The emitted laser pulse is scattered by each particle it encounters on its path through the atmosphere. A portion of this light is scattered back towards the instrument and is registered. The rest of the light is either absorbed or scattered in directions not seen by the ceilometer. The portion of backscattered light registered by the ceilometer is called attenuated backscatter.
Each particle also interacts with the laser pulse by either maintaining or altering the polarization of the emitted light. The ceilometer registers changes in polarization and reports them as profiles called the linear depolarization ratio. The information in these profiles can be used to differentiate between liquid and solid particles.
The following figures show attenuated backscatter and depolarization ratio data covering a period of 1.5 days. The detected data shows liquid cloud layers, ice clouds, and snow, as well as precipitation including the melting layer. The data also shows the aerosol signal in the boundary layer.
- 1
- Solid precipitation
- 2
- Supercooled liquid cloud
- 3
- Rain
- 4
- Melting layer
- 5
- Ice crystals