SMEX02 Tower-Based Radiometric Surface Temperature, Walnut Creek, Iowa
Summary
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 study was conducted during June and July 2002 in the Walnut Creek watershed in south-central Iowa, USA. The flux towers contained humidity and temperature probes, infrared thermometers, and anemometers. Data were recorded every 10 minutes from 06 June through 25 July 2002 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
Thomas Jackson and Michael Cosh. 2003. SMEX02 Tower-Based Radiometric Surface Temperature, Walnut Creek, Iowa. Boulder, CO: National Snow and Ice Data Center. Digital media.
Overview Table
| Category | Description |
|---|---|
| Data format | ASCII tab-delimited text files. |
| Spatial coverage | 42° N, 93° W |
| Temporal coverage and resolution | 25 June 2002 to 12 July 2002. Data were gathered every 10 minutes. |
| 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. |
| File size | File sizes range from 226 KB to 559 KB. |
| Parameter(s) | Air temperature, vapor pressure, wind speed, and brightness temperatures. |
| 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
Thomas J. Jackson, Hydrologist, and Fuqin Li, General Physical Scientist, USDA ARS Hydrology Lab.
Technical Contact
NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449 USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
e-mail: nsidc@nsidc.org
2. Detailed Data Description
Format
Data are ASCII tab-delimited text files.
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 |
File Size
File sizes range from 226 KB to 559 KB.
Spatial Coverage
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 25 June 2002 to 12 July 2002.
Temporal Resolution
Data were gathered every 10 minutes.
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
3. Data Access and Tools
Data Access
Data are available via FTP.
Volume
Total volume of combined files is 6.2 MB
Related Data Collections
See related information on the Soil Moisture Experiment (SMEX) Web site.
4. 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.
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.
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.
5. References and Related Publications
Bugbee, B., M. Droter, O. Monje, and B. Tanner, 1999. Evaluation and modification of commercial infrared-red transducers for leaf temperature measurement. Adv. Space Res., Vol., 22, no.10, pp 1425-1434
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 |
| FTP | File Transfer Protocol |
| HP | Hydra Probe |
| IRT | Infrared Thermometer |
| SB | Sensor Body |
| SMEX | Soil Moisture Experiment |
| WC | Walnut Creek |
Document Creation Date
August 2003
Document URL
http://nsidc.org/data/docs/daac/nsidc0186_smex_tower.gd.html
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