Close-Range Determination of Boresight Misalignment of a Laser Scanning System: Comparison of Point and Plane-Based Techniques

Lightweight laser scanning systems on UAV are becoming crucial for agriculture and forestry but require suitable calibration to ensure accuracy. Existing in situ calibration techniques rely on man-made features that may be lacking in field environments and require special manoeuvres. This study proposes a static calibration technique to estimate boresight misalignment angles between the IMU and the laser unit in a controlled setting. The approach can use two distinct control entities: points and planes. The process involves: (1) assembly of a calibration field; (2) levelling the system on a static platform; (3) data acquisition and raw data retrieval; and (4) determination of boresight angles via Least Squares Adjustment (LSA). The mathematical model was modified to integrate points and planes directly from raw sensor data, minimising errors from positioning systems and time synchronisation. The method was evaluated using an Ibeo LUX scanner. After applying the estimated boresight angles, the regenerated point cloud was validated by measuring distances between points and corresponding ground planes. The results yielded a standard deviation of approximately 2.5 cm. The proposed technique achieved suitable accuracy, with errors falling below the sensor’s nominal measurement uncertainty. This suggests the method is a promising pre-flight calibration solution, though further precision gains would require higher-end laser units.