Showing papers by "David Doxaran published in 2010"

Estimating turbidity and total suspended matter in the Adour River plume (South Bay of Biscay) using MODIS 250-m imagery

Abstract: The Basque coastal waters (South Bay of Biscay) are directly influenced by the Adour River freshwater plume. The Adour outflow leads to important variations of suspended matter concentrations and turbidity, which in turn may affect biological productivity and water quality. This study aims at both developing specific algorithms and testing the efficiency of atmospherically corrected MODIS-Aqua 250-m surface reflectance product (MYD09) to map total suspended matter concentrations and turbidity within the Adour coastal region. First, regional empirical algorithms based on in-situ data were tested to retrieve the concentration of total suspended matter and turbidity from the remote sensing reflectance. Then, the respective sensitivity of MODIS surface reflectance bands 1 and 2 for water quality application was investigated as well as the quality of atmospheric corrections. Finally, selected algorithms were applied to the MYD09 product. The resulting 250-m resolution maps were then compared to 1000-m maps produced by IFREMER and comparisons between satellite measurements and in-situ sampling points were performed. Results show that MODIS-Aqua band 1 (620–670 nm) is appropriate for predicting turbidity and total suspended matter concentrations using polynomial regression models, whilst band 2 is unadapted. Comparison between total suspended matter concentration 250-m resolution maps and mineral suspended matter 1000-m maps (generated by IFREMER) produced consistent results. A high correlation was obtained between turbidity measured in-situ and turbidity retrieved from MODIS-Aqua satellite data.

Uncertainties associated to measurements of inherent optical properties in natural waters

Abstract: Monte Carlo simulations are used to explain and quantify the errors in inherent optical properties (IOPs) (absorption and attenuation coefficients) measured using the WET Labs AC-9 submarine spectrophotometer, and to assess correction algorithms. Simulated samples with a wide range of IOPs encountered in natural waters are examined. The relative errors on the measured absorption coefficient are in general lower than 25%, but reach up to 100% in highly scattering waters. Relative errors on attenuation and scattering coefficients are more stable, with an underestimation mainly driven by the volume scattering function. The errors in attenuation and scattering spectral shapes are small.

Use of ocean color satellite data to study the dynamics of suspended particles in the Yangtze River plume (East China Sea)

Abstract: A multi-sensor algorithm is applied to MODIS and MERIS satellite data in order to quantify suspended particulate matter (SPM) in the Yangtze River plume (East China Sea). Several atmospheric correction methods are tested; a simple but operational method is finally selected as appropriate for MODIS, MERIS and GOCI satellite data. As most of the methods for atmospheric corrections of satellite data fail over such highly turbid waters, an adaptation of the black pixel assumption is used to correct for the aerosol contribution. The retrieved seawater reflectance at red wavebands appears as the most sensitive to SPM concentrations but tends to saturate at concentrations beyond 100 mg.l-1. By opposition the near-infrared seawater reflectance does not saturate even at extremely high concentrations of 1000 mg.l-1. Overall, the most robust relationship between the SPM concentration and seawater reflectance is obtained considering a spectral ratio between the near-infrared (e.g., 850 nm) and visible (e.g. 550 nm). This relationship is applied to atmospherically corrected ocean color satellite data to retrieve SPM concentrations in the Yangtze River plume. Results show that ocean color satellite data can be used to study the seasonal dynamics of SPM and better understand the role played by the main physical processes involved (river discharge, tidal cycles, wind and regional circulation).

Variability of total, back and side scattering to mass concentration of marine particles

Abstract: We investigate the relationship between various scattering properties (total, back and side scattering) and Total Suspended Matter (TSM), the dry mass concentration of marine particles in suspension, for coastal and offshore waters in various regions (Coastal Atlantic, Southern North Sea, Mediterranean Sea and French Guyana waters). We quantify the uncertainty on TSM concentration estimation from each scattering property. We further quantify the variability of the total (bp), side (bs) and back scattering (bbp) to mass concentration ratio and explain this variability in terms of the physical (size) and chemical (apparent density, refractive index) properties of the particles. We show that bbp, bp and bs correlate well with TSM (correlation coefficients higher than 0.92), though with considerable scatter along the regression line. We find that 75% of the predicted TSM concentrations from a model based on bs are within 29% of the measured TSM concentration and within 38% and 48% for bbp and bp based models, respectively. The variability of mass specific total scattering (bp*) is mainly explained by total geometric cross section (PSA) and backscattering ratio ( bbp ~ ), with observations above (below) the regression line having significantly higher (lower) bbp ~ and lower (higher) PSA. Variability of mass specific backscattering (bbp*) was smaller and could not be explained by a single parameter. We do find that points below the regression line have significantly lower densities (ρa), PSA, refractive index (n), bbp ~ and chlorophyll a:TSM ratio than points near or above the line. After classification of observations in Case 1 and 2 water types, we find that Case 2 waters (N=149) show significantly higher values of bbp*, ρa, n, bbp ~ and PSA and significantly lower values for bp* and chla:TSM than for Case 1 waters (N=123).