Observing Breaking Waves Using EO/IR Remote Sensing from a Rotary-Wing UAV

Breaking waves are an endemic feature of the air-sea interface and a key dissipative process impacting the physics across the air-sea transition zone (ASTZ). Breakers enhance ocean and atmospheric mixing and exchange at the interface, re-distributes surface wave energy, and ejects aerosols into the atmosphere. Wind-forced wave breaking, or whitecapping, occurs at a threshold wind speed as low as 3 m/s and is widespread across the global ocean. While depth-limited wave breaking may be geographically constrained, the intensity of this surface wave energy drives the dynamics in the shallow and coastal environment. Optical remote sensing remains the primary, direct means of observing wave breaking and quantify bulk statistics to develop parameterizations and models of this process. Uncrewed aerial vehicles (UAVs) provide a useful platform for remote sensing that can fill the observational gaps between space-borne satellite remote sensing, land-based towers, and sporadic ship- or aerial-based imaging.

Here, we present the development of a new remote sensing platform using a rotary-wing UAV and a gimballed electro-optical and infrared (EO/IR) imaging system. For the airframe, we based our selection around the following design criteria: (1) easily deployable from shore, and eventually a ship deck, (2) able to maintain station for >30 minutes to enable statistically robust samples comparable to other data sources, (3) can maintain station keeping in a wind forcing exceeding 5 m/s, and (4) a modular design that can allow for reconfigured payloads, etc. Based on these needs, we selected the Aerosystems West heavy lift multirotor hexacopter, which is rated to a maximum endurance of 55 minutes and maximum payload of 25 kg. For the EO/IR imaging system, we selected based on these criteria: (1) an all-in-one EO/IR imaging system configured for UAV-based applications to facilitate integration, (2) imaging capable of resolving circa decimeter features in both optical and IR bands from a sensor distance ~50 m, and (3) thermal imaging with a sensitivity <0.1 K. From these needs, we selected the Workswell WIRIS Pro Sc camera system. The system includes a 2 MP optical camera paired with an uncooled microbolometer (7.5 – 13.5 micron) with image resolution 640 x 512 pixels and a maximum sampling rate of 30 Hz. The platform was augmented with real-time kinetic (RTK) GPS and high-resolution video transmission for adaptive sampling and visualization. This presentation will highlight the system details and performance, as well as analysis from up-coming sampling flights.