How to calculate the volume of water passing through a plankton net
1. Generate a graph of your data and save.
2. On the saved graph use the Best Fit option to generate a best fit line.
The alternative is to take the raw data and calculate the average flow.
A further option if you want to know the area under one section of graph click
the area tool and highlight the area.
3. To calculate distance towed
Using the best fit line result in the graph above that is 1.1735 m flow per second
and the duration of tow from the axis of 60 seconds gives a towing
distance of 70.41 metres (60 x 1.1753)
The threshold velocity of this impeller without the resistance of a mechanical
counter in all its competitors is less than 0.1m/sec and is therefore far more
accurate at normal plankton sampling speeds. It is also far more responsive
to changes in flow for the same reason resulting in more accurate volume
measurements,
4. The opening area (throat area) of the net has to be known , With this the
volume that has passed through the net can be calculated
Net opening area x towing distance x 1000 = volume of water
A small 250mm wide EFE Plankton net has an opening area of 0.04909
In the above tow
0.04909 x 70.4 x 1000 = 3456 m3 of water
The same data for a 500 wide EFE Plankton Net would be 13824 m3