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This data set includes soil moisture measurements for the Oklahoma study region. Summary files containing field averages are also provided. This data set is part of the Soil Moisture Experiment 2003 (SMEX03).
Data Set ID:
NSIDC-0289
SMEX03 Regional Ground Soil Moisture Data: Oklahoma, Version 1
This is the most recent version of these data.
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Data: Data integrity verified
Documentation: Key metadata and links to supporting documentation available
User Support: Assistance with data access and basic data usage
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Geographic Coverage |
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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.
Jackson, T. and M. Cosh. 2006. SMEX03 Regional Ground Soil Moisture Data: Oklahoma, 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/KX8PGM1NYUK1. [Date Accessed].Collapse All / Open All
Detailed Data Description
Format
The data are in tab-delimited ASCII text files. The column headings and the information in each column are described in the following tables.
The raw soil moisture data files, ON_GVSM_Raw.txt and OS_GVSM_Raw.txt, contain the following information (ON_GVSM_Raw.txt does not contain a stop time column).
| Column Heading | Description |
|---|---|
| Date | Month/day/year |
| Site ID | Site location identifier number |
| Start_Time (CDT) | Start time of sampling in Central Daylight Time (CDT) |
| Stop_Time (CDT) | Stop time (CDT); stop time is not included in ON_GVSM_Raw.txt; most sampling was 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 |
| UTM_Easting WGS84 | Easting of sample site in meters, WGS84, Zone 14 |
| UTM_Northing WGS84 | Northing of sample site in meters, WGS84, Zone 14 |
| TP-mV A | Impedance probe (ThetaProbe) millivolt reading in V, position A |
| TP-mV B | ThetaProbe millivolt reading in V, position B |
| TP-mV C | ThetaProbe millivolt reading in V, position C |
| TP-VSM_gc A | ThetaProbe volumetric soil moisture (VSM) in m3/m3 from general calibration, position A |
| TP-VSM_gc B | ThetaProbe VSM in m3/m3 from general calibration, position B |
| TP-VSM_gc C | ThetaProbe VSM in m3/m3 from general calibration, position C |
| TP-VSM_scc A | ThetaProbe VSM in m3/m3 from site-specific calibration, position A |
| TP-VSM_scc B | ThetaProbe VSM in m3/m3 from site-specific calibration, position B |
| TP-VSM_scc C | ThetaProbe VSM in m3/m3 from site-specific calibration, position C |
| Can_ID 0-3 cm | Soil can identifier for 0-3 cm sample |
| Can_Wgt 0-3 cm | Soil can weight in grams for 0-3 cm sample |
| Wet_Wgt 0-3 cm | Wet weight in grams of soil for 0-3 cm sample |
| Dry_Wgt 0-3 cm | Dry weight in grams of soil for 0-3 cm sample |
| GSM 0-3 cm | Gravimetric soil moisture in g/g for 0-3 cm sample |
| Bulk_Density 0-3 cm | Bulk density in g/cm3 for 0-3 cm sample |
| VSM 0-3 cm | Volumetric soil moisture (VSM) 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 in grams for 3-6 cm sample |
| Wet_Wgt 3-6 cm | Wet weight of soil in grams for 3-6 cm sample |
| Dry_Wgt 3-6 cm | Dry weight of soil in grams for 3-6 cm sample |
| GSM 3-6 cm | Gravimetric soil moisture in g/g for 3-6 cm sample |
| Bulk_Density 3-6 cm | Bulk density in g/cm3 for 3-6 cm sample |
| VSM 3-6 cm | VSM in m3/m3 for 3-6 cm sample |
| Total VSM 0-6 cm | Total VSM in m3/m3 for 0-6 cm |
| Scoop? | Was a scoop tool used for this sample? If so, an average bulk density was used for the calculation of VSM. |
The summary soil moisture data files, ON_GVSM_Sum.txt and OS_GVSM_Sum.txt, contain the following information (ON_GVSM_Sum.txt does not contain a stop time column).
| Column Heading | Description |
|---|---|
| Date | Month/day/year |
| Site ID | Site location identifier number |
| Start Time (CDT) | Start time of sampling in Central Daylight Time (CDT) |
| Stop_Time (CDT) | Stop time (CDT); stop time is not included in ON_GVSM_Sum.txt; most sampling was 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 |
| UTM_Easting WGS84 | Easting of sample site in meters, WGS84, Zone 14 |
| UTM_Northing WGS84 | Northing of sample site in meters, WGS84, Zone 14 |
| TP-mV average | Average impedance probe (ThetaProbe) millivolt reading in V |
| TP-mV stdev | Standard deviation of ThetaProbe millivolt reading in V |
| TP-VSM_gc average | Average ThetaProbe volumetric soil moisture (VSM) in m3/m3 from general calibration |
| TP-VSM_gc stdev | Standard deviation of ThetaProbe VSM in m3/m3 from general calibration |
| TP-VSM_ssc average | Average ThetaProbe VSM in m3/m3 from site-specific calibration |
| TP-VSM_scc stdev | Standard deviation of ThetaProbe VSM in m3/m3 from site-specific calibration |
The raw temperature data files ON_Temp_Raw.txt and OS_Temp_Raw.txt contain the following information (some column headings may differ slightly between the two files).
| Column Heading | Description |
|---|---|
| Date | Month/day/year |
| Site ID | Site location identifier number |
| Start Time CDT | Start time of sampling in Central Daylight Time (CDT); ON_Temp_Sum.txt has "Local Time CDT" |
| Stop Time CDT | Stop time of sampling in CDT; stop time is not included in ON_Temp_Sum.txt; most sampling was 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 |
| UTM_Easting WGS84 | Easting of sample site in meters, WGS84, Zone 14 |
| UTM_Northing WGS84 | Northing of sample site in meters, WGS84, Zone 14 |
| Apogee IRT | Infrared thermometer reading in degrees Celsius |
| Temp 1 cm | Soil temperature probe reading in degrees Celsius at 1 cm |
| Temp 5 cm | Soil temperature probe reading in degrees Celsius at 5 cm |
| Temp 10 cm | Soil temperature probe reading in degrees Celsius at 10 cm |
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File Naming Convention
Files are named Od_param_type.txt, where
|
d |
= |
either N for Northern or S for Southern |
|
param |
= |
either GVSM for soil moisture data or Temp for temperature data |
|
type |
= |
either Raw for raw data or Sum for summary data |
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File Size
The data files range in size from approximately 35 KB to 126 KB.
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Volume
The total volume is approximately 415 KB.
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Spatial Coverage
Southernmost Latitude: 34.49º N
Northernmost Latitude: 36.80º N
Westernmost Longitude: 98.29º W
Easternmost Longitude: 97.97º W
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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 (g/g) | Manual soil collection |
| Volumetric soil moisture | Cubic meters of water per cubic meters of dry soil (m3/m3) | 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 from ON_GVSM_Sum.txt illustrates the data. The first four data rows are shown; only the first four columns and last four columns of each row are shown (the column headings in the sample indicate the included columns).
|
Date |
Site ID |
Start Time |
Latitude |
... |
TP-VSM_gc |
TP-VSM_gc |
TP-VSM_ssc |
TP-VSM_ssc |
|---|---|---|---|---|---|---|---|---|
|
CDT |
WGS84 |
... |
average |
stdev |
average |
stdev |
||
|
7/2/2003 |
ON01 |
14:01 |
36.8036 |
... |
0.148 |
0.012 |
0.113 |
0.01 |
|
7/3/2003 |
ON01 |
11:01 |
36.8036 |
... |
0.106 |
0.013 |
0.074 |
0.012 |
|
7/4/2003 |
ON01 |
11:20 |
36.8036 |
... |
0.076 |
0.005 |
0.045 |
0.004 |
|
7/5/2003 |
ON01 |
11:20 |
36.8036 |
... |
0.069 |
0.019 |
0.039 |
0.018 |
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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.
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; therefore, the average bulk density from all coring tool samples was used for computation of volumetric soil moisture for scoop samples. 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.
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Software and Tools
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Data Acquisition and Processing
Theory of Measurements
This Oklahoma regional soil moisture site is within a single AMSR-E/Aqua passive microwave footprint (approximately 50 km), and measurements were taken around the time of the Aqua satellite overpass (approximately 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 a quarter section (0.8 km by 0.8 km) in size. In Oklahoma South (OS), a grid of 51 individual sites was sampled, covering approximately 50 km by 100 km (4 by 13 sites; site # 15 was not sampled). In Oklahoma North (ON), a grid of 36 individual sites was sampled, covering approximately 50 km by 75 km (3 by 12 sites). One location in each of the sites was sampled. The sampling was conducted between 11:30 and 15:00 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. The coring tool extracts a known volume of soil which is used to compute a bulk density. Occasionally, a scoop tool was used to retrieve a soil sample when soil was excessively dry.
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 (ThetaProbes). The dielectric constant was 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.
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. For samples collected with the scoop tool, the average bulk density from all coring tool samples was used for computation of volumetric soil moisture.
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Sensor or Instrument Description
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.
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References and Related Publications
Contacts and Acknowledgments
Thomas J. Jackson
Hydrology and Remote Sensing Laboratory
US Department of Agriculture (USDA) - Agricultural Research Service (ARS)
Beltsville, MD 20705
USA
Mike Cosh
Hydrology and Remote Sensing Laboratory
US Department of Agriculture (USDA) - Agricultural Research Service (ARS)
Beltsville, MD 20705
USA
Ron Elliot
Oklahoma State University
Stillwater, OK 74078
USA
Acknowledgments:
Many graduate students and volunteers worked to collect the field data. The investigators thank the SMEX03 Science Team and the National Soil Tilth Lab 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. We would specifically like to acknowledge the contributions of:
- Pat Starks
- Gary Heathman
- Rajat Bindlish
- Doug Miller
- Binayak Mohanty
- Frank Archer
- James Famiglietti
- Daniel Itenfisu
Document Information
Document Creation Date
July 2006
No technical references available for this data set.
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