O2 saturation derived from concentration
Consider an RBRconcerto³ with an integrated RBRcoda³ T.ODO or Aanderaa Optode DO sensor . The dissolved oxygen sensor transfers both the foil temperature and the dissolved oxygen concentration (not compensated for salinity). The RBRconcerto³ calculates the concentration compensated for salinity first, then the air saturation (in %) via the following equation:
$\text{Air saturation} = 2.24457 \cdot \dfrac{(10.1325 - Pav) \cdot Cc}{(Patm - Pav) \cdot \text{Solubility}}$
where
- Cc is the concentration in uMol/L, compensated for salinity,
- Patm is atmospheric pressure, and
- Pav is air vapour pressure.
Solubility is calculated via Gordon and Garcia as:
\begin{equation*}
\begin{aligned}
\text{Solubility} = exp((&Ga_0 + Ga_1 \cdot Ts + Ga_2 \cdot Ts^2 + Ga_3 \cdot Ts^3 + Ga_4 \cdot Ts^4 + Ga_5 \cdot Ts^5) \\
+ S \cdot (&Gb_0 + Gb_1 \cdot Ts + Gb_2 \cdot Ts^2 + Gb_3 \cdot Ts^3) + Gc_0 \cdot S^2)
\end{aligned}
\end{equation*}
where S is the salinity in PSU and Ts is defined as:
$Ts = ln(\dfrac{298.15 - T}{273.15 + T})$
with T being the water temperature in °C and:
\begin{equation*}
\begin{aligned}
Ga_0 & = 2.00856 \\
Ga_1 & = 3.22400 \\
Ga_2 & = 3.99063 \\
Ga_3 & = 4.80299 \\
Ga_4 & = 9.78188e-1 \\
Ga_5 & = 1.71069 \\
Gb_0 & = -6.24097e-3 \\
Gb_1 & = -6.93498e-3 \\
Gb_2 & = -6.90358e-3 \\
Gb_3 & = -4.29155e-3 \\
Gc_0 & = -3.11680e-7
\end{aligned}
\end{equation*}
Air vapour pressure (in dbar) is calculated as:
$Pav = \dfrac{exp(52.57 - \dfrac{6690.9}{T + 273.15} - 4.6818 \cdot ln(T + 273.15))}{100}$