DO concentration - Gordon and Garcia

The equation by Gordon and Garcia is used to convert percent saturation to concentration for instruments using Oxyguard, Aanderaa, and Rinko sensors. 

If the logger has a conductivity, and Temperature sensor the derivation will use the salinity value derived from those sensors as well as that marine temperature. If neither are present, the derivation will use the parameters listed in the parameters tab.

The equation reads:

$//<![CDATA[ \begin{array}{l}Cc = \frac{ Sat O_2 \cdot Sol \cdot (Patm - Pav)}{2.24457 \cdot (10.1325 - Pav)}\end{array} //]]>$

where

• Cc is the concentration in μMol/L, compensated for salinity,
• Patm is atmospheric pressure, and
• Pav is air vapour pressure.

Solubility is calculated via Gordon and Garcia as:

$//<![CDATA[ \begin{array}{l}\begin{equation*} \begin{aligned} \text{Solubility} = exp((&Ga_0 + Ga_1 \cdot Ts + Ga_2 \cdot Ts^2 + Ga_3 \cdot Ts^3 + Ga_4 \cdot Ts^4 + Ga_5 \cdot Ts^5) \\ + S \cdot (&Gb_0 + Gb_1 \cdot Ts + Gb_2 \cdot Ts^2 + Gb_3 \cdot Ts^3) + Gc_0 \cdot S^2) \end{aligned} \end{equation*}\end{array} //]]>$

where S is the salinity in PSU and Ts is defined as:

$//<![CDATA[ \begin{array}{l}Ts = ln(\dfrac{298.15 - T}{273.15 + T})\end{array} //]]>$

with T being the water temperature in °C and:

$//<![CDATA[ \begin{array}{l}\begin{equation*} \begin{aligned} Ga_0 & = 2.00856 \\ Ga_1 & = 3.22400 \\ Ga_2 & = 3.99063 \\ Ga_3 & = 4.80299 \\ Ga_4 & = 9.78188e-1 \\ Ga_5 & = 1.71069 \\ Gb_0 & = -6.24097e-3 \\ Gb_1 & = -6.93498e-3 \\ Gb_2 & = -6.90358e-3 \\ Gb_3 & = -4.29155e-3 \\ Gc_0 & = -3.11680e-7 \end{aligned} \end{equation*}\end{array} //]]>$

Air vapour pressure (in dbar) is calculated as:

$//<![CDATA[ \begin{array}{l}Pav = \dfrac{exp(52.57 - \dfrac{6690.9}{T + 273.15} - 4.6818 \cdot ln(T + 273.15))}{100}\end{array} //]]>$