Our team utilizes heavy-lift UAVs to collect water, sludge, and sample data from hazardous mine pits, employing our patented Water Sampling Plate (WaSP). (https://youtube.com/playlist?list=PLxMWLUYcee_Mf4kyk6CBgwACienURTEx2&si=sM3UGYZPvRFZj7HR). In most of the mine pits we’ve worked in, we achieve reasonably good GPS coverage without significant issues. However, we recently undertook a project in a small, very deep, and steep mine pit characterized by a large headwall on its south side. This environment resulted in a low GPS count (only 8 satellites) and high Horizontal and Vertical Dilution of Precision (HDOP and VDOP) values, compelling us to adjust parameters to initiate our missions.
Typically, we program the sampling locations, allowing the UAV to fly automatically to the designated points. Once there, we manually lower the UAV to 10 meters above the water surface, using a radar altimeter to actively measure the range. The UAV maintains this altitude while we lower and raise our equipment to collect samples. In this particular pit, however, we had to manually navigate to the sampling location. Upon descending to 10 meters above the water, the UAV consistently dropped below this altitude. We attempted to stabilize the UAV by ascending to 20, then 30, 40, and finally 50 meters. At 50 meters, we were able to maintain altitude, but the UAV oscillated between 5 meters up and down while also drifting laterally.
Currently, we operate with a Pixhawk Cube Blue and dual CAN Here 3 GPS units. Given the challenging GPS conditions in this restricted environment, what enhancements would you recommend? Should we consider upgrading to multiband GPS units like the Here 4, integrating Real-Time Kinematic (RTK) positioning with a base station on the pit rim, or are there other strategies we should explore?