Abstract:
Instrument History:
The SAOZ (Système d'Analyse par Observation Zénithale, Goutail and Pommereau, 1988) instrument is part of the NDACC international network. There are 19 SAOZ owned by CNRS and other institutes at all latitudes including in the tropics. The SAOZ has been developed at Service d'Aéronomie (called LATMOS) in the late 1980s following the discovery of the ozone hole in Antarctica.
... The first SAOZ has been installed in 1988 at Dumont d'Urville in Antarctica to measure stratospheric ozone at high latitudes during the polar winter. In fact, the conventional techniques for measuring ozone in the ultraviolet range are useless for zenith angles greater than 80°. The SAOZ, which measures the absorption by the atmosphere of scattered sunlight at the zenith in the visible, allows the continuous monitoring of ozone in such conditions. In addition to the daily integrated ozone column, the SAOZ measures total NO2 column and determine the presence of polar stratospheric clouds from the color index.
The SAOZ was installed at Kerguelen in December 1995 to evaluate the impact the excursion of the ozone hole over sub-polar regions. It work continuously since then. The French Polar Institute (IPEV Institut Polaire Français Paul-Emile Victor) supplies recurrent funding and logistics.
Instrument description:
SAOZ is a UV-Visible diode array flat field spectrometer of 1 nm resolution looking at sunlight scattered at zenith during twilight. The SAOZ measures between 300 nm and 600 nm using the DOAS technique (Differential Optical Absorption Spectroscopy). As SAOZ was designed to measure especially in the Polar Regions, sometimes of difficult access, the system is completely automated, maintenance is simple (mechanical shutter and a box sealed tight and dehydrated).
Main characteristics of the instrument:
- Jobin-Yvon CP200 spectrometer, 360 gr/mm, 300-600 nm
- Slit of 50 μ
- NMOS detector of 1024 pixels and the pre-amplifier
- Electronic device (commands and acquisition)
- Push-pull shutter for detector dark current correction
- GPS (card and antenna) for Solar Zenith Angle (SZA) and time calculation
- Interface box and a PC for processing data
- Box (sealed tight and dehydrated) and quartz window
Algorithm description:
The data processing is achieved into 3 steps. The former two are realized in real time.
1. Acquisition of the spectrum and other parameters as GPS location and temperature inside the instrument (Level 0).
2. Spectroscopic analysis using the DOAS technique. Slant columns of different constituents are retrieved as ozone, NO2, O2, H2O and O4 (Level 1).
3. Conversion of slant columns into total columns by a single Air Mass Factor (AMF) using yearly mean profiles for Mid-Latitudes regions (Level 2 real time). Consolidated data are realized once a year using daily AMF calculated from ozone profiles climatology (Level 2 consolidate). 
