CL61 measurement is based on PPOL and XPOL attenuated backscatter profiles. The total attenuated backscatter profile (ABS) is calculated as a sum of PPOL and XPOL profiles.
The unit for attenuated backscatter profile intensity is one per meter per steradian (m-1 sr-1).
The following figures show examples of ABS, PPOL, and XPOL profiles from the same time window. All four 1‑dimensional profiles are moments in time contained in the 2‑dimensional data displayed in Figure 1. Specifically, the following profiles are taken from within a 1‑minute period.
The following figure shows the ABS profile. The signal between 3000 m and 4000 m (9843 … 13 123 ft) is caused by the falling precipitation. High signal returns between 4000 m and 4200 m (13 123 … 13 779 ft) originate from a cloud.
The same features can be seen in the PPOL return. The following figure shows the PPOL profile.
The orthogonally polarized return shows increased signal levels in the precipitation between 3000 m and 4000 m. The returns increase inside the cloud, but not nearly as much as for the parallel-polarized channel. The following figure shows the XPOL profile.