Maritime Vehicle Testing and Operational Testing in Complex Environments
(Room 275-276)
02 May 16
2:30 PM
-
3:00 PM
Tracks:
Commercial, Maritime, Research and Development, Technical Track: Underwater Vehicles Research
This session will present vehicle operating and sensor data demonstrating the challenges of operating in variable environments such as currents, salinity gradients, bottom types, water clarity and weather conditions. These challenges are inherent in operating currently fielded and developmental USVs and UUVs in locations that deviate from their optimum design conditions. A simple example would be deploying a UUV with a fixed ballast system designed to operate in water with a standard salinity value of approximately 35 parts per thousand (ppt.). As this system is operated in a littoral water mass, it may encounter unexpected plumes containing a mix of fresh water run-off thereby lowering the local salinity value below 35 ppt. This would reduce the vehicle’s buoyancy as it transits the salinity gradient. Operating in less saline water would have a negative effect on the vehicle’s ability to control its depth. Its speed would need to be increased to improve the effectiveness of the vehicle’s control surfaces in order to maintain programmed vehicle depth or altitude above the bottom. Other examples to be discussed include: 1. Current effects. Currents in the shallow water approaches to the littoral have the potential to generate a field in which the current varies in three dimensions. An USV/UUV, tasked to maintain a specific heading for sensor collection, would require crabbing with the current to deliver the appropriate sensor alignment and achieve prescribed data collection points. Operating with such a crab angle would reduce vehicle endurance and affect sensor data quality. Variable currents would also have a negative effect on projected sensor area coverage rates. 2. Salinity gradient effects on acoustic sensor performance. Acoustic sensor systems, designed based on a sound speed assuming standard 35 ppt. salinity, would yield erroneous results in less saline water. Operations in, or in the vicinity of, a fresh water plume would yield errors in the horizontal plane as sound bends away from the areas of higher salinity and sound speed. 3. Water turbidity effects. Turbidity and its effect on light transmissibility will affect the performance of optical sensors leading to reduced performance or the need to bring the vehicle closer to the object to be imaged. Increased turbidity due to suspended solids will have the effect of increasing local water density leading to variable buoyancy and degradation of acoustic sensor performance. 4. Operational effectiveness of vehicle autonomy. The mission performance of fully autonomous UUVs is dependent on how the vehicle perceives its environment and makes decisions based on the sensor and environmental sensor input. The factors above could cause a UUV to operate in an unanticipated environment and place the vehicle outside its design safe operating envelope. It is important to examine the above environmental and operational effects under controlled tests to measure system operational effectiveness and suitability during developmental and operational testing. The Gulf Unmanned Systems Center (GUSC) has begun unmanned systems operations where the Apalachicola River discharges to the Apalachicola Bay and the Gulf of Mexico. These water masses provide a natural environment where the above effects on USV and UUV system operations can be observed and measured. GUSC is working with the Apalachicola National Estuarine Research Reserve (ANERR) in an effort to apply the environmental data collected in the region to unmanned systems operations. The results of GUSC’s initial USV and UUV operations will be presented in this session. This data includes, USV collections in the region and those supporting the Florida Department of Transportation’s bridge piling inspection program.