Systematical underestimation of MODIS global chlorophyll-a concentration estimation algorithm associating with scale effect

Abstract

A framework for characterizing the scale effects while using ocean chlorophyll 4 algorithm of MODIS (OC3M) to estimate chlorophyll-a concentration (chl<i style="mso-bidi-font-style:normal">a</i>) from Moderate Resolution Imaging Spectroradiometer (MODIS) imageries is presented. An eight neighborhood algorithm is used to estimate the distribution variance of chl<i style="mso-bidi-font-style:normal">a</i> concentration, <i style="mso-bidi-font-style: normal">D</i>(<i style="mso-bidi-font-style:normal">R</i>_3M), from MODIS imageries. Based on the analysis for global data series of monthly composites of MODIS Aqua satellite data from 2008 to 2010 at 4 km resolution, the chl<i style="mso-bidi-font-style:normal">a</i> concentration estimated by OC3M algorithm would be smaller than <i>in situ</i> measurements in theory. This is a even if the atmospheric effects has been accurately removed owing to the scale effects. Relative scale error has characterizes associating with spatial and time dependents. Largely, scale error mostly distributed in the coastal waters, which is closely related with human society. In this study, <i style="mso-bidi-font-style:normal">D</i>(<i style="mso-bidi-font-style:normal">R</i>_3M) is estimated very coarsely, which would lead to the underestimation of scale errors of global chl<i style="mso-bidi-font-style:normal">a</i> data. As a result, how to accurately estimate <i style="mso-bidi-font-style:normal">D</i>(<i style="mso-bidi-font-style: normal">R</i>_3M) may be possible areas for scale effect study in future.