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CLPX-Ground: University of Michigan Ground-Based Microwave Radiometer

Summary

This data set contains microwave radiometry data collected at the Local Scale Observation Site (LSOS) of the Cold Land Processes Field Experiment (CLPX) in Colorado, USA, during IOP4 (March-April 2003). The LSOS is a 100 x 100 m study site located within the Fraser Intensive Study Area (ISA). The LSOS has flat topography with areas of both uniform and discontinuous pine forest, and a small clearing. The majority of the data consist of brightness temperatures at a 54 degree incidence angle of the accumulated snowpack at the small clearing in the LSOS. Other observations include upwelling brightness temperatures from short and tall trees, and downwelling brightness temperatures from tall trees. Snowpack ranged from 0 to 80 cm in depth.The microwave radiometers operated at 6.7, 19, and 37 GHz.

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

Sarabandi, K. 2003. CLPX-Ground: Ground-based L and Ku band polarimetric scatterometry. [indicate subset used]. Boulder, Colorado USA: NASA DAAC at the National Snow and Ice Data Center.

Overview Table

Category Description
Data format Tab-delimited ASCII
Spatial coverage CLPX Local Scale Observation Area (LSOS) in northern Colorado (100 m x 100 m).
39.9066 N, 105.8829 W
Temporal coverage 24 March - 2 April 2003 (IOP4)
File size 2 - 548 KB
Parameter(s) Brightness temperatures of the accumulated snowpack, upwelling brightness temperatures from short and tall trees, and downwelling brightness temperatures from tall trees
Procedures for obtaining data Data are available via FTP

Table of Contents

1. Contacts
2. Detailed Data Description
3. Data Access and Tools
4. Document Information

1. Contacts and Acknowledgments

Investigator(s) Name and Title

Anthony England
University of Michigan
3227 EECS Building
1301 Beal Street
Ann Arbor, MI 48109-2122
USA

Roger De Roo
Space Physics Research Lab
2116 Space Research Building
2455 Hayward Street
Ann Arbor, MI 48109-2143
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

Format

The radiometer data are provided in tab-delimited ASCII files. The first row contains ten column headers, which are:

freq - nominal frequency of radiometer, in GHz
year - year
mon - month
dom - day of month
hr - hour, MST
min - minutes
sec - seconds
ang - incidence angle, degree from looking straight down
TbH - Brightness temperature (K), Horizontal polarization
TbV - Brightness temperature (K), Vertical polarization (-9 indicates no data)

File and Directory Structure

Data are presented in five files: one each for snow dwell (small clearing), large tree downwelling, large tree upwelling, short tree upwelling, and snow elevation scan.

File Naming Convention

Files are named iop4XXX.tb, where XXX represents the target within the LSOS: dwell (snow dwell), ltd (large tree downwelling), ltu (large tree upwelling), ses (snow elevation scan), or stu (short tree upwelling), and tb represents brightness temperature.

File Size

File sizes range from 2 to 548 KB.

Spatial Coverage

Radiometer measurements were taken in the CLPX LSOS (39.9066 N, 105.8829 W). The following map shows the location of the radiometer, and the locations of other instruments in the LSOS.

Within the LSOS, there were five radiometer targets, shown in the following photo.

Temporal Coverage

Snow dwell, considered to be the most important measurement, was the default measurement target. Snow dwell temporal coverage was planned to be a continuous measurement, except for select periods of up to 45 minutes. The select periods occurred twice daily, in the morning (approximately 10 am, when the snow would not have started melting), and in the late afternoon (approximately 4 pm, after daily peak melting). The non-dwell measurements (ltd, ltu, ses, stu) were to be conducted on a rotating basis during the select periods, although some select periods were actually used for instrument maintenance. Actual measurement dates are summarized by frequency and target in the table below. Per the rotating schedule and maintenance work, data for the indicated targets were collected at some point during the indicated dates, but are not continuous throughout these periods

dwell 6.7 GHz 24 March 2 April 2003
  19.35 GHz 24 31 March 2003
  37 GHz 24 31 March 2003
ltd 6.7 GHz 29 and 31 March 2003
  19.35 GHz 29 and 31 March 2003
  37 GHz 29 and 31 March 2003
ltu 6.7 GHz 27 and 29 March, 2 April 2003
  19.35 GHz 27 and 29 March 2003
  37 GHz 27 and 29 March 2003
ses 6.7 GHz 25 March, 1 April 2003
  19.35 GHz 25 March 2003
  37 GHz 25 March 2003
stu 6.7 GHz 27 and 29 March, 2 April 2003
  19.35 GHz 27 and 29 March 2003
  37 GHz 27 and 29 March 2003

Parameter or Variable

Parameter Description

The parameter measured during this project is brightness temperature at a 54 degree incidence angle of the accumulated snowpack at the small clearing in the LSOS. Other observations include upwelling brightness temperatures from short and tall trees, and downwelling brightness temperatures from tall trees.

The radiometer operated at three frequencies: 6.7, 19.35, 37 GHz. Parameters recorded at each frequency are:

ang - incidence angle, degree from looking straight down
TbH - Brightness temperature, K, Horizontal polarization
TbV - Brightness temperature, K, Vertical polarization

Sample Data

The following figure is a sample brightness temperature time series during IOP4.

The following figure is a sample of IOP3 large tree upwelling data.

Quality Assessment

Accuracies:
The time in these files is corrected to Mountain Standard Time, +/-5 minutes. The inclinometer was calibrated at the beginning of IOP4, but was reading 6-7 degrees too high on 31 March 2003. For all the radiometers, the precision is +/-0.5 K. The 6.7, 19, and 37 GHz brightness temperatures are accurate to +/-3 K. The 6.7 GHz V-pol data could not be calibrated and is marked as "Not A Number" by the value" -9."

Data filters:
Data were removed for any of the following conditions:

1) Obvious malfunctions, e.g. out-of-range ADC values. Although the radiometer was capable of outputting voltages less than 0V or greater than 2.5V, these values were considered to be out of range, and were discarded by the ADC.

2) Unstable electronics. During a 4-second interval, each radiometer antenna monitored a reference brightness both before and immediately after the target observation. Data were discarded if the references differed by more than 3K, which was considered to be an indication of unstable electronics or thermal control of the electronics.

3) Unstable amplifier temperature. The amplifiers become more efficient (amplifier gain increases) at colder physical temperatures. Small changes in the physical temperature of the amplifiers can produce changes in the readiometer output that are indistinguishable from brightness changes. Data were flagged and discarded if the amplifier physical temperature changed, or differed from the calibration temperature by more and 1-degree Celsius."

3. Data Access

Data are available via FTP at ftp://sidads.colorado.edu/pub/DATASETS/CLP/data/ground_data/nsidc0167_lsos_um_radiometer/.

4. Document Information

Glossary and Acronyms


ADC = Analog to digital converter
CLPX = NASA Cold Land Processes Field Experiment
RF = Radio frequency
IOP = Intensive Observation Period
ISA = Intensive Study Area
K = Kelvin
LRSA = Large Regional Study Area
LSOS = Local Scale Observation Site
MSA = Meso-cell Study Area
Tb = Brightness Temperature