The process of getting data has improved!  Click the Download Data tab below to view all options for retrieving data. Read all about the new layout here.
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).

This is the most recent version of these data.

  • Atmospheric Temperature > Air Temperature
  • Atmospheric Pressure > Atmospheric Pressure Measurements
  • Infrared Wavelengths > Brightness Temperature
  • Microwave > Brightness Temperature
  • Atmospheric Temperature > Surface Air Temperature
  • Atmospheric Winds > Surface Winds
  • Atmospheric Winds > Vertical Wind Motion
  • Atmospheric Water Vapor > Water Vapor
Data Format(s):
  • ASCII Text
Spatial Coverage:
N: 42, 
S: 41.9, 
E: -93.4, 
W: -93.5
Temporal Coverage:
  • 25 June 2003 to 12 July 2003
Temporal ResolutionNot specifiedMetadata XML:View Metadata Record
Data Contributor(s):Thomas Jackson, Michael Cosh

Geographic Coverage

Once you have logged in, you will be able to click and download files via a Web browser. There are also options for downloading via a command line or client. For more detailed instructions, please see Options Available for Bulk Downloading Data from HTTPS with Earthdata Login.

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: [Date Accessed].

Back to Top

Collapse All / Open All

Detailed Data Description


Data are ASCII tab-delimited text files.

Background color on
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
Background color on
File Size

File sizes range from 226 KB to 559 KB.

Background color on

Total volume of combined files is 6.2 MB

Background color on
Spatial Coverage

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

Background color on
Temporal Coverage

Data were collected from 25 June 2002 to 12 July 2002.

Temporal Resolution

Data were gathered every 10 minutes.

Background color on
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
Background color on

Software and Tools

Background color on

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.

Background color on
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.

Background color on
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.

Background color on

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.

Access complete Knowledge Base

Questions? Please contact:
NSIDC User Services
Phone: 1 303 492-6199