An overview of the Cloud and Aerosol Lidar for Global Scale Observations of the Ocean-Land-Atmosphere System

The Cloud and Aerosol Lidar for Global Scale Observations of the Ocean-Land-Atmosphere System (CALIGOLA) is an advanced multi-purpose space lidar mission with a focus on atmospheric and oceanic observation aimed at characterizing the Ocean-Earth-Atmosphere system and the mutual interactions within it. This mission has been conceived by the Italian Space Agency (ASI) with the aim to provide the international atmospheric and ocean science communities with an unprecedented dataset of geophysical parameters capable to increase scientific knowledge in the areas of atmospheric, aquatic, terrestrial, cryospheric and hydrological sciences. The mission is planned to be launched in the time frame 2030-2031, with an expected lifetime of 3-5.

Exploiting the three Nd:YAG laser emissions at 354.7, 532 and 1064 nm and the elastic (Rayleigh-Mie), depolarized and Raman lidar echoes from atmospheric constituents, CALIGOLA will carry out 3λ profile measurements of the particle backscatter coefficient and depolarization ratio and 1-2λ (354.7 and 532 nm) profile measurements of the particle extinction coefficient from aerosols and clouds. These measurements allow for aerosol typing and the determination of aerosol size and microphysical properties. Furthermore, measurements of the elastic and depolarized backscattered echoes from the sea surface and the underlying layers will allow characterizing the optical properties of the marine surface (ocean color) and the suspended particulate matter in terms of oceanic particulate backscattering coefficient, while diffuse attenuation for downwelling irradiance at 1-2λ will be determined from the H₂O roto-vibrational Raman signals. These measurements will allow characterizing phytoplankton seasonal and inter-annual dynamics. Additionally, fluorescent scattering measurements at 1-3λ (450, 685 and 735 nm) from marine chlorophyll and atmospheric aerosols will be exploited to characterize ocean primary production and for atmospheric aerosol typing, respectively. CALIGOLA will also allow for accurate measurements of the small-scale variability of the earth's surface elevation, primarily associated with variations in the ice and snow, terrain, vegetation and forest canopy height.

The space mission CALIGOLA is explicitly included in the on-going ASI 2021-2023 Activity Plan. A Phase-A study focusing on the technological feasibility of the major sub-systems is on-going, commissioned by ASI to Leonardo S.p.A. (LDO). Scientific studies in support of the mission are also on-going, with the University of Basilicata (UNIBAS) being the leading scientific institution. In September 2023 NASA-LARC initiated a pre-formulation study to assess the feasibility of a possible contribution to CALIGOLA based on the development of the receiver detection chain and data down link capabilities. In September 2024 NASA will decide if proceed or not with the cooperation.

This conference contribution aims at illustrating the different atmospheric and ocean sciences’ objectives and a preliminary assessment of the mission observational requirements in terms of observable quantities, their vertical/horizontal resolution and precision/accuracy. The contribution also aims at illustrating the technical and technological solutions identified in the design of the instrument during the pre-feasibility and feasibility studies carried out by LDO, in cooperation with UNIBAS and other Italian research institutions. Expected system performance in a variety of environmental conditions will be provided based on the application of an end-to-end simulator developed at UNIBAS.