Strategic interest for satellite observations
The observation strategy adopted at the international level to improve the understanding of atmospheric processes requires the gathering of complementary and well co-located observation means, including some complex instruments such as lidars and radars. This strategy is applied in satellite observations, through large multi-instrumented platforms (Terra, Aqua, EarthCARE satellites) and satellite trains (A-train). It also applies to ground-based observations from multi-instrument sites, notably in Europe (ACTRIS research program in Europe) and in the USA (Atmospheric Radiation Measurement program), as described in Haeffelin et al. (2016). In this framework, SIRTA gathers its atmospheric observation means, to implement reference observation procedures, and to carry out test and validation campaigns of instruments (ground, airborne and satellite). This long-term commitment has allowed the development of multi-decadal data sets for the research needs of the national and international scientific community and for the teaching needs of geophysics training.
The observations and experiments carried out at SIRTA are essential for the preparation, validation and exploitation of satellite missions. The scientific teams that exploit the data from satellite missions develop their skills from ground and airborne measurements. Instrumental developments are initially tested on the ground; inversion algorithms are often tested on ground measurements; space measurements are validated on the basis of ground measurements. The cal/val of aerosol and cloud products can be achieved by using ground and satellite measurements almost co-located with lidars and radars at the same wavelength (or frequency). The advantage of ground-based observatories is that multi-year data sets already exist and a synergy of instruments to describe cloud and aerosol properties is possible. Statistical comparisons between ground-based and satellite-based Lidar and radar measurements have already been successfully performed (e.g., Protat et al. 2009; Dupont et al. 2010) for the CloudSat and CALIPSO missions. Currently, the measurement strategy at SIRTA is adapted to the Cal / Val activities of new or future missions: ADM-AEOLUS (aerosol and wind products by Lidar) external link and EarthCARE (aerosol and cloud products by Lidar ATLID, cloud products by CPR Radar).