Abstract
Abstract. Aeolus carries the Atmospheric LAser Doppler INstrument (ALADIN), the first high-spectral-resolution lidar (HSRL) in space. Although ALADIN is optimized to measure winds, its two measurement channels can also be used to derive optical properties of atmospheric particles, including a direct retrieval of the lidar ratio. This paper presents the standard correct algorithm and the Mie correct algorithm, the two main algorithms of the optical properties product called the Level-2A product, as they are implemented in version 3.12 of the processor, corresponding to the data labelled Baseline 12. The theoretical basis is the same as in Flamant et al. (2008). Here, we also show the in-orbit performance of these algorithms. We also explain the adaptation of the calibration method, which is needed to cope with unforeseen variations of the instrument radiometric performance due to the in-orbit strain of the primary mirror under varying thermal conditions. Then we discuss the limitations of the algorithms and future improvements. We demonstrate that the L2A product provides valuable information about airborne particles; in particular, we demonstrate the capacity to retrieve a useful lidar ratio from Aeolus observations. This is illustrated using Saharan dust aerosol observed in June 2020.
Highlights
The Aeolus satellite from the European Space Agency was launched on 22 August 2018, after a long development phase
We demonstrate that the L2A product provides valuable information about airborne particles; in particular, we demonstrate the capacity to retrieve a useful lidar ratio from Aeolus observations
This article gives an overview of the two main algorithms used in the Aeolus mission to derive the Level-2A product, i.e. the aerosol optical properties product
Summary
The Aeolus satellite from the European Space Agency was launched on 22 August 2018, after a long development phase. With a precise calibration of the instrument, the number of photons backscattered by both types of target can be separated This allows the independent measurement of the backscatter and extinction coefficients of aerosols or clouds (Flamant et al, 2008; Ansmann et al, 2007), and provides a direct measurement of the extinction to backscatter ratio called the “lidar ratio”. In Aeolus, a specific algorithm has been developed to exploit the high-spectral-resolution capacity of ALADIN It produces the Level-2A (L2A) product of the mission. Aeolus is a first step towards this goal before the launch of ESA EarthCARE mission (Illingworth et al, 2015) that will operate a high-spectral-resolution lidar in the UV, this time designed for the observation of aerosol and clouds.
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