Remote sensing of suspended sediment in Mayagüez bay associated with Inland soil erosion rates

Abstract

This study combined in situ optical measurements, satellite derived reflectance and geospatial data to evaluate total suspended sediment (TSS) spatial and temporal variations in Mayagüez Bay and their relationship with inland soil erosion rates. Several analyses were developed using in situ remote sensing reflectance (Rrs), backscattering (bb) and TSS data collected on research cruises carried out between January 2004 and October 2006. These analyses identified the range between 589 nm to 645 as the target spectral region of the electromagnetic spectrum to estimate TSS, and showed the potential of using red to green ratios to improve these estimations. Positive relationships were observed between these parameters and MODIS band 1 reflectance data, however, more data corresponding to high TSS conditions are necessary to better define and validate the results. Three algorithms to estimate TSS were generated for the study area. Best validation results (RMSE= 4.76 mg/l) were observed when using an exponential equation defining relationship between field Rrs at 645 nm and MODIS band 1 data. This study incorporated an innovative methodology which used satellite derived TSS products to estimate suspended sediment load in order to compared coastal variation with inland soil erosion estimations. Geographic Information Systems techniques were incorporated in this analysis by applying the Revised Universal Soil Loss Equation (RUSLE) to Mayagüez Bay watershed. Annual spatially variable soil erosion rates and sediment yield estimations were produced for this basin in a five years period (2001-2005), and compared with data collected at the Rio Rosario USGS gauge station. Results of this study represent an important advancement in the development and application of Remote Sensing and GIS based studies in tropical coastal waters.