SMEX03 Watershed Ground Soil Moisture Data: Oklahoma
Summary
This data set combines data for several parameters measured for the Soil Moisture Experiment 2003 (SMEX03). The parameters include bulk density, gravimetric and volumetric soil moisture, and surface and subsurface soil temperature. This study was conducted between 2 July 2003 and 17 July 2003 in the Little Washita watershed in Oklahoma, USA. Data were collected using a variety of methods and sensors. Data are formatted as ASCII text, 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
Jackson, Thomas J. and Michael H. Cosh. 2006 SMEX03 watershed ground soil moisture data: Oklahoma. Boulder, CO USA: National Snow and Ice Data Center. Digital media.
The following example shows how to cite the use of this data set in a publication. For more information, see our Use and Copyright Web page.
Overview Table
| Category | Description |
|---|---|
| Data format | Tab-delimited ASCII text |
| Spatial coverage and resolution | Southernmost Latitude: 34.90º N |
| Temporal coverage and resolution | 2 July 2003 to 17 July 2003 |
| File naming convention | LW_GVSM_Raw.txt LW_GVSM_Sum.txt LW_Temp_Raw.txt LW_Temp_Sum.txt |
| File size | The files sizes range from approximately 22 KB to 407 KB. |
| Parameter(s) | Gravimetric and volumetric soil moisture, bulk density, surface temperature, 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
Investigators
Thomas J. Jackson
Hydrology and Remote Sensing Laboratory
US Department of Agriculture (USDA) - Agricultural Research Service
(ARS)
Beltsville, MD 20705
USA
Michael H. Cosh
Hydrology and Remote Sensing Laboratory
US Department of Agriculture (USDA) - Agricultural Research Service
(ARS)
Beltsville, MD 20705
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 and the National Soil Tilth Laboratory for their assistance. 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 formatted as tab-delimited ASCII text. The column headings for each data file are described in Tables 1 through 4.
Note: Missing data are represented by -99.
| Column Heading | Definition |
|---|---|
| Date | Date of measurements, month/day/year |
| Field_ID | Watershed field number |
| Site_ID | Site location identifier number |
| Start Time | Start time of sampling, Central Daylight Time (CDT) |
| Stop Time | Stop time, CDT |
| Latitude | Latitude of sample, World Geodetic System 1984 (WGS84) degrees |
| Longitude | Longitude of sample site, WGS84 degrees |
| UTM_Easting | Easting of sample site in meters, WGS84 Universal Transverse Mercator (UTM), Zone 14 |
| UTM_Northing | Northing of sample site in meters, WGS84 UTM, Zone 14 |
| TP_mV A | ThetaProbe millivolt reading at position A, volts |
| TP_mV B | ThetaProbe millivolt reading at position B, volts |
| TP_mV C | ThetaProbe millivolt reading at position C, volts |
| TP_VSM_gc A | ThetaProbe volumetric soil moisture (VSM) from general calibration at position A, cubic meters/cubic meters |
| TP_VSM_gc B | ThetaProbe VSM from general calibration at position B, cubic meters/cubic meters |
| TP_VSM_gc C | ThetaProbe VSM from general calibration at position C, cubic meters/cubic meters |
| TP_VSM_scc A | ThetaProbe VSM from site-specific calibration at position A, cubic meters/cubic meters |
| TP_VSM_scc B | ThetaProbe VSM from site-specific calibration at position B, cubic meters/cubic meters |
| TP_VSM_scc C | ThetaProbe VSM from site-specific calibration at position C, cubic meters/cubic meters |
| Can_ID 0-3 cm | Can identification number for 0-3 cm sample |
| Can_Wgt 0-3 cm | Can weight for 0-3 cm sample, grams |
| Wet_Wgt 0-3 cm | Wet weight for 0-3 cm sample, grams |
| Dry_Wgt 0-3 cm | Dry weight for 0-3 cm sample, grams |
| GSM 0-3 cm | Gravimetric soil moisture (GSM) for 0-3 cm sample, grams water/grams dry soil |
| Bulk_Density 0-3 cm | Bulk density for 0-3 cm sample, grams/cubic meters |
| VSM 0-3 cm | VSM for 0-3 cm sample, cubic meters/cubic meters |
| Can_ID 3-6 cm | Can identification number of 3-6 cm sample |
| Can_Wgt 3-6 cm | Can weight of 3-6 cm sample, grams |
| Wet_Wgt 3-6 cm | Wet weight of 3-6 cm sample, grams |
| Dry_Wgt 3-6 cm | Dry weight of 3-6 cm sample, grams |
| GSM 3-6 cm | GSM of 3-6 cm sample, grams water/grams dry soil |
| Bulk_Density 3-6 cm | Bulk density of 3-6 cm sample, grams/cubic meters |
| VSM 3-6 cm | VSM of 3-6 cm sample, cubic meters/cubic meters |
| Total VSM 0-6 cm | Total VSM of 0-6 cm, cubic meters/cubic meters |
| Scoop? | Was a scoop tool used for this sample? If so, an average bulk density was used for the calculation of VSM. |
| Column Heading | Definition |
|---|---|
| Date | Date of measurements, month/day/year |
| Field_ID | Watershed field number |
| Start_Time | Start time of sampling, Central Daylight Time (CDT) |
| Stop_Time | Stop time, CDT |
| Latitude | Latitude of sample, World Geodetic System 1984 (WGS84) degrees |
| Longitude | Longitude of sample site, WGS84 degrees |
| UTM_Easting | Easting of sample site in meters, WGS84 Universal Transverse Mercator (UTM), Zone 14 |
| UTM_Northing | Northing of sample site in meters, WGS84 UTM, Zone 14 |
| Bulk_Density avg | Average bulk density, kilograms/cubic meters |
| Bulk_Density stdev | Standard deviation for bulk density, kilograms/cubic meters |
| VSM 0-3 cm, avg | Average VSM of 0-3 sample, cubic meters/cubic meters |
| VSM 0-3 cm, stdev | Standard deviation of 0-3 sample, cubic meters/cubic meters |
| VSM 3-6 cm, avg | Average VSM of 3-6 sample, cubic meters/cubic meters |
| VSM 3-6 cm, stdev | Standard deviation of 3-6 sample, cubic meters/cubic meters |
| VSM 0-6 avg | Average VSM of 0-6 sample, cubic meters/cubic meters |
| VSM 0-6 stdev | Standard deviation of 0-6 sample, cubic meters/cubic meters |
| V avg | Average ThetaProbe millivolt reading, volts |
| V stdev | Standard deviation ThetaProbe millivolt reading, volts |
| VSM-gc avg | Average ThetaProbe VSM from general calibration, square meters/square meters |
| VSM-gc stdev | Standard deviation ThetaProbe VSM from general calibration, square meters/square meters |
| VSM-ssc avg | Average ThetaProbe VSM from site specific calibration, square meters/square meters |
| VSM-ssc stdev | Standard deviation ThetaProbe VSM from site specific calibration, square meters/square meters |
| Column Heading | Description |
|---|---|
| Date | Date of measurements, month/day/year |
| Field_ID | Watershed field number |
| Site_ID | Site location identifier number |
| Start Time | Sampling start time, CDT |
| Stop Time | Sampling stop time, CDT |
| Latitude | Latitude of sample site, WGS84 degrees |
| Longitude | Longitude of sample site, WGS84 degrees |
| UTM_Easting | Easting of sample site in meters, WGS84, Zone 14 |
| UTM_Northing | Northing of sample site in meters, WGS84, Zone 14 |
| Apogee IRT | Infrared thermometer reading, degrees Celsius |
| Temp 1 cm | Temperature probe reading at 1 cm, degrees Celsius |
| Temp 5 cm | Temperature probe reading at 5 cm, degrees Celsius |
| Temp 10 cm | Temperature probe reading at 10 cm, degrees Celsius |
| Column Heading | Description |
|---|---|
| Date | Date of measurements, month/day/year |
| Field_ID | Watershed field number |
| Start Time | Sampling start time, CDT |
| Stop Time | Sampling stop time, CDT |
| Latitude | Latitude of sample site, WGS84 degrees |
| Longitude | Longitude of sample site, WGS84 degrees |
| UTM_Easting | Easting of sample site in meters, WGS84, Zone 14 |
| UTM_Northing | Northing of sample site in meters, WGS84, Zone 14 |
| Temp 1 cm avg | Average temperature probe reading at 1 cm depth, degrees Celsius |
| Temp 1 cm stdev | Standard deviation temperature probe reading at 1 cm depth, degrees Celsius |
| Temp 5 cm avg | Average temperature probe reading at 5 cm depth, degrees Celsius |
| Temp 5 cm stdev | standard deviation temperature probe reading at 5 cm depth, degrees Celsius |
| Temp 10 cm avg | Average temperature probe reading at 10 cm depth, degrees Celsius |
| Temp 10 cm stdev | Standard deviation temperature probe reading at 10 cm depth, degrees Celsius |
File and Directory Structure
Table 5 lists the files contained in this data set.
| File Name | Description | File Size |
|---|---|---|
| LW_GVSM_Raw.txt | Little Washita, OK gravimetric and volumetric soil moisture (GVSM) files for raw data. | 470 KB |
| LW_GVSM_Sum.txt | Little Washita, OK gravimetric and volumetric soil moisture (GVSM) files for summary data. | 33 KB |
| LW_Temp_Raw.txt | Little Washita, OK soil temperature and surface temperature (Temp) files for raw data. | 214 KB |
| LW_Temp_Sum.txt | Little Washita, OK soil temperature and surface temperature (Temp) files for summary data. | 22 KB |
Spatial Coverage
Southernmost Latitude: 34.90º N
Northernmost Latitude: 34.96º N
Westernmost Longitude: 98.30º W
Easternmost Longitude: 97.95º W
Temporal Coverage
Data were collected from 2 July 2003 to 17 July 2003.
Temporal Resolution
All parameters were collected daily. Surface soil moisture was sampled between 9:00 A.M. and 12:00 P.M. CDT.
Parameter or Variable
Parameter Description
Table 6 lists parameters of this data set, the sensor/method of measurement, and their units of measure.
| Parameter | Units of Measurement | Source/Sensor(s) |
|---|---|---|
| Gravimetric soil moisture | Grams of water per grams of dry soil (g/g) * 100 | Manual soil collection |
| Volumetric soil moisture | Grams water per grams dry soil (g/g) | Computed from bulk density |
| Volumetric soil moisture | Cubic meters per cubic meters (m3/m3) |
Impedance probes |
| Bulk density | Grams per cubic centimeter (g/cm3) | Manual soil collection |
| Surface and subsurface soil temperature | Degrees Celsius | Infrared pyrometers and temperature probes |
| Surface soil moisture | Water fraction volume cubic meters per cubic meters (m3/m3) * 100 | Impedance probes |
Sample Data Records
For each file of this data set, the first four and last four columns are displayed in the samples below.
The following sample shows the first five rows from LW_GVSM_Raw.txt. The value -99 is a fill value for missing values, and the entries for the column titled Scoop? are often left blank.
Date |
Field ID |
Site ID |
Start Time |
... |
Bulk_Density 3-6 cm |
VSM 3-6 cm |
Total_VSM 0-6cm |
Scoop? |
7/2/2003 |
LW02 |
1 |
13:45 |
... |
-99 |
-99 |
-99 |
|
7/3/2003 |
LW02 |
2 |
13:45 |
... |
1.547 |
0.272 |
0.274 |
|
7/4/2003 |
LW02 |
3 |
13:45 |
... |
-99 |
-99 |
-99 |
|
7/5/2003 |
LW02 |
4 |
13:45 |
... |
-99 |
-99 |
-99 |
The following sample shows the first five rows of the LW_GVSM_Sum.txt file. Some fields may contain fill values of -99:99 and other missing parameters are denoted by -99.
Date |
Field ID |
Start Time CDT |
Stop_Time CDT |
... |
VSM-gc avg |
VSM-gc stdev |
VSM-ssc avg |
VSM-ssc stdev |
7/2/2003 |
LW02 |
13:45 |
15:10 |
... |
0.21 |
0.05 |
0.187 |
0.023 |
7/2/2003 |
LW03 |
9:55 |
10:45 |
... |
0.11 |
0.051 |
0.128 |
0.038 |
7/2/2003 |
LW04 |
10:50 |
12:20 |
... |
0.089 |
0.041 |
0.087 |
0.029 |
7/2/2003 |
LW11 |
-99:99 |
-99:99 |
... |
-99 |
-99 |
-99 |
-99 |
The following sample shows the first five rows of the LW_Temp_Raw.txt file. Missing parameters are denoted by -99.
Date |
Field ID |
Site ID |
Start Time |
... |
Apogee IRT in Celsius |
Temp 1 cm |
Temp 5 cm |
Temp 10 cm |
7/2/2003 |
LW02 |
1 |
13:45 |
... |
-99 |
40.2 |
34.1 |
31.7 |
7/3/2003 |
LW02 |
2 |
13:45 |
... |
-99 |
36.5 |
31.3 |
31.3 |
7/4/2003 |
LW02 |
3 |
13:45 |
... |
-99 |
38.3 |
31.3 |
31.3 |
7/5/2003 |
LW02 |
4 |
13:45 |
... |
-99 |
35.5 |
31.3 |
31.3 |
The following sample shows the first five rows of file LW_Temp_Sum.txt. Some time fields contain fill values of -99:99, and other missing parameters are denoted by -99.
Date |
Field ID |
Start Time CDT |
Stop Time CDT |
... |
Temp 5 cm avg |
Temp 5 cm stdev |
Temp 10 cm avg |
Temp 10 cm stdev |
7/2/2003 |
LW02 |
13:45 |
15:10 |
... |
31.4 |
2.3 |
31.3 |
2.2 |
7/2/2003 |
LW03 |
9:55 |
10:45 |
... |
32.8 |
4.3 |
29.7 |
2.5 |
7/2/2003 |
LW04 |
10:50 |
12:20 |
... |
32.3 |
2.1 |
29.3 |
1.3 |
7/2/2003 |
LW11 |
-99:99 |
-99:99 |
... |
32.1 |
3.5 |
30.2 |
3 |
Error Sources
Volumetric Soil Moisture
Soil dielectric constants measured with impedance probes (ThetaProbes) were used in volumetric soil moisture computations. 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.
Bulk Density
The coring tool used extracts a known volume of soil that was used to compute a bulk density. There is potential for compaction with this tool, resulting in higher bulk densities when compared to other methods. Occasionally, a scoop tool was used to retrieve a soil sample when soil was excessively dry. This scoop tool does not allow for a bulk density estimate. In these situations, the average bulk density from all coring tool samples was used for computation of volumetric soil moisture for scoop samples.
The bulk density value from the 0-3 cm sample was considered less reliable than the 3-6 cm sample; therefore, the 3-6 cm bulk density value was used for volumetric soil moisture calculations.
3. Data Access and Tools
Data Access
Data are available via FTP.
Volume
The total volume is approximately 740 KB.
Related Data Collections
See related information on the NSIDC Soil Moisture Experiment (SMEX) Web site.
4. Data Acquisition and Processing
Theory of Measurements
Sampling
Sampling was performed on sites approximately one-quarter section, 0.8 km by 0.8 km, in size. Soil samples were collected and soil temperature, surface temperature, soil dielectric constants, and flux tower measurements were taken at 14 points in these sites. Figure 1 illustrates the sampling locations within the one-quarter section sites.
Gravimetric soil samples were taken with a coring tool at sites marked All on Figure 1. Four samples per field were retrieved.
Figure 1: Sampling Locations for SMEX03 Watershed Soil Moisture Data
Determining Gravimetric Soil Moisture
Gravimetric soil moisture was determined in the laboratory by weighing, drying, and weighing again soil samples collected with the coring tool.
Computing Bulk Density and Volumetric Soil Moisture
Bulk density was computed by dividing the dry soil mass by the volume of the coring tool, either 1 cm or 5 cm. The bulk density value computed from the 3-6 cm soil sample was deemed more reliable, and this value was used in the calculation of volumetric soil moisture:
VSM = GSM * BD
Note: For samples collected with the scoop tool, the average bulk density from all coring tool samples was used for computation of volumetric soil moisture.
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 such as the OMEGA OS643-LS Infrared Pyrometer. This 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.
Impedance Probes (ThetaProbes)
Investigators used impedance probes to measure surface volumetric soil moisture. The probes were Type ML2 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 delivered the electrical pulse, detected the return signal, and converted the period to voltage between 0 and about 1 V.
The software provided by the probe manufacturer calibrates the ThetaProbes 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 files.
Researchers also performed site-specific calibration for each field of sampling. ThetaProbe 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.
Field averages were calculated by counting each row reading twice for a total of four data points per sampling site. Field averages and standard deviations were calculated by computing the sampling site average, and then computing the average amongst the 14 field sampling sites. Finally, standard deviations were calculated.
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 |
| CDT | Central Daylight Time |
| FTP | File Transfer Protocol |
| GC | General Calibration |
| GSM | Gravimetric Soil Moisture |
| IRT | InfraRed Thermometer |
| NASA | National Aeronautics and Space Administration |
| NSIDC | National Snow and Ice Data Center |
| OK | Oklahoma |
| OS | Oklahoma South |
| SMEX | Soil Moisture Experiment |
| SMEX03 | Soil Moisture Experiment 2003 |
| SSC | Site-Specific Calibration |
| TP | ThetaProbe |
| URL | Uniform Resource Locator |
| USDA-ARS | United States Department of Agriculture - Agricultural Research Service |
| UTM | Universal Transverse Mercator |
| VSM | Volumetric Soil Moisture |
| WGS84 | World Geodetic System 1984 |
Document Creation Date
June 2006
Document URL
http://nsidc.org/data/docs/daac/nsidc0296_smex03_watershed_gsm_ok.gd.html
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