Example 18: deri_o2sat_garcia, derived O2 saturation from concentration

Consider an RBRconcerto³ C.T.D.DO logger, where the DO channel is a RBRcoda ODO. The RBRcoda ODO 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:

\[\text{Air saturation} = 2.23916 \cdot \dfrac{(10.1325 - Pav) \cdot Cc}{(Patm - Pav) \cdot \text{Solubility}}\]

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:

\[\begin{equation*} \begin{aligned} Ga_0 & = 2.00856 \\ Ga_1 & = 3.22400 \\ Ga_2 & = 3.99063 \\ Ga_3 & = 4.80299 \\ Ga_4 & = 9.78188e-1 \\ Ga_5 & = 1.71069 \\ Gb_0 & = -6.24523e-3 \\ Gb_1 & = -7.37614e-3 \\ Gb_2 & = -1.03410e-2 \\ Gb_3 & = -8.17083e-3 \\ Gc_0 & = -4.88682e-7 \end{aligned} \end{equation*}\]

Air vapour pressure (in dbar) is calculated as:

\[Pav = \dfrac{exp(52.57 - \dfrac{6690.9}{T + 273.15} - 4.6818 \cdot ln(T + 273.15))}{100}\]

The corresponding logger coefficients are:

  • n0, the index of the concentration channel, already compensated for salinity

  • n1, the index of the water temperature channel

  • n2, the index of the salinity channel

  • n3, the index of the atmospheric pressure channel (set to value in order to use settings atmosphere)

The O2 saturation equation was revised in firmware 1.094 of the RBRconcerto3, RBRmaestro3, RBRduo3, RBRlegato3 and RBRargo3. For the previous implementation of this equation, refer to the version B of this document.

Examples

>> calibration 9 type
<< calibration 9 type = doxy22

Confirm the channel type.

>> calibration 9
<< calibration 9 type = doxy22, datetime = 20171201000000, n0 = 4, n1 = 5, n2 = 8, n3 = value

Request confirmation of all channel indices.