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

Jackson, T. and M. Cosh. 2003. SMEX02 Tower-Based Radiometric Surface Temperature, Walnut Creek, Iowa. [indicate subset used]. Boulder, Colorado USA: NASA DAAC at the National Snow and Ice Data Center.

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