Evaluating AISA Hyperspectral Imager y for Mapping Black Mangr ove along the South Texas Gulf Coast

Mangrove wetlands are economically and ecologically important ecosystems and accurate assessment of these wetlands with remote sensing can assist in their management and conservation. This study was conducted to evaluate airborne AISA hyperspectral imagery and image transformation and classification techniques for mapping black mangrove populations on the south Texas Gulf coast. AISA hyperspectral imagery was acquired from two study sites and both minimum noise fraction (MNF) and inverse MNF transforms were performed. Four classification methods, including minimum distance, Mahalanobis distance, maximum likelihood, and spectral angle mapper (SAM), were applied to the noise-reduced hyperspectral imagery and to the band-reduced MNF imagery for distinguishing black mangrove from associated plant species and other cover types. Accuracy assessment showed that overall accuracy varied from 84 percent to 95 percent for site 1 and from 69 percent to 91 percent for site 2 among the eight classifications for each site. The MNF images provided similar or better classification results compared with the hyperspectral images among the four classifiers. Kappa analysis showed that there were no significant differences among the four classifiers with the MNF imagery, though maximum likelihood provided excellent overall and class accuracies for both sites. Producer’s and user’s accuracies for black mangrove were 91 percent and 94 percent, respectively, for site 1 and both 91 percent for site 2 based on maximum likelihood applied to the MNF imagery. These results indicate that airborne hyperspectral imagery combined with image transformation and classification techniques can be a useful tool for monitoring and mapping black mangrove distributions in coastal environments. Introduction Mangrove swamps are coastal wetlands characterized by salt-tolerant trees, shrubs, and other plants growing in intertidally inundated areas. Mangrove trees live on both shelEvaluating AISA Hyperspectral Imager y for Mapping Black Mangr ove along the South Texas Gulf Coast Chenghai Yang, James H. Everitt, Reginald S. Fletcher, Ryan R. Jensen, and Paul W. Mausel tered coasts and inlands as well as along the bank of estuaries and rivers (Ramasubramanian et al., 2006). Mangrove wetlands are found in tropical and subtropical regions of the world. In North America, they are found from the southern tip of Florida along the Gulf Coast to Texas. In the continental United States, only three species of mangrove grow: black mangrove [Avicennia germinans (L.) L.], red mangrove (Rhizophora mangle L.), and white mangrove [Laguncularia racemosa (L.) Gaertn. f.]. Black mangrove is the most common mangrove in the United States outside the Florida everglades (EPA, 2006). Mangrove wetlands are regarded as economically and ecologically important ecosystems due to their intermediate position between the marine and terrestrial environments (Pasqualini et al., 1999). They have high productivity of litter fall and woody biomass (Day et al., 1987 and 1996), provide habitat and detritus food for fish and shellfish, and function as nurseries for a variety of fishes, prawns, and shellfishes (Sasekumar et al., 1992; Primavera, 1997). Moreover, mangrove forests provide a natural barrier that helps to prevent shoreline erosion, shielding inland areas from severe damage during hurricanes and tidal waves (Marshal, 1994; EPA, 2006). They also act as a windbreak, prevent salinization of soils, and filter pollutants (Tam and Wong, 1999; Mao et al., 2006). Valiela et al. (2001) estimated from their compilation of most recent data for all countries where mangroves have been reported, that there are roughly 17 million hectares of mangrove habitats along the shorelines of the world. Although mangrove wetlands are one of the most productive ecosystems and provide large amounts of resources, they are being increasingly cleared for other land-use activities such as settlements, agriculture, and aquaculture. On a worldwide scale, mangroves have been lost each year since the early1980s with an annual areal loss rate of 2.1 percent, which exceeds the losses for tropical rain forests and coral reefs, two other well-known threatened environments. On a continental basis, losses vary and the largest losses occur in the Americas with an annual loss rate of 3.6 percent (Valiela et al., 2001). Efforts are needed to protect and restore these valuable ecosystems. To formulate effective management and PHOTOGRAMMETRIC ENGINEER ING & REMOTE SENS ING Ap r i l 2009 425 Chenghai Yang, James H. Everitt, and Reginald S. Fletcher are with the USDA-ARS Kika de la Garza Subtropical Agricultural Research Center, 2413 E. Highway 83, Weslaco, TX 78596 ([email protected]). Ryan R. Jensen and Paul W. Mausel are with the Department of Geography, Geology, and Anthropology, Indiana State University, Terre Haute, IN 47809. Photogrammetric Engineering & Remote Sensing Vol. 75, No. 4, April 2009, pp. 425–435. 0099-1112/09/7504–0425/$3.00/0 © 2009 American Society for Photogrammetry and Remote Sensing 425-435_07-088.qxd 3/19/09 1:14 PM Page 425