Study on Lightweight Acoustic Positioning for Combined Aerial and Underwater Drones

The authors are developing “combined aerial and underwater drones” to address issues such as manpower shortages in inspecting water area infrastructure and monitoring aquaculture farms. This system enables such work without sending out divers or boats. An aerial drone carries an underwater drone to the work area and after it lands on the water, the operator remotely controls the underwater drone while viewing live images and location information from both drones via a mobile network (LTE). Acoustic positioning provides the location information of the underwater drone. SSBL is adopted with a pinger on the underwater drone and a receiver on the aerial drone. It is expected that, in future, many underwater drones may be used simultaneously. Then it will be necessary to position many pingers simultaneously. SSBL usually includes cross-correlation using FFT, which increases the load when processing many targets. To reduce the load on the SSBL receiver, we propose the iterative gradient method (IGM) be used instead of the conventional cross-correlation method. IGM can reduce the SSBL load by an order of magnitude compared to the conventional method, and even in the presence of reflected waves, the proposed method can suppress positioning errors by appropriately selecting the computation interval. Future work includes validating the method using data from the actual environment.