Procedures used by Kevin Orzech for editing, graphing, naming and working with STRATAFORM logger data August 1999 – July 2000

Procedures used by Kevin Orzech for editing, graphing, naming and working with STRATAFORM logger data August 1999 – July 2000

1. Recalculating Poorly Calibrated Logging Data
   
   
   • Some average velocity and density data of calibration-standard runs were less than or greater than 2% of known accurate values. When this occurred, logger data of cores logged closest in time to these calibration runs were considered inaccurate and in need of recalculation. This occurred if any one of the following criteria held true for the calibration data:
     
     
     1. The average velocity value for the water section of the standard fell outside of the range 1.465-1.525 km/sec.
     2. The average density value for the water section of the standard fell outside of the range 0.98-1.02 g/cc.
     3. The average density value for aluminum section of the standard fell outside of the range 2.646-2.754 g/cc.
        
        
   • A few data points at the boundaries of the water, aluminum and void sections were usually dropped from these calculations. The aluminum standard sections often showed good density values for the first half of the Al rod and low values for the second half. When this occurred the average Al value was determined from the calibration data of the first half of the Al rod.
     
     
   • Logger data from about 10% of the cores from the four cruises (W95, T96, M97, W98) were in need of recalculation. New recalculated values for the core logging data were determined by a three-step process. These files are saved as files "STEP1…", "STEP2…" and "STEP3…" in a folder titled "3STEP template to Recalibrate" located in the folder "CORRECTION OF POOR CALIB.DATA". In STEP1 average values of Gamma Counts, Diameter and Travel Time are determined for each set of poor calibration data. These averages are imported into STEP2 to calculate Mu_sediment, Mu*Rho_liner, Mu_liner, and T_delay. These values are then imported into STEP3, a template file for calculating new density and velocity values for each poorly calibrated core. The core logger data of Increments, Travel Time, Gamma Counts, and Diameter data were imported/pasted into the STEP3 file below 2 rows of data left from the previous file. The formulas in these two rows for velocity and density are dragged down over the imported core data to calculate the corrected density and velocity for the core sediments. The two rows of old data are then erased and the file is ready for editing (below).
     
     
2. Editing of Logger Data
   
   
   • All original logger data was edited using the following rules:
     
     
     1. Discarded values fell outside of the following ranges: Density 1.3-2.1 g/cc; velocity 1.45-1.8 km/sec; magnetic susceptibility (MS) 0-3x10e-5 in cgs units.
        
     2. If a density value was edited out, the velocity and magnetic susceptibility (MS) values of the same increment were also edited out regardless of their value.
     3. When the last density, velocity or MS value of the core was within the acceptable range (above) but abnormally low compared with the rest of the core data, the datum was edited out. Values successively up-core from this bad datum were edited out following the same procedure, provided the datum down-core had been already cut out. Data was removed only from the lower 1 to 8 cm of core following this procedure. These values were considered inaccurate and low due looser or less sediment at the ends of cores. This data was much more commonly edited out for piston cores than for box or Lehigh cores.
     4. Edge data of magnetic susceptibility for all Melville 1997 cores were corrected using empirical correction factors. This procedure is explained in the next section.
     5. T96 piston cores had 2 sets of logger data; one set from the ship logged in July, the other on shore logged in October. Both sets are incomplete. Logger data for the open file report graphs were chosen first from the piston cores logged on the ship and supplemented with logger data of cores logged on shore that were not previously logged on the ship. Some increments were missing from both sets of logger files.
     6. Where "flow-in" occurred in the description records for piston cores all logger data corresponding to the flow-in and deeper (to the end of the piston core) were dropped from the graphed data and from the edited data. (Although I remember dropping the flow-in data for all graphs, I did not save the adjusted spreadsheets for a few cores).
     7. The file folders labeled "EXCELS Corrected…" contain the edited logger data. This is usually the final corrected data that was brought into Kaleidagraph and plotted. However, occasionally a few more points were eliminated from the final graphs and Kaleidagraph data (KDATA) without omitting these from the corrected excel. Therefore the final data used for the plots are saved as the KDATA files.
        
        
3. Correcting Magnetic Susceptibility Data:
   
   
   • Correcting for the diameter of cores

     The MS rings are set to read a specific diameter and length of core accurately. For our two Bartington rings accurate readings are obtained when the ratio of core diameter to coil diameter is 0.65. For all other ratios, MS readings must be divided by a number obtained from a graph in the Bartington manual (attached as Graph 1). For our box cores (~81 mm sediment diameter) scanned through the large MS ring, all MS readings should be divided by 0.49 to obtain values corrected for diameter. The value 0.33 is used for piston cores. For all Bartington MS rings the coil diameter is equal to the ring diameter plus 8-mm.

   • Correcting for MS Edge Effects for Melville 1997 cores

     MS data from M97 cores were corrected for edge effects. The 160-mm MS ring emits a magnetic field that extends about 12-cm beyond the ring in both directions along the logger. Because of this, edge effects (a decline in readings at the end of cores) occur over the first and last 12-cm of core. The value at the end of the core is about 1/2 of the actual reading because only half of the sensing region contains core sediment. To correct for edge effects, the leading and trailing MS values can be multiplied by a series of correction factors (see Table 1 and 2). The values were calculated from numerous scans of a 1-cm and a 30-cm MS standard. The correction values are specific to box cores scanned with the big MS ring through our logger system and its current set up. The corrections are not equal on both sides of the MS loop. The magnetic field is skewed about one cm in the scan direction along the logger. This is probably because of the lead protection around the cesium source and other metal objects. The edge effects for W95 cores were not corrected because the edge shifts were not consistent with correction factors determined in lab experiments. MS data for T96 and W98 were discarded because the values were often negative, very erratic and not reproducible. This was probably due to the lead protection around the Cs source at the time of logging.

   • Correction of time drift of data for Wecoma 1995 cores

     The average MS values for W95 cores increased consistently over the 8 days of logging. This increase is considered artificial and probably the result of not zeroing the MS system for the entire cruise. Comparing MS data from three box cores taken from the same location during the Wecoma 95 and Melville 97 cruises revealed the latter-logged W95 values approached the accurate M97 values by the end of the cruise. This relationship was linear. All W95 values were increased by a 15 to 72% depending upon the time of logging – the correction multiple decreased from 1.70 to 1.15 over the duration of logging.

     Table 1. Correction factors used to fix edge effects of Melville
     1997 box cores scanned with the big (160 mm) MS ring.

     BOX CORES

     Leading Increment (cm)	Correction Factor	Trailing Increment (cm)	Correction Factor
     0	1.97892916	14	1.00111748
     1	1.61517528	13	1.00246208
     2	1.38941105	12	1.00425732
     3	1.24968165	11	1.00651319
     4	1.16173557	10	1.00992452
     5	1.10657346	9	1.01472858
     6	1.07056497	8	1.02214384
     7	1.04701491	7	1.0325186
     8	1.03109372	6	1.0484954
     9	1.02097822	5	1.07212338
     10	1.01380917	4	1.10907786
     11	1.00878586	3	1.16726804
     12	1.00538221	2	1.25860133
     13	1.00268132	1	1.40445969
     14	1.00088624	0	1.64099848

     Table 2. Correction factors used to correct for edge effects of
     Melville 1997 piston cores scanned with the big (160mm) MS ring.

     PISTON CORES

     Leading Increment (cm)	Correction Factor	Trailing Increment (cm)	Correction Factor
     0	2.02703011	14	1.00063376
     1	1.65424799	13	1.00207075
     2	1.4175005	12	1.00367064
     3	1.2683884	11	1.00592291
     4	1.17387379	10	1.00915285
     5	1.11362136	9	1.0140492
     6	1.07487148	8	1.02098089
     7	1.0495085	7	1.03122349
     8	1.03240663	6	1.04741925
     9	1.02098253	5	1.07158883
     10	1.01339718	4	1.10833509
     11	1.00834801	3	1.16518752
     12	1.00463372	2	1.25598482
     13	1.00255056	1	1.39674192
     14	1.00095424	0	1.62020008

4. Graphing Core Data
   
   
   • Once core data was edited, each Excel file was opened in Kaleidagraph. A template velocity, density and magnetic susceptibility graph were created. Each set of core data was graphed onto these templates using Gallery/Template commands. A Master template layout file (titled –aMasterLayout) was opened so that the individual graphs would appear on the 3 box template. These layouts are saved as PICT files. The PICT files were opened in Adobe Photoshop, saved as jpgs and imported into an Adobe Illustrator header template. Next, titles, core I.D. and borders were added to the layout for each core.
     
     
5. File Management
   
   
   • M97 Corrected Excels: No "EXCELS Corrected…" folders or files for Melville 97 BOX Cores exist. This is because edited and mostly corrected data was already saved as Kaleidagraph data in the original Homa Lee Strataform Master files. This made creating corrected-excels unnecessary.
     
     
   • Original logger file names saved at cruise time are usually used in Kevin’s 1999 files as the name of the files or folders for each core. Original core names were only changed when there was a known error in the name of the original logger file. These naming errors are listed in the "INVENTORY of cores" files.
     
     
   • Naming of files for graphs: Abbreviations of V, D, and M at the end of the file name indicate Velocity, Density and Magnetic Susceptibility respectively. For the Piston core graphs that are 200-cm increments, the numbers 2, 4, 6, and 8 are used after the letter in the saved file name to indicate the highest depth shown on the graph (2 for 200cm, 4 for 400cm, etc.). For example, the file name G110 Pist.-D6 is the name of the file for the density graph for the increment 400-600 cm in depth for core G110 Pist. The files with names that have no number following the V, D or M for piston cores contain graphs from 0-600 cm. For example, G110 Pist.-V is the velocity graph for the 0-600 cm increment.

Back to CORE DATA