Monitoring the Oceans from Above

A new sensor from The Aerospace Corporation can detect the speed and type of vessel by the wakes it leaves behind.

Measuring human activity at sea has multiple applications, including environmental monitoring, resource management and national security, but the ability to effectively detect vessels in expansive ocean settings is a challenge with technologies like sonar and radar. Potential threats and bad actors deliberately maintain a low profile at sea, skirting international maritime laws and radio/cell transmission to avoid detection.

A new alternative measurement tool developed at Aerospace analyzes Kelvin wakes, something all sea-faring vessels leave upon the water. The V-shaped impressions trailing vessels as they move are typically 38 degrees across and produce wave characteristics influenced by its speed. The resulting alteration of structure and temperature of surface water can be linked to specific types of vessels, providing information where sonar and radar cannot.

The Wake Infrared Night/Day Sensing (WINDS) sensor uses a polarized longwave infrared (LWIR) sensor to detect wakes. LWIR is a subset of the infrared band of the electromagnetic spectrum that enables radiating heat to be visible to a thermal imaging camera. Polarimetric signatures highlight subtle spatial structures, providing an additional level of insight.

“We have the capability to geo-reference images and couple our sensor with a spectrometer that can detect exhaust fumes emanating from vessels at sea.”

“We’ve found that polarized light can resolve wakes and waves and analyzing their patterns can tell us how fast a vessel is traveling and where it’s headed,” said Dr. John A. Hackwell, a Technical Fellow at Aerospace. “Another benefit of using infrared is that it allows for day and night imaging, and the sensors can be placed on any aircraft.”

The WINDS prototype was integrated onto an Aerospace flight test gimbal on a Twin Otter aircraft and performed its first flight test, seeking boat wakes in both day and night scenarios. This initial pathfinder project went from concept to flight in six months and now has critical data needed for evaluation.

“We have the capability to geo-reference images and couple our sensor with another spectrometer that can detect carbon monoxide and other exhaust fumes emanating from vessels at sea,” said Hackwell.

Radar and sonar remain indispensable for exploring and mapping the ocean. Radar employs reflected pulses of high-frequency electromagnetic waves to detect the presence, direction, distance, and speed of objects, while sonar uses reflected pulses of sound.

However, these traditional methods of surveying the ocean aren’t effective at detecting objects on the ocean surface. Radar is ill-suited for discerning vessels against a backdrop of maritime “noise,” and sonar is primarily used to detect underwater hazards to navigation, search for objects on the seafloor, and map the seafloor itself as sound waves travel further in water than radar and light.

Preliminary tests have proven that the technology works, and expanded testing will determine its large-scale practicality. Aerospace’s ability to rapidly test new concepts has proven to be a critical element in quickly evaluating this new technology.