Data Set ID: 
SNEX17_GPR

SnowEx17 Ground Penetrating Radar, Version 2

This data set contains the results of a ground penetrating radar survey conducted at Grand Mesa, Colorado. Data include the two-way travel time, calculated snow depth, and calculated snow water equivalent. Data were collected between 08 February 2017 and 25 February 2017 as part of the 2017 SnowEx campaign.

The unprocessed, raw data are also archived at NSIDC (DOI: 10.5067/ZPOLBRHVWG5V).

This is the most recent version of these data.

Version Summary: 

Updated the radar velocity used to convert radar travel time to snow depth; updated the assumed density used to calculate snow water equivalent, which is now provided in cm rather than mm; updated data files to no longer include column 12 (Transect #); and removed Week 3 data (21 February to 23 February 2017).

Week 3 data (21 February to 25 February) was later added as part of a minor version update.

STANDARD Level of Service

Data: Data integrity and usability verified

Documentation: Key metadata and user guide available

User Support: Assistance with data access and usage; guidance on use of data in tools

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Parameter(s):
  • SNOW/ICE > SNOW DEPTH
  • SNOW/ICE > SNOW WATER EQUIVALENT
Data Format(s):
  • Comma-Separated Values (.csv)
Spatial Coverage:
N: 39.11115, 
S: 38.9935, 
E: -107.85785, 
W: -108.22367
Platform(s):GROUND-BASED OBSERVATIONS
Spatial Resolution:Not applicableSensor(s):GPR
Temporal Coverage:
  • 8 February 2017 to 25 February 2017
Version(s):V2
Temporal ResolutionNot applicableMetadata XML:View Metadata Record
Data Contributor(s):Webb, R., D. McGrath, K. Hale, and N. P. Molotch.

Geographic Coverage

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As a condition of using these data, you must cite the use of this data set using the following citation. For more information, see our Use and Copyright Web page.

Webb, R., D. McGrath, K. Hale, and N. P. Molotch. 2019. SnowEx17 Ground Penetrating Radar, Version 2. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/G21LGCNLFSC5. [Date Accessed].
Created: 
20 July 2018
Last modified: 
18 February 2020

Data Description

Parameters

Table 1. Parameters 
Parameter Description Units
Two-way travel time Time between the transmission of the ground penetrating radar (GPR) signal and the reflection of that signal back to the transmitting device from the base of the snowpack nanoseconds, ns
Snow depth Calculated from two-way travel time, assuming a velocity of 0.235 m/ns meters, m
Snow water equivalent (SWE) Calculated from snow depth, assuming a density of 325 kg/m3 centimeters, cm

File Information

Format

Data are provided in Comma-Separated Value (.csv) format. 

Extensible Markup Language (.xml) files with associated metadata are also provided. 

File Contents

Each plain text file includes 12 columns of data. Column titles and descriptions are shown below:

  1. COLLECTION: Collection information in the format of GPR_[LineNumber]_[date]:
    Table 2. Column Definitions
    Variable Description
    GPR Short for Ground Penetrating Radar
    [LineNumber] Value associated with the raw file
    [date] Date in mmddyy format
  1. TRACE: Trace number corresponding to the raw data files; each trace is the individual recording of a received signal from the GPR pulse
  2. LONG: Longitude
  3. LAT: Latitude
  4. ELEV: Elevation, in meters (m)
  5. TWTT: Two-way travel time, in nanoseconds (ns), of the interpreted ground surface reflection
  6. THICKNESS: Snow depth, in meters (m)
  7. SWE: Snow water equivalent (SWE), in millimeters (cm)
  8. X: Easting, calculated from the recorded longitude
  9. Y: Northing, calculated form the recorded latitude
  10. UTM_ZONE: UTM grid zone for the calculated easting and northing

More details about column definitions can be found in the SnowEx17 Ground Penetrating Radar Column Definitions document.

Naming Convention

The data files are named:
SnowEx17_GPR_Version2_Week1.csv
SnowEx17_GPR_Version2_Week2.csv
SnowEx17_GPR_Version2_Week3.csv

File Size

The data files are between 50 and 85 MB.

Spatial Information

Coverage

Data were collected in the Grand Mesa, Colorado study area:

Northernmost Latitude: 39.11115° N
Southernmost Latitude: 38.99350° N
Easternmost Longitude: 107.85785° W

Westernmost Longitude: 108.22367° W

Resolution

Point measurements

Geolocation

All data falls within the project coordinate system WGS 84 / UTM Zone 12 North, details of which are presented in Table 3. 

Table 3. Geolocation Details
Geographic coordinate system WGS 84
Projected coordinate system WGS 84 / UTM Zone 12 North
Longitude of true origin -111
Latitude of true origin 0
Scale factor at longitude of true origin 0.9996
Datum WGS 1984
Ellipsoid/spheroid WGS 84
Units meters
False easting 500000
False northing 0
EPSG code 32612
PROJ4 string +proj=utm +zone=12 +datum=WGS84 +units=m +no_Defs
Reference https://epsg.io/32612 

The plain text files indicate that all geographic coordinates fall within UTM Grid Zone 12S. This designation corresponds to the intersection of longitudinal projection zone 12 and latitudinal projection zone S, as shown in Figure 1. Users should be aware that UTM Grid Zone 12S falls within the projected coordinate system WGS 84 / UTM Zone 12 North. 
Figure 1: UTM Grid Zones

Temporal Information

Coverage

Data collection occurred over three weeks:

  • Week 1: 08 February 2017 - 10 February 2017
  • Week 2: 14 February 2017 - 17 February 2017
  • Week 3: 21 February 2017 - 25 February 2017

Data Acquisition and Processing

Acquisition

Ground penetrating radar (GPR) surveys were conducted using a MALA Geosciences Professional Explorer (ProEx) control unit and a shielded 1.6 GHz antenna. Both the MALA Geosciences ProEx unit and antenna were pulled in a plastic sled behind users, who were on skis, snowshoes, or snowmobiles. Manual snow depth measurements were taken in parallel to GPR surveys but only used to estimate the two-way travel time velocity needed to calculate snow depth. 

Data were collected along transects at the Grand Mesa, Colorado study site. Transects were walked in their entirety, with some transects surveyed more than once (multiple days apart). When there was sufficient time available, grids were surveyed alongside individual transects to build a more robust dataset of directional spatial patterns. Additional grids corresponding to the locations of terrestrial lidar (light detection and ranging) scans were also surveyed for future comparisons.

Field Notes are available.

Processing

Raw data files were processed in MALA RadExplorer and ReflexW2D software. Data were processed by applying a time-zero correction, dewow filter, linear gain, and high-pass filter over a 30-trace window. The GPR had a horizontal resolution of approximately 0.8 m, a sample rate of 0.05 ns, and an average trace spacing of approximately 0.15 m when pulled behind a snowmobile or approximately 0.07 m when towed by a skier or snowshoer. In all instances the base of the snow pack was semi-automatically picked using a phase-following algorithm.

Snow depth (meters, m) was calculated from the two-way travel time by assuming a radar velocity of 0.235 m/ns. This assumption represents the average velocity calculated from comparisons between ground penetrating radar data and manual snow depth measurements. 

Snow Water Equivalent (centimeters, cm) was calculated from the estimated snow depth by assuming a density of 325 kg/m3. This assumed density was based on snow pit observations.

Quality, Errors, and Limitations

Uncertainty of snow depth is approximately 3.5 cm. 

A known source of error was that the GPR path along the transects and manual snow depth measurements did not always align precisely.

Instrumentation

Description

Data were collected using a MALA Geosciences Professional Explorer (ProEx) control unit. More information about this instrument can be found on the MALA Ground Penetrating Radar website.

Related Data Sets

SnowEx Data | Overview

Related Websites

NASA SnowEx

Contacts and Acknowledgments

Ryan Webb
Institute of Arctic and Alpine Research
University of Colorado - Boulder
4001 Discovery Drive, Rm N202

Boulder, CO 80309

Daniel McGrath
Department of Geosciences

Colorado State University

Katherine Hale

University of Colorado - Boulder

Noah Molotch
University of Colorado - Boulder

Version History

Table 4. Version History
Version Number Version Summary
2.1

Minor version update to reflect the addition of "Week 3" data.

  • This "Week 3" data covers the period between 21 February and 25 February 2017
  • The Version 1 "Week 3" file only included data from 21 February to 23 February 2017, but the Version 2 "week 3" file contains GPR measurements from terrestrial glider plots, which extended to 25 February 2017
2

Changes to this version revolve around how the data were processed and the file structure. They include:

  • Updated the radar velocity (0.2284 m/ns) used to convert the two-way travel time to snow depth
  • Updated to the density (325 kg/m3) used to calculate snow water equivalent
  • SWE is now reported in cm not mm
  • Removed column 12 (Transect #) from the data files
  • Removed "Week 3" data (21 February to 23 February 2017)
1 Initial Release

No technical references available for this data set.

How To

Programmatic Data Access Guide
Data from the NASA National Snow and Ice Data Center Distributed Active Archive Center (NSIDC DAAC) can be accessed directly from our HTTPS file system or through our Application Programming Interface (API). Our API offers you the ability to order data using specific temporal and spatial filters... read more