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CLPX-Airborne: Airborne Gamma Snow and Soil Moisture Surveys

Summary

Airborne gamma surveys were conducted over each of the three Cold Land Processes Field Experiment (CLPX) Meso-cell Study Areas (MSAs) in northern Colorado, USA, during September 2001 and 2002, and during the three Intensive Observation Periods (IOPs) in February 2002 (IOP1), February 2003 (IOP3) and March 2003 (IOP4). Data collected in September 2001 and 2002 provided background gamma radiation measurements necessary to calculate measurements of snow water equivalent (SWE) and soil moisture during subsequent winters. Airborne gamma radiation measurements of SWE and soil moisture are based on the attenuation of natural terrestrial gamma radiation by the mass of water contained in the soil and snow. Measurements were collected at 500 feet AGL along flight lines of variable length and 300 m width. Measurements are integrated along the entire length of a flight line. Flight lines in the North Park MSA were each 9 km in length, with a series of three lines (27 km total length) flown in a regular N-S parallel pattern spaced 1 km apart. Flight lines in the Fraser and Rabbit Ears MSAs are of variable length and direction.

The NASA CLPX is a multi-sensor, multi-scale experiment that focuses on extending a local-scale understanding of water fluxes, storage, and transformations to regional and global scales. Within a framework of nested study areas in the central Rocky Mountains of the western United States, ranging from 1-ha to 160,000 km2, intensive ground, airborne, and spaceborne observations are collected. Data collection focuses on two seasons: mid-winter, when conditions are generally frozen and dry, and early spring, a transitional period when both frozen and thawed, dry and wet conditions are widespread.

Citing These Data

Cline, D. and T. Carrol. 2004. CLPX-AIrborne: Airborne Gamma Snow and Soil Moisture Surveys. Boulder, CO: National Snow and Ice Data Center. Digital Media.

Overview Table

Category Description
Data format SHEF (ASCII), Comma-separated ASCII, and ESRI shapefiles
Spatial coverage Fraser, North Park, and Rabbit Ears MSAs in northern Colorado, USA (41.0°N, 39.5°N; 105.0°E,107.5°E)
Temporal coverage BG1: 20–22 September 2001
BG2: 17 September 2002
IOP1: 19-23 February 2002
IOP3: 19-21 February 2003
IOP4: 25-31 March 2003
File size 13.6 MB in total. Each flight line consists of less than 8 KB.
Parameter(s) Snow water equivalent derived from gamma radiation measurements, and snow cover (extent) and soil moisture
Procedures for obtaining data Data are available via FTP.

Table of Contents

1. Contacts
2. Detailed Data Description
3. Data Access
4. Data Acquisition
5. Document Information

1. Contacts

Investigator(s) Name and Title

Don Cline
NOHRSC
National Weather Service
1735 Lake Drive West
Chanhassen, Minnesota 55317-8582
USA

Tom Carrol
NOHRSC
National Weather Service
1735 Lake Drive West
Chanhassen, Minnesota 55317-8582
USA

Technical Contact

NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449  USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
e-mail: nsidc@nsidc.org

2. Detailed Data Description

A full description of how the airborne gamma radiation data are collected, processed, and presented can be found in a User Guide (gamma_user_guide.pdf) provided for the airborne gamma radiation snow survey program by the National Operational Hydrologic Remote Sensing Center (NOHRSC).

For each over-snow flight line during the CLPX IOPs, the following information was collected:

Data from no-snow flights, or background data collection (in September 2001 and 2002) are incorporated into over-snow files as parameters that are listed above. Background data do not appear as individual data sets.

Location parameters of the mid-point of each flight line include:
- Flight line ID
- CLPX Meso-cell Study Area
- Latitude
- Longitude
- Elevation

Geographic attributes within the Small Regional Study Area (SRSA) include:
- Flight lines
- Elevation
- Rivers (major and minor)
- Lakes
- Cities
- Highways

Data Format

SWE and soil moisture parameters are recorded in Standard Hydrometeorological Exchange Format (SHEF), as used by the US National Weather Service to distribute forecasted and point data for use in hydrologic operations. SHEF messages are presented in tab-delimited ASCII format. An example file structure is given below. The first 14 rows are header information (rows 12-13 are column headers). General comments are included after the data (between rows marked ‘.END' and ‘NNNN').

SRUS43 KMSR 191627
RRMASP
.BR GAMMA 020219 /SAIRF/SWIRF
:TO ------ Service Hydrologist (Please give HARDCOPY to SH)
:FROM ---- Tom Carroll, (952) 361-6610 ext 225, Minneapolis , Minnesota
:Visit our web page at www.nohrsc.nws.gov
:SUBJECT - AIRBORNE SNOW WATER EQUIVALENT DATA 020219162753
:-----------------------------------------------------------------------
: Total No. of flight lines sent = 7
:-----------------------------------------------------------------------
:Line Survey %SC SWE SWE %SM Est Fall %SM Pilot
:No. Date (in) (35%) (M) Typ Date (F) Remarks
:=======================================================================
CO102 DY020219 / 100 / 3.1 : 2.2, 20 SE 0 , 20 LARGE SNOW DRIFTS
CO125 DY020219 / 100 / 3.2 : 2.3, 20 SE 0 , 20 MTN OBSCUR.
CO126 DY020219 / 100 / 2.3 : 1.4, 20 SE 0 , 20 DUSTING OF NEW SNOW
EX101 DY020219 / 100 / 3.0 : 1.9, 16 GM 10922 , 16 OLDER SNOW
EX102 DY020219 / 100 / 4.7 : 4.4, 28 GM 10922 , 28 SAGE BRUSH THROUGH S
EX120 DY020219 / 100 / 3.7 : 3.1, 24 GM 10922 , 24 MTN OBSCUR.
EX121 DY020219 / 100 / 3.7 : 2.9, 21 GM 10922 , 21 SOME SNOW IN TREES
.END
There was new snow on most lines. All lakes and most rivers were frozen.
NNNN 

SHEF Message Key
  Line No.       Flight line number
  Survey Date    Survey Date
  %SC            Visual estimate of percent snow cover over flight line made by pilots
  SWE(in)        SWE, in inches, made using the %SM(M) soil moisture estimate
  SWE(35%)       SWE, in inches, made using an assumed 35% soil moisture
  %SM(M)         Percent soil moisture used in SWE calculation
  Est type       Type of estimate for %SM(M):
        AM       Airborne soil moisture measurement
        AI       Interpolated from airborne measurements
        GM       Ground-based soil moisture measurement
        GI       Interpolated from ground measurements
        SE       Subjective estimate
  Fall date      Survey date for fall soil moisture survey
  %SM(F)         Percent soil moisture measured/estimated in the fall
Pilot Remarks    Pilot remarks for flight line.

Summaries of flight line locations (mid-points of each flight line) are presented in comma-separated value (.csv) format.

Geographic attributes are formatted as ESRI shapefiles (*.shp, *.shx and *.dbf) and layer files (*.lyr).

File and Directory Structure

The gamma radiation data are presented in three formats, in the following directory structure:

ArcView_shapefiles/
SWE_SHEFs/
Flight_lines.csv

File Naming Convention

SWE and soil moisture parameters for groups of flight lines collected during the same day are in files named wYYMMDDa.atw where YY is year, MM is month, and DD is day.

The latitude, longitude and elevation of the mid-points of all 129 flight lines are available in the file named Flight_lines.csv.

Geographic attributes are in ArcView shape files named co_####.dbf, co_####.shp, and co_####.shx where #### represents either cities (cities), highways (hways), lakes (lk), major rivers (maj_rivers), minor_rivers (minor rivers), or flight lines (flines).

Terrain elevation data are in the ArcView layer file named elevations_west32.tif.lyr.

File Size

This data set is 13.6 MB in total. Each flight line consists of less than 8 KB.

Spatial Coverage

Flight lines were flown throughout Fraser, North Park, and Rabbit Ears MSAs, which are all within the CLPX Small Regional Study Area (SRSA - 41.0°N, 39.5°N; 105.0°E,107.5°E).

Flight lines are of variable length and variable direction. Mid-points of each flight line (latitude, longitude, and elevation) are available in the file Flight_lines.csv. The number of flight lines flown and the dates of data collection are:

MSA
BG1
BG2
IOP1
IOP2
IOP3
IOP4
Fraser
23
23
23
0
23
23
North Park
84
84
84
0
36
84
Rabbit Ears
22
22
22
0
0
22

BG1: 20–22 September 2001
BG2: 17 September 2002
IOP1: 19-23 February 2002
IOP3: 19-21 February 2003
IOP4: 25-31 March 2003

Spatial Coverage Maps

Overview Map

Fraser MSA flight lines

North Park MSA flight lines

Rabbit Ears MSA flight lines

Temporal Coverage

Airborne gamma flights were made on the following days:

BG1: 20–22 September 2001
BG2: 17 September 2002
IOP1: 19-23 February 2002
IOP3: 19-21 February 2003
IOP4: 25-31 March 2003

Parameter or Variable

This data set presents snow water equivalent (SWE) derived from gamma radiation measurements, and snow cover (extent) and soil moisture.

For each over-snow flight line collected during the IOPs, parameters are:

3. Data Access

Data Access

Data are available via FTP at ftp://sidads.colorado.edu/pub/DATASETS/CLP/data/airborne/nsidc0158_gamma_snow/.

Related Data Collections

All CLPX Data Sets

Quality Assessment

All SWE data have been through QC associated with standard SHEF message production.

4. Data Acquisition and Processing

For a full description of how the airborne gamma radiation data are collected and processed, please refer to the User Guide (gamma_user_guide.pdf) provided for the airborne gamma radiation snow survey program by the National Operational Hydrologic Remote Sensing Center (NOHRSC).

5. Document Information

List of Acronyms

AGL = above ground level
CLPX = NASA Cold Land Processes Field Experiment
ISA = Intensive Study Area
LRSA = Large Regional Study Area
LSOS = Local Scale Observation Site
MSA = Meso-cell Study Area
SWE = snow water equivalent

Document Creation Date

December 2, 2004

 

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