SMEX03 Little Washita Micronet Soil Moisture Data: Oklahoma

Summary

This data set contains volumetric soil moisture, soil temperature, soil conductivity, soil salinity, and surface temperature data collected during the Soil Moisture Experiment 2003 (SMEX03). The data were collected from 1 June 2003 to 31 August 2003 using in situ soil moisture sensors and radiometric surface temperature sensors in the Little Washita Creek Watershed in southwestern Oklahoma, USA. Data are provided in ASCII text files 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., M. Cosh, P. Starks, and G. Heathman. 2007. SMEX03 Little Washita Micronet 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 files
Spatial coverage and resolution Southernmost Latitude: 34.8° N
Northernmost Latitude: 35.1° N
Westernmost Longitude: 98.2° W
Easternmost Longitude: 97.9° W
Temporal coverage and resolution 1 June 2003 to 31 August 2003
Measurements were recorded every 30 minutes.
File naming convention LW_Micronet_HPA_####.txt where #### identifies the Micronet Station ID.
File size 400 KB to 600 KB
Parameter(s) Volumetric soil moisture
Soil salinity
Soil temperature
Soil conductivity
Surface 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)

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

Michael Cosh
Hydrology and Remote Sensing Laboratory
US Department of Agriculture (USDA) - Agricultural Research Service (ARS)
Beltsville, MD 20705
USA

Patrick Starks
Grazinglands Research Lab
US Department of Agriculture (USDA) - Agricultural Research Service (ARS)
Beltsville, MD 20705
USA

Gary Heathman
Grazinglands Research Lab
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

The investigators would like to acknowledge the USDA ARS Grazinglands Research Laboratory and the many graduate students and volunteers who collected the field data.

2. Detailed Data Description

Format

Data are provided in tab-delimited ASCII text files. Table 1 lists the column headings and data field descriptions for the files.

Table 1: Column Headings and Data Field Descriptions
Column Heading
Units
Description
Year YYYY Year measurement was made
DOY DDD Numerical day of year (Julian Date)
HHMM HHMM Time of day in Central Standard Time (CST)
Lat decimal degrees Latitude (WGS84)
Lon decimal degrees Longitude (WGS84)
Easting meters UTM Easting Zone 14 ( WGS84)
Northing meters UTM Northing Zone 14 (WGS84)
AppTarT °C Apparent Target Temperature
SenBodT °C Sensor Body Temperature
CCT °C Corrected Surface Temperature
V1 volts Voltage 1
V2 volts Voltage 2
V3 volts Voltage 3
V4 volts Voltage 4
RECONST
-
Real Dielectric Constant
IECONST
-
Imaginary Dielectric Constant
TEMP °C Soil Temperature
CRECONST
-
Real Dielectric Constant, Temperature Corrected to 25°C
CIECONST
-
Imaginary Dielectric Constant, Temperature Corrected to 25°C
WATERFV m3/m3 Water Fraction Volume  (Volumetric Soil Moisture)
NACL g NaCl/liter Soil Salinity (grams of sodium chloride per liter)
SCOND S/m Soil Conductivity in Siemen/meter
TSCOND S/m Temperature corrected (25°C) Soil Conductivity (Siemen/meter)
TSWCOND S/m Temperature corrected (25°C) Soil Water Conductivity (Siemen/meter)

File Naming Convention

Files are named according to the following convention.

LW_Micronet_HPA_####.txt

where #### identifies the Micronet Station ID. See Spatial Coverage for a list of station IDs and locations.

File Size

File sizes range from 400 KB to 600 KB.

Spatial Coverage

Southernmost Latitude: 34.8 N
Northernmost Latitude: 35.1 N
Westernmost Longitude: 98.2 W
Easternmost Longitude: 97.9 W

Table 2 lists the geographic locations of the 12 Micronet stations.

Table 2: Micronet Station Locations
Station ID
Latitude
(decimal degrees)
Longitude
(decimal degrees)
Easting
(meters)
Northing
(meters)
111 35.0159 -97.9518 595633 3875308
133 34.9491 -98.1281 579612 3867745
134 34.9366 -98.0753 584446 3866402
136 34.9277 -97.9656 594475 3865513
144 34.8790 -97.9171 598963 3860159
146 34.8854 -98.0231 589269 3860769
149 34.8984 -98.1809 574837 3862082
154 34.8552 -98.1370 578889 3857325
159 34.7966 -97.9932 592100 3850948
162 34.8133 -98.1417 578499 3852674
Berg 35.0456 -97.9167 598800 3878636
NOAA 34.9614 -97.9720 593852 3869245

Temporal Coverage

Data were collected from 1 June 2003 through 31 August 2003.

Temporal Resolution

Hydra Probe and Apogee data were recorded every 30 minutes.

Parameter or Variable

Parameter Description

Parameters in this data set are volumetric soil moisture (m3/m3), soil temperature (°C), soil conductivity (S/m), soil salinity (g NaCl/liter), and surface temperature (°C).

Sample Data Record

The following sample shows the first four columns and the last four columns for the first five rows of the LW_Micronet_HPA_111.txt file.


Year DOY HHMM Lat .... NACL SCOND TSCOND TSWCOND
2003 152 0 35.0159 .... 0.25 0.0148 0.0149 0.3199
2003 152 30 35.0159 .... 0.2422 0.0145 0.0146 0.304
2003 152 100 35.0159 .... 0.2431 0.0145 0.0147 0.3053
2003 152 130 35.0159 .... 0.2492 0.0146 0.0148 0.3198

Error Sources

Corrupted HP voltages resulted from factors such as faulty installation, lightening strikes, and rodent impact. Erroneous samples were removed, therefore, the data are not continuous for every Hydra Probe. 

Quality Assessment

These data have been quality controlled and suspect or missing data have been removed. Consequently, the data are not continuous.

3. Data Access and Tools

Data Access

Data are available via FTP.

Volume

The total volume of all data files is approximately 7 MB.

Related Data Collections

4. Data Acquisition and Processing

The USDA Agricultural Research Service (ARS) has measured hydrologic conditions in the Little Washita Watershed in southwestern Oklahoma since 1961. In 1994, the ARS began monitoring the meteorological conditions in this watershed with an automated 42-station network called the ARS Micronet. Refer to Figure 1. For more information, visit the ARS Micronet Web site.

During the Summer of 2002, surface soil moisture and surface temperature probes were installed at select Micronet sites to provide coverage for large scale estimation of these parameters. Twelve stations were operational during SMEX03. See the Spatial Coverage section for a list of station IDs and locations.

Figure 1: ARS Micronet Stations

Sensor or Instrument Description

Surface temperature was measured using an Apogee infrared thermometer. The instrument has a wavelength range of 6.5 to 14 micrometers and an accuracy of ± 0.4°C for targets at 5°C to 45°C and ± 0.1°C when the sensor body and target are at the same temperature. An infrared thermometer (IRT) is used because they are filtered to allow only a specific waveband, about 8 to 14 microns, to be transmitted to the IRT detector. Visit the Apogee Instruments Inc. Web site for more information.

Soil moisture and soil temperature were measured using Vitel Type A Hydra Probes (HP), shown in Figure 2. This version is compatible with Campbell CR-10 data loggers; the temperature output voltage never exceeds 2.5 V. Visit the Stevens Web site for more information.

Figure 2: Vitel Hydra Probe

Data Acquisition Methods

HP and IRT measurements were recorded every 30 minutes at 12 Micronet stations in Oklahoma. See the Spatial Coverage section for a list of station IDs and locations.

The HP has three main structural components: a multiconductor cable, a probe head, and sensing tines. The probes were installed horizontally in the soil, with the center tine at a depth of 5 cm. The HP installation techniques aimed to minimize disruption to the site as much as possible so that the probe measurement reflects the undisturbed site. 

Derivation Techniques and Algorithms

Soil Temperature

IRTs are filtered to allow only a specific waveband, about 8 to 14 microns, to be transmitted to the IRT detector. This transmitted energy (E) is converted to temperature (T) via the Stefan-Boltzman Law which states E=σεT4, where ε is the emissivity of the object and σ is the Stefan-Boltzmann constant (5.68 x 10-8 Joules m-2 s-1 K-4) (Bugbee et al. 1999).

The apparent target temperature also includes an effect due to the casing temperature of the instrument or the Sensor Body (SB) temperature. A formula is provided by the instrument manufacturers to make this correction (Bugbee et al. 1999).

The basic equation to estimate target temperature for a given SB is:

Corrected Target Temperature = Apparent Target Temperature - Sensor Error Correction

and

Sensor Error Correction = (0.25/P)*[(Apparent Target Temperature - H)2 - K]

where P, H, and K are related to the sensor body temperature Tsb as:

P = 26.168 + 2.8291* Tsb - 0.03329* Tsb2 r2= 0.708
H = 5.8075 - 0.08016* Tsb + 0.00849* Tsb2 r2=0.674
K = -85.943 + 11.740* Tsb + 0.08477* Tsb2 r2=0.893

Volumetric Soil Moisture, Soil Temperature, and Soil Salinity

The HP soil moisture probe determines soil moisture and salinity by making a high frequency (50 MHz) complex dielectric constant measurement, which simultaneously resolves the capacitive and conductive parts of a soil's electrical response. The capacitive part of the response is most indicative of soil moisture, while the conductive part reflects mostly soil salinity. Temperature is determined from a calibrated thermistor incorporated into the probe head.

The measured raw electrical parameters determined by the HP are the real and imaginary dielectric constants. These two parameters serve to fully characterize the electrical response of the soil at the frequency of operation, 50 MHz. These are both dimensionless quantities. Because both the real and imaginary dielectric constants will vary somewhat with temperature, a temperature correction using the measured soil temperature is applied to produce temperature corrected values for the real and imaginary dielectric constant. The temperature correction amounts to calculating what the dielectric constants should be at 25°C.

As a soil is wetted, the low dielectric constant component, air, is replaced by water with its much higher dielectric constant. Thus as a soil is wetted, the capacitive response, which depends upon the real dielectric constant, increases steadily. Through the use of appropriate calibration curves, the dielectric constant measurement can be directly related to soil moisture. The dielectric constant of moist soil has a small, but significant, dependence on soil temperature. The soil temperature measurement that the HP makes can be used to remove most of the temperature effects.

The output data from an HP consists of a time stamp and four voltages (V1-V4), which are converted to estimate the soil moisture and soil temperature through a program provided by Stevens, the HP manufacturer. Refer to the Stevens Web site for the hydra.exe or the hyd-file.exe program. The program requires the four voltages and a soil classification (sand=1, silt=2, and clay=3). Table 3 lists the soil type used for each station in the Stevens program.

Table 3: Station Soil Classification
Station ID
Calculation
Soil Type
111 Silt
133 Sand
134 Sand
136 Silt
144 Sand
146 Silt
149 Silt
154 Silt
159 Sand
162 Sand
Berg Silt
NOAA Silt

5. References and Related Publications

Bugbee, Bruce, M. Droter, O. Monje, and B. Tanner. 1999. Evaluation and Modification of Commercial Infra-red Transducers for Leaf Temperature Measurement. Advances In Space Research 22:1425-1434.

Please see the USDA SMEX03 Web site for in depth information on the science mission and goal of the SMEX project.

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
ARS Agricultural Research Service
ASCII American Standard Code for Information Interchange
CST Central Standard Time
FTP File Transfer Protocol
HP Hydra Probe
IRT Infrared Thermometer
NASA National Aeronautics and Space Administration
NSIDC National Snow and Ice Data Center
SB Sensor Body
SMEX Soil Moisture Experiment
URL Uniform Resource Locator
USDA US Department of Agriculture
WGS84 World Geodetic System 1984

Document Creation Date

October 2007

Document URL

http://nsidc.org/nsidc0320_smex03_gsm_network_ok.gd.html