We obtain satellite earth images from the Operational Land Imager (OLI) sensor aboard the Landsat 8 satellite through the USGS Earth Explorer online interface. Landsat imagery is then processed using various spatial analysis tools to calculate for vegetation indices such as Normalized Difference Vegetation Index (NDVI), Triangular Vegetation Index (TVI), and Green Normalized Difference Vegetation Index (GNDVI). We seek to use these indices to characterize vegetation on the marsh and determine if there are linkages between carbon cycling processes on the marsh and within the estuary. We are also using water quality indices derived from Landsat satellite imagery such as the Red/Green index to compare to in-situ water samples in the Rhode River. A YSI EXO2 sensor sits at the marsh-estuary interface and continuously measures water parameters such as turbidity, depth, fDOM (Fluorescent Dissolved Organic Matter (fDOM) refers to the fraction of CDOM (Colored Dissolved Organic Matter) that fluoresces) and chlorophyll-A. We are attempting to understand if the marsh vegetation indices, water quality indices (remote sensing), and in-situ measurements of water quality are related to one another.
Initially using uncalibrated digital number data, we found a good comparison between remotely sensed NDVI data and in-situ fDOM data with an R-value of 0.93. Now, we would like to do the same comparisons using scientific physical quantities such as T.O.A (Top of Atmosphere) radiance and reflectance values to see how the correlation changes as we have more precise data. Understanding the processes affecting carbon cycling within wetlands is pivotal to knowing how to manage them in the future.