CLARE 98 (CHILBOLTON, UK)

Data set of the DLR Lidar ALEX onboard the FALCON aircraft

Arbeitsgruppe LIDAR - DLR Oberpfaffenhofen, D-82234 Weßling

Tel.: 0049 +8153-281103

Fax: 0049 +8153 281271

Contents:

 Campaign

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 Evaluation/Interpretation

The quicklook files contain:

The 3-panels of vertical along-flight-path sections are contour plots of the backscatter ratio at 1064nm and at 532nm as well as the depolarisation at 532nm. The backscatter ratio (total scattering of particles + molecules devided by molecular scattering) gives the relative contribution of particle scattering to the received signal. It is always larger than 1 and is equal to1 if only Rayleigh scattering by molecules occurs.

The depolarisation is the ratio of received light intensities in two different channels polarized paralelly and perpendicularly towards the incident laser beam. It is a qualitative measure of the non-spericity of the scattering particles. A depolarisation about 1.4% occurs if only the unsymmetric air-molecules contribute to depolarisation. If depolarising (non-spherical, solid) particles are within the measured volume the volume-depolarisation is between 1.4% and 100% depending on the concentration and shape of the scatterers. Clouds with spherical (liquid) particles cause a depolarisation below 1.4% since only the intensity in the parallel channel is increased.

Since the backscatter ratios are not corrected for extinction, shading occurs behind dense clouds due to the attenuation inside them. The relatively low remaining light intensity behind the cloud feigns low backscatter.

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 Quicklooks

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 Data

HDF-FILES

Part of the FALCON Lidar data on this server are in Hierarchical Data Format (HDF) carrying the extension .hdf.

The .hdf files in the ...falcon/data directory are named in analogy to the Quicklook (...igd*.ps) files described above. (e.g. clare981021.4.hdf corresponds to the Quicklook clare981021.igd4.ps which means the 4th flight leg on 21 Oct 98, and so on).

However the data is given in terms of backscatter coefficient, while the Quicklooks show backscatter ratio as explained above. Available wavelengths are 1064nm, 532nm, and 354nm.

Reading the .hdf files is quite easy (idl Version 5.1): As is documented in the idl online help (see 'hdf_read') there are mainly two ways, either creating a reusable template with the function 'hdf_browser' or extracting the data directly (also by use of 'hdf_browser' but without re-use option) with the function 'hdf_read'' e.g. by typing '' datastructure=hdf_read()'' to the idl prompt. You then will be asked for the filename and the browser will be opened automatically. Reading of two lowermost items can be dis- or enabled by de- / activating the read button for the single datasets. (With this I think it is not neccessary to provide an additional .pro to read the files.)

ASCII-FILES

Single Profiles of attenuated backscatter-coefficient are available in ASCII format like this:

Backscatter coefficient [1/m sr] at ***nm on 'date'...'time'....'#shots'...'latitude'...'longitude'

This file contains each 896 entries of altitude and bs-coefficient

-0.03345 -0.03278 .................[km]

2.9753e-8 2.756e-8 .................[1/m sr]

(eof)

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More explanations can be requested from Arbeitsgruppe LIDAR

Last modified: 26 Feb1999, 11:00 CET

by Harald Flentje (harald.flentje@dlr.de)