Booz Allen Hamilton Colloquium: Dr. Linda Mullen, Naval Air Warfare Center
Friday, September 15, 2017
3:30 p.m.-4:30 p.m.
1110 Jeong H. Kim Engineering Building
301 405 4471
Abstract: Laser sensing and communicating in the underwater environment
Dr. Linda Mullen, Senior Science and Technology Manager (SSTM)
Avionics Department, Naval Air Warfare Center Aircraft Division (NAWCAD)
Patuxent River, MD
Laser-based sensors have inherently high resolution for imaging applications and high bandwidth for high speed, wireless communications. However, when used in water, the performance of such sensors can be limited due to absorption and scattering. The higher absorption of certain wavelengths or colors of light leads to the blue-green hue of underwater imagery, while scattering of light in water causes the haze or blurring of details in underwater photography.
Despite the challenges of light propagation in water, laser sensors can adapt to the underwater environment. Lasers operating in the blue-green portion of the spectrum can be selected to minimize absorption and maximize transmission in water. The scattering problem is more difficult to overcome as light can scatter back to the receiver without ever reaching the object of interest (backscatter) and scatter multiple times at small angles on its path to and from the area of illumination (forward scatter).
Scientists and engineers at the Naval Air Warfare Center Aircraft Division (NAWCAD) in Patuxent River, MD have been investigating the use of radar-encoded optical signals to help a laser sensor distinguish between scattered and nonscattered light. By encoding the laser pulse with a radar signal, the receiver can ‘lock on’ to a signal reflection from an object and distinguish it from light scattered randomly from the environment. Using a laser to ‘carry’ a radar signal through the water provides a way to use the sophisticated radar modulation, demodulation, and signal processing techniques developed for above-water object detection and identification for similar applications in water, an environment where radar signals cannot be used directly due to their high absorption. The encoded waveform can also be altered to include information to be transmitted to another location, which would enable the sensor to be used for both object detection/imaging and wireless optical communications.
The main challenges of this research are to determine how optical scattering and absorption by water affects the encoded radar waveform and to use this information to optimize the radar frequency and bandwidth for a particular application and environment. For the communications application, the effects of small angle forward scattering on the link bandwidth must be evaluated, while for the imaging application, the effects of scattering in both the forward and backward directions on the encoded radar signal must be studied. Research conducted to study these topics, along with recent work completed in testing prototype systems in laboratory and in-situ environments, will be presented.
Dr. Linda J. Mullen is a Senior Science and Technology Manager (SSTM) in the Avionics Department at the Naval Air Warfare Center, Aircraft Division in Patuxent River, MD. Her team’s research focuses on the application of radar technology to optical modulation and detection in underwater laser-radar system design. The current emphasis is on improving optical detection and identification of underwater objects in turbid, murky water. Dr. Mullen has published over 40 papers in technical journals and conference publications, and she holds 4 patents for her work in modulated laser system development. Dr. Mullen is a Senior Member of IEEE and the Optical Society of America and is a NAVAIR Fellow.