Rohardt, Gerd

Electronic Publication Information Center

General processing report of continuousthermosalinograph oceanographyfrom RV POLARSTERN cruises: PS110, PS111, PS113, PS112(20.12.2017 - 10.06.2018)Contents1 Introduction 12 Workflow 13 Sensor Details 24 Campaign Details 35 Processing results 36 Appendix 10Contact:Gerd RohardtAlfred-Wegener-InstituteAm Handelshafen 12, D-27570 Bremerhaven, GERMANYMail: info@awi.deProcessing Agency:FIELAXGesellschaft für wissenschaftliche Datenverarbeitung mbHSchleusenstr. 14, D-27568 Bremerhaven, GERMANYTel: +49 (0) 471 30015 0Fax: +49 (0) 471 30015 22Mail: info@fielax.deRef.: Polarstern_PS110toPS113_TSG.pdf Vers.: 1 Date: 2018/10/24 Status: final11 IntroductionThis report describes the processing of raw data acquired by the thermosalinographs on boardRV Polarstern during the expeditions PS110, PS111, PS113, PS112 to receive cleaned up andcorrected salinity data.2 WorkflowThe different steps of processing are visualized in Figure 1. Two thermosalinographs (SBE21, Sea-Bird GmbH) are installed in the same tank in the keel of RV Polarstern for simultaneous measure-ments of temperature and conductivity. Both sensors are equipped with an internal and an exter-nal temperature sensor (SBE38, Sea-Bird GmbH). The external temperature sensors are installedclose to the sea water inlet. After the cruise, the measured conductivity and temperature data ofboth sensors are extracted in hexadecimal form as 1 sec values from the DAVIS SHIP database(https://dship.awi.de). Data of every cruise are processed separately. First, the hexadecimal sen-tences are converted to raw data according to the instruction given by the manufacturer and timeshifts between the sensors of max. 1sec are aligned. Afterwards the raw data are converted totemperature and conductivity values using the calibration coefficients from the calibration before de-ployment. However, data can only be finally processed after replacement and renewed calibrationbecause correction values for the sensor drift can only be obtained by the post cruise calibration.The sensor drift is treated as a linear function during deployment and correction factors are calcu-lated and applied for every day of deployment. See chapter 5 for further details on conductivity slopeand temperature offset corrections. From the obtained internal temperature and conductivity datathe salinity can be calculated according to the instructions from the Practical Salinity Scale PSS-78.Afterwards 10-min-means are calculated with outliers outside a 2-times standard deviation rangebeing removed from the calculations of the 10-min-means. Statistics about the differences betweenboth sensors are calculated and referred to in this report. The 10-min-means are visually inspectedand - if necessary - manually despiked. Finally, the positions from the corrected mastertracks areassigned as spot-positions for the corresponding times. A speed filter of 0.5 knots minimum speedis applied to avoid redundant data.Measurements of salinity with an OPTIMARE Precision Salinomter conducted during the cruisesare represented for comparison in the Appendix of this report. Drift corrections using bottle sampleswere not attempted.Both sensors are processed together and treated as equal. If there are no further objections, datafrom the sensor with the slope correction closer to 1.0 are prepared for the upload in PANGAEA.Also see the single detailled processing reports for each cruise.Page 1 of 10Figure 1: Workflow of Salinity data processing3 Sensor DetailsTSG1 TSG2Serial number SBE21-3203 SBE21-3354Installation 2017-12-20 2017-12-20Deinstallation 2018-06-15 2018-06-15Days installed 177 177External temperature sensor SBE38-136 SBE38-154Calibration before installation 2016-05-31 2016-05-31Calibration after installation 2018-07-12 2018-07-12Temperature offset 0.001100 0.000400Conductivity slope 0.9999727 0.9998394Page 2 of 104 Campaign DetailsData of following cruises were processed with the above mentioned sensors and calibration data.(Data extracted from https://www.pangaea.de/expedition)Campaign Start Stop From To DaysPS110 2017-12-20 2018-01-15 Bremerhaven Cape Town 26PS111 2018-01-19 2018-03-14 Cape Town Punta Arenas 54PS112 2018-03-17 2018-05-06 Punta Arenas Punta Arenas 50PS113 2018-05-08 2018-06-10 Punta Arenas Bremerhaven 33Following table shows the data details of the cruises considered in this report. The number of TSG1and TSG2 messages is the number of data downloaded from DSHIP for the individual cruises.The number of result messages is the number of data remaining after calculation of 10min means,manual flagging and speed flagging.Campaign first message last message TSG1messagesTSG2messagesResultmessagesPS110 2017-12-25T15:00:02 2018-01-09T15:08:14 314704 314628 2080PS111 2018-01-19T13:08:46 2018-03-12T17:47:57 1121201 1121203 5752PS112 2018-03-21T00:39:32 2018-05-03T02:47:40 927714 927713 4629PS113 2018-05-10T17:17:04 2018-06-09T13:08:18 635222 635214 41075 Processing resultsCorrection for conductivity and temperature driftCorrection for conductivity and temperature drift of the sensors was accomplished following theinstructions by SEA-BIRD Application Note 31 (Revision June 2016). Conductivity slope and tem-perature offset values were calculated for each day of deployment of the TSG1 and TSG2 sensorsusing following equations.Correction of conductivity data: islope = 1.0 + (b / n) [(1 / postslope) - 1.0]b = number of days between begin of deployment and day of measurementn = number of days between deployment and deinstallationpostslope = slope from post-cruise calibration sheetcorrected conductivity = islope * computed conductivityCorrection of temperature data: offset = b * (residual / n)b = number of days between begin of deployment and day of measurementn = number of days between deployment and deinstallationresidual = residual from post-cruise calibration sheetcorrected temperature = offset + computed temperaturePage 3 of 10Data for the correction values are given in the following two table for TSG1 and TSG2 respectively.The deployed days columns indicate the number of the first and the last day of each cruise withinthe deployment interval of TSG1 (177 days) and TSG2 (177 days). The start and stop values in thecolumns conductivity slope and temperature offset show the correction values for the first and lastday of the cruise.TSG1 deployed days Conductivity slope Temperature offsetCruise first last start stop start stopPS110 5 20 1.00000077 1.00000308 0.00003107 0.00012429PS111 30 82 1.00000463 1.00001265 0.00018644 0.00050960PS112 91 134 1.00001404 1.00002067 0.00056554 0.00083277PS113 141 171 1.00002175 1.00002638 0.00087627 0.00106271TSG2 deployed days Conductivity slope Temperature offsetCruise first last start stop start stopPS110 5 20 1.00000454 1.00001815 0.00001130 0.00004520PS111 30 82 1.00002722 1.00007441 0.00006780 0.00018531PS112 91 134 1.00008258 1.00012160 0.00020565 0.00030282PS113 141 171 1.00012796 1.00015518 0.00031864 0.00038644Measured dataData from the time range considered are show in Figures 2 and 4. Salinometer measurementsof bottle samples are depicted in the plots of the salinity of TSG1 and TSG2 (also see Appendix:Measurements of salinity with the OPTIMARE salinometer). Also given are plots of the standarddeviations of the 10min means for every parameter (Figures 3 and 5).Page 4 of 10Figure 2: 10min means of data from TSG1Figure 3: Standard deviations of 10min means of data from TSG1Page 5 of 10Figure 4: 10min means of data from TSG2Figure 5: Standard deviations of 10min means of data from TSG2Page 6 of 10Differences between TSG1 and TSG2Differences between the two thermosalinographs are show in Figure 6. Only data within 2-timesstandard deviation are depicted. For the comparison of the spot values only data with a maximumtime difference of 1sec between TSG1 und TSG2 are considered.Parameter Spot measurements 10min meansInternal temperature [◦C] 0.00008 ± 0.01068 0.00013 ± 0.00468Conductivity [mS/cm] -0.00403 ± 0.04352 -0.00377 ± 0.02536External temperature [◦C] 0.00080 ± 0.00278 0.00079 ± 0.00076Salinity [PSU] -0.00478 ± 0.05374 -0.00426 ± 0.03523Figure 6: Differences between 10min means TSG1 - TSG2Post calibration values show a higher temperature offset (0.001100) but less slope correction (0.9999727)for TSG1 compared to TSG2 (0.000400 and 0.9998394). Post calibration values therefore give noclear indication for a more consistent behaviour of TSG1 or TSG2. The histogramm (Figure 7) forthe comparison of TSG1 and TSG2 internal temperatures indicate bimodal behaviour and there isa trend to be seen in the variation of the internal temperatures in Figure 6 from negative (TSG1 <TSG2) to positive (TSG1 > TSG2) differences. This change in behaviour may also explain the highertemperature offset for TSG1 given by the post calibration. Therefore the TSG2 (SBE21-3354) dataof the cruises dealed with in this report are uploaded to PANGAEA.Page 7 of 10Figure 7: Histogramm of differences TSG1 - TSG2Differences between internal and external temperature of TSG1 and TSG2 sensorsTemperature differences between the internal and the external temperature sensors have to be smallunder normal circulation conditions. Means and standard deviations for the temperature differencesare given in the following table and are shown in Figure 8.TSG1 (mean ± std. dev.) TSG2 (mean ± std. dev.)Spot values 0.05373 ± 0.06230◦C 0.05411 ± 0.06527◦C10-min means 0.05450 ± 0.05645◦C 0.05516 ± 0.05683◦CPage 8 of 10Figure 8: Temperature differences between internal and external temperature sensors of 10minmeansResult fileResult files are given for each cruise individually. The result file is a plain text (tab-delimited values)file named *Cruise*_surf_oce.tab with one data row in 10-min interval. The water depth in the resultfile is the depth of the water inlet for the thermosalinographs. Further information about process-ing of the data of each cruise can be obtained from following cruise reports: PS110_TSG_nav.pdf,PS111_TSG_nav.pdf, PS112_TSG_nav.pdf, PS113_TSG_nav.pdf .Column separator Tabulator "\t"Column 1 Date and time expressed according to ISO 8601Column 2 Latitude in decimal format, unit degreeColumn 3 Longitude in decimal format, unit degreeColumn 4 Water depth, unit metreColumn 5 Temperature, unit degree CelsiusColumn 6 Salinity PSUPage 9 of 106 AppendixMeasurements of salinity with the OPTIMARE salinometerBottle samples of sea water were continously taken during the cruises. Those samples were mea-sured with the Optimare Salinometer onboard after temperature equalization. The bottle data aregiven here for reference. Drift correction using the bottle data was not applied.Time of sampling OPS Salinity [PSU]2018-01-01T13:06:30 35.51162018-01-03T09:51:00 34.68912018-01-06T08:41:00 36.31122018-01-23T09:31:00 33.74692018-01-26T09:43:30 34.07432018-02-03T08:58:00 33.14172018-02-08T11:06:30 33.86832018-02-13T08:48:00 34.31582018-02-17T14:57:00 34.00612018-02-22T17:28:00 33.95002018-03-21T17:03:30 33.64292018-03-21T17:05:00 33.64022018-04-01T17:03:00 33.96952018-04-01T17:04:00 33.98202018-04-10T16:54:30 33.67612018-04-14T12:08:00 34.14102018-04-29T17:51:30 34.18302018-04-29T17:53:00 34.18732018-05-02T19:30:30 33.67722018-05-02T19:31:30 33.6763Page 10 of 10

General processing report of continuous thermosalinograph oceanography from RV POLARSTERN cruises: PS110, PS111, PS113, PS112 (20.12.2017 - 10.06.2018)

https://epic.awi.de/id/eprint/48248/1/TSG_Data_PS100toPS113.pdf

General processing report of continuous thermosalinograph oceanography from RV POLARSTERN cruises: PS110, PS111, PS113, PS112 (20.12.2017 - 10.06.2018)

Abstract

Similar works

Full text

Available Versions

Electronic Publication Information Center