Testing the limits of hyperspectral airborne remote sensing by mapping eelgrass in the turbid waters of Elkhorn Slough

Kelley Bostrom, University of Connecticut, kelley.bostrom@uconn.edu (Presenter)
Heidi Dierssen, University of Connecticut, heidi.dierssen@uconn.edu

Seagrass ecosystems are a valuable resource, but vulnerable to changing conditions in the coastal ocean. Quantification of seagrass density and distribution from aerial imagery can be applied as a tool in resource management and ecosystem health and stability monitoring. This study investigates analysis methods for successfully mapping eelgrass in an optically complex shallow, turbid estuary. Hyperspectral imagery of Elkhorn Slough, CA was collected by the Spectroscopic Aerial Mapper with Onboard Navigation (SAMSON) instrument. In-situ data of water column and benthic optical properties and Hydrolight Radiative Transfer model were used to create a spectral library describing the reflectance of Elkhorn Slough at different depths with bottom coverage of seagrass or sediment. However, the modeled spectra did not match spectra from the imagery, which showed very subtle spectral differences between deep water and shallow water containing sediment or eelgrass. A second set of spectral libraries was created by selecting endmembers from the SAMSON imagery with known depth and benthic coverage ranging from sediment to dense eelgrass. The Spectral Information Divergence classification algorithm compared the hyperspectral image pixels to the spectral libraries. This approach produced maps of eelgrass with 61% accuracy using 18 validation points along three transects covering sediment, sparse eelgrass, and dense eelgrass. A classification accuracy matrix shows that errors confusing sparse and dense eelgrass were the most prevalent. In the dark, turbid waters of Elkhorn Slough with optical properties changing on tidal cycles, we could not match the derived spectra with those from a radiative transfer model, but achieved satisfactory results using predefined endmembers from the imagery. In future work, better calibration of sensor and atmospheric correction of the imagery coupled with concommitant characterization of the inherent optical properties with the overflight should lead towards the use of more radiative transfer-based approaches to mapping benthic constituents in these turbid estuaries.

Presentation Type:  Poster

Session:  Global Change Impact & Vulnerability   (Tue 11:30 AM)

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Poster Location ID: 114