal is researched through electrical component tests. The linearity of the radar system frequency sweep is critical in FM-CW radars. Hence, it is studied in this thesis. When TomoRadar works, the output of the whole system is analog signal in intimidate frequency (IF) band. A digitizer samples and records the output analog signal. With these signal, the information around forest cannot be obtained. To draw stand profile of forest and research forest information, the IF band signals need to be further processed. This is signal processing part of the thesis work.As a result of this thesis work, TomoRadar range calibration was achieved. The calibration results were verified by the helicopter based flying tests. The results present that the calibration completed on ground test field applied with the situation that TomoRadar works in air and scans targets in long distance. The linearity of system frequency sweep generated by DDS (Direct Digital Synthesizer) is verified. Finally, the test forest backscattered data was processed and the ranges were evaluated. Some targets stand profiles are generated and presented in this thesis