Attenuation correction artifact

[kirknorth]

Processing C-band data from 24-May-2011 revealed a new artifact I had not seen before when performing phase processing and/or attenuation correction. I'll provide code snippets of how I created this later. In the meantime check out the image below. The thin slice in the corrected reflectivity is the artifact I'm referring too, and those values are the missing value -9999.0. I was using min_ncp = 0.3 and min_rhv = 0.7, and using the default values (min_ncp=0.5 and min_rhv=0.8) produces more of these artifacts.

[josephhardinee]

Can you add a plot of Phi_dp and K_dp?

[kirknorth]

@josephhardinee please see updated image.

[scollis]

Hmm.. might be that thin slice of 2nd trip right at the receiver.. Did you hardset the system phase? Or did you let the algorithm try to find it?

BTW this is one of the issues we hope to address with CMAC2.0

[josephhardinee]

Does Kdp go negative in that ray?

[kirknorth]

@scollis, here's the phase processing code snippet:

pdp_corr, kdp_corr = pyart.correct.phase_proc_lp(
                       radar, -2.0, self_const=60000.0, low_z=0.0,
                       high_z=55.0, min_phidp=0.01, min_ncp=0.3, min_rhv=0.7, 
                       fzl=3900.0, overide_sys_phase=False, sys_phase=332.0,
                       nowrap=291, LP_solver='cylp_mp', window_len=35, proc=8,
                       debug=False, really_verbose=False)

@josephhardinee, no, please see the updated image for clarity. That being said, there certainly are negative pixels...

[scollis]

Hmm.. interesting..

One workaround to keep you going is to set the ray to _FillValue and
then it will not be used in the gridding.. Is it badvalue from first
gate? Could you add a rayplot?

On 6/30/14, 2:45 PM, Kirk North wrote:

@scollis https://github.com/scollis, here's the phase processing
code snippet:

pdp_corr, kdp_corr = pyart.correct.phase_proc_lp(
radar, -2.0, self_const=60000.0, low_z=0.0,
high_z=55.0, min_phidp=0.01, min_ncp=0.3, min_rhv=0.7,
fzl=3900.0, overide_sys_phase=False, sys_phase=332.0,
nowrap=291, LP_solver='cylp_mp', window_len=35, proc=8,
debug=False, really_verbose=False)

@josephhardinee https://github.com/josephhardinee, no, please see
the updated image for clarity.

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[kirknorth]

@scollis, yup it's _FillValue for the entire ray(s). The May 24th case suffered from second trip echoes much more than the other cases I've processed, so my first guess is these artifacts are linked to that. That being said, these artifacts decrease the more I lower ncp_min towards 0, i.e. the more I allow second trip pixels in. Furthermore, I see this artifact on several tilts at different azimuths.