Measuring the sky spectral radiance within seconds

Spectral radiance and its temporal dependence on incident and azimuth angle plays an important role for radiative transfer because all other radiative quantities may be derived from the spectral radiance. It depends on time, wavelength, incident angle, azimuth angle, height and geographic location as well as polarization. The modeling of spectral radiance is therefore the goal of many investigations. In practice, however, spectral radiance can often not be determined by calculation due to the absence of the necessary input parameters. In Antarctica the albedo of snow can reach 100%, so that nearly all incoming radiation is reflected back in the visible and UV range. This extremely high reflectance changes the spatial distribution of spectral radiance significantly. We found for example that the zenith radiance in Antarctica near the horizon can be up 16 times higher than at the zenith in the red part of the spectrum.

For the measurement of the spectral radiance traditional techniques and instruments are too slow to capture the rapid changes mainly caused by varying cloudiness. A newly developed advanced multidirectional spectroradiometer (AMUDIS) is capable of measuring spectral radiance from the UV to NIR with more than 100 directions within seconds. The presentation will demonstrate metrological, meteorological, medical and biological challenges and how to overcome these. Since turning of the input optics would change its sensitivity new methods for the calibration and characterization of instrument AMUDIS have been developed and tested.

 

References

EEAP. 2019. Environmental Effects and Interactions of Stratospheric Ozone Depletion, UV Radiation, and Climate Change. 2018 Assessment Report. Nairobi: Environmental Effects Assessment Panel, United Nations Environment Programme (UNEP) 390 pp. https://ozone.unep.org/science/assessment/eeap

Seckmeyer G., Lagos Rivas L., Gaetani C., Heinzel J.W., Schrempf M.: (2018) Biologische und medizinische Wirkungen solarer Strahlung (Biological and medical effects of solar radiation), in Promet, Heft 100, Strahlungsbilanzen, chapter 13, Deutscher Wetterdienst (DWD), 2018

Seckmeyer G., Bais A., Bernhard G., Blumthaler M., Lantz K., McKenzie R.L., Kiedron P., Drüke S., Riechelmann S. (2010): Instruments to measure solar ultraviolet radiation, part 4: Array Spectroradiometers, 43 pages, WMO-GAW report 191, TD 5038

Tobar Foster M., Luiz Weide E., Niedzwiedz A., Duffert J., Seckmeyer G.: Characterization of the Angular Response of a Multi-Directional Spectroradiometer for measuring spectral Radiance, EPJ Techniques and Instrumentation, https://doi.org/10.1140/epjti/s40485-021-00069-4, 28 July, 2021

Niedzwiedz A., Duffert J., Tobar M., Quadflieg E., Seckmeyer G.: Laboratory calibration for multidirectional spectroradiometers, Measurement Science and Technology, https://doi.org/10.1088/1361-6501/abeb93, March, 2021