Lidar Measurements for Desert Dust Characterization: An Overview

Table 1

Products for each specific lidar technique. Quantities obtained by directly measured parameters, (𝑆 is the lidar ratio, Å(𝛼) is the Angstrom extinction related exponent, and Å(𝛽) is the Angstrom backscatter related exponent), are also reported. Finally, critical assumptions/points for each technique are reported too.

Lidar techniques	Aerosol layering	Extensive properties	Intensive properties	Critical aspects	Systematic errors
Ceilometer	- PBL top; - FT layers* (top, base, center of mass)	Aerosol backscatter*	n.a.	- S assumption; - Calibration often not  possible	Calibration: up to 60% in free troposphere; (larger at longer 𝜆); S assumption: also 150% in the free troposphere; (larger at shorter 𝜆)
Backscatter lidar	- PBL top; - FT layers (top, base, center of mass)	Aerosol backscatter	𝑆^†	S assumption	Calibration: up to 60% in free troposphere; (larger at longer 𝜆); S assumption: also 150% in the free troposphere; (larger at shorter λ)
Raman lidar	- PBL top; - FT layers (top, base, center of mass)	- Aerosol backscatter; - Aerosol extinction	𝑆	Low SNR in daytime	Density: <15% for backscatter; <5% for extinction; Angstrom assumption; <1% for backscatter; <4% for extinction
HSRL	- PBL top; - FT layers (top, base, center of mass)	- Aerosol backscatter; - Aerosol extinction	𝑆	Instrumental complexity	Calibration: about 2.5% (backscatter and extinction); Density; <5% for extinction
Multi-wavelength HSRL/Raman lidar	- PBL top; - FT layers (top, base, center of mass)	- Aerosol backscatter at 3  wavelengths; - Aerosol extinction at 2  wavelengths	1 𝑆; 1 Å(ext); 2 Å(back)	Low SNR in daytime (Raman); Instrumental complexity (HSRL)	Typical total systematic errors: <5% for backscatter; <10% for extinction

The symbol ^† indicates that S can be retrieved for specific cases with clean air below and above identified intense aerosol layer. Depolarization capability could be added to each one of these techniques resulting in the additional aerosol linear depolarization ratio measurement capability. The symbol * denotes products that could be not available because of the low signal-to-noise ratio.