SMEX03 Little River Micronet Soil Moisture Data: Georgia

Summary

Parameters for this data set include precipitation, soil temperature, volumetric soil moisture, soil conductivity, and soil salinity measured in the Little River Watershed (LRW) Micronet regional study areas of southeastern Georgia, USA. Data for this study were collected from 01 May 2003 through 31 August 2003 using in situ soil moisture sensors at depths of 2, 8, and 12 inches in addition to tipping bucket rain gauges as part of the Soil Moisture Experiment 2003 (SMEX03). These data are provided in ASCII comma-delimited text format 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

The following example shows how to cite the use of this data set in a publication. For more information, see our Use and Copyright Web page.

Bosch, David D., and Michael H. Cosh. 2008. SMEX03 Little River Micronet Soil Moisture Data: Georgia. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media.

Overview Table

Category	Description
Data format	ASCII comma-delimited text
Spatial coverage and resolution	Southernmost Latitude: 31.4° N Northernmost Latitude: 31.8° N Westernmost Longitude: 83.75° W Easternmost Longitude: 83.4° W ~9 km resolution
Temporal coverage and resolution	01 May 2003 - 31 August 2003 Measurements were made every 30 minutes.
File naming convention	RG##_MJJA_2003.dat
File size	494 - 649 KB per file
Parameter(s)	Precipitation Soil Temperature Volumetric Soil Moisture Soil Salinity Soil Conductivity
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)

David D. Bosch
Southeast Watershed Research Laboratory (SEWRL)
US Department of Agriculture (USDA) - Agricultural Research Service (ARS)
Tifton, GA 31794 USA

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

Technical Contact

Acknowledgements

The investigators would like to acknowledge the USDA ARS SEWRL in addition to the many graduate students and volunteers who collected the field data. They would also like to acknowledge NASA for their generous contributions to the study.

2. Detailed Data Description

Format

Data are presented in ASCII comma-delimited text files. Table 1 details the data fields for each of the nineteen text files.

Table 1. Column Format for All Data Files

Column Heading	Units	Description
Date	MM/DD/YYYY (Month/Day/Year)	Date reading was made
Time	HH:MM (Hour:Minute)	Eastern Daylight Time (EDT)
2Temp	°F (Degrees Fahrenheit)	Soil temperature measurement 2 inches below surface
2WtrCnt	cm3/cm3 (Cubic Centimeters/Cubic Centimeters)	Soil water content measurement 2 inches below surface
2Sal	g/L (Grams/Liter)	Soil salinity measurement 2 inches below surface
2Con	mhos/m (Electrical Conductance/Meter)	Soil conductivity measurement 2 inches below surface
8Temp	°F (Degrees Fahrenheit)	Soil temperature measurement 8 inches below surface
8WtrCnt	cm3/cm3 (Cubic Centimeters/Cubic Centimeters)	Soil water content measurement 8 inches below surface
8Sal	g/L (Grams/Liter)	Soil salinity measurement 8 inches below surface
8Con	mhos/m (Electrical Conductance/Meter)	Soil conductivity measurement 8 inches below surface
12Temp	°F (Degrees Fahrenheit)	Soil temperature measurement 12 inches below surface
12WtrCnt	cm3/cm3 (Cubic Centimeters/Cubic Centimeters)	Soil water content measurement 12 inches below surface
12Sal	g/L (Grams/Liter)	Soil salinity measurement 12 inches below surface
12Con	mhos/m (Electrical Conductance/Meter)	Soil conductivity measurement 12 inches below surface
PrecipPrd	in (Inches)	Total precipitation rain gauge measurement per record period
PrecipDay	in (Inches)	Total precipitation rain gauge measurement per day

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File and Directory Structure

Data are available on the FTP site in the soil_moisture_network directory. Nineteen ASCII files, each representing a different LRW Micronet station, are contained within this directory.

File Naming Convention

Files are named according to the following convention:

RG##_MJJA_yyyy_.dat

Where:

Table 2. Description of File Name Variables

Variable	Description
RG	LRW Micronet rain gauge station (RG = rain gauge)
##	LRW Micronet station identification number
MJJA	Indicates data collected during May, June, July, and August
yyyy	Four-digit year
.dat	Indicates that this is a data file.

Example: RG08_MJJA_2003.dat

File Size

File sizes range from 494 to 649 KB each.

Spatial Coverage

The data set covers LRW Micronet stations located in southeastern Georgia:

Southernmost Latitude: 31.4° N
Northernmost Latitude: 31.8° N
Westernmost Longitude: 83.75° W
Easternmost Longitude: 83.4° W

Table 3 lists a detailed geographic description of the 19 LRW Micronet stations. Location information is georeferenced to the World Geodetic System 1984 (WGS 84) datum.

Table 3. Geolocation of Measurements

LRW Micronet Rain Gauge Station	Latitude (Decimal Degrees)	Longitude (Decimal Degrees)	Northing (Meters)	Easting (Meters)
RG08	31.48656	-83.5737	3486396	255514
RG12	31.52344	-83.63895	3490633	249416
RG16	31.55747	-83.56733	3494245	256307
RG22	31.59112	-83.65478	3498174	248094
RG26	31.62946	-83.61244	3502329	252215
RG31	31.67102	-83.69819	3507136	244193
RG32	31.67275	-83.64213	3507197	249514
RG34	31.69171	-83.69268	3509417	244772
RG37	31.70929	-83.75400	3511512	239007
RG39	31.70491	-83.70537	3510911	243605
RG40	31.71093	-83.67384	3511504	246611
RG43	31.72600	-83.71642	3513275	242616
RG50	31.75212	-83.69296	3516117	244911
RG52	31.75630	-83.75168	3516720	239359
RG63	31.52143	-83.54790	3490205	258057
RG65	31.64325	-83.41135	3503419	271327
RG66	31.67191	-83.60215	3507013	253304
RG67	31.56676	-83.70344	3495586	243409
RG68	31.41240	-83.36482	3477727	275188

Spatial Resolution

The LRW Micronet stations are approximately 9 km apart.

Temporal Coverage

Data were acquired from 01 May 2003 to 31 August 2003.

Temporal Resolution

This data set includes soil moisture data and precipitation data at 30 minute intervals. Hydra Probe (HP) measurements were recorded every five minutes, then averaged, and rain gauge measurements were recorded every minute, then summed.

Parameter or Variable

Parameter Description

Parameters for this data set include:

• Precipitation (inches)
• Soil Temperature (°F)
• Volumetric Soil Moisture (cm³/cm³)
• Soil Conductivity (mhos/m)
• Soil Salinity (g/L)

Sample Data Record

Table 4 displays a partial sample of the data file RG08_MJJA_2003.dat. The first four columns and last four columns of the data file are shown for the first four rows.

 

Table 4. Sample Data Record

Date,	Time,	2Temp,	2WtrCnt,	...	12Sal,	12Con,	PrecipPrd,	PrecipDay
"05/30/2003",	"11:00",	75.28,	0.1673,	...	0.0196,	0.00088,	0,	0
"05/30/2003",	"11:30",	76.15,	0.1658,	...	0.0187,	0.00084,	0,	0
"05/30/2003",	"12:00",	77.04,	0.1657,	...	0.0221,	0.00098,	0,	0
"05/30/2003",	"12:30",	77.94,	0.1658,	...	0.0197,	0.00088,	0,	0

 

Error Sources

The quality control of this data set was limited to removing samples for which the program returned erroneous data due to corrupted voltages. These voltages may be a result of several things, including for example, faulty installation, lightening strikes, and rodent impact. Erroneous samples were removed; therefore, the data are not continuous for every HP.

Quality Assessment

These data have been quality controlled and suspect or missing data have been removed. Consequently, the data are not continuous. Quality control and quality assurance have been limited, but investigations have led to some improvements. Several sensors have been eliminated from this averaging due to poor or suspicious performance. Arithmetic averages and averages based on nearest neighbor weighting are based on the same set of sensors. Standard deviations are also calculated for reference. Table 5 lists regions where measurements are either poor or outside the LRW Micronet.

 

Table 5. Geolocation of Data of Poor Quality or Outside LRW Micronet

Micronet Station rain gauge	Latitude (Decimal Degrees)	Longitude (Decimal Degrees)	Northing (Meters)	Easting (Meters)	Quality
RG08	31.48656	-83.5737	3486396	255514	Poor
RG26	31.62946	-83.61244	3502329	252215	Poor
RG37	31.70929	-83.75400	3511512	239007	Poor
RG39	31.70491	-83.70537	3510911	243605	Poor
RG43	31.72600	-83.71642	3513275	242616	Poor
RG66	31.67191	-83.60215	3507013	253304	Outside LRW Micronet
RG67	31.56676	-83.70344	3495586	243409	Outside LRW Micronet
RG68	31.41240	-83.36482	3477727	275188	Outside LRW Micronet

 

3. Data Access and Tools

Data Access

Data are available via FTP.

Volume

The total data volume is approximately 12 MB.

Related Data Collections

• AMSR-E Soil Moisture Validation Data: Data sets from SMEX campaigns available at NSIDC.
• AMSR-E/Aqua Data at NSIDC: AMSR-E standard products available at NSIDC.

4. Data Acquisition and Processing

The LRW Micronet

The USDA-ARS SEWRL collected hydrologic and climatic data on the 334 km² LRW near Tifton, Georgia, USA since 1968. The LRW Micronet hydrologic network consists of rain gauges and stream gauges within nested watersheds as shown in Figure 1. It is located in the headwaters of the Suwannee River Basin, a major interstate basin that begins in Georgia and empties into the Gulf of Mexico in the Big Bend region of Florida. The Suwannee River Basin is completely contained in the Coastal Plain Physiographic Region and is the largest free-flowing river in the Southeastern United States Coastal Plain. The Little River is a tributary of the Withlacoochee River which, along with the Alapaha River, is one of two main tributaries of the Suwannee River.

Figure 1. LRW Micronet Hydrologic Network: Georgia, USA

The paired and nested arrangement of the experimental watershed facilitates testing of analytical formulas and modeling concepts. Instrumentation was installed in the late 1960s and early 1970s and has been in continuous operation since that time. Continued operation of this hydrologic network supports hydrologic research as well as the environmental quality and riparian research programs of the SEWRL and cooperators.

Extensive land use information (Williams 1982)(Perry, et al 1999) and physical characterization data (Sheridan and Ferreira 1992) exist for the LRW Micronet. The watershed land use is a mixture of row-crop agriculture, pasture and forage production, upland forest, and riparian forest. Sub-watersheds range from approximately 25 pecent to 65 percent agricultural land. Figures 2 and 3 show vegetation conditions in the Georgia regional study area as expected in late June. Rainfall in the region is poorly distributed and often occurs as short-duration, high-intensity convective thunderstorms (Bosch et al 1999). Hydrologic and water quality measurements collected on the watershed include: stream flow; precipitation; and nutrient, pathogenic bacteria, and pesticide content. The hydrologic measurement network consists of eight horizontal broad-crested weirs with v-notch center sections. Five minute continuous upstream and downstream stage data are recorded. Within the watershed, a network of 35 tipping bucket precipitation gauges record five minute cumulative rainfall. The spacing between the precipitation gauges varies from 3 to 8 km. A detailed data management system exists to provide processing, editing, and summarization of LRW Micronet data (Sheridan, et al 1995).

 

Figure 2. Peanut Crop in Georgia, USA. Vegetation conditions in the Georgia regional study area as expected in late June.		Figure 3. Cotton Crop in Georgia, USA. Vegetation conditions in the Georgia regional study area as expected in late June.

 

Theory of Measurements

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. Since 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.

Sensor or Instrument Description

Soil moisture and temperature were measured using Stevens-Vitel Type A Hydra Probes, as shown in Figure 4. This version is compatible with Campbell CR-10 data loggers; the temperature output voltage never exceeds 2.5 volts. The HP has three main structural components: a multiconductor cable, a probe head, and sensing tines. Precipitation was measured using Texas Electronics tipping bucket rain gauges.

Figure 4. Stevens-Vitel Hydra Probe

 

Data Acquisition Methods

In 2001, as part of the NASA Aqua Calibration/Validation Program, surface soil moisture sensors were installed at a number of locations in the LRW and surrounding region. Thirty-nine Stevens-Vitel soil moisture Hydra Probes were installed at thirteen locations within or near the watershed, spaced approximately 9 km apart. The data have been collected consistently since early 2002. An additional six LRW Micronet soil moisture sites were established in 2003, and are distributed at existing rain gauge sites and areas outside of the watershed. Refer to the Spatial Coverage section for a list of station locations.

Each of the nineteen LRW Micronet locations contain three soil moisture probes and a digital-recording rain gauge. The soil moisture sensors are installed at 2, 8, and 12 inches below the surface. 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 installation technique aims to minimize disruption to the site so that the probe measurement reflects the undisturbed site as much as possible. Precipitation totals are recorded every minute during rainfall events and half-hour soil moisture averages are calculated from five minute readings. All ongoing data are transferred daily and available on a near-real-time basis from the SEWRL Web site. For SMEX03, hourly rainfall measurements were summed for 30 minute intervals and five minute soil moisture measurments were averaged for 30 minute intervals. The selected subset of Little River rain gauge sites provides watershed-area coverage and covers a range of soil types. Please refer to the LRW Web site for more information.

Derivation Techniques and Algorithms

The output data from the HP consists of a time stamp and four voltages (V1-V4). These voltages are converted to estimate the soil moisture and soil temperature through a program provided by the HP manufacturer, Stevens-Vitel. Refer to the Stevens-Vitel Web site for the Hydra.exe or the hyd-file.exe program. These programs require the four voltages and a soil classification, for example: Sand=1, Silt=2, and Clay=3. Each site was considered sand for this data set.

5. References and Related Publications

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

Refer to the Stevens-Vitel Web site for the Hydra.exe or the hyd-file.exe program.

6. Document Information

Acronyms

Table 6 lists acronyms used in this document.

Table 6. Acronyms

AEMN	Automated Environmental Monitoring Network
AMSR-E	Advanced Microwave Scanning Radiometer - Earth Observing System
ARS	Agricultural Research Service
ASCII	American Standard Code for Information Interchange
FTP	File Transfer Protocol
HP	Hydra Probe
LRW	Little River Watershed
NASA	National Aeronautics and Space Administration
NRCS SCAN	Natural Resources Conservation Service Soil Climate Analysis Network
NSIDC	National Snow and Ice Data Center
SMEX	Soil Moisture Experiment
SEWRL	Southeast Watershed Research Laboratory
URL	Uniform Resource Locator
USDA	United States Department of Agriculture
WGS 84	World Geodetic System 1984

Document Creation Date

March 2008

Document URL

http://nsidc.org/data/docs/daac/nsidc0329_smex03_little_river_micronet_ga.html