Instrument: Cloud Physics LiDAR (CPL)

The Cloud Physics LiDAR (CPL) is a multi-wavelength backscatter Light Detection And Ranging (LiDAR) instrument used for aerosol and cirrus cloud studies. The CPL uses laser technology to detect, locate, and identify aerosol and cloud particles by measuring the backscatter coefficient for a volume of targets, retrieving information about their location and composition. Similar to radar and sonar technology, LiDAR transmits pulses of electromagnetic radiation, or light in this case, towards a target. When the radiation contacts the target, some of the light energy is absorbed and scattered while some is reflected back, or backscattered, towards the instrument’s receiver. The time that it takes this reflected energy to return to the receiver indicates the target’s distance from the instrument (i.e., its location), and the characteristics of the returned signal give information regarding the target’s properties. The CPL uses three operating wavelengths: 1,064 nm, 532 nm, and 355 nm. These relatively short wavelengths give CPL the ability to detect the minute particles that make up aerosols and cirrus clouds. Its laser pulse has a high repetition frequency and is low energy, allowing CPL to use photon-counting detection; a technique for providing a more accurate target location by counting the number of photons returned in the backscattered signal. CPL’s high-resolution measurements of aerosol and cirrus cloud properties can be applied to various operational and research areas including air quality monitoring and climate studies.

Measures the backscatter coefficient of aerosols and cirrus clouds to derive the depolarization ratio, extinction coefficient, and optical depth (level of transparency) values. These measurements allow CPL to identify the aerosol type, cloud phase, layer types and boundaries (e.g., planetary boundary layer), ice water content, and plume and cloud structure.

Air Quality
Land-Atmosphere Processes
Volcanic Ash Plumes

Horizontal: 200 m at 20 km altitude

Vertical: 30 m

100 microradians

Raw data: 1/10 s

Processed data: 1 s

Minimum detectable backscatter (at 532 nm)

Cirrus (daytime): 1.2 x 10-7 m-1 sr-1

Cirrus (nighttime): 5.0 x 10-8 m-1sr-1

Aerosol (daytime): 3.1 x 10-7 m-1sr-1

Aerosol (nighttime): 6.8 x 10-8 m-1sr-1

1064 nm

532 nm

355 nm

Pulse repetition rate: 5 kHz


Relevant Publications
McGill, M.J., Hlavka, D.L., Hart, W., Scott, V.S., Spinhirne, J., & Schmid, Beat (2002). Cloud Physics Lidar: instrument description and initial measurement results. Applied Optics, 41(18), 3725-3734.
McGill, M.J., Hlavka, D.L., Hart, W.D., Welton, E.J., & Campbell, J.R. (2003). Airborne lidar measurements of aerosol optical properties during SAFARI-2000. Journal of Geophysical Research, 108(D13), 29-1 - 29-12.
McGill, M.J., Hlavka, D.L., & Hart, W.D. (2005). Applications of Data from the Cloud Physics Lidar. 2nd Symposium on Lidar.
McGill, M.J., Vaughan, M.A., Trepte, C.R., Hart, W.D., Hlavka, D.L., Winker, D.M., & Kuehn, R. (2007). Airborne validation of spatial properties measured by the CALIPSO lidar. Journal of Geophysical Research, 112, 1-8.
NASA. (1996). Atmospheric Aerosols: What Are They, and Why Are They So Important?
NASA. (2017). NASA Armstrong Fact Sheet: ER-2 High-Altitude Airborne Science Aircraft.
Vaughan, M.A., Liu, Z., McGill, M.J., Hu, Y., & Obland, M.D. (2010). On the spectral dependence of backscatter from cirrus clouds: Assessing CALIOP’s 1064 nm calibration assumptions using cloud physics lidar measurements. Journal of Geophysical Research, 115(D14206), 1-17.


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