SMEX03 Regional Ground Soil Moisture Data: Georgia

Summary

The parameters for this data set include gravimetric soil moisture, volumetric soil moisture, bulk density, and surface and soil temperature for the Georgia study region. This data set is part of the Soil Moisture Experiment 2003 (SMEX03). The United States portion of SMEX03 was conducted during June and July, 2003. Data are provided in a tab-delimited ASCII text file, and are available via FTP.

These data were collected as part of a validation study for the Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E). AMSR-E is a mission instrument launched aboard NASA's Aqua Satellite on 04 May 2002. AMSR-E validation studies linked to SMEX are designed to evaluate the accuracy of AMSR-E soil moisture data. Specific validation objectives include assessing and refining soil moisture algorithm performance; verifying soil moisture estimation accuracy; investigating the effects of vegetation, surface temperature, topography, and soil texture on soil moisture accuracy; and determining the regions that are useful for AMSR-E soil moisture measurements.

Citing These Data

We kindly request that you cite the use of this data set in a publication using the following citation. For more information, see our Use and Copyright Web page.

Bosch, D., T. Jackson, V. Lakshmi, and J. Jacobs. 2006. SMEX03 Regional Ground Soil Moisture Data: Georgia. [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 text
Spatial coverage

Southernmost Latitude: 31.20º N
Northernmost Latitude: 31.82º N
Westernmost Longitude: 83.94º W
Easternmost Longitude: 83.43º W

Temporal coverage 23 June 2003 to 2 July 2003
File naming convention GA_GVSM_Raw.txt
File size approximately 247 KB
Parameter(s) Gravimetric and volumetric soil moisture, bulk density, surface and soil temperature
Procedures for obtaining data Data 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)

David Bosch
Southeast Watershed Research Laboratory
US Department of Agriculture (USDA) - Agricultural Research Service (ARS)
Tifton, GA 31794
USA

Thomas J. Jackson
Hydrology and Remote Sensing Laboratory
US Department of Agriculture (USDA) - Agricultural Research Service (ARS)
Beltsville, MD 20705
USA

Venkat Lakshmi
University of South Carolina
Columbia, SC 29208
USA

Jennifer Jacobs
University of New Hampshire
Durham, NH 03824
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

Acknowledgements

Many graduate students and volunteers worked to collect the field data. The investigators thank the SMEX03 Science Team, the staff of the Southeast Watershed Research Lab, graduate students from the University of South Carolina and the University of Georgia, Scientists from the NASA Goddard Space Flight Center, and scientists from the United States Department of Agriculture - Agricultural Research Service (USDA-ARS) National Soil Tilth Lab for their critical roles in data collection. The investigators also thank NASA for their generous contributions to the study. This work was supported by the NASA Aqua AMSR, Terrestrial Hydrology and Global Water Cycle Programs.

2. Detailed Data Description

Format

The data are in a tab-delimited ASCII text file. Missing data are represented with -999 in the data file. The column headings and the information in each column are described in the following table. See the Parameter or Variable section for more information about the parameters.

Column Heading in File
Description
Site ID Site location identifier number
Date Month/day/year
Crop_type

Type of land cover:
  peanuts
  double-row peanuts
  forest
  young pines
  strip-till cotton
  cotton
  pasture
  corn
  cucumbers

Sample_Time (EDT) Sampling time in Eastern Daylight Time (EDT); most sampling is 5-10 minutes in duration
Latitude WGS84 Latitude of sample site in decimal degrees, World Geodetic System 1984 (WGS84)
Longitude WGS84 Longitude of sample site in decimal degrees, WGS84
Easting in m WGS84 Zone 17 Easting of sample site in meters, WGS84, Zone 17
Northing in m WGS84 Zone 17 Northing of sample site in meters, WGS84, Zone 17
TP_V row Impedance probe (ThetaProbe) millivolt reading in V in row
TP_V 1/4 row ThetaProbe millivolt reading in V at ¼ row
TP_V 1/2 row ThetaProbe millivolt reading in V at ½ row
TP_gc row ThetaProbe volumetric soil moisture (VSM) in m3/m3, from general calibration in row
TP_gc 1/4 row ThetaProbe VSM in m3/m3 from general calibration at ¼ row
TP_gc 1/2 row ThetaProbe VSM in m3/m3 from general calibration at ½ row
TP_ssc row ThetaProbe VSM in m3/m3 from site-specific calibration in row
TP_ssc 1/4 row ThetaProbe VSM in m3/m3 from site-specific calibration at ¼ row
TP_ssc 1/2 row ThetaProbe VSM in m3/m3 from site-specific calibration at ½ row
TP_V average ThetaProbe volt reading, average
TP_V stdev ThetaProbe volt reading, standard deviation
TP_gc average ThetaProbe volumetric soil moisture from general calibration, average
TP_gc stdev ThetaProbe volumetric soil moisture from general calibration, standard deviation
TP_ssc average ThetaProbe volumetric soil moisture from site-specific calibration, average
TP_ssc stdev ThetaProbe volumetric soil moisture from site-specific calibration, standard deviation
ST_C 1 cm Soil temperature in degrees Celsius at 1 cm
ST_C 5 cm Soil temperature in degrees Celsius at 5 cm
ST_C 10 cm Soil temperature in degrees Celsius at 10 cm
Surf_Temp C Surface temperature in degrees Celsius
Can_ID 0-1 cm Soil can identifier for 0-1 cm sample
Can_Wgt 0-1 cm Soil can weight for 0-1 cm sample
Wet_Wgt 0-1 cm Wet weight of soil for 0-1 cm sample
Dry_Wgt 0-1 cm Dry weight of soil for 0-1 cm sample
GSM 0-1 cm Gravimetric soil moisture in g/g for 0-1 cm sample
BD 0-1 cm Bulk density in g/cm3 for 0-1 cm sample
VSM 0-1 cm Volumetric soil moisture (calculated from sample) in m3/m3 for 0-1 cm sample
Can_ID 0-3 cm Soil can identifier for 0-3 cm sample
Can_Wgt 0-3 cm Soil can weight for 0-3 cm sample
Wet_Wgt 0-3 cm Wet weight of soil for 0-3 cm sample
Dry_Wgt 0-3 cm Dry weight of soil for 0-3 cm sample
GSM 0-3 cm Gravimetric soil moisture in g/g for 0-3 cm sample
BD 0-3 cm Bulk density in g/cm3 for 0-3 cm sample
VSM 0-3 cm Volumetric soil moisture (calculated from sample) in m3/m3 for 0-3 cm sample
Can_ID 3-6 cm Soil can identifier for 3-6 cm sample
Can_Wgt 3-6 cm Soil can weight for 3-6 cm sample
Wet_Wgt 3-6 cm Wet weight of soil for 3-6 cm sample
Dry_Wgt 3-6 cm Dry weight of soil for 3-6 cm sample
GSM 3-6 cm Gravimetric soil moisture in g/g for 3-6 cm sample
BD 3-6 cm Bulk density in g/cm3 for 3-6 cm sample
VSM 3-6 cm Volumetric soil moisture (calculated from sample) in m3/m3 for 3-6 cm sample
VSM 0-6 cm Total volumetric soil moisture in m3/m3 for 0-6 cm
rain/irrig (mm) Notes about amount of rain the previous night (if any); whether or not the field was irrigated, etc.

File Naming Convention

The single data file is named GA_GVSM_Raw.txt.

File Size

The data file is approximately 247 KB.

Spatial Coverage

Southernmost Latitude: 31.20º N
Northernmost Latitude: 31.82º N
Westernmost Longitude: 83.94º W
Easternmost Longitude: 83.43º W

Temporal Coverage

Data were collected from 23 June 2003 to 2 July 2003.

Temporal Resolution

Data were collected once daily at multiple sites. The sampling was conducted between 11:30 A.M. and 3:00 P.M. local time. Most sampling was 5 to 10 minutes in duration.

Parameter or Variable

Parameter Description

Parameters in this data set are gravimetric soil moisture (GSM), volumetric soil moisture (VSM), bulk density (BD), and surface and soil temperature. The following table describes the units of measurement and sources of each parameter.

Parameter Units of Measurement Source/Sensor(s)
Gravimetric soil moisture Grams of water per grams of dry soil Manual soil collection
Volumetric soil moisture Cubic meters of water per cubic meters of dry soil Manual soil collection and impedance probes (ThetaProbes)
Bulk density Grams per cubic centimeter (g/cm3) Manual soil collection
Surface and soil temperature Degrees Celsius Infrared thermometers, temperature probes

Sample Data Record

The following sample illustrates the data. The first 12 data rows are shown; only the first 4 columns and last 4 columns of each row are shown (the column headings in the sample indicate the included columns). Missing data are represented with -999 or -99:99 in the data file.

Site ID
Date
Crop_type
Sample_Time
(EDT)
 
...
BD
3-6 cm
VSM
3-6 cm
VSM
0-6 cm
rain/irrig (mm)
GA01
6/23/2003
peanuts
-99:99
 
...
1.479
0.12
0.115
nd
GA01
6/24/2003
peanuts
-99:99
 
...
1.386
0.101
0.08
0
GA01
6/25/2003
peanuts
-99:99
 
...
1.37
0.092
0.076
0
GA01
6/26/2003
peanuts
14:00
 
...
1.531
0.108
0.09
nd
GA01
6/27/2003
peanuts
13:35
 
...
1.609
0.102
0.075
0
GA01
6/28/2003
peanuts
13:50
 
...
1.279
0.091
0.057
0
GA01
6/29/2003
peanuts
13:18
 
...
1.395
0.09
0.091
1
GA01
6/30/2003
peanuts
13:32
 
...
1.382
0.087
0.089
3
GA01
7/1/2003
peanuts
13:38
 
...
1.487
0.099
0.098
5
GA01
7/2/2003
peanuts
13:43
 
...
1.425
0.139
0.139
21
GA02
6/23/2003
forest
11:50
 
...
1.547
0.094
0.104
nd
GA02
6/24/2003
forest
13:34
 
...
1.309
0.096
0.095
0

Error Sources

Impedance Probes

Impedance probes (ThetaProbes) were used for volumetric soil moisture sampling. For various reasons, including extremely dry conditions, severe weather restrictions, miscommunication among personnel, and cultivation, some sites were not sampled on particular days. Occasionally, a ThetaProbe rod was broken because of very hard and dry soil conditions. When possible, the broken rod was replaced. When it was not possible to replace the rod, a new instrument was used. The site-specific calibration resulted in an average root mean square error of 0.02 m3/m3.

Bulk Density

The coring tool extracts a known volume of soil that is used to compute a bulk density. There is potential for compaction with this tool, which results in higher bulk densities when compared to other methods. For the 0-1 cm sample, and for the other sample depths when dry moisture conditions prevented using the coring tool, a 13 cm x 10 cm x 2 cm rectangular shaped scoop tool was used to retrieve the soil sample. This tool does not allow for a bulk density estimate, so the average bulk density from all coring tool samples was used for computation of volumetric soil moisture. Also, the bulk density of the 0-3 cm sample was considered less reliable than the 3-6 cm sample; therefore, the 3-6 cm bulk density was used for all calculations. The bulk density for all 0-1 cm samples was assumed to be 1.5 g/cm3.

3. Data Access and Tools

Data Access

Data are available via FTP.

Volume

The total volume is approximately 247 KB.

Related Data Collections

See related information on the NSIDC Soil Moisture Experiment (SMEX) Web site.

4. Data Acquisition and Processing

Theory of Measurements

This regional soil moisture site is within a single Aqua satellite passive microwave footprint (approximately 50 km), and measurements were taken around the time of the AMSR-E/Aqua overpass (13:30 local time). The goal of soil moisture sampling in these regional sites is to provide a reliable estimate of volumetric soil moisture and variance within the AMSR-E footprint.

Sampling

Sampling was performed on sites approximately one quarter section (0.8 km by 0.8 km) in size. A grid of 49 individual sites was sampled, covering approximately 50 km by 75 km. One location in each of the sites was sampled. The sampling was conducted between 11:30 A.M. and 3:00 P.M. local time.

Volunteers used a coring tool to extract a single soil moisture sample of the 0-3 cm and 3-6 cm soil layers. Surface samples of the 0-1 cm soil were taken with a rectangular shaped scoop tool.

For volumetric soil moisture sampling, the primary measurement was the 0-6 cm dielectric constant at a single location in each site using impedance probes. The dielectric constant is converted to volumetric soil moisture using a calibration equation.

Computing Bulk Density and Soil Moisture

In the laboratory, samples were weighed, dried, and then weighed again. Gravimetric soil moisture (GSM) was computed as:

GSM = (wet weight - dry weight) / dry weight

The bulk density (BD) was determined by dividing the dry soil mass by the volume of the sample (3 cm cylinder of sample length). The bulk density for all 0-1 cm samples was assumed to be 1.5 g/cm3.

Volumetric soil moisture (VSM) was computed as:

VSM = GSM * BD

Note: For the 0-3 cm samples, the 3-6 cm bulk density was used due to the unreliability of the 0-3 cm samples.

Sensor or Instrument Description

Manual Soil Collection

Samples were collected manually in the field using coring tools, rectangular shaped scoop tools, and soil cans.

Infrared Thermometer (Pyrometer) and Temperature Probe

The surface temperature was sampled using handheld infrared thermometers, which are OMEGA OS643-LS Infrared Pyrometers. The instrument has an emissivity of 0.95, accuracy of ± 3%, and temperature range of 0 to 260°C (32 to 500°F). Refer to OMEGA Engineering for more information. Soil temperature was obtained using a temperature probe inserted to depths of 1 cm, 5 cm, and 10 cm. Several different temperature probes were used, but all have a metal rod, plastic top, and digital readout.

OS643-LS Infrared Pyrometer
Temperature Probe

Impedance Probes (ThetaProbes)

Investigators used impedance probes to measure surface volumetric soil moisture. The probes were Type ML2 ThetaProbe manually-operated impedance instruments manufactured by Delta-T Devices, Ltd. The ThetaProbes have four separate 6 cm stainless steel rods that were inserted vertically into the soil. Each instrument was connected to a handheld reader that delivers the electrical pulse, detects the return signal, and converts the period to voltage between 0 and about 1 V.


ML2 ThetaProbe

The software provided by the probe manufacturer calibrates the theta probes by calculating an estimate of volumetric soil moisture according to the following equation:

Theta =
1.07 + 6.4V - 6.4V2 + 4.7V3 - a0

a1

where a0 and a1 are 1.6 and 8.4, respectively. These estimates are provided in the data file.

Researchers also performed site-specific calibration for each field of sampling. Probe voltage readings from a row sampling point were compared to the volumetric soil moisture measured at the same point. A regression relationship was developed and new volumetric soil moisture values were estimated.

For several sites (GA01, GA08, GA09, GA24), recalibration of the probes was inappropriate because of the small dynamic range of the moisture values. For these sites, the general calibration coefficients were used for the site-specific calibration.

5. References and Related Publications

Please see the SMEX03 Web site for more information, and the NSIDC SMEX Web site to access data.

6. Document Information

Acronyms and Abbreviations

The following acronyms and abbreviations are used in this document.

AMSR-E Advanced Microwave Scanning Radiometer - Earth Observing System
ASCII American Standard Code for Information Interchange
BD Bulk Density
EDT Eastern Daylight Time
FTP File Transfer Protocol
GA Georgia
GC General Calibration
GSM Gravimetric Soil Moisture
NASA National Aeronautics and Space Administration
NSIDC National Snow and Ice Data Center
SMEX Soil Moisture Experiment
SMEX03 Soil Moisture Experiment 2003
SSC Site-Specific Calibration
ST Soil Temperature
TP ThetaProbe
URL Uniform Resource Locator
USDA-ARS United States Department of Agriculture - Agricultural Research Service
VSM Volumetric Soil Moisture
WGS84 World Geodetic System 1984

Document Creation Date

March 2006

Document URL

http://nsidc.org/data/docs/daac/nsidc0288_smex03_reg_gsm_ga.gd.html