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A precise view of the Sun

UV array spectroradiometer to measure the thickness of the ozone layer of the Earth's atmosphere

PTBnews 1.2019
Especially interesting for

climate resvearch


Within the scope of a cooperation project involving PTB and the Gigahertz- Optik company, a new compact array spectroradiometer was developed, characterized and field-tested. This new device can measure the direct spectral irradiance of the Sun on Earth with very little effort and at short intervals, thus allowing conclusions to be drawn as to the total ozone column of the Earth's atmosphere.

At an altitude of 2400 m, the spectroradiometer is facing the rising sun in Izaña.

The ozone layer of the Earth's atmosphere is our most vital protection against harmful UV radiation from the Sun. Climate change and the thickness of the ozone layer are closely interrelated; determining the so-called ozone column is therefore an important part of global investigations on climate change. Measuring the thickness of the ozone layer indicates how much ozone is contained in the air column between the Earth's surface and the upper edge of the atmosphere. Accurate measurements involve considerable efforts, both with regard to equipment and to personnel. To date, it had not been possible to employ easy-touse compact array spectroradiometers for this purpose because their measurement uncertainties and systematic errors were too high due to the limitations of the spectral resolution, their dynamics and stray light suppression.


An important characteristic of the new device that was developed specifically to measure solar UV irradiance is that it efficiently reduces the stray light – a parameter that is vital for high-quality spectral measurements. Stray light inside the instrument is physically reduced right from the beginning by means of appropriate design adjustments. Moreover, it can be effectively corrected by means of additional measurements. The instrument thus provides accurate and stable measurements of the direct solar UV irradiance. Based on this information, it is possible to deduce the ozone column at the moment of the measurement by comparison with the simulated spectral irradiance of an irradiance transfer model.

The instrument was thoroughly tested and characterized at PTB in Braunschweig before being used at the Izaña Atmospheric Research Center (IARC) on Tenerife for an international comparison measurement campaign aimed at determining the ozone column. During the measurement campaign, the comparison measurements showed excellent agreement with conventional – and more timeconsuming – measurement procedures involving Dobson or Brewer instruments within the range of the stated measurement uncertainties.

Due to its compact design and its fast, continuous measurement sequence, the spectroradiometer represents an efficient supplement to established measurement procedures. Thanks to these properties, it is now possible to set up, for example, a close-mesh measurement network and mobile measuring stations that enable a partly automated determination of the ozone column worldwide.


Peter Sperfeld
Department 4.1
Photometry and Spectroradiometry
Phone: +49 531 592-4144
Opens window for sending emailpeter.sperfeld(at)ptb.de

Stefan Riechelmann
Department 4.5
Applied Radiometry
Phone: +49 531 592-4149
Opens window for sending emailstefan.riechelmann(at)ptb.de

Scientific publication

R. Zuber, P. Sperfeld, S. Riechelmann, S. Nevas, M. Sildoja, G. Seckmeyer: Adaption of an array spectroradiometer for total ozone column retrieval using direct solar irradiance measurements in the UV spectral range. Atmos. Meas. Tech. 11, 2477–2484.