At work the other day I was trying to make sense of a bunch of water quality sensor data from the Indian River Lagoon in Florida. The sensor had measured electrical conductivity as a proxy for salinity (saltier water conducts electricity better because the salt ions ferry the charges), but no conversion had been made from conductivity to actual salinity.
It turns out that converting from conductivity to salinity is tricky, because the mathematical relationship depends in a complicated way on both temperature and pressure. (Although you don't have to worry about the pressure part if you're dealing with surface waters at 1 atm pressure.) In my Google search for answers I found a website that will do the conversion for you if you enter a particular conductivity and temperature into a box. But that's not much use if you have hundreds or thousands of concurrent temperature and conductivity recordings that you need to convert in a spreadsheet. So I dug deeper and found a 1983 UNESCO paper that had the actual formulas needed for the conversion. I put the formulas into a Microsoft Excel worksheet and fed them the Indian River Lagoon sensor data. It worked! I think.
Interestingly, it seems that the part of the Indian River Lagoon where the readings were taken gets a bit saltier than the ocean in Florida's winter dry season, but is only about 2/3 as salty as the ocean in the summer wet season.
Anyway, I'm making the Excel file that does the conversion available for download here, along with an example using the sensor data from the IRL. I'm trying to embed it below. If you're a scientist and you notice some error in my calculations, let me know ASAP so I can fix it. Thanks.