20 years of light scattering measurements by the PROGRA2 program Instrumental concept and new developments

International audienceThe analysis of light scattered by dust in planetary and cometary atmospheres, by interplanetary dust and by regolith on small body surfaces, can provide some information on the physical properties of the grains, mainly their nature, size and porosity. Many remote sensing observations of these bodies have been conducted from telescopes on the ground and from space. A laboratory data base is needed to interpret such measurements, for various kinds of irregularly shaped dust grains. This is the aim of the PROGRA2 project, for deposited and free-floating particles. The PROGRA2 concept encompasses a suite of five instruments carrying out measurements at different wavelengths between 540 and 1500 nm: PROGRA2-VIS (visible domain), PROGRA2-IR (near infra red domain), PROGRA2-SURF (laboratory deposited grains, in the visible domain), PROGRA2-REGOLITH (deposited particles during reduced gravity, preliminary studies), and PROGRA2-AERO (measurements on liquid aerosols, under development). This instrumental suite enables documenting optical properties (polarization, brightness) of particles in various configurations, ranging from large several hundreds of micrometers free-floating grains to micron-sized grains, and for deposited particles. In particular the instrument allows the measurement of these parameters on very absorbing particles (carbonaceous compounds). For free-floating particles typically larger than 10 micrometers, the project operates during parabolic flight campaigns on board the European Airbus 300 "Zero-G", and will have logged 45 campaigns at the end of 2012. CNES and ESA have been sponsoring this project and associated campaigns since 1993. For the smaller free-floating particles, the measurements are conducted on the ground using an air draught technique. PROGRA2-VIS, -IR, and -SURFACE use cameras as detectors to distinguish between isolated grains, aggregates, and to reject images with multiple scattering. We will present the instrumental technique of measurement, and the new results obtained with PROGRA2-IR. The database of measurements done with PROGRA2-VIS and -SURF is available at the PROGRA2 website: http://www.icare.univ-lille1.fr/progra2/indexeng.htm