Comparing MODIS and MERIS spectral shapes for cyanobacterial bloom detection

Abstract

A spectral shape algorithm applied to Medium Resolution Imaging Spectrometer (MERIS) imagery has detected cyanobacterial blooms, with extensive examples in Lake Erie. The detection algorithm uses an approximation of the second derivative as a measure of spectral shape around the 681 nm band S _2d(681). With the end of the MERIS mission on 8 April 2012, an analogue was developed for the Moderate Resolution Imaging Spectroradiometer (MODIS) to continue monitoring for these blooms. The MODIS analogue uses the standard ρ_s (Rayleigh-corrected reflectance) to determine S _2d(678), which is computationally equivalent to the negative of the MODIS fluorescent line height (FLH). A comparison was made of the two products from image pairs during a period of relatively severe blooms of cyanobacteria (2008–2011). When the MODIS bands do not saturate due to surface scums from high cyanobacteria biomass or conditions of glint or dense aerosols, the algorithms produce comparable results with a linear transform of the MODIS S _2d(678). The results indicate that MODIS can be used to monitor these blooms. Dense cyanobacteria blooms will produce negative FLH showing a limitation of FLH for bloom detection. The S _2d(678) offers a tool to support monitoring for dense algal blooms.

Acknowledgements

MERIS imagery was provided by the European Space Agency (Category-1 Proposal C1P.3975). Funding was provided the NASA Applied Science Program announcement NNH08ZDA001N under contract NNH09AL53I.