Detection and Classification of Military Munitions Underwater Using Active Fluorometric Imaging (AFI)
Dr. Steven Ackleson | Naval Research Laboratory
The core work will test the ability of underwater Active Fluorescence Imaging (AFI) for classifying benthic features and detecting anthropogenic objects, including military munitions. In this initial one-year project, two core hypotheses will be examined:
1) Recent advances in underwater hyperspectral imaging combined with new high intensity, low power, shortwave light-emitting diodes (LEDs) can be combined to create a low cost, robust AFI system capable of imaging benthic features > 1 attenuation lengths stand-off distance; and
2) Benthic fluorescence signals can be parsed into natural and anthropogenic sources based on spectral responses and spatial morphology.
The approach will develop and test the AFI concept within a controlled laboratory environment. A solid state, non-scanning AFI concept will be developed that utilizes high intensity, shortwave LED illumination and a hyperspectral line scanner as a detector. The LED illuminator will flood the area of interest with UV-blue light and the line imager will collect hyperspectral fluorescence signatures (380 – 750 nanometers [nm], Δλ = 5 nm) across an array of pixels. Since the illuminator will emit light at short, excitation wavelengths, all longer wavelength signals received may be regarded as inelastic scatter (fluorescence), primarily from benthic features. The AFI will be tested under controlled conditions in laboratory water tanks using benthic targets of variable shape and fluorescence emission spectra. The AFI system will be simulated using a three dimension (3-D) Monte Carlo model that includes a complete description of the system components, water column optical properties, bottom depth, and the reflectance and fluorescence spectra of benthic features. The model will be used to verify and examine the laboratory results and investigate system modifications that can improve performance. In addition to the test scenarios, the model will be used to simulate and examine a wide variety of environmental conditions, including AFI operations with and without background solar illumination (i.e., day versus night collections), in order to examine the limits of the concept applicability.
This project will demonstrate how AFI can be used to survey shallow aquatic systems for natural and anthropogenic benthic features, including unexploded munitions, with greater accuracy, less system complexity, and lower cost compared with traditional optical approaches and stand-alone acoustical approaches. If successful, the project will pave the way towards an operational system that can be tested and demonstrated under a variety of operational scenarios.