Publications

Jena, B (2017). The effect of phytoplankton pigment composition and packaging on the retrieval of chlorophyll-a concentration from satellite observations in the Southern Ocean. INTERNATIONAL JOURNAL OF REMOTE SENSING, 38(13), 3763-3784.

Abstract
The Antarctic waters are known to be optically unique and the standard empirical ocean colour algorithms applied to these waters may not address the regional bio-optical characteristics. This article sheds light on the performance of current empirical algorithms and a regionally optimized algorithm (ROA) for the retrieval of chlorophyll-a (chl-a) concentration from Aqua-Moderate Resolution Imaging Spectroradiometer (Aqua-MODIS) and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) in the Indian Ocean Sector of Southern Ocean (IOSO). Analysis indicated that empirical algorithms used for the retrieval of chl-a concentration from Aqua-MODIS and SeaWiFS underestimate by a factor varying from 2 to 2.9, resulting in underestimation when in situ chl-a exceeds about 0.3 mg m(-3). To explain these uncertainties, a study was carried out to understand the effect of phytoplankton pigment composition and pigment packaging on remote-sensing reflectance (R-rs,R-lambda), from the analysis of phytoplankton-specific absorption coefficient (a(ph,)*(lambda)). The spatial variation of phytoplankton groups analysed using diagnostics pigments (DP) indicated shifting of the phytoplankton community structure from offshore to coastal Antarctic, with a significant increasing trend for diatoms and a decreasing trend for haptophytes population. The diatomdominated population exhibits lower a(ph,*lambda) in the 405-510 nm region (with relative flattening in 443-489 nm) compared with the a(ph,)*(lambda) spectra of the haptophytes-dominated population that peaks near 443 nm. The flattening of a(ph,)*(lambda) spectra for the diatom-dominated population was attributed to its larger cell size, which leads to pigment packaging (intracellular shading) and in turn results in higher R-rs,R-lambda The relationship between pigment composition (normalized by chl-a) and blue: green absorption band ratios (a(ph),*(443): a(ph),*(555) and a(ph),*(489): a(ph),* (555)) corresponding to the Aqua-MODIS and SeaWiFS bands showed in-phase associations with most of the pigments such as 19'-hexanoyloxyfucoxanthin, 19'-butanoyloxyfucoxanthin, peridinin, and zeaxanthin. In contrast, the out-of-phase association observed between the blue: green absorption ratios and fucoxanthin indicated apparent deviations from the general pigment retrieval algorithms, which assumes that blue: green ratios vary in a systematic form with chl-a. The out-of-phase correspondence suggests that the increasing trend of fucoxanthin pigments towards the Antarctic coast was associated with the decreasing trend of blue: green absorption ratios and in turn results in higher R-rs,R-lambda Therefore, an increase in Rrs,. leads to underestimation of chl-a from Aqua-MODIS and SeaWiFS in the IOSO region.

DOI:
10.1080/01431161.2017.1308034

ISSN:
0143-1161