Modified MODIS fluorescence line height data product to improve image interpretation for red tide monitoring in the eastern Gulf of Mexico

Chuanmin Hu,Lian Feng

doi:10.1117/1.jrs.11.012003

Abstract

Several satellite-based methods have been used to detect and trace Karenia brevis red tide blooms in the eastern Gulf of Mexico. Some require data statistics and multiple data products while others use a single data product. Of these, the MODIS normalized fluorescence line height (nFLH) has shown its advantage of detecting blooms in waters rich in colored dissolved organic matter, thus having been used routinely to assess bloom conditions by the Florida Fish and Wildlife Conservation Commission (FWC), the official state agency of Florida responsible for red tide monitoring and mitigation. However, elevated sediment concentrations in the water column due to wind storms can also result in high nFLH values, leading to false-positive bloom interpretation. Here, a modified nFLH data product is developed to minimize such impacts through empirical adjustments of the nFLH values using MODIS-derived remote sensing reflectance in the green band at 547 nm. The new product is termed as an algal bloom index (ABI), which has shown improved performance over the original nFLH in both retrospective evaluation statistics and near real-time applications. The ABI product has been made available in near real-time through a Web portal and has been used by the FWC on a routine basis to guide field sampling efforts and prepare for red tide bulletins distributed to many user groups.

Highlights

Harmful algal blooms (HABs) of the toxic dinoflagellate, Karenia brevis, occur annually on the West Florida shelf (WFS) in the eastern Gulf of Mexico (GOM),[1] often causing fish and marine mammal mortality as well as other environmental and economic problems.[2]
What is more important is that some of the high-normalized fluorescence line height (nFLH) low-K. brevis points appear to be shifted to the left on the algal bloom index (ABI)-K. brevis plot, confirming that the design of Eq (4) to avoid false positive in sediment-rich waters may be effective
The MODIS nFLH data product has been shown effective in detecting blooms in CDOM-rich waters and has been used by the Fish and Wildlife Conservation Commission (FWC) for routine assessment of K. brevis HABs in the eastern GOM

Summary

Introduction

Harmful algal blooms (HABs) of the toxic dinoflagellate, Karenia brevis, occur annually on the West Florida shelf (WFS) in the eastern Gulf of Mexico (GOM),[1] often causing fish and marine mammal mortality as well as other environmental and economic problems.[2] Timely information of K. brevis blooms in terms of their spatial extent, intensity, transport, and dissipation provides guidance on field sampling and mitigation efforts, and retrospective information on such bloom characteristics helps understand bloom formation and their impact on the ocean’s biophysical and biogeochemical properties. Satellite remote sensing has proven to be an effective tool to provide such information because K. brevis blooms cause water discoloration, making bloom waters greenish, brownish, or reddish as compared with the nearby nonbloom waters. For the reason of discoloration, K. brevis blooms are often called “red tides.”. The discoloration is caused primarily by the light absorption pigments in the dinoflagellate cells.

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