The airborne radar-lidar platform for cloud and aerosol observations

The airborne radar-lidar platform for cloud and aerosol observations

RALI is “Instrument National INSU” at OVSQ and the instruments have been developed at LATMOS and DT-INSU.

RALI project consists of an airborne platform (F20 and ATR42 operated by SAFIRE) combining a multibeam 95 GHz Doppler cloud radar named RASTA, a sidewards looking 95 GHz Doppler radar named BASTA and a triple-wavelength dual-polarization lidar (High spectral resolution capability) named LNG for the characterisation of the macrophysical, microphysical, radiative, and dynamical properties of clouds, aerosols, and convection.

Configuration since 2022 onboard the ATR42
Example of measurements collected during NAWDEX field campaign (2016) with the F20 (radar reflectivity, molecular backscatter at 355nm, particulate basckatter at 355nm, lidar line of sight velocity at 355nm, radar vertical velocity and horizontal cloud wind)

Scientific objectives clouds, aerosols and their interaction

  • What are the mechanisms involved in the water cycle ?
  • What control the partitioning of liquid water/ice in mixed phase clouds ?
  • What is the radiative effect of mixed phase clouds ?
  • How do clouds and aerosol interact?
  • How are dynamics, microphysics and radiative processes of clouds related ?

Other objectives instrumental development

  • Satellite demonstrator
  • Satellite calibration and validation

Why radar and lidar?

These two types of instruments, the millimetre-wave radar and the backscatter lidar are the most relevant instruments to address aerosols/clouds studies. The cloud radar detects most of the clouds in the troposphere, however it is very difficult for the radar to observe very thin cirrus. The cloud radar also has the potential to document convectivestorms, except the most intense storms which produce total extinction of the radar signal. On the other hand, the lidar can document both clouds and aerosols. Unfortunately, it cannot detect clouds of optical depth larger than 3-4 though, but it is very well suited to document the very thin ice clouds missed by the cloud radar in airborne and spaceborne configurations. The cloud-radar lidar combination is therefore really unique in the sense that it can characterise the vertical distribution of the properties of many clouds (with the cloud radar alone, the lidar alone, or the combination of both) and also document the aerosol properties (in the absence of clouds).