Presentation for 2017 Argo Steering Team David Murphy Sea-Bird Scientific

Topics Kistler Pressure Sensors Review of problem Current Status Status of permission to use anti-foulant in EU Discussion of response characteristics on Argo CTDs measured in WHOI stratified tank

Kistler Pressure Sensor Failures – Summary Problem detected in Spring of 2016, traced to failure of electronic component Time of use of lot containing defective components December 2015 – May 2016 Extended burn testing initiated Screened calibration data looking for defective sensors Customers notified To date 305 sensors shipped in suspect time period 14 failures found in factory 8 failures reported from shipped CTDs 25 additional sensors returned to factory for replacement regardless of symptoms

Kistler Pressure Sensors Problems – Cause Failure is in a component with in the temperature compensation portion of the circuit Causes the Bridge Impedance to change Pressure Bridge Temperature Compensation Network Becomes Electrically Open When Failure Occurs

Kistler Pressure Sensors Problems – Cause Cont. Damage to thermistor causes the part to become open circuit Temperature cycling provokes the failure shown in X-Ray photomicrograph GAP

Kistler Pressure Sensors – Effect Calibration after failure Failure can be shown in calibration as a span shift Sensor reports higher values than is correct. Sensors are calibrated once for pressure, many times for temperature Screening of all Kistler sensors Built CTDs are temperature calibrated at least 4 times Temperature cycled from 1 to ~35 C each time Calibration of pressure temperature reviewed for artifacts Calibration before failure Calibration after failure Calibration before failure

Kistler Pressure Sensors – Deep Argo CTD Acceptance testing for 7K Kistler sensors Sensors are kept at 40 C and 3500 psia for 1000 – 1500 hours Cycled to room temperature and one atmosphere twice weekly to measure drift Screening Many temperature calibrations done (10 +) cycling 1 – 35 degrees Results examined for artifact observed in previous slide

Update on use of TBTO anti-foulant in the European Union Sea-Bird has been working with EU regulators in individual countries to allow an exception to regulations prohibiting import and use of TBTO However, agreement has been reached that Argo is outside of this convention Because deployment (or “use”) is in the deep ocean Sea-Bird and our OEM partners (Webb, NKE, etc) can ship floats or CTDs with TBTO to or within the EU because they will be exported for use Addressed directly by EU law under the following condition: End customers can do normal testing and preparation for deployment in the deep ocean because deployment qualifies as export Incidentally, this ruling applies to moored equipment as well

Alternatives to TBTO We have been researching alternatives to TBTO in cold and warm water deployments over the past 3 years To date we have not found a material that matches the efficacy of TBTO We have had success in UV method through partnering with Danaher sister companies Enclosed sample path is ideal Work in progress on optimizing the technology

Stratified Tank Results This analysis was done by Kim Martini Thanks to Breck Owens and Ray Schmitt for time in the stratified tank All variants of Argo CTDs were tested, 41,61, STS Conductivity and temperature data presented here were over sampled at 16 Hz Paper in preparation for JAOT with results for response times and cell thermal mass coefficients demonstrating results using field and lab data acquired at 1Hz

Stratified tank experiment for correction of dynamic errors 0.05 m/s 0.10 m/s 0.15 m/s Thermistor thermal mass Time lag between T and C due to sensor separation Conductivity cell thermal mass

Thermistor thermal mass Temperature profile approximates an ideal diffusive interface. dT/dt should be a symmetric Gaussian bump. With no corrections applied the first difference of T will be asymmetric because of thermal lag. Iterate through range of lags and maximize symmetry to find correction coefficient. Sharper and narrow interface which approaches the temperature in the lower layer faster (i.e. no lag) This correction is really close to the laboratory values. The correction increases slightly with profiling speed

T-C lag due to physical separation of sensors As in Johnson et al. 2009, once the thermal mass correction is applied no need to apply a T-C lag correction Thicker temperature interface because the diffusion of heat is two orders of magnitude higher than salinity. corrected T interface aligns with C

Conductivity cell thermal mass Coefficients determined by exploiting expected shape of diffusive salinity gradient at interface Salinity does not “overshoot” lower layer Minimize “rebound” due to over correction Unable to apply the same symmetry argument to conductivity as changing the cell thermal mass had little effect on salinity. Should note that here the change in salinity is so great, that it dominates conductivity rather than temperature.

Conductivity cell thermal mass Correction uses Morison et al. [1994] method of correcting cell temperature This is the correction for the 5 m/s profile which is the slowest, but shows the effect of thermal lag the most.

Conductivity cell thermal mass For SBE41cp profiling at 0.10 m/s: This is the correction for 0.1 m/s which is about the profiling speed of ARGO floats. Here alpha is the initial error, while tau_CTM is the response time. Changing alpha has a much bigger effect on the salinity profile than changing tau_CTM the lag. We find that alpha increases with increasing velocity, which may explain why the Johnson et al. 2009 correction seems way off, profiling speeds on the ITPs are 0.3 m/s

Improvements to SBE 61 Deep Argo CTD We have worked towards the development of drift history before deployment Have purchasing and inventory challenges Conductivity stability Experiments have been conducted on the WHOTS mooring. Problem is there is a 1 year interval between fielding an experiment and getting the results I need an open ocean exposed mooring site at 10 – 20 meters that can be accessed at 3 month intervals. Pressure Performance improvements will require trade offs More mass and higher volume More processing on board Or transmit more data back to shore