Nail Cadalli, Peter J. Shargo,  David C. Munson, Jr.,  Andrew C. Singer

Abstract

Detection and localization of ocean mines is an important problem for safe operation of naval platforms. A number of new technologies exploit airborne LIDARs, which can penetrate the air-water interface and optically detect and
localize underwater mines.   This is typically done by capturing parts of the reflected optical  field, which is generated by scattering within the water column,  with sensors such as CCDs (charge coupled devices) and PMTs (photomultiplier tubes).  The CCDs   generate images of the scatterers in the illuminated water column, while the PMT returns provide information about the scene
in the range direction. The images and PMT returns are analyzed and processed to accurately determine which objects are likely mines, and where they are located.

We formulate the above detection and localization problem as a 3-D tomographic reconstruction problem: We have described
the relation between the airborne CCD/PMT returns and corresponding tomographic projections of an underwater object. Having CCD/PMT data at various angular orientations with respect to the object, a 3-D tomographic reconstruction can be obtained. In our reconstructions, we worked with a data set from a previous study (1998 Competitive Evaluation Field Test (CEFT)). We also have developed software to simulate lidar returns in PMT and CCD sensors. Our simulator can model multiple scattering and absorption for various water types and system parameters. Simulated data fits the characteristics of real data very well. We present our reconstruction results from the simulated and real data, and comparatively discuss the results.

Keywords: Lidar imaging, mine imaging,  3-D tomography, lidar simulation, multiple scattering.

Proc. SPIE's 46th Annual Meeting: The  International Symposium on Optical  Science and Technology,  vol. 4488, July  29 - Aug. 3,  2001, San Diego, CA.