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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

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

Jackson, T. and M. Cosh. 2006. SMEX03 Watershed Ground Soil Moisture Data: Oklahoma. [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 and resolution

Southernmost Latitude: 34.90º N
Northernmost Latitude: 34.96º N
Westernmost Longitude: 98.30º W
Easternmost Longitude: 97.95º W

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.

Table 1: Column Headings and Definitions for the LW_GVSM_Raw.txt File
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.


Table 2: Column Headings and Definitions for the LW_GVSM_Sum.txt File
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


Table 3: Column Headings and Definitions for the LW_Temp_Raw.txt File
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


Table 4: Column Headings and Definitions for the LW_Temp_Sum.txt File
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.

Table 5: 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.

Table 6: Parameters In This Data Set
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