To measure the salinity gradient as we travel upriver, our students collect water samples at a series of predetermined locations, which our students find using landmarks (such as buoys and river markers) and GPS coordinates.
On the Half Moon, we collect water samples the old-fashioned way: by simply heaving a tethered canvas bucket overboard and hauling it back on board.
These water samples are then collected in sample jars for later analysis by the entire student crew. We continue to collect samples regularly until the salinity gradient consistently drops to zero, which is to say, until the water is completely fresh.