Simultaneous measurements of acoustic backscatter (ABS) and optical backscatter (OBS) are made while a suspended sediment concentration (SSC) sample is collected with a P-61 point sampler. An OBS-3 is attached to the fin of the P-61 sampler (see picture above) and measures the OBS of the adjacent water once per second while the P-61 sample valve is open and collecting water. At the same time, an ADCP mounted off the opposite side of the boat is collecting ABS data for the same length of time. An average of the OBS-3 measurements made during sample collection is used to correlate OBS with SSC and ABS. An average of the ABS measurements made in the bin corresponding to the P-61 sampling depth is used to correlate ABS with SSC and OBS.