Data Set ID: 
SNEX17_SBR

SnowEx17 Radiometrics Surface-Based Radiometer Brightness Temperatures, Version 1

This data set consists of surface-based radiometer (SBR) brightness temperatures of the snow surface and vegetation at Grand Mesa, CO, USA, acquired during NASA's 2017 SnowEx campaign. Four SBRs were deployed in the field and obtained measurements at 89, 37, 19, and 10.67 GHz in both vertical (V-pol) and horizontal (H-pol) polarizations. Data are available for 37 locations across Grand Mesa collected over five days in February, 2017. They include both 2-4 minute observations and 20 minute, continuous measurements during surface melt, with the latter designed to capture the brightness temperature increase caused by the presence of liquid water in the snow.

This data set also contains snowfork measurements of snow wetness for 13 sites.

This is the most recent version of these data.

Version Summary: 

Initial release

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):
  • MICROWAVE > BRIGHTNESS TEMPERATURE
  • SNOW/ICE > SNOW MELT > Snow Wetness
Data Format(s):
  • JPEG
  • Comma-Separated Values (.csv)
Spatial Coverage:
N: 39.10552, 
S: 39.02098, 
E: -107.846975, 
W: -108.23134528824981
Platform(s):GROUND-BASED OBSERVATIONS
Spatial Resolution:
  • Varies x Varies
Sensor(s):RADIOMETERS
Temporal Coverage:
  • 14 February 2017 to 18 February 2017
Version(s):V1
Temporal ResolutionVariesMetadata XML:View Metadata Record
Data Contributor(s):Alexandre Roy, Alexandre Langlois, Ludovic Brucker

Geographic Coverage

Other Access Options

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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.

Roy, A., A. Langlois, and L. Brucker. 2019. SnowEx17 Radiometrics Surface-Based Radiometer Brightness Temperatures, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/JWONK1ZTSBXX. [Date Accessed].
Created: 
5 July 2018
Last modified: 
14 March 2019

Data Description

Parameters

The main parameters for this data set are shown in Table 1.

Table 1: Parameters
Parameters Units Measurement Device Measurement Site
Brightness temperature (Tb) kelvins, K Four surface-based radiometers (SBR) at 89, 37, 19, and 11 GHz Snow Pits, County Line parking site, MegaTrench
Snow wetness vol./vol. Snow Fork Snow Pits

File Information

Format

Data are presented in Comma Separated Values (.csv) format. Compressed images (.jpg) are also provided. Both data files (.csv) and images (.jpg) are grouped in zip folders (.zip).

Each data file also has an associated XML file that contains metadata.

File Contents

Brightness temperature data files begin with a nine-line header that describes the file contents, the methods used to collect data, and missing data values. An example of this header is shown in Figure 1. Brightness temperature data are presented in 23 columns, which are described in Table 2.

Figure 1. Header for the brightness temperature data file, SnowEx17_SBR_Trench_TBcalibrated.
Table 2. Brightness Temperature Data File Content Descriptions
Column Header Description
File_SITE_Position_View_YYYYMMDD_HHMM_MST Includes the file name for the raw brightness temperature data from which row values were calculated; raw files not archived at NSIDC
PITID Name of the most adjacent snowpit to the SBR measurements
Snow Depth Depth of snow at the site of the measurement, in cm; snow depth was measured with an avalanche probe
UTM Coordinate system
TBrrP(K) Brightness temperature in kelvins (K) at frequency rr and polarization P:
rr = 89, 37, 19, or 11
P = H (horizontal) or V (vertical)
stdrrP(K) The standard deviation for the brightness temperature reading in kelvins (K) at frequency rr and polarization P:
rr = 89, 37, 19, or 11
P = H (horizontal) or V (vertical)
IDPhoto Identifies the browse images associated with the SBR measurement site
Comments General comments on where and how the SBR readings were taken

Continuous data files contain 16 columns of data, described in more detail in Table 3. Figure 2 shows 10 lines of data from the file SnowEx17_SBR_Corrected_SnowEx_GM_84N_20170217_1221.

Table 3. Continuous File Content Descriptions
Column Header Description
Frequency Frequency at which SBR measurements were collected (GHz)
Year Year of data acquisition
Month Month of data acquisition
Day Day of data acquisition
Hour Hour of data acquisition
Minute Minute of data acquisition
Seconde Second of data acquisition
Vload1 Internal load observations
VloadND1 Internal load noise diode
Tload1 Radiometer temperature
Tcase1 Case temperature
V (V-Pol) (V) Voltage at V-pol
V (H-Pol) (V) Voltage at H-pol
Incidence Angle (∞) Angle at which SBR measurements were collected (measured from the horizontal)
 Tb (V-Pol) (K)  Brightness temperature at the vertical polarization (K)
 Tb (H-Pol) (K)  Brightness temperature at the horizontal polarization (K)
1Raw values taken directly from the instrument, see the Technical References tab for more details
Figure 2. Continuous SBR Data Sample File

Snow fork data files begin with a four-row header that specifies the date and time of acquisition, the snowpit ID where measurements were collected, and descriptions of the data columns. Table 4 contains a more detailed description of each data column, and Figure 3 shows sample data from file SnowEx17_SBR_Snow_Fork_21S_16Feb.csv.

Table 4. Snow Fork File Content Descriptions
Column Header Description Units
Depth Depth at which the snow fork measurement was taken (v = vertically inserted)  cm
Snow Wetness Snow fork measurement vol./vol.
Snow Density Density of snow kg / cm3
Figure 3. Snow Fork Sample File

Directory Structure

Data files and images are provided in zip folders, labeled by measurement site, as shown in Figure 1. See the "File Naming Convention" of this user guide for more details on the files stored within these zip folders.

Figure 4File Directory Structure

File Naming Convention

The brightness temperature data files are named according to the following convention and as described in Table 5:
SnowEx17_SBR_<measurement site>_Tbcalibrated.csv

Example:
SnowEx17_SBR_CountyLine_TBcalibrated.csv

Table 5: Brightness Temperature File Naming Convention
Parameters Measurement Site
SnowEx17_SBR Abbreviation for SnowEx17 Radiometrics Surface-Based Radiometer Brightness Temperatures
<measurement site> Where the data were collected (County Line, Snowpits, Trench)

The snow fork data files are named according to the following convention and as described in Table 6:
SnowEx17_SBR_Snow_Fork_<site ID>_##Feb.csv

Example:
SnowEx17_SBR_Snow_Fork_24E_15Feb.csv
SnowEx17_SBR_Snow_Fork_21S_16Feb.csv

Table 6: Snow Fork File Naming Convention
Parameters Measurement Site
SnowEx17_SBR Abbreviation for SnowEx17 Radiometrics Surface-Based Radiometer Brightness Temperatures
Snow_Fork Indicates that this file contains snow fork measurements
<side ID> Snow pit ID
##Feb Date of measurement

The continuous data files (where measurements were recorded continuously over approximately 20 minutes) are named according to the following convention and as described in Table 7:
SnowEx17_SBR_Corrected_SnowEx_GM_<site ID>_YYYYMMDD_hhmm.ext

Example:
SnowEx17_SBR_Corrected_SnowEx_GM_32S_20170216_1158.csv
SnowEx17_SBR_Corrected_SnowEx_GM_84N_20170217_1221.csv

Table 7: Continuous Data File Naming Convention
Parameters Measurement Site
SnowEx17_SBR Abbreviation for SnowEx17 Radiometrics Surface-Based Radiometer Brightness Temperatures
Corrected_SnowEx_GM Indicates that the file contains corrected, continuous SBR measurements collected in Grand Mesa, CO
<side ID> Snow pit ID
YYYYMMDD Date of measurement, in four-digit year, 2-digit month, 2-digit day format
hhmm Start time of measurement in hours (hh) and minutes (mm) MST

Images are named according to the following convention and as described in Table 8:
SnowEx17_SBR_<measurement site>_TB_image_####.jpg

Example:
SnowEx17_SBR_Snowpits_TB_image_0899.jpg
SnowEx17_SBR_Snowpits_TB_image_0900.jpg

Table 8: Image Naming Convention
Parameters Measurement Site
SnowEx17_SBR Abbreviation for SnowEx17 Radiometrics Surface-Based Radiometer Brightness Temperatures
<measurement site> Where the data were collected (County Line, Snowpits, Trench)
image_#### Image ID (e.g. image 0899, image 0900)

File Size

Zip folders range in size from approximately 1.5 to 3.2 KB.

CSV files range in size from approximately 0.3 KB to 141 KB.

JPG files range in size from approximately 1.8 MB to 5.0 MB.

The total data volume is approximately 894 MB.

Spatial Information

Coverage

Grand Mesa, Colorado:
Northernmost Latitude: 39.1° N
Southernmost Latitude: 39.0° N
Easternmost Longitude: 107.8° W
Westernmost Longitude: 108.2° W

Resolution

Brightness temperature readings taken at 89, 37, and 19 GHz had a footprint of approximately 0.6m X 0.6m.

Brightness temperature readings taken at 11 GHz had a footprint of approximately 0.8m X 0.8m.

Geolocation

Data falls within the projected coordinate systems WGS 84 / UTM Zone 12 North and WGS 84 / UTM Zone 13 North, details of which are presented in Table 9. 

Table 9. Geolocation Details
Geographic coordinate system WGS 84 WGS 84
Projected coordinate system WGS 84 / UTM Zone 12 North WGS 84 / UTM Zone 13 N
Longitude of true origin -111 -105
Latitude of true origin 0 0
Scale factor at longitude of true origin 0.9996 0.9996
Datum WGS 1984 WGS 1984
Ellipsoid/spheroid WGS 84 WGS 84
Units meters meters
False easting 500000 500000
False northing 0 0
EPSG code 32612 32613
PROJ4 string +proj=utm +zone=12 +datum=WGS84 +units=m +no_Defs +proj=utm +zone=13 +datum=WGS84 +units=m +no_defs
Reference https://epsg.io/32612  https://epsg.io/32613
Data files indicate that all coordinates fall within Universal Transverse Mercator (UTM) Grid Zone 12S or UTM Grid Zone 13S. These designation correspond to the intersection of latitudinal projection zone S and longitudinal projection zone 12 or 13, as shown in Figure 2. 
Figure 5: UTM Grid Zone

Temporal Information

Coverage

Data were acquired between 14 February 2017 and 18 February 2017.

Resolution

N/A

Data Acquisition and Processing

Background

Snow Water Equivalent (SWE) is often estimated from Satellite Passive Microwave (PMW) observations of brightness temperature (Tb) using algorithms which assume a linear relationship between SWE and spectral Tb. However, seasonal variability in snow grain metamorphism and vegetation can produce variabilities that are not captured in these calculations. As an improvement on PMW algorithms, Microwave Snow Emission Models (MSEM) account for multiple sources of spectral Tb measurements (e.g. water, vegetation) and adjust for inter-annual variability in snow and vegetation quality. However, MSEM are limited by the coarseness of satellite-scale measurements, which typically have a spatial resolution greater than 10 km X 10 km.

As an alternative to satellite observations of Tb, Surface-Based Radiometers (SBR) offer a better means of isolating and measuring microwave emissions from snow-covered surfaces. SBR readings were incorporated into the 2017 SnowEx campaign in Grand Mesa, CO to quantify the relative importance of different geophysical parameters (e.g. SWE, snow grain) and identify the small-scale spatial variability in Tb measurements.

Acquisition

SBR Measurements

Four surface-based radiometers (SBR) attached to a sleigh and pulled behind a snow mobile collected brightness temperature (Tb) measurements of snow surfaces and vegetation around Grand Mesa, Colorado. The SBR, mounted approximately 1.5 m off the ground and at an angle of 55°, measured Tat 89, 37, 19, and 11 GHz in both the vertical (V-pol) and horizontal (H-pol) polarizations. Measurements were taken every six seconds over two- to four-minute intervals at each site. The 89, 37, and 19 GHz SBR had a beamwidth of 6° and a footprint of 0.6 m X 0.6 m., while the 11 GHz SBR had a beamwidth of 8° and a footprint of 0.8 m X 0.8 m. 

On 14 Feb. 2017, SBR measurements were collected at two Local Scale Observation Site (LSOS) locations, one close to the radar (RS) and one close to the Michigan radiometers (JC).

Between 15 Feb. and 17 Feb. 2017, measurements were conducted at 29 Grand Mesa (GM) Snow Pit locations. 

On 18 Feb. 2017, the SBR measured emissions from the snow surface and the forest (SBR positioned at 55°, looking at the sky and vegetation) behind two Mega Trenches (LSOS_MegaTrenchAspen and LEP_MegaTrench). Measurements were also done at the County Line parking area on a scissor lift. The scissor lift was placed at two heights, 970 cm and 1240 cm. At both heights, the SBR measured Tb from three footprints, one open area (S1) and two forested areas (S2, S3). 

Continuous SBR Measurements

During periods of surface melt, continuous SBR measurements were collected over approximately 20 minutes at three snow pits (32S, 97S, and 84N). Continuous measurements quantify how Tb increases as the liquid water content of the snow increases.

Snow Fork Measurements

Between February 15 and February 18 2017, a snow fork was used to measure wetness (% vol) and snow density (kg/cm3) at 13 snow pits.

Processing

SBR were calibrated with liquid nitrogen (LN2) and an ambient black body (BB) on 18 February 2017. Calibration coefficients, optimized using the LN2 and ambient BB measurements, were then used to correct Tb measurements over the whole campaign.

Quality, Errors, and Limitations

During the campaign, several ambient BB measurements were recorded to quantify the radiometers' stability. The mean absolute error between the radiometers' measurements and physical measurements of the BB was around 1 K. Errors are slightly higher (~1.4 K) for the 37 GHz Tb measurements, specifically those done at LSOS-JCTruck site on 14 Feb. 2017, where a more than 5 K difference between Tb and BB temperature was noted. Caution should be taken when using those 37 GHz observations. All other Tb measurements are reliable within ±1 K.

Biases are under 1 K for all radiometers.

Instrumentation

Description

The SBR used for this study were all PR-Series radiometers produced by Radiometris Corporation:

  • PR-1065: 10.65 GHz dual-polarization, single-channel radiometer
  • PR-1900: 19 GHz dual-polarization, single-channel radiometer
  • PR-3700: 36.5 GHz dual-polarization, single-channel radiometer
  • PR-8900: 89 GHz dual-polarization, single-channel radiometer

Visit the Radiometris Corporation website for more details..

Related Data Sets

Other SnowEx Data Sets

Related Websites

NASA SnowEx 

Contacts and Acknowledgments

Alexandre Roy
Université du Québec à Trois-Rivières
Trois-Rivières, Quebec G8Z 4M3

Canada

Alexandre Langlois
Université de Sherbrooke

Département de Géomatique Appliquée

Ludovic Brucker
Goddard Space Flight Center
Greenbelt, MD 20771

References

Langlois, A. 2015. Applications of the PR Series Radiometers for Crysopheric and Soil Moisture. Research, Technical Report. Vol. 2015. © Radiometrics Corporation, p. 40.

Roy, A., A. Royer, O. St-Jean-Rondeau, B. Montpetit, G. Picard, N. Marchand, and A. Langlois. 2016. Microwave snow emission modeling uncertainties in boreal and subarctice environments. The Crysophere 10: 623-638.

Roy, A., A. Royer, J. P. Wigneron, A. Langlois, J. Bergeron, and P. Cliche. 2012. A simpler parameterization for a boreal forest radiative transfer model at microwave frequencies. Remote Sensing of the Environment 124. https://dx.doi.org/10.1016/j.rse.2012.05.020

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