Thresholding polarization parameters

The thresholding of polarization parameters by the processor eliminates bins with weak or uncertain signals. Note that the thresholding can be disabled if you want to see all of the data regardless of the data quality.

All the polarization parameters are based on power ratios. RVP10 requires that each power term in a ratio pass a signal-to-noise test similar to the log power test. For example, there are up to four different powers that can be calculated (alternating dual-channel case) so the tests for each of these are:

\frac{< {| S_{h h} |}^{2} >}{N_{h}} > N_{t h r e s h}

\frac{< {| S_{h v}}^{2} | >}{N_{h}} > N_{t h r e s h}

\frac{< {| S_{v v} |}^{2} >}{N_{h}} > N_{t h r e s h}

\frac{< {| S_{v h} |}^{2} >}{N_{h}} > N_{t h r e s h}

where the linearized threshold that is input as the dB LOG threshold, that is:

N_{t h r e s h} = 10^{\frac{L O G t h r e s h}{10}}

For example, a valid LDRH requires both a valid S_hh and a valid S_vh. The parameters RhoH and PhiH have the same requirement since they are the magnitude and phase of the cross-correlation function which is based on S_hh and S_vh.

There are 2 exceptions:

Z_dr: Z_dr requires that S_hh and S_vv pass the signal-to-noise tests noted above. However, Z_dr can be additionally thresholded by any of the other threshold parameters (LOG, SIG, SQI, CSR) similar to a standard moment.
PhiDP for single channel alternating case: PhiDP requires that S_hh and S_vv pass the signal-to-noise tests noted above. In the single channel alternating case, PhiDP must also satisfy the additional test that the Doppler velocity at the range bin must be valid, that is, not thresholded by its own criteria. This is because the algorithm for PhiDP in this case subtracts the phase change due to the Doppler velocity. If the Doppler velocity is uncertain, the algorithm cannot produce reliable results.