Depolarization ratio (LDR) is the ratio of the perpendicular or cross-polarized (XPOL) components and parallel (PPOL) signal components.
The following figure presents the same time period as Figure 1, Figure 2 and Figure 3.
The linear depolarization ratio reveals the precipitation between 3 000 m and 4 000 m (9843 ft and 13 123 ft) to consist of non‑symmetrical solid particles. The ratio falls near zero at the beginning of the cloud signal, signifying a liquid cloud. The ratio increases inside the liquid cloud due to the presence of multiple scatterers.
Interpreting depolarization
Vertical depolarization ratio profiles allow straightforward identification of several weather phenomena, such as liquid vs. solid precipitation, cloud phase, and melting layer. Near-zero values from liquid scatterers are clearly distinguished from larger values from complex ice crystal shapes.
In most cases it is better to do a side-by-side visual inspection of the time-height figures of ABS and LDR.
Characteristic behavior of local weather events, seen in signal strength, variance, and shape of patterns, are clearly recognizable with some practice.
For example, by looking only at LDR values, it may be difficult to distinguish some aerosols from liquid clouds without the ABS information. Aerosol characterization is also possible, especially when additional information is available, such as in model forecasts and backward trajectories, or complimentary lidar measurements.
Polarization lidars operating in one wavelength cannot provide independent, unambiguous aerosol type identification. Aerosols can also exist in mixtures and go through hygroscopic growth, which complicates identification. However, they can help quickly and confidently identify several weather conditions, such as snowfall, supercooled liquid clouds, and freezing rain, and support research lidars in aerosol studies.
| The ranges of values shown below the color bar may not accurately represent observations at 910 nm. |
