ATLID Overview
About ATLID
Atmospheric Lidar (ATLID) is a high spectral resolution atmospheric backscatter Light Detection and Ranging (LIDAR) instrument carried onboard the EarthCARE satellite, which detects cloud boundaries and profiles optically thin clouds and aerosols.
ATLID measures atmospheric profiles in a direction close to the nadir (3 degree shift along the satellite track), with a vertical resolution of about 103 m (for ground to 20.2 km altitude) and 500 m (for 20.2-40 km altitude).
| Parameter | Value | |||
|---|---|---|---|---|
| Operating Wavelength | 354.8 nm | |||
| Emitted Energy | 38 mJ | |||
| Receiver Footprint Diameter | ≤ 30 m | |||
| PRF | 51 Hz | |||
| Transmit Pulse Width | 20 ns | |||
| Altitude Range | -0.5 to +40 km | |||
| Vertical Sampling Interval | 103 m (up to 20.2 km) and 500 m (20.2 km - 40 km) | |||
| Along Track Sampling Interval | 285 m (2 shots accumulated onboard) | |||
| Dynamic Range | 10-7 to 9.61 x 10-3 sr-1 m-1 | |||
| Radiometric Stability | 1% | |||
The instrument transmitter emits short laser pulses at ~355 nm with a repetition rate of 51 Hz - corresponding to about 140 m spatial resolution - along the horizontal track of the satellite so that several shots can be locally averaged to improve the signal to noise ratio.
The ATLID receiver collects the backscattered photons with a ~60 cm diameter telescope. The energy from ultraviolet (UV) pulses transmitted by ATLID will be subject to narrow-band particle scattering from atmospheric aerosols (Mie scattering), which do not affect the spectrum shape of the incident light, and Rayleigh scattering due to the Brownian motion of atmospheric molecules, which causes broadening of the incident spectrum.
When backscattered photons are collected by the telescope, the receiver chain uses a high spectral resolution etalon filter to separate the particle and Rayleigh components in order to retrieve the aerosol optical depth. Co-polarised and cross-polarised components of the particle scattering contribution will also be separated and measured on dedicated channels to allow aerosol classification.
The sensitivity of the Rayleigh channel is such that accurate measurements of aerosols and cirrus optical thicknesses as low as 0.05 can be performed. Furthermore, the depolarisation channel must be able to determine cirrus clouds with a backscatter signal of 2.6 10-5 m-1 sr-1 and 10% depolarization ratio.
Additionally, ATLID will perform measurements with a linearity error lower than 3%, as well as ensuring a radiometric stability of the order of 1%. The instrument also provides an in-flight calibration of the absolute channel response for the Mie and Rayleigh channels better than 10%.