Atmospheric backscatter profiling lidar

Atmospheric backscatter profiling lidar fires short laser pulses and records the range-gated return signal as a function of altitude, producing vertical profiles of aerosol and cloud attenuated backscatter and extinction across the troposphere and lower stratosphere. The method relies on elastic scattering of photons from aerosol particles and molecules, with depolarisation channels capable of distinguishing liquid water droplets from non-spherical ice crystals and dust.

Spaceborne implementations have operated at wavelengths including 532 nm, 1064 nm, and 355 nm. CALIPSO/CALIOP established a reference architecture with a dual-wavelength, three-channel receiver achieving 30 m vertical and 333 m horizontal resolution at a 705 km orbit, measuring from the surface to 40 km altitude.^[1][2] EarthCARE/ATLID extends the technique with a 355 nm high-spectral-resolution lidar (HSRL) that separates molecular and particulate backscatter without relying on assumed aerosol models, improving extinction retrieval accuracy at 100 m vertical resolution to 20 km.^[3][4] China's ACDL on DQ-1 combines a 532 nm HSRL and polarisation channel with a 1064 nm elastic channel for coincident aerosol and cloud profiling.^[5] The ISS-hosted CATS demonstrated three-wavelength backscatter (355/532/1064 nm) with 532 nm HSRL from February 2015 to October 2017, validating HSRL retrievals from a low-inclination orbit.^[6] ICESat/GLAS carried a dual-purpose design: primary ice-sheet altimetry at 1064 nm, with coincident 1064 and 532 nm backscatter channels producing cloud and aerosol boundary and extinction data products.^[7][8] Aeolus/ALADIN produces aerosol backscatter at 355 nm through its Mie-channel Fizeau interferometer as a co-product alongside its primary Doppler wind retrieval.^[9]

Core data products include attenuated backscatter coefficient profiles, particulate extinction, column optical depth, aerosol layer top and base heights, cloud thermodynamic phase, and aerosol subtype classifications. These products feed air-quality monitoring, climate radiation budget assessments, and numerical weather prediction assimilation.