ox_units

 OX_UNITS  converts between 3 different oxygen units
              ml/l, micromole/kg, micromole/l

 INPUTS:
        ox: oxygen in original units
        salt: salinity in PSU
        temp: potential temperature.
        from_to: string indicating original and desired units.
                 possible cases are:
                 mll2mml: ml/l to micromoles/l
                 mll2mmk: ml/l to micromoles/kg
                 mml2mmk: micromoles/l to micromoles/kg
                 mml2mll: micromoles/l to ml/l
                 mmk2mll: micromoles/kg to ml/l
                 mmk2mml: micromoles/kg to micromoles/l
           

  Usage: o = ox_units(ox,salt,potentialtemp,from_to);

 Derrick Snowden, 2002;

 Based on code by
 Paul Robbins 1995

0001 function o = ox_units(ox,salt,temp,from_to);
0002 % OX_UNITS  converts between 3 different oxygen units
0003 %              ml/l, micromole/kg, micromole/l
0004 %
0005 % INPUTS:
0006 %        ox: oxygen in original units
0007 %        salt: salinity in PSU
0008 %        temp: potential temperature.
0009 %        from_to: string indicating original and desired units.
0010 %                 possible cases are:
0011 %                 mll2mml: ml/l to micromoles/l
0012 %                 mll2mmk: ml/l to micromoles/kg
0013 %                 mml2mmk: micromoles/l to micromoles/kg
0014 %                 mml2mll: micromoles/l to ml/l
0015 %                 mmk2mll: micromoles/kg to ml/l
0016 %                 mmk2mml: micromoles/kg to micromoles/l
0017 %
0018 %
0019 %  Usage: o = ox_units(ox,salt,potentialtemp,from_to);
0020 %
0021 % Derrick Snowden, 2002;
0022 %
0023 % Based on code by
0024 % Paul Robbins 1995
0025 
0026 if nargin < 4
0027     disp(['No units indicator (from_to) was passed.'])
0028     disp('')
0029     disp(['Valid units are:']);
0030     print_usage(1);
0031 end
0032 
0033 % First compute potential density assuming temp is potential temp
0034 % equivalent to sw_pden(salt,temp,press,press_ref==0) if temp is in situ
0035 pdens = sw_dens(salt,temp,0);
0036 
0037 switch from_to
0038 case 'mll2mmk' %ml/l to micromoles/kg
0039    o = ox*1e3./pdens/.022403;
0040 case 'mll2mml' %ml/l to micromoles/l
0041    o = (ox*1e3./pdens/.022403).*pdens./1000;
0042 case 'mml2mmk' % micromoles/l to micromoles/kg
0043    o = ox*1000./pdens;
0044 case 'mml2mll' % micromoles/l to ml/l
0045    o = (ox.*1000./pdens) .* (.022403 .* pdens ./ 1000);
0046 case 'mmk2mll' % micromoles/kg to ml/l
0047    o = ox .* (0.022403 .* pdens ./ 1000);
0048 case 'mmk2mml' % micromoles/kg to micromoles/l
0049    o = ox.*pdens./1000;
0050 
0051 otherwise
0052    disp(['Incorrect units passed to ox_units.'])
0053    disp('')
0054    disp(['Valid units are:']);
0055    print_usage(1);
0056 end
0057 
0058 return
0059 
0060 function [] = print_usage(err)
0061 
0062 disp(['mll2mml: ml/l to micromoles/l']);
0063    disp(['mll2mmk: ml/l to micromoles/kg']);
0064    disp(['mml2mmk: micromoles/l to micromoles/kg']);
0065    disp(['mml2mll: micromoles/l to ml/l']);
0066    disp(['mmk2mll: micromoles/kg to ml/l']);
0067    disp(['mmk2mml: micromoles/kg to micromoles/l']);
0068    disp('')
0069    error('Set from_to to one of the strings above;');
0070 return