Study of suitability of AvaSpec array spectrometer for solar UV field measurements I. Ansko1,2, K. Eerme1, S. Lätt1,2, M. Noorma2, and U. Veismann1 1Tartu Observatory, 61602, Tõravere, Estonia 2Tartu University, Ülikooli 18, 50090, Tartu, Estonia
Abstract. A system to record the ultraviolet (UV) spectra of atmospheric global
irradiance with the miniature fiber optic spectrometer AvaSpec-256 was
developed for continuous computer-aided spectrometry at Tartu Observatory in
2005. As a result, the database of spectra recorded with 15-min-interval
round 24 h over 300–400 nm, has been developed. The quantities retrieved
from the spectra have been compared with those measured by the Scintec
erythemal UV-SET sensor and the Kipp & Zonen narrowband 306 nm sensor.
Almost clear and overcast days were selected for comparison. Reliable
results on the spectral distribution of the UV global irradiance as well as
the integrated daily spectral doses could be obtained at least during the
bright half-year. The results were compared with the calculations performed
by means of the LibRadtran package. The biases in irradiance were
significant at SZA above 70–75°. At dominating larger SZA the recorded
values need sophisticated corrections and remain less reliable. At lower
latitudes than that of the study site (58.3°), the reliability of the
spectrometer is expected to increase due to a smaller contribution of data
measured at large SZA.
The variations of the ratio of UV-A/UV-B irradiance, retrieved from the
spectra, were investigated. Also the covariation of the narrowband 306 nm
irradiance and the irradiance integrated over the whole UV-B range was
studied. The biases between the UV-A/UV-B irradiances calculated by means of
the LibRadtran package and measured with the AvaSpec were small at SZA below
70°. At larger SZA the values of the ratio as well as the biases
increased, significantly depending on total ozone.
Citation: Ansko, I., Eerme, K., Lätt, S., Noorma, M., and Veismann, U.: Study of suitability of AvaSpec array spectrometer for solar UV field measurements, Atmos. Chem. Phys., 8, 3247-3253, doi:10.5194/acp-8-3247-2008, 2008.