Field observations of SPM using ADV, ADP, and OBS in a shallow estuarine system with low SPM concentration-Vitoria Bay, SE Brazil

The present study investigated direct and indirect methods using optical and acoustic instruments for the acquisition of information required to estimate the concentration of suspended particulate matter (SPM) in Vitria Bay, a shallow estuarine system in SE Brazil. The aim was to calibrate and compare the use of different instruments (OBS, ADP, and ADV) to estimate SPM concentration in the water column and near the bed. Concentration was determined by correlating filtered water samples with the optical and acoustic measurements. In general, the methodology proved tenable for the chosen shallow estuarine environment with low SPM concentration (< 60 mg/L). Pearson's coefficient ranged from 0.75 to 0.85, when correlating measurements taken at three sampled depths. Differences in the correlation coefficient values showed that calibration at three depths (near the bed, mid-water column, and near the surface) was more effective than for surface samples alone, even in shallow (similar to 3 m deep) water. When calibration was attempted for concentration in the entire water column with samples at just one elevation, the correlation value was very low, thus increasing the error in estimating the SPM concentration.