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Data Set ID: 

SMAPVEX08 In Situ Soil Moisture Data, Version 1

This data set includes several parameters that were obtained from field surveys as part of the Soil Moisture Active Passive Validation Experiment 2008 (SMAPVEX08).

Geographic Coverage

  • Soils > Electrical Conductivity
  • Soils > Soil Moisture/Water Content > Gravimetric Soil Moisture
  • Soils > Soil Temperature
  • Soils > Soil Moisture/Water Content > Volumetric Soil Moisture (Fraction)
Spatial Coverage:
  • N: 39.09, S: 38.93, E: -75.55, W: -76.25

Spatial Resolution:
  • 0.8 km x 0.8 km
Temporal Coverage:
  • 29 September 2008 to 13 October 2008
Temporal Resolution: 2 days to 3 days
Data Format(s):
  • Microsoft Excel
  • ASCII Text
Version: V1
Data Contributor(s): Cosh, M. and T. Jackson.

Data Citation

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.

Cosh, M. and T. Jackson. 2015. SMAPVEX08 In Situ Soil Moisture Data, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: [Date Accessed].

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Detailed Data Description

This data set is comprised of several parameters from in situ measurements for the Soil Moisture Active Passive Validation Experiment 2008 (SMAPVEX2008). The study site was divided into regional squares, approximately .08 km by .08 km in size, with several sample point locations.


Data are provided in Microsoft Excel and ASCII text files. An associated Extensible Markup Language (XML) metadata file is also provided for each data file. Table 1 describes the soil sampling data columns of the data file, SMAPVEX08_GVSM_Final.xls.

Table 1. Data Fields and Descriptions
Column Heading Description
Date 2-digit month/2-digit day/2-digit year
Site_ID Field site: watershed sampling identification number
Sample Sample location number within the field site
Start time Start Time of sampling in Central Daylight Time
IRT_SG Infrared Thermometer Reading, Shadowed Ground
IRT_EG Infrared Thermometer Reading, Sun-Exposed Ground
IRT_SV Infrared Thermometer Reading, Shadowed Vegetation
IRT_EV Infrared Thermometer Reading, Sun-Exposed Vegetation
Temp_1cm Soil Temperature at 1 cm depth
Temp_5cm Soil Temperature at 5 cm depth
Temp_10cm Soil Temperature at 10 cm depth
A_mv Theta Probe millivolt reading in V, position A
B_mv Theta Probe millivolt reading in V, position B
C_mv Theta Probe millivolt reading in V, position C
A_VSM Theta Probe Volumetric Soil Moisture (VSM) from general calibration in m3/m3, position A
B_VSM Theta Probe VSM from general calibration in m3/m3, position B
C_VSM Theta Probe VSM from general calibration in m3/m3, position C
A_VSM_SCC Theta Probe VSM from site specific calibration in m3/m3, position A
B_VSM_SCC Theta Probe VSM from site specific calibration in m3/m3, position B
C_VSM_SCC Theta Probe VSM from site specific calibration in m3/m3, position C
CanID_0-6cm Can identification number for 0-6 cm measure
Can_Wgt_0-6cm Weight of Can (g) for 0-6 cm measure
Wet_Wgt_0-6cm Wet weight (g) for 0-6 cm measure
Dry_Wgt_0-6cm Dry weight (g) for 0-6 cm measure
GSM Gravimetric Soil Moisture in cm3/cm3 for 0-6 cm
GVSM Volumetric Soil Moisture in m3/m3 for 0-6 cm

Blank fields indicate missing data.

Table 2 describes the latitude and longitude columns of the data file, AllTeamGPS.txt.

Table 2. Data Fields and Descriptions
Column Heading Description
Point Field site (Site ID) and sample location number; for example, A01 is A01-4 field site with sample location number 4).
Latitude WGS84 Latitude
Longitude WGS84 Longitude
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File and Directory Structure

Data files are available at:

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File Naming Convention

SV08SM_SMAPVEX08_GVSM_Final.xls contains the soil moisture data from ground sampling. 

SV08SM_AllTeamGPS.txt contains the latitude and longitude data for the sampling points.

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File Size

The data file is approximately 595 KB.

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Spatial Coverage

Southernmost Latitude: 38.93°N
Northernmost Latitude: 39.09°N
Westernmost Longitude: 76.25°W
Easternmost Longitude: 75.55°W

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Spatial Resolution

Sampling was performed on sites approximately one quarter section (0.8 km by 0.8 km) in size. Eight points were sampled in each site.

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Latitude and longitude are provided in World Geodetic System 1984 (WGS84) coordinates.

Grid Description

No grid.

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Temporal Coverage and Resolution

Measurements were taken every two to three days from 29 September 2008 through 13 October 2008.

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Parameter or Variable

Parameters in this data set include gravimetric soil moisture, volumetric soil moisture, soil and surface temperature, electrical conductivity. The following table describes the units of measurement and sources of each parameter.

Table 3. Parameter Units and Sensors
Parameter Unit of Measurement Sensor
Gravimetric soil moisture grams of water per grams of dry soil*100% Manual soil collection
Surface and soil temperature °C OS643-LS Infrared Pyrometers and Temperature Probes
Volumetric Soil Moisture Water Fraction Volume (m3/m3)*100% Theta Probes and manual soil collection
Electrical Conductivity millivolts Theta Probe

Parameter Range

Valid parameter values are as follows:

Gravimetric soil moisture: 0 - 60 %
Volumetric soil moisture: 0 - 60 % 
Surface and soil temperature: 0 - 40°C
Electrical conductivity: 0 - 60 %

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Software and Tools

No special tools are required to view these data. A spreadsheet program which recognizes tab-delimited text files, such as Microsoft Excel, is recommended. Any word-processing program or Web browser will also display the data.

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Data Acquisition and Processing

Theory of Measurements

Section Sampling

Sampling for this SMAPVEX08 data set was performed on sites approximately one quarter section (0.8 km by 0.8 km) in size. Eight points were sampled in a field for Theta Probe volumetric soil moisture and voltage measurements.

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Sensor or Instrument Description

Theta Probes

Investigators used theta probes to measure surface volumetric soil moisture. The probes were Type ML2 manually-operated impedance instruments manufactured by Delta-T Devices, Ltd. The theta probes have 4 separate 6-cm stainless steel rods inserted vertically into the soil. Each instrument was connected to a handheld reader, which delivers the electrical pulse, detects the return signal, and converts the period to a voltage between 0 V and about 1 V. Watershed surface soil moisture was sampled each morning (9:00AM-12:00AM) during the experiment.

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Processing Steps

Gavimetric Processing

Researchers weighed the wet soil obtained in the field, heated the soil in an oven to dry it, and then weighed the dry soil.

Calibration of Probe Measurements

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+6.4*V-6.4*V2+4.7*V3-a0) /a1

(Equation 1)

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

Researchers also performed field-specific calibration for each sampled field. Soil moisture values obtained using the gravimetric sampling technique were compared with the theta probe readings of the corresponding locations. A regression relationship was developed, and revised volumetric soil moisture values were estimated for the theta probe measurements.

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Error Sources

Theta Probe

For various reasons, including severe weather restrictions and cultivation, some sites were not sampled on particular days.


Most field locations have an error of 15 meters.

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Quality Assessment

The field-specific calibration of the soil moisture values (using the soil core samples) ensures high accuracy and minimized the potential errors.

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References and Related Publications

Contacts and Acknowledgments

Michael H. Cosh, Thomas J. Jackson
United States Department of Agriculture - Agricultural Research Service (USDA ARS) 
Hydrology and Remote Sensing Laboratory
10300 Baltimore Avenue
Bldg. 007, Rm. 104
Beltsville, MD 20705


Many graduate students and volunteers worked to collect the field data. We would like to thank the Soil Moisture Active Passive Science Team, George Mason University, George Washington University and University of Maryland Cooperative Extension, specifically Mr. Francis Breeding for their assistance. We would also like to thank the National Aeronautics and Space Administration for their generous contributions to the study.

Document Information


June 2015



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