ATLID aerosol and cloud products.

The Earth Clouds, Aerosol and Radiation explorer is a joint ESA (European Space Agency)/JAXA (Japan Aerospace Exploration Agency)
satellite mission. EarthCARE was launched in May 2024 and is providing unique data well-suited for studying the role of clouds and aerosols in Earth's
atmosphere.

EarthCARE carries 4 different instruments. A Cloud profiling Doppler radar, a multi-spectral imager, a broad-band radiometer and a
cloud/aerosol lidar.  The Atmospheric Lidar (ATLID) instrument is the High Spectral Resolution Lidar (HSRL) carried on EarthCARE. ATLID
provides high-resolution vertical profiles of cloud and aerosol optical properties.

In order to transform raw ATLID measurements into scientifically meaningful products, specialized HSRL specific processing is
required. This paper presents an overview of two key ATLID processing streams: the A-FM (ATLID Feature Mask) and A-PRO (ATLID Profile)
processors.

The A-FM processor focuses on the detection and classification of atmospheric features. Using calibrated backscatter signals, it applies
a sequence of algorithms for noise filtering, signal threshold, and layer detection to distinguish between clear sky, attenuated regions,
and significant targets.

The A-PRO processor builds upon A-FM results in order to generate quantitative atmospheric profiles. It retrieves parameters such as
backscatter coefficient, extinction coefficients, lidar-ratio, and linear depolarization ratio. The processor uses the optical properties
to classify the detected atmospheric targets (e.g. water cloud, ice clouds, and aerosol-type).

This paper outlines the core algorithms underlying both processors, highlighting their design principles. A number of illustrative
examples are presented to demonstrate their performance across different atmospheric scenarios, including cirrus clouds,
boundary-layer aerosols, and complex multi-layer structures. Applications of the derived products are also discussed