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B 5. Sunphotometers and Spectral Radiometers
B 5.1 Kipp and Zonen POM-01L Sky Radiometer
The POM-01L Sky Radiometer is a research instrument intended for the analysis and determination of
optical aerosol depth and particle size distribution. The POM-01L is capable of performing high accuracy
angular and spectral scans for both direct and diffuse sky solar radiation, across seven different spectral
bandwidths. The POM-01L consists of a fast automated tracking system, multi-filter spectral scanning
radiometer, control unit, and operating software. The POM-01L’s unique single (temperature stabilized)
detector design completely eliminates sensitivity differential errors, or temperature dependence errors,
inherent in dual/twin detector type instruments. In addition, both absolute (utilizing improved Langley method)
and solid opening angle calibrations can be performed on site.
B 5.2 WRC/PMOD Precision Filter Radiometer (PFR)
The Precision Filter Radiometer (PFR) is a research grade instrument to measure direct solar irradiance
in 4 narrow spectral bands centered at wavelengths recommended by World Meteorological Organization
for the determination of atmospheric aerosol optical depth (AOD). The PFR consists of an optical sensor
head with signal amplifiers and an electronic box with power supply and data logger. Both units are designed
for automated operation under harsh weather conditions when the sensor is mounted on a suitable solar
tracker. The data logger communicates over a serial link with software available for Windows PC’s and
has a data storage capacity of 1 month.
The instrument is designed for radiometric stability. The detectors are operated in a controlled environment
and are expose to solar radiation only during actual measurements. A Peltier thermostat maintains the
ion-assisted deposition filters and silicon detectors at a constant temperature of 20.5 +/- 0.1 °C over an
ambient temperature range from -20 °C to +35 °C; an internal shutter shades the detector between
measurements and the vacuum tight sensor head is filled with dry nitrogen gas. At PMOD/WRC, the PFR
spectral sensitivity can be calibrated periodically against an absolute trap detector traceable to a primary
cryogenic radiometer at Physikalisch-Technische Bundesanstalt, Berlin.
Internal barometric and electronic pointing sensors plus a complementary set of house-keeping parameters
support evaluation and quality control of the measurements.
Specifications
Table B 5.1. Optical characteristics of typical instrument.
Ch1 Ch2 Ch3 Ch4 unit
Central Wavelength 861.6 500.5 411.4 367.6 nm
FWHM bandwidth 5.4 5 4.5 3.8 nm
Sensitivity 0.28 0.49 0.46 0.28 A m nm
-2 -1
Extraterrestrial Signal 3.47 3.88 3.81 4.24 V
Field of View
opening angle 2.5°
slope angle 0.7°
Entrance Window 3mm fused silica
Pointing monitor +/- 0.75° in two axis
Calibration:
0
Extraterrestrial V comparison with PMOD/WORCC standard, calibrated at high
altitude observatories.
Radiometric against absolute trap detector of FEL lamp.
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