Preliminary Studies and Performance Simulations in support of the mission “CALIGOLA”

CALIGOLA (Cloud Aerosol Lidar for Global Scale Observations of the Ocean-Land-Atmosphere System) is a mission funded by the Italian Space Agency (ASI), aimed at the development of a space-borne Raman Lidar. A Phase A study to assess the technological feasibility of the laser source and receiver system is currently underway at the Leonardo S.p.A., while scientific studies in support of the mission are conducted by the University of Basilicata. Scientific and technical studies are furthermore supported by other Italian institutions (CNR-ISMAR, CNR-IMAA), with NASA also having expressed an interest in contributing to the mission .

Mission objectives include the observation of the Earth atmosphere, surface (ocean and land). Among the atmospheric objectives, the characterization of the global scale distribution of natural and anthropogenic aerosols, their radiative properties and interactions with clouds, and the measurements of ocean color, suspended particulate matter and marine chlorophyll.

The expected performance of CALIGOLA has been assessed based on the application of an end-to-end lidar simulator. Specifically, sensitivity studies have been carried out to define the technical specifications for the laser source, the telescope, the optics of transceiver, the detectors and the acquisition system. Simulations reveal that the system can measure Rotational Raman echoes from nitrogen and oxygen molecules stimulated at the three lengths wavelength of 355, 532 and 1064 nm. Simulations also reveal that elastic signals are strong enough to meet the requirements under different environmental conditions. As reference signal, several options have been considered. Among others, a temperature-insensitive rotational Raman signal including rotational lines from nitrogen and oxygen molecules.

A careful analysis of different potential orbits is ongoing, with the goal to identify solutions which maximize performance and scientific impact of both atmospheric and oceanic measurements. Near noon-midnight equatorial crossing times are preferable on the ocean side for diel vertical migration and phytoplankton observations, but degrade significantly the performances of atmospheric measurements due to the high solar background. For this reason is essential to find an orbit in which the solar contribution is low enough to obtain acceptable atmospheric results and at the same time the oceanic measurements are far enough from the night-day transitions for as many days a year as possible to assure correct interpretation of phytoplankton physiology. To counterbalance the degraded signal performances also lower obit height are considered, as well as the use of polarized filters to reduce the amount of solar radiation. The estimated performances under different conditions and considering different orbits will be showed during the presentation.