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March 24, 1994
Sharon DeCarlo and Fernando Santiago-Mandujano
1.0 Summary
An error was found in one of our bottle data processing programs that affected some of the previously released HOT files. Although this error affected some cruises back to HOT-16, its effect can be considered minimal.
Only the last cast of cruises 16, 26, 29, 34, 36, 38, 39; station 2 cast 14 of cruise 18 and station 1 cast 1 of cruise 34 were affected. The error was in determining the down-cast location of the bottle marks obtained in the up-cast. This determination was faulty for the casts mentioned above, leading to erroneous CTD oxygen values corresponding to the up-cast marks. This problem affected only the bottle files (hot#.sea) of the corresponding cruises.
The differences between corrected and uncorrected CTD oxygens for these casts are of less than 0.5 umol/kg for cruises 16, 18, 29 and 34. Cruises 36, 38 and 39 have mean differences of about 0.5 umol/kg, with maximum differences of up to 4.5 umol/kg. Cruise 26 shows the largest differences of up to 9 umol/kg with a mean of 5 umol/kg.
2.0 Error in UPDMATCH.SC
An error was found in the UPDMATCH.SC program. This program determines where the upcast marks correspond to the downcast. The downcast `marks' are used to calibrate CTD oxygen. The old algorithm reads the hot#.cal bottle file until it reads the next cast and gets the conductivity correction for the next cast. It stores the previous individual cast conductivity offset correction (which is actually for the cast that is currently being processed) in pccor to correct the downcast conductivities, but it does NOT save the previous cast's polynominal correction coefficients. This luckily works for all casts (because all the casts within a cruise have the same coefficients),except for two cases.
Case 1: For the cast right before a two temperature cast, polynominal coefficients are not found because there are no conductivity sensors and therefore there are no conductivity corrections for that cast. These uncalibrated salinities are used to calculate the downcast densities which are compared to the upcast mark's density to find the upcast `mark' location. This salinity is also used to calculate the oxygen saturation in the calculation of CTD oxygen at the mark.
Case 2: The last cast of a cruise will have had the previous cast's c onductivity offset applied to it. This occurs since the program does not detect a new cast and therefore does not transfer the ccor to pccor for the last cast. The last cast's CTD conductivities will be `corrected' with the previous cast's offset in the calculation of the downcast marks. For many cruises this did not result in incorrect results, since the offsets are often 0.0 for the last 2 casts.
Affected Casts:
· Last casts for cruises: 16, 26, 29, 34, 36, 38, 39. Only the CTD oxygen value in the sea file was affected.
· HOT-18 station 2 cast 14: The cast after it was a 2-T cast. Only the CTD oxygen value in the sea file was affected
· HOT-34 stn 1 cast 1 (Station2 Cast 1 was aborted, therefore, no coefficients were read for Station 2 Cast 1, so Station 1 Cast 1 was processed without the polynominal correction)
3.0 UPDMATCH.SC correction
The UPDMATCH.SC program was modified to stop getting the next cast's calibrations before processing the current cast.
4.0 Ramifications
The problem in UPDMATCH.SC did not affect any of the CTD files and only the bottle file CTD oxygen values in the last cast of some cruises were modified. We checked for cruises in which the last cast had oxygen bottle data that could have been used in the oxygen calibration of the whole cruise, but none of them were in this situation.