Borehole Optical Stratigraphy Modeling, Antarctica

Summary

This data set consists of scripts and code designed for modeling the properties of boreholes in polar ice sheets, under a range of variations in the borehole geometry, firn layering, and camera pointing and position. The data set contains two folders. One includes two perl scripts and a piece of C code, along with directions for setting up and running a Monte Carlo model of photons traveling to and from a borehole in the firn. The second includes scripts for generating ray-tracing input files to be used with the POV-Ray package (a standard, free raytracing package) to generate simulated borehole video frames based on the results of the Monte Carlo model. The data set also contains example input and output files for the Monte Carlo model. The project was conducted between February 2005 and April 2010.

The codes to run the models are available via FTP, in Perlscript (.pl) and C code.

Citing These Data

The following example shows how to cite the use of this data set in a publication. List the principal investigators, year of data set release, data set title, publisher: NSIDC, and digital media.

Smith, B., B. Hawley, T. J. Fudge, and E. Waddington. 2010. Borehole Optical Stratigraphy Modeling, Antarctica. Boulder, Colorado, USA: National Snow and Ice Data Center. http://dx.doi.org/10.7265/N5H70CR5.

Overview Table

Category	Description
Data format	Perlscript (.pl) and C code
Spatial coverage and resolution	Antarctica: Southernmost Latitude: 90°S Northernmost Latitude: 60°S Westernmost Longitude: 180°W Easternmost Longitude: 180°E
Temporal coverage and resolution	The project was conducted between February 2005 and April 2010.
Tools for accessing data	Data can be viewed using the Persistence of Vision Raytracer (POV-Ray), a ray-tracing program, freely available at http://www.povray.org/.
File naming convention	generate_scattering_parameters.pl grain_params mc_borehole.c
File size	Files range in size from 4 KB to 164 KB.
Parameter(s)	Borehole Wall Reflectance Measured Brightness Estimation
Procedures for obtaining data	The scripts in this data set are available via FTP.

Table of Contents

1. Contacts and Acknowledgments
2. Detailed Data Description
3. Data Access and Tools
4. Data Acquisition and Processing
5. References and Related Publications
6. Document Information

1. Contacts and Acknowledgments

Investigator(s)

Dr. Ben Smith
University of Washington
Department of Earth and Space Sciences
Seattle, Washington, USA

Dr. Bob Hawley
University of Washington
Department of Earth and Space Sciences
Seattle, Washington, USA

Dr. T. J. Fudge
University of Washington
Department of Earth and Space Sciences
Johnson Hall 4000 15th Avenue NE
Seattle, Washington, USA

Dr. Edwin Waddington
University of Washington
Department of Earth and Space Sciences
Box 351310
Seattle, Washington, USA

Technical Contact

Acknowledgements

This research was supported by NSF OPP Grant Number 0335330.

2. Detailed Data Description

Format

Two readme files, README_borehole_mc and README_Borehole_raytrace, provide detailed information required for running the two programs.

File and Directory Structure

Data are available on the FTP site in the ftp://sidads.colorado.edu/pub/DATASETS/AGDC/nsidc0468_waddington_V01 directory. Within this directory, there are two subdirectories as described in Table 1.

Table 1. Directory Description

Directory	Description
borehole_montecarlo_model	The files in this folder allow Monte Carlo modeling of light transport in a borehole in firn. For more information, see the README_borehole_mc file.
borehole_raytrace_simulation	The programs in this folder allow modeling of borehole optical stratigraphy measurements, undera range of variations in the borehole geometery, firn layering, and camera pointing and position. For more information see the README_Borehole_raytrace file.

Program descriptions

Borehole Raytrace Simulation

Programs in the borehole_raytrace_simulation folder are described in Table 2. These programs generate 16 bit Portable Network Graphics (PNG) files that may be read with standard image processing software. This folder also includes five POV-Ray (.pov) files: these serve as template files to generate valid inputs for the POV-Ray program.

Additional information for using the raytrace files is provided in the README_Borehole_raytrace file.

Table 2. Description of Programs for Running the Borehole Raytrace Simulation

Name	Description
scan_3layer	This program generates a set of images as the camera moves past a layer of contrasting reflectance in an otherwise uniform firn pack.
scan_scar	This program generates a set of images as the camera moves past an annular scar in the borehole wall of specified radius.
scan_bump	This program generates a set of images as the camera moves past an annular bump on the borehole wall of specified radius.
run_point_error	This program generates a set of images as the camera and its light source rotate away from the down-borehole axis.
run_ctr_error	This program generates a set of images as the camera and its light source move laterally away from the borehole center.

 

Monte Carlo Modeling

Programs for the borehole_montecarlo_model folder are described in Table 3. These programs allow Monte Carlo modeling of light transport in a borehole in firn. They simulate the path of packets of photons from the borehole wall, through the firn, and back to the borehole wall. This folder also contains example output files: grain_summary_1 and bubble_summary_1, which are based on example parameter files grain_params and bubble_params.

For detailed information on running the Monte Carlo model, see the README_borehole_mc file.

Table 3. Description of Programs for Running the Monte Carlo Model

Name	Description
mc_borehole.c	This C program tracks the photons and stores their output locations in a file
read_mc_results.pl	This Perlscript program sums the contributiosn ot the total reflectance to give reflectance values.
generate_scattering_parameters.pl	This Perlscript program generates the single-scattering parameters of firn, based on different density and grain or bubble size parameters.

File Size

Files in this data set range in size from 4 KB to 106 KB.

Spatial Coverage

Antarctica:

Southernmost Latitude: 90°S
Northernmost Latitude: 60°S
Westernmost Longitude: 180°W
Easternmost Longitude: 180°E

Temporal Coverage

The project was conducted between February 2005 and April 2010.

Parameter or Variable

This data set allows the modeling of optical properties of boreholes in polar ice sheets, under a range of variations in the borehole geometry, firn layering, and camera pointing and position.

3. Data Access and Tools

Data Access

The data set is available via FTP.

Volume

Total volume of the files is approximately 225 KB.

Software and Tools

Data can be viewed using the Persistence of Vision Raytracer (POV-Ray), a ray-tracing software, freely available at http://www.povray.org/.

Related Data Collections

• Optical Logging for Dust and Microbes in Boreholes in Glacial Ice (NSIDC-0403)

4. References and Related Publications

Fudge, T. J. and B. Smith. 2010. Light Propagation in Firn: Application to Borehole Video.Journal of Glaciology.Vol. 56, No. 198, pp. 614-624.

Table 4 lists related documents that are available on the NSIDC Web site.

Table 4. Related Documents

Document	Description	URL
Antarctic Glaciological Data Center	Data Center Web site	http://nsidc.org/agdc/
Persistence of Vision Raytracer	POV-Ray Software Web site	http://www.povray.org

5. Document Information

Acronyms

The acronyms used in this document are listed in Table 5.

Table 5. Acronyms and Abbreviations

Acronym	Description
FTP	File Transfer Protocol
NSIDC	National Snow and Ice Data Center
POV-Ray	Persistence of Vision Raytracer
URL	Uniform Resource Locator

Document Creation Date

10 June 2010

Document URL

http://nsidc.org/data/data/docs/agdc/nsidc0468_smith/index.html