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This data set includes air temperature, vapor pressure, wind speed, and brightness temperatures taken at 12 flux towers as part of the Soil Moisture Experiment 2002 (SMEX02).
Data Set ID:
NSIDC-0186
SMEX02 Tower-Based Radiometric Surface Temperature, Walnut Creek, Iowa, Version 1
This is the most recent version of these data.
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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.
Jackson, T. and M. Cosh. 2003. SMEX02 Tower-Based Radiometric Surface Temperature, Walnut Creek, Iowa, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/BJZU6IV9HUTE. [Date Accessed].Collapse All / Open All
Detailed Data Description
Format
Data are ASCII tab-delimited text files.
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File Naming Convention
The first four digits identify the WC site in which the flux tower was located. If there are multiple towers in a field, another digit identifies the flux tower. For example, WC151 and WC152.
The following table lists each file name and the location of the corresponding tower.
| File | Latitude | Longitude | Easting in m | Northing in m |
|---|---|---|---|---|
| WC03_Ts.txt | 41.98381 | -93.75497 | 437459 | 4648254 |
| WC06_Ts.txt | 41.93290 | -93.75332 | 437547 | 4642600 |
| WC13_Ts.txt | 41.95215 | -93.68766 | 443007 | 4644692 |
| WC14_Ts.txt | 41.94598 | -93.69622 | 442292 | 4644013 |
| WC151_Ts.txt | 41.93782 | -93.66313 | 445027 | 4643085 |
| WC152_Ts.txt | 41.93782 | -93.66470 | 444897 | 4643086 |
| WC161_Ts.txt | 41.93414 | -93.66270 | 445060 | 4642676 |
| WC162_Ts.txt | 41.93548 | -93.66406 | 444949 | 4642826 |
| WC23_Ts.txt | 41.99245 | -93.53582 | 455620 | 4649077 |
| WC24_Ts.txt | 41.99291 | -93.52858 | 456219 | 4649124 |
| WC25_Ts.txt | 41.94227 | -93.53938 | 455290 | 4643507 |
| WC33_Ts.txt | 41.97534 | -93.64431 | 446619 | 4647239 |
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File Size
File sizes range from 226 KB to 559 KB.
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Volume
Total volume of combined files is 6.2 MB
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Spatial Coverage
Southernmost Latitude: 41.9° N
Northernmost Latitude: 42.0° N
Westernmost Longitude: 93.8° W
Easternmost Longitude: 93.4° W
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Temporal Coverage
Data were collected from 25 June 2002 to 12 July 2002.
Temporal Resolution
Data were gathered every 10 minutes.
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Parameter or Variable
Parameter Description
Parameters in this data set include air temperature, vapor pressure, wind speed, and brightness temperatures. The following table describes all the columns in the data tables. Where the columns correspond to parameters, the units of measurement and sensors are also shown.
| Column label/Parameter | Unit of Measurement | Description/Sensor |
|---|---|---|
| DOY | Day of year (Julian date) | |
| Hour | Time stamp from data logger (Central Standard Time) | |
| Decimal Time | Decimal time and midpoint of averaging period | |
| Site | Tower location number | |
| Air Temp | °C | Humidity and temperature probe |
| Vapor pressure (Ea) | mbar | Humidity and temperature probe |
| Wind speed | m/s | Anemometer |
| IRT Temp surface | °C | Surface brightness temperature from nadir-viewing sensor. |
| IRT Body | °C | Calculated temperature of sensor housing needed to correct for bias (see Apogee. |
| IRT Temp ground | °C | Surface brightness temperature from sensor under the canopy viewing (off nadir) ground soil surface. |
| IRT Body | °C | Calculated temperature of sensor housing needed to correct for bias (see Apogee. |
Parameter Source
The sources are twelve flux towers placed in crop fields in the study area.
Sample Data Record
The following sample comes from the data file "WC13_Ts.txt."
DOY Hour Decimal Site AirTemp Ea WindSpd IRTTemp IRT IRTTemp IRT Time surface Body ground Body (deg.C) (mbar) (m/s) (deg. C) (deg. C) 165 1030 10.417 13 19.55 12.85 6.79 24.89 20.55 24.20 21.99 165 1040 10.583 13 19.35 12.71 6.79 24.43 20.19 23.52 21.13 165 1050 10.750 13 19.32 12.09 6.79 24.13 20.11 23.20 21.01 165 1100 10.917 13 20.55 12.56 7.26 29.65 21.80 28.55 23.17 165 1110 11.083 13 21.16 12.23 7.26 31.28 22.47 30.18 24.53
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Software and Tools
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Data Acquisition and Processing
Theory of Measurements
Tower sampling was intended to provide continuous measurements of the surface temperature for a single target at each of the surface flux towers locations.
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Derivation Techniques and Algorithms
The transmitted energy (E) is converted to temperature (T) via the Stefan-Boltzman Law, which states:
E=εσT4, where ε is the emissivity of the object and σ is the Stefan-Boltzman constant (5.68 x 10-8 Joules m-2 s-1K-4)(Bugbee, et al., 1999.)
The instrument manufacturer (Apogee Instruments, Inc.) provides a formula to correct for the casing temperature of the instrument, called the sensor body (SB) temperature:
Corrected Target Temperature = Apparent Target Temperature -SEC
SEC = (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
The Apogee IRT manual contains more information about calibration and derivation techniques for their IRTs.
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Sensor or Instrument Description
An infrared sensor was installed on each tower to provide surface temperature observation. This device recorded both the measured (radiometric) surface temperature and the sensor body (contact) temperature.
Infrared thermometers (IRTs) allow only a specific waveband, approximately 8 to 14 microns, to transmit to the IRT detector.
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References and Related Publications
Contacts and Acknowledgments
Thomas J. Jackson, Hydrologist, and Fuqin Li, General Physical Scientist, USDA ARS Hydrology Lab.
Document Information
DOCUMENT CREATION DATE
August 2003
No technical references available for this data set.
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