The de-polariztion lidar functions based on linear polarization of laser. An electro -optical Q-Sw Nd:YAG laser is usually used. The depolarization ratio is measured by the detection of perpendicular polarized intensities of the receiving signal to assess the ratio. The latter is a function of particle size and its asymmetric shape. This technique is efficient to identify the particles such as aerosol, water drop, vapor, volcanic ash, smoke, ice debris etc, in the various atmospheric layers. I believe that the interaction of linearly ploarized laser with atmospheric particles is lucidly different from the circularly polarized beam. What is your comments?
Hi, I recommend you this nice paper, where depolarization in Lidar, as well as polarization changes, is analysed in depth (JOSA A, Vol. 29, Issue 4, pp. 400-409 (2012), DOI:10.1364/JOSAA.29.000400).
The article recommended by Juan is very interesting.
They have analyzed lidar depolarization for linear, circular and elliptical polarization of transmitted light theoretically. It is shown that for a given target, circular polarization is depolarized more than linear one. In both cases, scattered polarized component is the same as the transmitted polarization state. But for elliptical transmitted polarization, the scattered polarized component will not be the same state as the transmitted polarized component which induces some difficulties in data analysis.
Depolarization lidar formalism is based on the polarization dependent backscattering analysis.
In the case of polarization dependent extinction in atmosphere, does any method exist for data corrections?
Why is the circular polarization depolarized more than linear one, for a given target ?
Very nice discussion, thanks!
It depends on the depolarization mechanisms (simmetry, particle size,...). From a theoretical point of view, pure polarization states can be influenced by depolarization independently (for instance, linear polarization can be fully depolarized whereas circular polarization is not depolarized). However, if you calculate the light scattering of spherical particle dimmers (or ellipsoids, see SPIE contributions on depolarization by S.M.Nee) and you mix incoherently the resulting stokes vectors (s0,s1,s2,s3) for a given scattering direction (like a system of two particles randomly oriented in a fluid media), circular polarization (s3) is more influenced by depolarization than s1 and s2 (related to linear polarization). In particular, for dense media imaging you can obtain M44 in the Mueller matrix equal to 0 (see, for instance, DOI:10.1364/OE.1.000441 and DOI: 10.1016/j.jqsrt.2014.03.008, the first one is free). Although these articles are not fully related to Lidar, I think that can be helpful to understand depolaAdd your answerrization mechanisms. There are also studies that conclude 'circular polarization is twice as sensitive to the depolarization compared to linear polarization' (DOI: 10.1364/AO.47.003795, p.3799), based on Mischenko&Hovenier's theory.
Dear Juan
Interesting response. Thank you.
It pretends that asymmetry in particle shape is the dominant factor for sensitivity of circular polarization to depolarization.
Fly ash eruption from volcanoes may be detected by depolarization lidar. It is suitable to identify volcanic ash hazardous for airplanes.
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