Eccentric angle between IMU and the collimation axis of airborne sensor is one of main reasons causing geometric correction error. Currently, the application of the hyperspectral and LIDAR integrated system are greatly affected by lack of universal calibration methods which can calibrate the hyperspectral data and LiDAR data simultaneously. An eccentric angle calibration model for hyperspectral and LiDAR integrated system is proposed, meanwhile a self-calibration method using “#” shaped flight strip is designed to validate the new calibration model. Firstly, the homogeneous points are searched from all geometrically corrected flight strips by automatic matching methods. Secondly, control points obtained by averaging the coordinates of the homogeneous points are applied to solve the calibration model to get the eccentric angle. Finally, the point clouds are corrected geometrically with the solved eccentric angle, then the above steps are repeated until the solved eccentric angles are stable. An experiment was carried to testify the new calibration model and resolving method, which shows that the proposed model is of high-precision, validity and the resolving method is of fast convergence. The airborne sensors can acquire a plane precision of 0.807 m (about 1.2 pixels) without any ground control points, and the LiDAR can acquire a plane precision of 0.437 m and elevation precision of 0.15m.
For a direct-detection 3D imaging ladar, the use of Geiger-mode avalanche photodiode (APD) could greatly enhance the
detection efficiency of the receiver since each range measurement requires only one detected photon. Single photon
sensitivity of the detector offers significant advantages in reducing receiver size, mass and power and reducing laser
complexity. This paper studies the 3D imaging ladar using APDs which are actively quenched and gated to operate at
Geiger-mode to detect short weak laser echo pulse. The detection model of this detector as well as the detection
probability and false alarm probability for this ladar is analyzed and discussed. The analysis shows that the major factors
influencing system design are the background light noise and the dead time of the Geiger-mode APD. Then the noise
which affects the false alarm probability is analyzed and calculated and the measures to extract the weak signal echo
from a high noise background are put forward. The research also shows that using a detector array instead of a single
detector could reduce the false alarm probability by orders of magnitude. Finally a 3D imaging brassboard system which
utilizes Geiger-mode APDs, a fast pulse, high repetition rate laser, and an optical scanner is described, and some
experimental results obtained by this system are presented and analyzed. The results suggest that if the background light
noise is sufficiently suppressed, 3D images of the targets could be successfully taken by the ladar using Geiger-mode
APDs.
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