Microphytobenthos biomass mapping using the optical model of diatom biofilms: Application to hyperspectral images of Bourgneuf Bay

A new fast mapping approach based on an optical model was developed and applied to hyperspectral airborne HySpex images of Bourgneuf Bay (French Atlantic coast). The aims were (1) to discriminate diatom biofilms (from the Bacillariophyceae class) constituting microphytobenthos on any mudflat and (2) to estimate their biomass expressed in mg Chl a.m(-2) by remote sensing of poorly accessible mudflats. Due to the distinct absorption peaks of certain pigments of different microalgae classes constituting microphytobenthos, the high spectral resolution of hyperspectral images was employed in order to detect the pigment assemblage characterizing diatom biofilms. Thus, the HySpex 1600 VNIR camera was used both in the laboratory for estimating biomass under controlled conditions and in an airborne setting. 1) The mapping approach used known spectral indices (NDVI and MPBI) and new ones (I-Diatom and I-Euglenid) to characterize quickly the key pigments of two main microphytobenthos classes, for a fast selection of diatom and euglenid biofilms by two different masks. 2) The inherent spectral properties of biofilms in the 700-900 nm range were also used to calculate an original estimate of the substrate/environmental effects in each mask. 3) Biomass quantification of the diatom biofilms was finally performed by application of the microphytobenthos optical model (MPBOM). This approach was first tested on laboratory HySpex images of synthetic biofilms for which the in vitro biomass measurements by chromatography (HPLC) were available. The comparison between estimated and measured biomass values showed the reliability of the mapping approach for biomass estimation. Finally, a map of diatom biomass was obtained at the scale of the entire Bourgneuf Bay. The range of biomass variation (0-35 mg Chl a.m(-2)) was in close agreement with the biomass maps presented in previous studies. (c) 2012 Elsevier Inc. All rights reserved.