The surf zone is a challenging environment for conducting mine countermeasures operations. The performance of acoustic sensors in this environment is extremely limited. Airborne LIDAR sensors have significantly better prospects for successfully working in this environment. However, the complex environment will be a driving factor limiting their performance. The environmental factors influencing the performance of airborne LIDAR sensors will be examined in this paper. These factors can be highly dynamic. Breaking surf action causes bottom sediment resuspension and the formation of bubbles and foam. The resuspended sediments then begin the process of settling, while the bubbles and foam begin to dissipate. All of these phenomena impact the optical properties of the water, which, in turn, impact the performance of the LIDAR system. An experiment was designed and conducted to study the impact of these dynamic processes on the optical properties of the water. The experiment was conducted in September 2002 at the Army Corp of Engineers Field Research Facility in Duck, North Carolina. Preliminary results from the analysis of this data are presented here. This work is being conducted by the Airborne Littoral Reconnaissance Technology (ALRT) project under ONR sponsorship.
Current Laser Line Scanner (LLS) sensor performance is limited in turbid water and in bright solar background conditions. In turbid water, backscattered and small angle forward scattered light reaching the receiver decreases underwater target contrast and resolution. Scattered solar energy reaching the detector also decreases detection sensitivity by increasing receiver noise. Thus, a technique which rejects unwanted, scattered light while retaining image-bearing photons is needed to improve underwater object detection and identification. The approach which we are investigating is the application of radar modulation and detection techniques to the LLS. This configuration will enable us to use optical modulation to discriminate against scattered light. A nonscanning mock-up of an existing LLS, the Electro-Optic Identification sensor, has been developed with off-the-shelf components. An electro-optic modulator will be added to this system to create a modulated LLS prototype. Laboratory tank experiments will be conducted to evaluate the performance of the modulated LLS as a function of water clarity and solar background levels. The new system will be compared to its unmodulated counterpart in terms of target contrast.
During the summer of 1996 a series of field trials were conducted in the Florida Keys and Bahama Islands to
evaluate the ability of a unique laser line scan system to measure and map the fluorescent characteristics of
coral reef environments. Typical fluorescence maps that were obtained are presented and compared with
monochrome and RGB color images of the same reefs. The monochrome images were obtained with the laser
line scan system simuftaneously with the fluorescent maps. The RGB images, which were also obtained with the
laser line scan system, were recorded in the same location on a subsequent thai.
The Electro-Optic Identification (EOID) Sensors project is developing a Laser Visual Iidentification Sensor (LVIS) for identification of proud, partially buried, and moored mines in shallow water/very shallow water. LVIS will be deployed in small diameter underwater vehicles, including unmanned underwater vehicles (UUVs). Since the mission is mine identification, LVIS must: a) deliver high quality images in turbid coastal waters, while b) being compatible with the size and power constraints imposed by the intended deployment platforms. This project is sponsored by the Office of Naval Research, as a part of the AOA Mine Reconnaissance/Hunter program. High quality images which retain target detail and contrast are required for mine identification. LVIS will be designed to produce images of minelike contacts (MLC) of sufficient quality to allow identification while operating in turbid coastal waters from a small diameter UUV. Technology goals for the first generation LVIS are a) identification range up to 40 feet for proud, partially buried, and moored MLCs under coastal water conditions; b) day/night operation from a UUV operating at speeds up to 4 knots; c) power consumption less than 500 watts, with 275 watts being typical; and d) packaged within a 32-inch long portion of a 21-inch diameter vehicle section.
An imaging model for predicting the performance of underwater range-gated imaging systems has been developed. Using this model, image quality as a function of the inherent optical properties of the water and as a function of the parameters of the optical system (e.g., laser pulse width, camera gate width and time, laser and camera FOVs, and laser-camera separation) can be determined.
Conference Committee Involvement (4)
Ocean Sensing and Monitoring III
26 April 2011 | Orlando, Florida, United States
Ocean Sensing and Monitoring II
5 April 2010 | Orlando, Florida, United States
Ocean Sensing and Monitoring
13 April 2009 | Orlando, Florida, United States
Detection and Remediation Technologies for Mines and Minelike Targets IX