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Data Set ID:

SMEX02 Tower-Based Radiometric Surface Temperature, Walnut Creek, Iowa, Version 1

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).

Geographic Coverage

  • Atmospheric Temperature > Air Temperature
  • Atmospheric Pressure > Atmospheric Pressure Measurements
  • Microwave > Brightness Temperature
  • Infrared Wavelengths > Brightness Temperature
  • Atmospheric Temperature > Surface Air Temperature
  • Atmospheric Winds > Surface Winds
  • Atmospheric Winds > Vertical Wind Motion
  • Atmospheric Water Vapor > Water Vapor
Spatial Coverage:
  • N: 42, S: 41.9, E: -93.4, W: -93.5

Spatial Resolution: Not Specified
Temporal Coverage:
  • 25 June 2003 to 12 July 2003
Temporal Resolution: Not specified
Data Format(s):
  • ASCII Text
Version: V1
Data Contributor(s): Thomas Jackson, Michael Cosh
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.

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: http://dx.doi.org/10.5067/BJZU6IV9HUTE. [Date Accessed].

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Detailed Data Description


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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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


August 2003

No technical references available for this data set.
No FAQs or How Tos available for this data set.

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