Depth calculation for the CTD data files

   The depth values in these CTD files have been calculated from
pressure by the US JGOFS Data Management Office using the algorithm
below.  The latitude used in computation was the latitude recorded
in the CTD data file.  The CHECKVALUE was used to verify the
accuracy of the computation.  The stated accuracy of this algorithm
is 0.1 meters.  The calculated depths have been rounded to the
nearest whole meter.



 function DEPTH=depth(P,LAT);

  DEPTH   Computes depth given the pressure at some latitude
          D=DEPTH(P,LAT) gives the depth D (m) for a pressure P
              (dbars) at some latitude LAT (degrees).

          Fofonoff and Millard (1982). UNESCO Tech Paper #44.

  Notes:  (ETP3, MBARI)
          This algorithm was originally compiled by RP @ WHOI.
          It was copied from the UNESCO technical report.
          The algorithm was endorsed by SCOR Working Group 51.
          The equations were originally developed by Saunders
              and Fofonoff (1976).  DSR 23: 109-111.
          The parameters were re-fit for the 1980 equation of
              state for seawater (EOS80).

  CHECKVALUE: D=9712.653 M FOR P=10000 DECIBARS, LAT=30 DEG

  CALCULATON ASSUMES STD OCEAN: T = 0 DEG C; S = 35 (IPSS-78)


  X = sin(LAT/57.29578);
  X' = X*X;


  GR = GRAVITY VARIATION WITH LAT: ANON (1970) BULLETIN GEODESIQUE

  GR = 9.780318*(1.0+(5.2788E-3+2.36E-5*X')*X') + 1.092E-6*P


  D = DEPTH BEFORE GRAVITY CORRECTION

  D = (((-1.82E-15*P+2.279E-10)*P-2.2512E-5)*P+9.72659)*P

  DEPTH = D/GR