---TITLE: Borehole Optical Stratigraphy measurements through 4 full years at Summit, Greenland ---AUTHOR(S): Edwin D. Waddington Professor, Dept of Earth and Space Sciences Box 351310 University of Washington Seattle WA 98195-1310 USA TEL: (206) 543-4585 FAX: (206) 543-0489 Bob Hawley Assistant Professor, Department of Earth Sciences Dartmouth College HB 6105 Fairchild Hall Hanover, NH 03755 Voice: (603) 646-1425 Fax: (603) 646-3922 email: robert.l.hawley@dartmouth.edu web: http://www.dartmouth.edu/~ice (PLEASE CONTACT HAWLEY FOR QUESTIONS) ---FUNDING SOURCE AND GRANT NUMBER: NSF-OPP 0352584 "A Unique Opportunity for In-Situ Measurement of Seasonally-Varying Firn Densification at Summit, Greenland." ---DATA SET OVERVIEW: This data set was produced from the NSF OPP grant listed above. In the project, we made measurements of Borehole Optical Stratigraphy profiles on a monthly basis at Summit, Greenland (72N, 38W, 3200 m.a.s.l.) , through the summer and winter from 2004 through summer 2008. At our site near Summit, we established 4 boreholes roughly 50 meters from one another in a square. The boreholes were named after the first science technicians to work the project: Katie, Meg, Toby, and Phillips. ---INSTRUMENT DESCRIPTION: Borehole Optical Stratigraphy (BOS) is a method for recording the visual stratigraphy in a snow/firn borhole, generating a profile of brightness versus depth. The BOS instrument is a downward-looking video camera that is lowered down a borehole. Since the lens is wide-angle, the view includes the walls of the borehole. In post-processing, we sample an annulus of pixels around the circumference of the borehole wall, and take the mean pixel value as the brightness at the depth of the annulus. The camera captures frames at a rate of 29.97 frames per second. The depth counter measurement wheel has a resolution of 0.003 m. At our standard loging speed, we collect a frame every 0.005 m. For Further information, see Hawley and Waddington 2011, Journal Of Glaciology, Instruments and Methods: In-situ measurements of firn compaction profiles using Borehole Optical Stratigraphy ---DATA COLLECTION and PROCESSING: Each month, the science technicians took the BOS instrument from the station to the site (about 1 km away), and made BOS profiles of each of the holes. Generally, both a downward and upward log were collected. Occasionally, if videotape ran short, only a down or up log was collected. Since this was a long-duration (several hours) activity away from the safety of the station, the technicians waited for good weather to run these logs; thus the interval is "nominally" monthly. In addition, particularly early on there were equipment failures that could not be overcome quickly, so there are several long gaps in coverage. As described above, our in-house post-processing software "boils" the raw video down to a single brightness value for each frame. The depth of the frame is read from the image itself using optical characer recognition. The result is a log of brightness vs Depth. The in-house software was written in Objective-C using the cocoa framework on a mac OS operating system, and can be made available to investigators wishing to either see or improve the code. Contact Hawley (contact info above) for details. ---DATA FORMAT: The data are in ASCII test files. FILENAMES: All files are named with the convention Summit___.txt where is either katie, meg, toby, or phillips, is the date of the log in MMDDYY format, is the numeric sequence of logs on that particular day (for most files, this is 1), and is either d or u (for down or up, respectively). So an example filename would be Summit_meg_111806_1d.txt, the first downward log of the "meg" borehole on 18 Nov 2006. FILE FORMAT: The ASCII files each have 37 header lines, all either starting with a '#' or a blank line, so a plotting package like GNUplot will be able to work with the files immediately. After the 37 header lines, the data comes in 6 columns- Depth, Brightness, Timecode Hours, Timecode Minutes, Timecode Seconds, and Timecode Frames. The Timecode columns refer to the exact frame on the videotape, so that any data point can be traced back to its original frame. Raw video files corresponding to these logs can be obtained by contacting Hawley. ---DATA REMARKS: The only real issue with the processing methodology described above is that the Optical Character Recognition software is not perfect in reading the depth. Therefore, there are sometimes sudden spikes in the depth series, which can usually be corrected by incrementing a digit in one place. Alternatively the point can be removed, as the data series are quite large, and easily characerize the fluctuations of bright and dark in the borehole walls even at a lower resolution. These files as noted above can be used as-is with many unix utilities for plotting, such as GNUplot, or the '#' comment character can be replaced with a '%' character for matlab compatibility by using the unix 'tr' command. ---REFERENCES: Hawley, R.L., E.D. Waddington, R.B. Alley, and K.C. Taylor. 2003. Annual layers in polar firn detected by Borehole Optical Stratigraphy. Geophysical Research Letters 30(15), doi:10.1029/2003GL017675 Hawley, R.L., E.M. Morris. 2006. Borehole Optical Stratigraphy and neutron-scattering density measurements at Summit, Greenland. Journal of Glaciology. 52(179), 491-496. Hawley, R.L., E.M. Morris, and J. R. McConnell. 2008. Rapid techniques for determining annual accumulation applied at Summit, Greenland. Journal of Glaciology. 54(188), 839-846. Hawley, R.L., E.D. Waddington. In-Situ Measurements of Firn Compaction Profiles Using Borehole Optical Stratigraphy. Submitted to Journal of Glaciology. Status: Accepted, awaiting galley proofs. L M Kehrl, R L Hawley. 2010. A quantitative record of seasonally-varying densification rates at Summit, Greenland, from 2004-2008, using Borehole Optical Stratigraphy. EOS, Trans. AGU, fall meeting supplement, Abstract C33D-0570 Hawley, R.L., E. M. Morris, and O. Brant. 2008. High-Resolution borehole/core techniques for snow and firn stratigraphy. EOS, Trans. AGU, fall meeting supplement, Abstract C21C-557. Hawley, R. L. 2007. (Invited) In-Situ measurements of Firn Compaction using Borehole Optical Stratigraphy. Workshop on the Micrrostructure and Properties of Firn, Dartmouth College, Hanover NH, 10-11 March, 2008. Hawley, R.L. and E.D. Waddington. 2006. In-situ measurements of temporal and spatial variability in firn compaction rates at Summit, Greenland using Borehole Optical Stratigraphy. EOS, Trans. AGU, fall meeting supplement, Abstract C41A-229. Hawley, R.L., E. M. Morris, and E.D. Waddington. 2004. Borehole Optical Stratigraphy and Neutron Scattering Density Measurements at Summit, Greenland. EOS, Trans. AGU, fall meeting supplement, Abstract C31B-0323. Hawley, R.L. and E.M. Morris. 2004. How snow/firn density affects scattering of visible light: Current events in Borehole Optical Stratigraphy. Northwest Glaciologists Meeting, November 2004. Hawley, R.L., E.D. Waddington, J.R. McConnell, and D.P. Winebrenner. 2003. Lightweight shallow ice coring and borehole logging can provide decadal- to millennial-scale indicators of climate change around the arctic basin. SEARCH Open Science Meeting, Seattle, Washington. Hawley, R.L., and E.D. Waddington. 2002. Borehole Optical Stratigraphy: Investigating Paleoclimate through the optical properties of ice. EOS, Trans. AGU, 83(47) fall meeting supplement, Abstract C62A-0907.