Simulating Bottom Reflectance Retrievals Using an Analytical Solution for the Two-Flow Irradiance Models
Abstract
Existing analytical solutions to the two-flow irradiance equations are used
to obtain new relations for simulating hyperspectral bottom reflectance signatures.
Synthetic bottom reflectance signatures are compared to measured bottom
reflectance signatures in order to test the model equation limitations of the
formulations.
Measured hyperspectral bottom reflectance signatures for a dead reef,
Elkhorn coral, seagrass and sand, sand, and turtle grass are used. Estimated
collimated and diffuse irradiances are inputs needed to run model formulations.
Also, specific absorption, specific backscattering coefficients, and water depth for
ocean, coastal, and estuarine waters are used as inputs to simulate bottom
reflectance retrievals. The specific coefficients are coupled with estimates of dissolved organic matter (DOM), seston (SM), and chlorophyll (CHL)
concentrations, pure water absorption, and backscattering coefficients. Resulting
hyperspectral synthetic bottom reflectances are used to test the depth limitations for
predicting bottom reflectances.
Model results suggest that in clear natural water the Case I and Case II
model can be used to estimate bottom reflectances down to 15 m in a water column
between 440 and 560 nm with a 95% confidence level. In water types that include
dissolved organic matter, seston, and chlorophyll both models lose the ability to
predict the bottom type with an acceptable confidence level at depths of greater
than 1-2 m depending upon the constituent concentrations.
Surface reflectances provided by aircraft, satellite, or vessels can provide
the essential input data needed to retrieve bottom water reflectances. Application of
the results may provide a means to help assess water quality and shallow water
bottom types through the mathematical inversion techniques developed for bottom
feature detection and mapping of seagrasses, coral reef types, sand, and mud
bottoms.