Discrimination of mangrove species and mudflat classes using in situ hyperspectral data: a case study of Indian Sundarbans

摘要

This study attempts to assess whether canopy spectra of mangrove species and mudflat spectra recorded under field conditions contain adequate spectral information for discerning mangroves at species rank and mudflats at the class level. This article highlights the hyperspectral characteristics of canopies of 17 tropical mangrove species, belonging to nine families, creek water and four mudflat classes found in the tidal forests of Indian Sundarbans. Hyperspectral observations were recorded using a field spectroradiometer, and pre-processed and averaged reflectance values of samples were subjected to various statistically tests such as t-means cluster analysis, one-way analysis of variance (ANOVA), stepwise linear discrimination and factor analysis. k-means cluster analysis showed highest Euclidean distance between Rhizophoraceae and Myrsinaceae/Plumbaginaceae. ANOVA results indicated that all the canopy spectra were statistically different at all the spectral locations except one with majority of the bands exhibiting 99% confidence level, and for the mudflat classes and creek water, all bands showed p＜ 0.01. Discriminant analysis was performed in different combinations/cases to identify the bands for maximum separability. Optimal Wilks' Lambda (L) were achieved with two, six, four, eight, one, four, two and three for differentiating canopies of the species of Avicennia, Sonneratia, Xylocarpus, Bruguiera, Ceriops, Bruguiera and Rhizophora, all species of Rhizophoraceae, two species of Arecaceae, respectively. For mudflat classes and creek water, the best possible Wilks' Lambda were attained with four, five and two for discriminating upper, intermediate and mud lower, mud lower and water, mud upper with and without roots, correspondingly. Factor analysis was the tool used to identify the wavelengths that were uncorrelated and contained maximum information in the combination of selected wavelengths. The most significant bands for canopy discrimination were 960, 970, 1000, 1070, 1120,1160, 2070, 2080, 2150, 2200, 2240 and 2340 nm; for discrimination amongst mudflat classes and creek water, the bands were 540, 550, 730, 740, 770, 780, 880, 1190, 1290, 2010 and 2150 nm. Overall, hyperspectral data showed potential for discriminating between mangrove canopies of different species and for discerning mudflat classes. The outcomes of the study also indicated the efficacy of the applied statistical tools for discrimination.