NCAR Airborne Instrumentation Inventory
1. INSTRUMENT IDENTIFICATION
Instrument Designation:
NCAR-modified Eppley PIR Pyrgeometer
Instrument Acronym:
IRT, IRTC, IRB, IRBC
Instrument Measurements:
a) Trace Gas
b) Cloud Physics/Aerosol
c) Radiation/Optical/Electrical
Hemispheric infrared radiation
d) Additional Capabilities
Resource Person/Developer:
| Name: | Krista Laursen | Bruce Morley
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| Affiliation: | NCAR/ATD/RAF | NCAR/ATD/RAF
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| Phone: | (303) 497-1031 | (303) 497-1018
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| Email: | krista@ucar.edu | bruce@ucar.edu
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Principle of Measurement:
A silicon dome within the pyrgeometer provides the 3.5 to 50 uM passband
filtering for this instrument. In determining the correct infrared irradiance
measured by the pyrgeometer, the sink and dome temperatures of the radiometer
must be taken into account. This is necessary because the sink and dome each
emit energy that influence the energy incident on the pyrgeometer's sensing
thermopile. The equation used to calculate the corrected IR irradiance is:
IRC = IR + e0 S TS^4 - k S (TD^4 - TS^4),
where IRC = the corrected IR irradiance (W/m2), IR = the calibrated, amplified
thermopile output (W/m2), TD = the dome temperature (K), TS = the sink
temperature (K), e0 = the emissivity of the blackened thermopile surface,
k = the ratio of the dome material emissivity to transmissivity, and S = the
Stefan-Boltzmann constant. In RAF processing, k is given a value of 4.3.
One NCAR modification added a stable amplifier to the housing to increase
the millivolt signal to a range of 0.0 to 1.0 Vdc.
In situ/Remote/Flux Measurement:
Remote
2. INSTRUMENT APPLICATION
3. Instrument Deployment
Altitude:
all
Aircraft Platform:
all
Inlet Configuration/Location:
fuselage-mounted, up- or down-looking
Calibration/Cross Calibration:
EPLAB black body target and annual calibration of the sensing element at
Eppley Laboratories, Inc.
Operator Requirements:
Data Collection:
external
Post-flight Data Validation, Processing, Hours per Flight Hour etc.
RAF NIMBUS software processor
Post-project validation by RAF Project Manager
Physical Characteristics:
Dimensions: 14.6 cm diameter x 17.1 cm high
Weight: 1.8 kg
Power:
Other:
4. Instrument Performance
Linear Range:
-150 to 450 W/M2
Response Time:
2.0 s time constant
Detection Limits:
0.12 W/M2
Accuracy:
± 2.0 %
Precision:
Limitations (such as altitude, airspeed, etc.)
5. Alternative Techniques
6.Status/Plans
Status: Operational
Plans: None
7.Comments
Because the instrument is hard-mounted to the aircraft frame,
measurements of net incoming and outgoing infrared radiation is
strongly dependent on aircraft attitude angle. No attempt is yet
being made to adjust the data for this phenomenon.
Due to atmospheric attenuation and scattering, a large portion of the
solar radiation in the pyrgeometer passband does not reach the surface
of the earth. Because of this, there is no direct solar IR radiation
reaching ground level. At some flight levels, however, the amount of
direct solar IR radiation measured by the pyrgeometer can be
significant. The user should, therefore, be aware of the
pyrgeometer's sensitivity to direct solar IR radiation and also to the
sensitivity of the instrument to the attitude of the aircraft with
respect to the sun. These problems are reported in greater detail by
V. Glover and D.McFarland in their 1991 article "Modification to and
data correction methods for some radiometers used on aircraft,"
Preprints of the Seventh Symposium on Meteorological Observations and
Instrumentation," January 14-18, 1991, New Orleans, LA, pp. 118-120.
Information submitted on: Dec 20, 1996
Information submitted by: Ronald L. Ruth
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