Kipp & Zonen CGR 4 Instruction Manual

Kipp & Zonen CGR 4 Instruction Manual Manual pdf 11 page image

2.2.4. Installation for shaded measurement of downward long-wave radiationFor amplification of the pyrgeometer signal Kipp & Zonen offers the AMPBOX signal amplifier.This amplifier will convert the micro-Volt output from the pyrgeometer into a standard 4 – 20 mA signal.The use of the AMPBOX amplifier is recommended for applications with long cables (> 100m), electricallynoisy environments or data loggers with a current-loop input.The AMPBOX can be factory adjusted to suit the sensitivity of an individual pyrgeometer to produce adefined range, typically 4 mA represents -300 W/m², 16 mA represents 0 W/m2 and 20 mA represents+100 W/m².2.4. OperationAfter completing the installation the pyrgeometer will be ready for operation. The downward atmosphericlong-wave radiation can be calculated with Formula 1 by measuring the detector output voltage Uemf [μV],the housing temperature Tb [K], and taking the sensitivity calibration factor S [μV/W/m²] into account.Formula 1=Downward atmospheric long-wave radiation [W/m²]=Net radiation (difference between the downward [W/m²]longwave radiation emitted from the atmosphereand the upward irradiance of the CGR 4 detector)=Upward irradiance of the CGR 4 detector [W/m²]Note that the net radiation term (Uemf / S) is mostly negative, so the calculated downward atmosphericlong-wave radiation is smaller than the detector’s upward irradiance ( ).This refers to the net radiation within the pyrgeometer, not the ‘net radiation’ as referred to in 2.2.5.In the Baseline Surface Radiation Network (BSRN) manual (WMO/TD-No.897) an extended formula isdescribed. This formula corrects for window heating and so called “solar radiation leakage”. Due to thevery low window heating offset and optimal spectral cut-on wavelength, these corrections are notnecessary for the CGR 4.To be certain that the quality of the data is of a high standard, care must be taken with daily maintenanceof the pyrgeometer. Once a voltage measurement is taken, nothing can be done to retrospectivelyimprove the quality of that measurement.During field measurements the pyrgeometer is exposed to varying atmospheric conditions with typicalradiating properties. Therefore we define the two most common conditions as ‘overcast sky’ and ‘clearsky’, refer to 2.4.1 and 2.4.2 respectively.Page 11Ld = bUemfS + 5.67 • 10-8 • T 4LdUemfSb5.67 • 10-8 • T 4b5.67 • 10-8 • T 4CGR 4 Manual