# Dissolved oxygen (DO) measurements in saline (sea)water

Dissolved oxygen measurements in saline water using an instrument/probe needs to be corrected by temperature and salinity. Most DO probes already compensate for temperature, but still need to correct the readings for salinity. To correct for salinity both the salinity as well as the temperature have to be measured at the same time as performing a DO measurement. In this blog article we’ll tell you more about this.

## How to use calculation channels for correct DO readings

The YDOC data loggers are provided with up to 8 calculation channels, which can a/o be used to correct DO readings.

• The equation to compensate DO readings for salinity is as follows:

DO_C = :DO * exp(-1*:SAL*(0.017674+(-10.754+2140.7/:TEMPK)/:TEMPK)))

Where :DO is the measured dissolved oxygen in mg/l, :SAL is the salinity in g/kg brine and :TEMPK the water temperature in Kelvin.
• The equation to express DO as a percent of saturation is:

DO% = (:DO_C/:DOSAT)*100

Where :DO_C is the compensated DO reading in mg/l and :DOSAT the dissolved oxygen saturation value in mg/l at the measured temperature and salinity.
• The equation to calculate DO saturation in mg/l is:

DOSAT = exp(-139.34411+(1.575701E5+(-6.642308E7+(1.2438E10-8.621949E11/:TEMPK)/:TEMPK)/:TEMPK)/:TEMPK)*exp(-1*:SAL*(0.017674+(-10.754+2140.7/:TEMPK)/:TEMPK)))

Where :SAL is the measured salinity in g/kg brine and :TEMPK the water temperature in Kelvin.

The used equations are based on published equations by Benson and Krause (1984).