Abstract
Abstract. This paper provides a detailed description of a first-principle optimal estimation method (OEM) applied to ozone retrieval analysis using differential absorption lidar (DIAL) measurements. The air density, detector dead times, background coefficients, and lidar constants are simultaneously retrieved along with ozone density profiles. Using an averaging kernel, the OEM provides the vertical resolution of the retrieval as a function of altitude. A maximum acceptable height at which the a priori has a small contribution to the retrieval is calculated for each profile as well. Moreover, a complete uncertainty budget including both systematic and statistical uncertainties is given for each individual retrieved profile. Long-term stratospheric DIAL ozone measurements have been carried out at the Observatoire de Haute-Provence (OHP) since 1985. The OEM is applied to three nights of measurements at OHP during an intensive ozone campaign in July 2017 for which coincident lidar–ozonesonde measurements are available. The retrieved ozone density profiles are in good agreement with both traditional analysis and the ozonesonde measurements. For the three nights of measurements, below 15 km the difference between the OEM and the sonde profiles is less than 25 %, and at altitudes between 15 and 25 km the difference is less than 10 %; the OEM can successfully catch many variations in ozone, which are detected in the sonde profiles due to its ability to adjust its vertical resolution as the signal varies. Above 25 km the difference between the OEM and the sonde profiles does not exceed 20 %.
Highlights
Stratospheric ozone plays a critical role, allowing life to thrive on Earth by absorbing the ultraviolet (UV) radiation emitted by the Sun
This paper introduces a first-principle optimal estimation method (OEM) retrieval for stratospheric ozone density from differential absorption lidar (DIAL) measurements
For both nights the difference between the sonde and the calculated profiles below 13.5 km is larger than 80 % and is not shown here. These two additional nights help to demonstrate that the OEM can produce high-quality ozone density profiles that are consistent with the traditional profiles found using the traditional method
Summary
Stratospheric ozone plays a critical role, allowing life to thrive on Earth by absorbing the ultraviolet (UV) radiation emitted by the Sun. G. Farhani et al.: Optimal estimation method retrievals of stratospheric ozone profiles from a DIAL. DIAL (differential absorption lidar) measures the vertical distribution of ozone density with high temporal and vertical resolution. To determine a single ozone profile, the optimal estimation method (OEM) uses photocounts from multiple channels, without merging or applying corrections. We are applying the first principles of OEM to retrieve stratospheric ozone profiles from measurements at the Observatoire de Haute-Provence (OHP) located in France. Ozone profiles are retrieved from raw (Level 0) measurements of four digital channels, two high altitude and two low altitude. In this method, no prefiltering or post-filtering of retrievals is needed. This paper introduces a first-principle OEM retrieval for stratospheric ozone density from DIAL measurements.
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