EARLINET - CALIPSO

EARLINET-CALIPSO is a ESA funded project to create a long term database of aerosols and clouds from spaceborne lidar measurements. It is a spaceborne-lidar-related EARLINET-activity during the CALIPSO mission.

Coordinators of the project are Ulla Wandinger and Gelsomina Pappalardo.

Overview

After the successful launch of the CALIPSO mission by NASA/CNES in April 2006, the satellite-borne lidar CALIOP provides vertically resolved information on aerosol and cloud parameters since June 2006. This date can be regarded as the starting point of a unique longterm, global, 4-dimensional data set that will substantially improve our knowledge on the role of aerosols and clouds in the Earth’s climate system. We can expect a historical data set on the global aerosol and cloud distribution and respective trends in cloud cover, cloud amount, and aerosol pollution state.

However, the lidar instruments (CALIOP, ALADIN, ATLID) onboard the three missions represent different system types with different sets of measured parameters. Whereas CALIOP is a two-wavelength backscatter lidar operating at 532 and 1064 nm, ALADIN and ATLID make use of the high-spectral-resolution lidar technique in the UV. Consequently, ALADIN and ATLID will deliver independent information on extinction and backscatter coefficients at 355 nm and thus on the extinction-to-backscatter ratio (lidar ratio) at this wavelength. From CALIOP we get backscatter coefficients at 532 and 1064 nm and thus also the so-called colour ratio. To derive extinction profiles and optical-depth information from CALIOP measurements, assumptions on the lidar ratio are needed. CALIOP and ATLID also measure the depolarization ratio at 532 and 355 nm, respectively.

With respect to CALIPSO the following topics are of special relevance: the selection of an adequate lidar ratio including the correct scene identification, multiple scattering and the wavelength dependence of the optical properties of clouds and aerosols. The well-established European Aerosol Research Lidar Network (EARLINET) is an optimum tool to work on all the topics discussed above. Several EARLINET stations operate multiwavelength Raman lidars, most of them measure particle depolarization as well. These core stations deliver the entire CALIOP/ALADIN/ATLID parameter set, so that conversion factors for a variety of aerosol types and clouds can be derived experimentally over a comparably long time period. In the case of aerosols, these instruments allow us to estimate important microphysical particle properties like parameters of the size distribution, refractive index, and derived quantities such as particle mass and surface-area concentration or single-scattering albedo. This detailed information from the EARLINET core stations offers the unique chance to investigate the potential of space-borne lidar instruments to identify certain aerosol types and to distinguish man-made from natural aerosol. In this context, the capabilities of CALIOP and of ALADIN/ATLID can be compared to each other.

The high-performance EARLINET stations are complemented by a larger number of stations which determine aerosol scattering parameters at either 355 or 532 nm. Measurements from these stations can be used for the direct satellite validation. In addition, the network structure is helpful for the investigation of the spatial and temporal variability of aerosol and cloud fields on scales which are relevant to space-borne lidar observations.

EARLINET has started a CALIPSO ground-truth measurement program in June 2006. A large number of correlative measurements since the launch of the CALIPSO mission are available.