When a team of scientists from Defence Research and Development Canada (DRDC) started analyzing data from an experiment to better understand the performance of RADARSAT-2 for ship detection, the results were startling.
The conventional wisdom of the day was that there was no useful information to be found about the ocean surface or wind speed in cross-polarized radar (a technique that combines horizontally and vertically oriented radar waves). A closer look at the data, however, demonstrated just the opposite.
“If I have the cross-polarized backscatter, I immediately know what the wind speed is,” Dr. Paris W. Vachon, the DRDC project lead, remarked on the surprising simplicity. “You don’t have to account for wind direction or the acquisition geometry. The correlation is extremely strong.”
In cross-polarized radar, ships pop out as bright pixels from a noisy background – the ocean surface. A surface complicated by wind, temperature and currents that makes finding ships a highly technical game not unlike finding needles in an ocean-sized haystack that is always changing its shape.
Real-world use of cross-polarized radar has been shown to have tremendous advantages when it comes to discriminating between the background-clutter of the ocean floor and ships at sea. A better understanding of the relationship between wind speed and the ocean’s background clutter in synthetic aperture radar (SAR) imagery improves ship detection accuracy for the Royal Canadian Navy (RCN).
DRDC recognizes that the bottom line for the Department of National Defence always comes back to operational value. With the correct insight into the physics, DRDC has been able to implement practical, straightforward algorithms to get useful information that is operationalized and used routinely.
DRDC’s space-based radar research has been operationalized through several national and international collaborative projects, most notably DND’s capital project Polar Epsilon. DRDC’s advice on new beam modes, called Maritime Satellite Surveillance Radar (MSSR) modes, which were added to RADARSAT-2, enabled a significant improvement in imagery for ship detection over large regions.
“The development of the MSSR modes has helped to deconflict orders and has an expanded radar swath while still allowing us to detect ships 25 metres or greater,” said Lieutenant Commander Chad Kabatoff, Project Director for Polar Epsilon 2, from Director General Space. “This reduces our image requirements, which means it costs us less to cover the same area.”
In June 2013 the RCN began using DRDC’s Synthetic Aperture Radar (SAR)–AIS Association System (SAAS). The system leverages RADARSAT-2 and combines its radar ship detections with Automatic Identification System (AIS) signals that all ships are legally required to broadcast. It allows the Canadian Armed Forces to detect potentially unfriendly or trespassing vessels and to deploy other surveillance assets much more effectively.
Combined with new software and imagery analysis techniques, the Royal Canadian Navy is taking full advantage of DRDC’s solutions to detect suspicious ships within Canadian and international waters in support of global surveillance operations.
[mappress] Press Release, June 19, 2014; Image: Canadian Navy