WHOI SOLO FSI Problem

1. WHOI SOLO FSI Problem Status Report for AST-9 Breck Owens

2. Initial Identification of Errordue to J. Willis and J. Gilson WHOI SOLO FSI floats had both large systematic errors with depth and increased random error compared to other floats.

3. Source of Problem for FSI CTDs • Some WHOI SOLO floats used FSI CTDs • All WHOI floats have CTDs do the pressure binning • Requested that binning occur from top to bottom (this is the case for SBE CTDs). • FSI programmed the CTD to start from deepest pressure and bin average starting from the highest pressure. • Deep Bin intervals are larger than shallow bins. Transition for bin intervals for FSI CTD sensitive to starting pressure. The transition can change from profile to profile depending on the deepest pressure for each profile.

4. Example Full Profile - Error increases at depths where bin interval changes. Red - Correct values Green - Present values original files Blow-up of bin transitions - Shows increase in error at transitions

5. Additional Information available in Engineering Message • Number of bins, top bin pressure and bottom bin pressure, temperature, and salinity included in engineering message. • For some floats error in float controller software returned null values for bottom bin pressure.

6. Recovering Profiles • For floats with correct information in engineering message, the data can be completely corrected. • 39 floats with a total of 3,698 profiles have been corrected in this manner. These floats have been corrected and resubmitted to the GDACs.

7. Remaining Floats • The remaining floats, 165 floats and 7652 profiles, will require more work to recover the pressure information and it will not be as accurate as the corrected floats. • Typically the engineering information includes the number of bins and pressure for the shallowest bin. • Investigated several ways to estimate bin pressures, including:a. Match to values at end of drift phase - can be 4-5 hrs delay, so contamination by internal waves [Rejected].b. Examine profiles at transition depths and estimate transitions that do not give erroneous temperature (density) gradients.

8. Matching vertical gradients Choose profile that has gradients at transition that matches gradients over larger scales. This allows us to estimate pressure for deepest bin. This part of the procedure can be automated. Top bin averaged over variable number of bins, so some uncertainty in solution. Top bin pressure is dithered and solution with minimim rms differences at breakpoints from smooth stratification is chosen.

9. Time Series of Bottom Pressure Estimates Green points are ones edited out by hand. Red curve is running fit to remaining good points. Have trained and tested this procedure on floats that have bottom and top pressures. RMS errors are ~12 dbars.

10. Status for Correction problem FSI data • Problem has been identified. • Developed procedure to correct floats with full information. These floats have been corrected. • Completed procedures to estimate pressures for problematic floats. This procedure will still produce increased pressure error, but it should not be systematic. Increased pressure error reported in file. • These floats have been processed through estimating bottom pressure. A few problematic floats remain. • Still need to work with Josh Willis to compare this data with other data to determine that no systematic errors remain.

11. WHOI SBE Data Errors • In reviewing pressure processing, it was discovered that I had incorrectly interpeted how the bin averages for the SBE CTDs were being set. The pressures were being reported as the bottom of the bins rather than the center of the bins. • The data for all WHOI SBE equipped floats have been reprocessed.

12. Further Problems with the a subset of SBE floats • Josh Willis has identified a sub-set of the SBE floats that appear to still have a systematic error. These appear to be a batch of floats deployed in 2004.

13. Examination of these floats is still underway trying to determine the problem. • Most floats successfully reported both top and bottom pressures in engineering data. These agree with pressure that is reported in profile files. • Presently, I am stumped by this one. The lab has carefully over the checkout logs for these floats to see if there is any difference in how the CTDs were configured. We are also checking with the manufacturer of the float controllers to make sure no changes were made to this batch of floats.

14. Lessons Learned • Significantly better supervision of the manufacturing process has been implemented. A new hire has responsibility to implement better check out procedures and methodology. • A relational database in being expanded so that performance can be more easily correlated with float types and configurations. • Only SBE CTDs are now being used. • Paul Robbins started last week to help eliminate the back log in WHOI DMQC.

15. Further Lessons • Close interactions with products produced by investigators who are very familiar with the Argo floats can identify problems. The FSI problem might not have been found without Josh Willis, John Gilson, and Greg Johnson’s help. • Comparisons between subsets of floats and other careful checking of the data is invaluable.