Quantifying the performance of the bistatic Frame-based Laser Imager (FLI)

Abstract

Optical sensors play a significant role in maritime sensing. The high spatial resolution of cameras is vital to object identification, but the performance of flood illuminated CCD/CMOS cameras quickly deteriorates in degraded visual environments (DVE) such as turbid coastal waters and murky harbors. Several laser-based sensors have been developed over the past few decades to enhance optical imaging in DVEs. However, since conventional approaches require the laser and receiver be located on the same platform, the size, weight, and power (SWaP) requirements are incompatible with small remotely operated vehicles (ROVs).Researchers at the Naval Air Warfare Center -Aircraft Division in Patuxent River, MD (NAWCAD PAX) developed [6] and patented [8] an optical imager utilizing a bistatic geometry where the laser and receiver are mounted on separate, smaller platforms. This allows the SWaP of the sensor components to be optimized for small platforms, like ROVs. The transmitter uses a modulated laser beam and a microelectromechanical system (MEMS) scanner to sequentially illuminate an underwater object in a raster fashion. A distant receiver collects the object reflected laser light and reconstructs the imagery. The transmitter scans the object at frame rates comparable to video cameras, producing a laser video stream. This paper will report on laboratory tests comparing the spatial resolution performance, as a function of attenuation length, of the bistatic frame-based laser imager (FLI) to a conventional flood illuminated camera typical of small ROVs.