A sensitivity study using the ATLID lidar simulator and upcoming plans for the validation of EarthCARE mission

The Earth Clouds, Aerosol and Radiation Explorer (EarthCARE) is a joint mission of the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA) for monitoring the aerosols, clouds, and precipitation, and for radiation closure studies. The Atmospheric Lidar (ATLID) is a High Spectral Resolution Lidar system and one of the four instruments that will be deployed onboard the platform. ATLID will use linearly polarized emission at 355 nm while pointing at 3^o off-nadir and will detect the molecular (Rayleigh) and particulate (Mie) backscattered signals as well as the cross-polar component of the backscatter signals, aiming to provide profiles of the optical properties of aerosols and optically thin clouds such as the particle backscatter and extinction coefficients, and the depolarization ratio. In preparation for the calibration and validation (cal/val) activities that will be performed for ATLID upon the EarthCARE launch in May 2024, a lidar simulator tool (CARDINAL Campaign Tool; CCT) has been developed for providing realistic simulations of the ATLID lidar signals and the Level 1 (L1) products of the attenuated particulate (Mie) backscatter, the attenuated molecular (Rayleigh) backscatter, and the attenuated cross-polar backscatter. In brief, the CCT workflow includes the parametrization of an atmospheric scene with the use of model fields and/or measurements from airborne or ground-based lidars, a lidar radiative transfer model, and an instrument model based on the ATLID design. The CCT simulates the lidar signals that would be recorded from ATLID for the provided atmospheric scene and obtains the corresponding ATLID L1 products.

In this study, measurements of eVe lidar from the ASKOS campaign (Cabo Verde, 2021/2022), are used as an input in the simulator for obtaining realistic ATLID L1 profiles. eVe lidar is a combined linear/circular polarization Raman lidar operating at 355 nm for aerosol profiling and consists ESA’s ground reference system for the cal/val of the ESA Aeolus and EarthCARE missions. Several cases of different aerosol layers and cirrus clouds are investigated.

Furthermore, the simulated ATLID L1 profiles will be used in the Level 2A processing chain (A-PRO) to derive realistic profiles of the particle backscatter and extinction coefficients, and the linear depolarization ratio. The realistic ATLID L2A profiles will be compared with the corresponding L2 profiles from eVe lidar, aiming to investigate the detection sensitivity of ATLID products on real aerosol layers.

Upcoming plans for the validation of EarthCARE mission include the exploitation of eVe lidar in an overpass cross point. The key aspects of this validation will be presented. In brief, the system will undergo an upgrade to enhance its capabilities for the cal/val activities of EarthCARE mission, retaining its combined linear/circular configuration while incorporating state-of-the-art equipment tailored for measurements on multiple scattering effects and automations to enhance the measurement procedures.