Assessing the ability of hyperspectral data to detect Lyngbya SPP a potential biological indicator for presence of metal objects in the littoral environment

摘要

The aquatic filamentous bacteria (Cyanobacterium) Lyngbya majuscula is a nitrogen-fixer found in coastal waters often attached or adjacent to sea grass, algae and coral. It is characterized by phycobiliproteins, unique pigments found only in cyanobacteria. To sustain photosynthesis and nitrogen fixation, L. majuscula requires iron proteins and is therefore sensitive to the availability of this metal. The hypothesis tested in this study concerns the potential use of hyperspectral imaging in detecting L. majuscula in coastal regions as biological indicators for the presence of iron debris or metal objects in the littoral environment. This concept would have potential benefits and applications in mine detection and countermeasure techniques. Using a USB2000 field spectroradiometer, a spectral library was developed for the benthic substrates of Midway Atoll, Northwest Hawaiian Islands, spectrally characterizing L. majuscula and the surrounding coral reef substrates. The data was analyzed to determine unique spectral characteristics of the benthic cyanobacteria in a mixed coral environment and evaluated against the resampled spectral resolution of a number of hyperspectral sensors: Airborne Visible/Infrared Imaging Spectrometer (AVIRIS), Hyperspectral Mapper (HyMap) and Compact Airborne Spectrographic Imager (CASI). The results of the in situ spectroscopy suggest a strong potential for all three sensors to detect these cyanobacteria in a mixed coral reef environment at four distinct wavelengths attributable to phycobiliprotein pigment absorptions unique to cyanobacteria. Of these four discriminative absorption ranges, the phycoerythrin absorption of 565-576 nm shows the greatest potential for segregating cyanobacteria from a mixed algal/ coral / sand environment so long as the coral Montipora spp. is not present within the scene, since it has an overlapping absorption in those wavelengths. In the presence of Montipora corals, these cyanobacteria are more difficult to detect. However, in a mixed environment composed of L. majuscula and Montipora corals, the cyanobacteria can be distinguished by a different phycocyanin absorption, at 615-632 nm.