SMEX02 Watershed Vitel Network Soil Moisture Data, Walnut Creek, Iowa

Summary

This data set contains several parameters measured for the Soil Moisture Experiment 2002 (SMEX02). The parameters include soil moisture, temperature, conductivity, and salinity. This study was conducted during June and July 2002 in the Walnut Creek watershed in south-central Iowa, USA. Data were collected in crop fields, using a network of Vitel Hydra Probes that were located near the flux towers installed in the study area. 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

Jackson, T., and M. Cosh. 2003. SMEX02 watershed Vitel network soil moisture data, Walnut Creek, Iowa. Boulder, CO: National Snow and Ice Data Center. Digital media.

Overview Table

Category	Description
Data format	Data consist of tab-delimited ASCII text files.
Spatial coverage	Southernmost Latitude: 41.9° N Northernmost Latitude: 42.0° N Westernmost Longitude: -93.8° W Easternmost Longitude: -93.4° W
Temporal coverage and resolution	Data were collected hourly from 23 June 2002 to 12 July 2002.
File naming convention	File names are of the form "WCxxx_HP_VSM.txt," where: WC signifies the Walnut Creek watershed site xxx is a number that corresponds to the flux tower location near which the probe was installed HP signifies Hyrda Probe VSM signifies volumetric soil moisture
File size	25 KB to 145 KB
Parameter(s)	Soil moisture, soil temperature, soil conductivity, and soil salinity
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) Name and Title

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

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

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

Technical Contact

Acknowledgements

Many graduate students and volunteers collected the field data.

2. Detailed Data Description

Format

Data consist of tab-delimited ASCII text files. The following table describes the column headings for each data file.

Heading	Description
Year	Four-digit year
DOY	Numerical day of year
Hour	Local daylight savings time
Site	Watershed site number (corresponds to the data file name):    3 =   WC03    41.9802° N   93.7399° W    6 =   WC06    41.9330° N   93.7534° W   13 =  WC13    41.9521° N   93.6877° W   14 =  WC14    41.9460° N   93.6961° W 151 = WC151    41.9378° N   93.6632° W 152 = WC152    41.9378° N   93.6647° W 161 = WC161    41.9342° N   93.6627° W 162 = WC162    41.9355° N   93.6641° W   23 =  WC23    41.9925° N   93.5351° W   24 =  WC24    41.9928° N   93.5288° W   25 =  WC25    41.9423° N   93.5394° W   33 =  WC33    41.9755° N   93.6444° W
V1	Voltage 1
V2	Voltage 2
V3	Voltage 3
V4	Voltage 4
Soil	Soil type (1 = Sand; 2 = Silt; 3 = Clay)
Ercent	Real dielectric constant
Eicent	Imaginary dielectric constant
Temp	°C
Ercent25	Real dielectric constant, temperature corrected to 25° C
Eicent25	Imaginary dielectric constant, temperature corrected to 25° C
Waterwfv	Water fraction volume in m3/m3 (volumetric soil moisture)
NACLburden	Soil salinity in g NaCl/liter
Concent	Soil conductivity in S/m
concent25	Temperature-corrected (25 C) soil conductivity in S/m
watercond	Temperature-corrected (25 C) soil water conductivity in S/m

File and Directory Structure

There are 12 data files (ASCII text files), one for each probe. All files are located in the tower_vitel_sensors directory.

File Naming Convention

File names are of the form "WCxxx_HP_VSM.txt," where:

• WC signifies the Walnut Creek watershed site
• xxx is a number that corresponds to the flux tower location near which the probe was installed
• HP signifies Hyrda Probe
• VSM signifies volumetric soil moisture

File Size

File sizes range from 25 KB to 145 KB.

Spatial Coverage

Data were collected at sites within approximately:

Southernmost Latitude: 41.9° N
Northernmost Latitude: 42.0° N
Westernmost Longitude: -93.8° W
Easternmost Longitude: -93.4° W

Temporal Coverage

Data were collected from 23 June 2002 to 12 July 2002.

Temporal Resolution

Data were collected hourly.

Parameter or Variable

Parameter Description

Parameters in this data set include the following:

Parameter	Unit of Measurement
Soil temperature	°C
Soil moisture	Water fraction volume (m3/m3)
Soil salinity	g NaCl/liter
Soil conductivity	MKS unit S/m

Sample Data Record

The following is a sample from file "WC23_HP_VSM.txt." Only the header and the first four data rows are shown; only the first 10 of the 19 columns are shown.

Year	DOY	Hour	Site	V1	V2	V3	V4	Soil	Ercent
2002	177	1000	23	1.9783	1.538	1.2116	0.6332	2	8.8
2002	177	1100	23	1.9745	1.5322	1.2018	0.56798	2	8.82
2002	177	1200	23	1.9718	1.5279	1.1944	0.53559	2	8.83
2002	177	1300	23	1.9711	1.5262	1.1908	0.50254	2	8.84

3. Data Access and Tools

Data Access

Data are available via FTP.

Software and Tools

No special tools are required to view these data.

Related Data Collections

See related information on the Soil Moisture Experiment (SMEX) Web site.

4. Data Acquisition and Processing

A network of Vitel Hydra Probes was installed near most of the flux towers that were established for the SMEX02 experiment. A total of 12 probes were installed in mid-June 2002 throughout the Walnut Creek watershed area at a depth of 5 cm. The probes recorded data on an hourly basis.

Flux Tower

Sensor or Instrument Description

Measurements were taken using Vitel Type A Hydra Probes (HP). This version is compatible with Campbell CR-10 data loggers; the temperature output voltage never exceeds 2.5 V. Refer to the manufacturer, Stevens-Vitel for more information.

Vitel Hydra Probe

Processing Steps

The Vitel Type A Hydra Probe (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 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 measured the real and imaginary dielectric constants. Because both the real and imaginary dielectric constants 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.

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-Vitel. The program requires the four voltages and a soil classification (sand=1, silt=2, and clay=3). For this region, silt was used as the appropriate soil type for each of the HP installations. Preliminary calibration of the probes indicated that with the exception of the WC33 site, the probes measured volumetric soil moisture accurately for the installation location. Therefore, the quality control of these data was limited to removing samples for which the program returned erroneous data because of corrupted voltages. These voltages may be a result of several things, including faulty installation, lightning strikes, and rodent impact. Erroneous samples were removed, so the data are not continuous for every HP.

5. References and Related Publications

Please see the SMEX02 site for more information, and the NSIDC SMEX 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
FTP	File Transfer Protocol
HP	Hydra Probe
NSIDC	National Snow and Ice Data Center
SMEX	Soil Moisture Experiment
UTM	Universal Transverse Mercator
WC	Walnut Creek

Document Creation Date

20 August 2005

Document URL

http://nsidc.org/data/docs/daac/nsidc0277_smex_wc_vitel.gd.html