Optimal estimation method retrievals of stratospheric ozone profiles from a DIAL
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 %.