Kipp&Zonen BSRN Scientific Solar Monitoring System - Manual (Page 120)

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B 5. Sunphotometers and Spectral Radiometers
B 5.1 Kipp and Zonen POM-01L Sky Radiom eter
The POM-01L Sky Radiom eter is a research instrum ent intended for the analysis and determ ination of
optical aerosol depth and particle size distribution. The POM-01L is capable of perform ing 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 autom ated tracking system , m ulti-filter spectral scanning
radiom eter, control unit, and operating software. The POM-01L’s unique single (tem perature stabilized)
detector design com pletely elim inates sensitivity differential errors, or tem perature dependence errors,
inherent in dual/twin detector type instrum ents. In addition, both absolute (utilizing im proved Langley m ethod)
and solid opening angle calibrations can be perform ed on site.
B 5.2 W RC/PMOD Precision Filter Radiom eter (PFR)
The Precision Filter Radiom eter (PFR) is a research grade instrum ent to m easure direct solar irradiance
in 4 narrow spectral bands centered at wavelengths recom m ended by W orld Meteorological Organization
for the determ ination of atm ospheric aerosol optical depth (AOD). The PFR consists of an optical sensor
head with signal am plifiers and an electronic box with power supply and data logger. Both units are designed
for autom ated operation under harsh weather conditions when the sensor is m ounted on a suitable solar
tracker. The data logger com m unicates over a serial link with software available for W indows PC’s and
has a data storage capacity of 1 m onth.
The instrum ent is designed for radiom etric stability. The detectors are operated in a controlled environm ent
and are expose to solar radiation only during actual m easurem ents. A Peltier therm ostat m aintains the
ion-assisted deposition filters and silicon detectors at a constant tem perature of 20.5 +/- 0.1 °C over an
am bient tem perature range from -20 °C to +35 °C; an internal shutter shades the detector between
m easurem ents and the vacuum tight sensor head is filled with dry nitrogen gas. At PMOD/W RC, the PFR
spectral sensitivity can be calibrated periodically against an absolute trap detector traceable to a prim ary
cryogenic radiom eter at Physikalisch-Technische Bundesanstalt, Berlin.
Internal barom etric and electronic pointing sensors plus a com plem entary set of house-keeping param eters
support evaluation and quality control of the m easurem ents.
Specifications
Table B 5.1. Optical characteristics of typical instrum ent.
Ch1 Ch2 Ch3 Ch4 unit
Central W avelength 861.6 500.5 411.4 367.6 nm
FW HM 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 W indow 3m m fused silica
Pointing m onitor +/- 0.75° in two axis
Calibration:
0
Extraterrestrial V com parison with PMOD/W ORCC standard, calibrated at high
altitude observatories.
Radiom etric against absolute trap detector of FEL lam p.