beam_profile_overlap  R Documentation 
Calculates the distribution overlap between a vertical profile ('vp') and the vertical radiation profile of a set of emitted radar beams at various elevation angles as given by beam_profile.
beam_profile_overlap( vp, elev, distance, antenna, zlim = c(0, 4000), noise_floor = Inf, noise_floor_ref_range = 1, steps = 500, quantity = "dens", normalize = T, beam_angle = 1, k = 4/3, lat, re = 6378, rp = 6357 )
vp 
a vertical profile of class vp 
elev 
numeric vector. Beam elevation(s) in degrees. 
distance 
the distance(s) from the radar along sea level (down range) for which to calculate the overlap in m. 
antenna 
radar antenna height. If missing taken from 
zlim 
altitude range in meter, given as a numeric vector of length two. 
noise_floor 
The system noise floor in dBZ. The total system noise
expressed as the reflectivity factor it would represent at a distance

noise_floor_ref_range 
the reference distance from the radar at which

steps 
number of integration steps over altitude range zlim, defining altitude grid size used for numeric integration 
quantity 
profile quantity to use for the altitude distribution, one of 'dens' or 'eta'. 
normalize 
Whether to normalize the radiation coverage pattern over the altitude range specified by zlim 
beam_angle 
numeric. Beam opening angle in degrees, typically the angle between the halfpower (3 dB) points of the main lobe 
k 
Standard refraction coefficient. 
lat 
radar latitude. If missing taken from 
re 
Earth equatorial radius in km. 
rp 
Earth polar radius in km. 
This function also calculates the overlap
quantity in the output of
integrate_to_ppi.
Overlap is calculated as the Bhattacharyya coefficient (i.e.
distribution overlap) between the (normalized) vertical profile vp and the
(normalized) radiation coverage pattern as calculated by
beam_profile. In the calculation of this overlap metric, NA and NaN values
in the profile quantity specified by quantity
are replaced with zeros.
The current implementation does not (yet) take into account the system noise floor when calculating the overlap.
In the ODIM data model the attribute /how/NEZ
or /how/NEZH
specifies the system noise floor (the Noise Equivalent Z or noise
equivalent reflectivity factor. the H refers to the horizontal channel of a
dualpolarization radar). In addition, the attribute /how/LOG
gives
"security distance above mean noise level (dB) threshold value". This is
equivalent to the log receiver signaltonoise ratio, i.e. the dB above the
noise floor for the signal processor to report a valid reflectivity value.
We recommend using NEZH
+LOG
for noise_floor
, as this
is the effective noise floor of the system below which no data will be
reported by the radar signal processor.
Typical values are NEZH
= 45 to 50 dBZ at 1 km from the radar.
LOG
is typically around 1 dB.
Need to evaluate beam by beam the returned signal relative to a uniform beam filling of at least NEZH + LOG If returned signal is lower, the gate is below noise level.
A data.frame with columns distance and overlap.
# locate example volume file: pvolfile < system.file("extdata", "volume.h5", package = "bioRad") # load the example polar volume file: pvol < read_pvolfile(pvolfile) # let us use this example vertical profile: data(example_vp) example_vp # calculate overlap between vertical profile of birds # and the vertical radiation profile emitted by the radar: bpo < beam_profile_overlap(example_vp, get_elevation_angles(pvol), seq(0, 100000, 1000)) # plot the calculated overlap: plot(bpo)
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