Normalized difference chlorophyll index: A novel model for remote estimation of chlorophyll-a concentration in turbid productive waters

We propose a normalized difference chlorophyll index (NDCI) to predict chlorophyll-a (chl-a) concentration from remote sensing data in estuarine and coastal turbid productive (case 2) waters. NDCI calibration and validation results derived from simulated and MEdium Resolution Imaging Spectrometer (MERIS) datasets show its potential application to widely varying water types and geographic regions. A quadratic function (R2 = 0.95, p < 0.0001) accurately explained the variance in the simulated data for a chl-a range of 1–60 mg m− 3. Similarly a twofold calibration and validation of chl-a models using MERIS dataset, (chl-a range: 0.9–28.1 mg m− 3) yielded R2 of 0.9, and RMSE of ~ 2 mg m− 3 respectively. NDCI was applied on images over the Chesapeake Bay and Delaware Bay, the Mobile Bay, and the Mississippi River delta region in the northern Gulf of Mexico. The newly developed algorithm was successful in predicting chl-a concentration with approximately 12% overall bias for all above study regions. Findings from this research imply that NDCI can be successfully used on MERIS images to quantitatively monitor chl-a in inland coastal and estuarine waters. In case of remote coastal waters with no ground truth data, NDCI can be used to detect algal bloom and qualitatively infer chl-a concentration ranges very similar to NDVIʹs application in terrestrial vegetation studies.