Radiometry – Davos Instruments

New Article on Adaptive Diffraction Corrections

Proceedings from the WMO Technical Conference on Meteorological and Environmental Instruments and Methods of Observation
(TECO-2022) are now publicly available here. Markus Suter (Davos Instruments) and Wolfgang Finsterle (PMOD/WRC) have contributed their work: Adaptive diffraction corrections in solar radiometry, a prerequisite for the ISO 9060:2018 AA class.

Adaptive Diffraction Corrections

The Diffraction Effect and its implications

Diffraction effects in solar radiometry become more and more important once the target uncertainty goes below 0.1%. At the radiometric two aperture system, diffraction occurs at the front aperture, and thus reduces or enhances the amount of solar radiation passing the second aperture and reaching the detector. This strongly wavelength dependent effect has an impact in the order of 0.1% and can increase by up to 50% depending on the spectral conditions. This leads to an error in the measurement that needs to be corrected if high accuracy is needed.

An HF-Radiometer in active mode

At the IPC-XIII, Davos Instruments has been successfully operating a Hickey-Frieden (HF) radiometer from Eppley Laboratory Inc. in active mode, using a slightly modified control unit Linard.

It has been found that the HF radiometer is very well suitable for active operation. While the HF-radiometer is traditionally operated in the passive mode, it has all the necessary features needed for active mode operation.

First results have been presented in the symposium of the IPC-XIII, a preprint of the proceedings-article is available here.

Diffraction effects and the AA-class

Diffraction effects in solar radiometry are nothing new, they have been discussed at several occasions, mostly in conjunction with establishing absolute scales. When it comes to extremely precise measurements, as the ISO 9060 AA-class calls for, it is worth to look at diffraction a little closer.