Documentation for Digital Images of Thin Sections from Siple Dome, Version 1

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Detailed Data Description

The images in these files are low-resolution jpeg images of thin sections from the drilling season at Siple Dome during the 1997/1998 field season.  The images were acquired on both the SDM-A or main 13.2 cm core and on the hot water core recovered by Hermann Englehardt.  Files prefixed with the letters SDMA- followed by the depth are images from the main core; files prefixed with the letters HE- followed by the depth are images from the 2" hot water core. At this time, no depth overlap exists between the two cores.  The core depth intervals are annotated onto the images.  Images annotated with a range of depths are vertical thin sections.  These images are also annotated with an "up" arrow.  Images annotated with a single depth are horizontal thin sections.  With one exception, all images shown here were recorded in cross-polarized light.

File Size and Naming Convention

In order to keep the image files at a size smaller than 1Mb, the images presented here have been re-written at a resolution of 72 dpi.  Archived images (those actually used for image processing) are recorded at 275 dpi and are generally 5 to 9 Mb in size. Two examples are provided for direct comparison of low- and high-resolution images.  These are:
HE-299.40o...................... a 72 dpi image of a bubble section from 299.40 meters<BR>
HE-299.HRo...................... the 275 dpi archived image of the same scene
SDMA-119.229................a 72 dpi image of a thin section in crossed polars from 119.229 meters<BR>
SDMA-119.HR...................the 275 dpi image of the same scene

In both cases, side-by-side comparison of the two images at 72 (LR) and 275 (HR) dpi will indicate how much more information is contained in the high resolution image.  In the case of the bubble section, individual bubbles in the annular zone around the outside of the core in which bubbles have been mobilized by the drilling process is clearly visible in the high-resolution image.  This part of the HR image clearly shows distorted, enlarged, and combined bubbles whereas bubbles in the central part of the image are unambiguously spherical and undisturbed.  This level of detail is not resolvable in the LR image.  The same can be said for features in the image of the thin section from the SDMA core.

As the statistical information on the grain size distributions from these images becomes available, additional annotation files containing this information will be added to this site.  Judging from the images recorded from the hot water core, it seems likely that the grain size statistics will cease to be meaningful somewhere between 200 to 300 meters.  Bubble statistics, however, should remain valid throughout the length of the core.

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Contacts and Acknowledgments

Joan Fitzpatrick and Elizabeth Rogers
U.S. Geological Survey
U.S. National Ice Core Laborator