Modeling satellite-based open water fraction via flexible Beta regression: An application to wetlands in the north-western Pacific coast of Mexico

Carbon sequestration and water filtering are two examples of many ecosystem services provided by wetlands. Open water mapping is an effective means to measure any wetland extension as these can be comprised of several open water bodies. An economical, though indirect, approach towards mapping open water bodies is through applying geo-computational methods to satellite images. In this work we propose the flexible Beta regression (FBR) model to estimate open water fraction from measurements of the Modified Normalized Difference Water Index B
6
(MNDWI6). We focus on observations derived from two MODIS images acquired during the dry season of 2008 in Marismas Nacionales, a wetland located in the north-western Pacific coast of Mexico. A Bayesian estimation procedure is presented to fit the FBR model; in particular, we provide details of a nested Metropolis-Hastings and Gibbs sampling algorithm to carry out parameter estimation. Our results show that the FBR model produces valid estimates of water fraction unlike the standard model. Our work is complemented by software developed in the R language which is available through a GitHub repository.