Development and Experiences with a Fully-Digital Handheld Mapping System Operated from a Helicopter

This paper presents a self-contained, light and flexible mapping system that can be quickly deployed into inaccessible areas. Although designed to measure wind-transported snow volumes and the avalanche mass balance over an experimental site, the system is suitable to any large-scale 3-D terrain mapping. The system is comprised of supporting electronics that is loosely linked to a light but ridged sensor block containing digital camera, Lidar, an IMU and a GPS antenna. The relatively small size and weight of the sensor block permits manual pointing of the camera and the Lidar either towards the mountain face or the valley bottom. Such hand-held steering allows mapping of the avalanche/land slides release and deposit zones during the same flight with an optimal geometry. At the same time it dampens the engine-induced vibrations on the sensors. The installation time of the system in a helicopter is less than 15 minutes and its re-installation does not require new calibration. The exterior orientation (EO) parameters of the camera and laser are determined directly by GPS/IMU integration. Optionally, the orientation performance of the navigation solution may be improved by integrating the data from the second GPS antenna placed on the helicopter tail. Once the system is calibrated (once per sensor assemblage) and with EO determined for both sensors, an automated DTM and orthophoto generation can be achieved. The practical experience with CCD/GPS/INS has demonstrated a mapping accuracy of 10cm and 15cm in the horizontally and vertically, respectively. The performance of recently added Lidar is under evaluations