Correlation analysis of water wave reflectance and local TSM concentrations in the breaking zone with remote sensing techniques

The coastal zone is a dynamic area in which processes with different origins and scales interact. Several techniques can be used for coastal zone monitoring. Remote sensing is a powerful tool for monitoring coastal processes and oastal areas. The quality of coastal water is a very important issue, and remote sensing optical sensors can be used to quantify water quality parameters such as suspended sediments. Therefore, it is possible to estimate the total suspended matter (TSM) concentration with multispectral satellite images. To extract meaningful information, the satellite data need to be validated with in situ measurements. The main objective of this work was to quantify TSM concentrations in the breaking zone with in situ measurements. In situ validation is important for the accuracy of correlations established. A section of the northwest coast of Portugal, near Aveiro city, was chosen as a test area, and all in situ measurements were done in this area. Several in situ techniques have been used to establish a relationship between seawater reflectance and TSM concentration for the range of wavelengths from 400 to 900 nm. Empirical relationships were established for equivalent reflectance values by SPOT/HRVIR (high-resolution visible Terra/ASTER (advanced spaceborne thermal emission and reflection radiometer), and Landsat TM (thematic mapper) at visible and near-infrared equivalent bands and TSM concentrations. The reflectance values were used to estimate TSM concentration with the use of the relationships established by in situ measurement. The reflectance of all bands of the satellite images tested showed high correlation with TSM in the wavelengths between 500 and 900 nm. The water leaving equivalent reflectance for each sensor equivalent band in the visible and near-infrared wavelengths was calculated, and a relationship between seawater reflectance and TSM concentration was established. The model coefficients and correlation factors for identical bands on different sensors presented good similarity. The work presented shows that TSM concentration in the breaking zone can be obtained directly from simulated multispectral satellite data. However, in situ measurements are essential to calibrate the process and establish the empirical relationships between TSM concentration and water leaving reflectance. The same empirical relationships found with in situ measurements will be used to estimate the TSM concentrations directly from real satellite data to try to quantify the sedimentary balance in the study area for the period of the satellite data.