Results of intercomparison and calibration of Dobson spectrophotometer no.112, Japan-1996

An international comparison of Dobson spectrophotometer operated in the RA II and V regions was conducted in Japan during 1996. Countries participating with Dobson instruments were India, Japan, Korea, Philippines and Thailand. The reference standard instrument for the comparison was regional standard Dobson instrument no.116 maintained by Japan. The comparisons confirmed that the Indian standard no.112 was in good state of calibration and the data derived from the instrument was reliable.

Comparison of total ozone retrieved from NOAA satellite and measured from Dobson spectrophotometer over Indian region

An attempt has been made to compare the total ozone retrieved from HIRS channel-9 of NOAA-12 satellite using ITPP software at the facility of lMDPS, New Delhi with that of conventional Dobson spectrophotometer over Indian network stations. The satellite-retrieved total ozone agrees within an accuracy of +-8% with that of Dobson-measured total ozone except during the passage of a weather system over the Indian region. It is seen that whenever a western disturbance is passing over north India and neighbourhood, the difference between the satellite-retrieved and Dobson-measured total ozone becomes more than +- 8% (or +-20 DU).

Total column ozone measurements by the Dobson spectrophotometer at Belsk (Poland) for the period 1963–2019: homogenization and adjustment to the Brewer spectrophotometer

The total column ozone (TCO3) measurements by the Dobson spectrophotometer (serial no. 84) have been carried out at Belsk station (51∘50′ N, 20∘47′ E), Poland, since 23 March 1963. In total, ∼115 000 intraday manual observations were made by 31 December 2019. These observations were performed for different combinations of double wavelength pairs in the ultraviolet range and observation types, i.e., direct sun (DS), zenith blue (ZB), and zenith cloudy (ZC) depending on weather conditions. The long-term stability of the instrument was supported by frequent (almost every 4 years) intercomparisons with the world standard spectrophotometer. Trend analyses, based on the monthly and yearly averaged TCO3, can be carried out without any additional corrections to the intraday values. To adjust these data to the Brewer spectrophotometer observations, which were also performed at Belsk, a procedure is proposed to account for less accurate Dobson observations under low solar elevation, presence of clouds, and the temperature dependence of ozone absorption. The adjusted time series shows that the Brewer–Dobson monthly averaged differences are in the range of about ±0.5 %. The intraday TCO3 database, divided into three periods (1963–1979, 1980–1999, and 2000–2019), is freely available at https://doi.org/10.1594/PANGAEA.919378 (Rajewska-Więch et al., 2020).

Expanding the spatial coverage of a ground-based station to validate satellite total ozone data; The case of TROPOMI and Athens Dobson

<p>In this work we present the validation results of the daily observations of the Total Ozone Column (TOC) obtained by the TROpospheric Monitoring Instrument (TROPOMI), and the Dobson spectrophotometer No. 118 located in Athens, Greece, (WOUDC Station ID: 293) during the period November 2017 to February 2021. Simultaneous observations of both instruments are used for this validation.</p><p>The increased spatial resolution of TROPOMI observations in relation to the push-broom configuration (non-scanning) of the instrument (swath width of ~2600 km) offers the opportunity to study the spatial analysis of the observed differences in a large area around the ground-based station. By using the ground-based station in Athens we attempt to analyze spatial and temporal behavior of the TOC differences between Dobson and TROPOMI data in an area enclosed by a 500 km radius during the period from August 2019 to February 2021.</p>

Total column ozone measurements by the Dobson spectrophotometer at Belsk (Poland) for the period 1963–2019: homogenization and adjustment to the Brewer spectrophotometer

The total column ozone (TCO3) measurements by the Dobson spectrophotometer #84 have been carried out at Belsk (51°50', 20°47'), Poland, since March 23, 1963. In total, ~115,000 intra-day manual observations have been taken up to December 31, 2019. These observations were made for various combinations of double wavelength pairs in UV range (AD, CD) and the observation category, i.e., direct Sun, zenith blue, and zenith cloudy depending on the weather conditions. The long-term stability of the instrument was supported by frequent (~almost every 4 yr.) intercomparisons with the world standard spectrophotometers. Trend analyses, based on the monthly and yearly averaged TCO3, can be carried out without any additional corrections to the intraday values. To adjust this data to the Brewer spectrophotometer observations also performed at Belsk, a procedure is proposed to account for: less accurate Dobson observations under low solar elevation, presence of clouds, and sensitivity of the ozone absorption on temperature. The adjusted time series shows that the Brewer-Dobson monthly averaged differences are in the range of about ±0.5 %. The intra-day TCO3 data base, divided into three periods (1963–1979, 1980–1999, and 2000–2019), is freely available at https://doi.pangaea.de/10.1594/PANGAEA.919378 (Rajewska-Więch et al., 2020).

A fully Automated Dobson Sun Spectrophotometer for total column ozone and Umkehr measurements

The longest ozone column measurements series are based on the Dobson sun spectrophotometers developed in the 1920s by Prof. G. B. W. Dobson. These ingenious and robustly designed instruments still constitute an important part of the global network presently. However, the Dobson sun spectrophotometer needs manual operation which leads to the discontinuation of its use at many stations. To overcome this problem, MeteoSwiss developed a fully automated version of the Dobson spectrophotometer. The description of the data acquisition and automated control of the instrument is presented here with some technical details. The results of different tests performed regularly to control the instrument good working operation are illustrated and discussed. Compared to manual operation, the automation results in higher frequency measurements with lower random error and additional housekeeping information to characterise the measuring conditions. The automated Dobson instrument allows a continuous observation of the ozone column with a resolution of ~1 DU unit under clear sky conditions.