Bathymetry and Water Column Correction using 4SM – A HyPhoon user success story

This is part of a series on user success stories that showcase applications and accomplishments using HyPhoon datasets. Send us your story!

The Accomplishment: Dr. Yann Morel derived bathymetry and water column corrected reflectance for Heron Reef using his Self-calibrated Supervised Spectral Shallow-sea Modeler (4SM). Output includes water depth, as shown below, and water column corrected reflectance at the seafloor. Both products are being added to the Heron Reef dataset, and will soon be available for the community to download.

4SM Heron Reef

CASI hyperspectral (left) and 4SM derived bathymetry (right)

Data: The source data used for this success story was the 2002 CASI hyperspectral imagery from the Heron Reef dataset provided courtesy of the Center for Spatial Environmental Research at the University of Queensland. Heron Reef is located at the southern end of the Great Barrier Reef in Australia. The imagery has 1 m pixels and a spectral range from 400-800 nm with 19 spectral bands.

4SM Overview: The 4SM model is based on established physical principles of shallow water optics, operates without need for field data or atmospheric correction, and works with both multispectral and hyperspectral imagery. The model assumes both water and atmospheric conditions are uniform throughout the given scene, requires the presence of both deep water and bare land pixels, and is most applicable to clear shallow water at 0-30 meters depth.

At its core, 4SM utilizes a variant of Lyzenga’s method to calculate the slopes for all bi-dimensional band pairs, which are then used to interpolate diffuse attenuation coefficients for all visible bands. Surface glint is minimized using information from a NIR or SWIR band, bare land pixels are used to derive the slope of the soil line and the water volume reflectance, and deep water pixels are used to approximate deep water radiance. All of this information is then combined to drive an optimization approach for estimating water depth.

Output ultimately includes both water depth and water column corrected reflectance, which can both be used for further habitat and geomorphic analyses.

For more on 4SM: http://www.watercolumncorrection.com/

To access HyPhoon data: http://hyphoon.hyspeedcomputing.com/data-sets/

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