Background
In July 2023, a boat with three people on board sank in Laguna San Pablo, one of the largest and deepest lakes in Ecuador. The local search and rescue team couldn't locate the wreck to recover the bodies. The diving team contacted our partner, Aerial Development Services (ADS), for help. ADS decided to test SPH Engineering's dual-frequency echo sounder, known for its ability to provide underwater mapping.
Using a boat or a Remotely Operated Vehicle (ROV) with Multi-Beam Echo Sounders (MBES) or side-scanning sonar would be considered the best choice in such operations of underwater search. However, the Single Beam Echo Sounder (SBES) was more readily available, as access to the more advanced MBES technology required more time and coordination with National Emergency Services. The waiting time for the delivery of the MBES system was too long.
Therefore, the team decided to locate the sunken boat using what was more accessible—a drone system with SBES. It wasn’t a straightforward decision since the SBES is typically not the first choice for such detailed search operations. However, later the system became an instrumental tool in the operation, showcasing how innovative thinking can often outweigh having the most advanced technology.
Challenges
The operation encountered four significant challenges:
- The remote location of Laguna San Pablo. Situated in the uplands of Ecuador, the lake is far from major urban centers, which makes the mobilization of heavy search equipment difficult and costly.
- The search area was located 450 meters from the shore. This requires a solution that would effectively work over a substantial distance.
- The lake's altitude is high—2650 meters above sea level. Drone operations at high altitudes are discouragingly challenging due to the thinner air, which can impact the drone’s lift and overall performance. This was crucial since the drone must maintain stability and control while carrying the additional weight of the echo sounder.
- The choice of using SBES over MBES technology. SBES doesn't offer the same level of coverage in a single pass. As a result, detecting the wreck with SBES required a much denser survey grid to achieve comparable results.
Solution & Outcome
Aerial Development Services (ADS) conducted the survey over the lake using the DJI RTK M350 drone equipped with SkyHub, a radar altimeter, an obstacle avoidance sensor, and an ECT D052S echo sounder. The mission was planned using the Area Scan function of UgCS, flight planning software. Based on the available information, the boat was approximately 3 meters in length, 5 meters in width, and 2 meters in height.
The SBES-equipped drone was deployed to perform bathymetric measurements from the shore, covering the 450-meter distance to the search area. Since the lake had no vegetation or obstacles and the waters were calm, the echo sounder was dragged at a max speed of 0.7m/s parallel to the vector from west to east.
To calculate the separation between lines for the survey, the estimated depth of the lake in the survey area and the echo sounder beam width of 7° were taken into account. The calculated footprint of the beam on the bottom was 4.28 meters. The separation used in the mission was 5m to assure almost 90% coverage in the survey area and close the 0 probability of missing the target.
The check line was included in the mission.
During the survey, ADS closely monitored real-time data from the echosounder to detect enhancements of two meters on the southeastern side of the search area, which matched the boat's dimensions. The results were shared with the rescue team, who confirmed the boat was in that area. The team’s ability to interpret and use the data was fundamental to the mission's successful outcome.
This mission required precise control and coordination to ensure the drone could maintain stability throughout the operation. The echo sounder system provided the necessary data to precisely pinpoint the location of the wreck. Despite all the limitations of SBES, it proved to be an effective tool in the hands of skilled operators.
Conclusion
The discovery of the sunken boat in Laguna San Pablo demonstrates how the use of the echo sounder on the drone helped overcome significant logistical and environmental challenges. It’s an example of adaptability within the rigid constraints of the region and the technology available.
As drone and echo sounder technology continues to develop, its applications in various fields will expand as it offers new solutions to complex tasks. The ADS team’s result will serve as a precedent for future operations with similarly challenging conditions. It highlights the significance of creative thinking, adaptability, and expertise.
