Abstract
Abstract. In this study, we investigated the susceptibility of the Dobson spectrophotometer No. 118 to stray light interference. In this regard, a series of total ozone content measurements were carried out in Athens, Greece for air-mass values (μ) extending up to μ = 5. The monochromatic-heterochromatic stray light derived by Basher's model was used in order to evaluate the specific instrumental parameters which determine if this instrument suffers from this problem or not. The results obtained indicate that the measurements made by the Dobson instrument of the Athens station for air mass values up to 2.5, underestimates the total ozone content by 3.5 DU in average, or about 1 % of the station's mean total ozone content (TOC). The comparison of the values of the same parameters measured 15 years ago with the present ones indicates the good maintenance of the Dobson spectrophotometer No. 118. This fact is of crucial importance because the variability of the daily total ozone observations collected by the Athens Dobson Station since 1989 has proved to be representative to the variability of the mean total ozone observed over the whole mid-latitude zone of the Northern Hemisphere. This stresses the point that the Athens total ozone station, being the unique Dobson station in south-eastern Europe, may be assumed as a ground truth station for the reliable conversion of the satellite radiance observations to total ozone measurements.
Highlights
The Dobson spectrophotometer was the very first instrument developed in the early 1920s by G
According to Basher (1982), for direct AD measurements, errors of 1, 3 and 10 % may be present at air mass values of 2.5, 3.2 and 3.8, respectively. This is a permanent problem for instruments operating in high latitudes and affects ozone vertical profile (Umkehr) measurements performed by using the Dobson spectrophotometer (e.g. Petropavlovskikh et al, 2009, 2011)
The combination of the new levels of stray light with the previously detected ones will enable a re-calculation of the longterm time series and the reduction of the inaccuracies of the Athens Dobson Station total ozone content (TOC) measurements, which according to the literature (e.g. Chandra et al, 1996) tracks the seasonal trends of TOC as they are estimated using averaged data for different latitudinal zones of the mid-latitudes of the Northern Hemisphere
Summary
The Dobson spectrophotometer was the very first instrument developed in the early 1920s by G. According to Basher (1982), for direct AD measurements, errors of 1, 3 and 10 % may be present at air mass values of 2.5, 3.2 and 3.8, respectively This is a permanent problem for instruments operating in high latitudes and affects ozone vertical profile (Umkehr) measurements performed by using the Dobson spectrophotometer Basher (1982) created a monochromatic, heterochromatic stray light model in order to estimate stray light levels present in the measurements of a particular instrument This model uses two parameters that determine whether or not an instrument suffers from this problem. The combination of the new levels of stray light with the previously detected ones will enable a re-calculation of the longterm time series and the reduction of the inaccuracies of the Athens Dobson Station TOC measurements, which according to the literature (e.g. Chandra et al, 1996) tracks the seasonal trends of TOC as they are estimated using averaged data for different latitudinal zones of the mid-latitudes of the Northern Hemisphere
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