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GISP2-D Temperature

Authors
Publisher
PANGAEA
Publication Date
Identifiers
DOI: 10.1594/pangaea.55517
Keywords
  • Drilling
  • Gisp
  • Gisp2-D
  • Greenland Ice Core Projects
  • Grip/Gisp/Ngrip
  • Sampling/Drilling Ice
  • Temperature
  • Ice/Snow

Abstract

DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY Deconvolution of Continuous Borehole Temperature Logs: Example from the Greenland GISP2 Icecore Hole by R.W. Saltus1 and G.D. Clow2 Open-File Report 94-254 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards. Use of brand names is for descriptive purposes and does not constitute endorsement by the U.S. Geological Survey. 1994 1 U.S. Geological Survey, Denver, Colorado 2 U.S. Geological Survey, Menlo Park, California Deconvolution of continuous borehole temperature logs 1 Abstract Measurements of borehole temperatures obtained from a continuously moving ther- mistor probe are a convolution of the actual borehole temperatures with the finite thermal response function of the temperature measurement system. To estimate actual tempera- tures from the measurements requires deconvolution, an operation that can magnify noise. We discuss the use of optimal (Wiener) filtering for noise reduction, followed by an exact deconvolution using serial division. We test the method using synthetic data and then apply it to measurements made in May 1992 at the GISP2 icecore hole in Greenland. After optimal filtering of the 1992 GISP2 measurements, the data power spectrum falls to 10% of maximum as frequencies drop below 0.004 Hz (periods of 250 seconds, equivalent to about 20 m in depth at a logging velocity of about 7.4 cm/s). The noise at higher frequencies (shorter wavelengths) is probably a result of noise caused by the mechanical slip-ring that provides electrical connection to the thermister cable. 2 Salt us and Clow Contents 1 INTRODUCTION 4 2 TEMPERATURE MEASUREMENT 4 2.1 Response time of thermistor probe ...................... 5 3 TEMPERATURE DECONVOLUTION 6 3.1 Theory ...................................... 6 3.2 Noise removal .................................. 7 3.3 Discrete deconvolution by division ...................... 8 3.4 Implications of d

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