Calculate a new scan parameter

Source: R/calculate_param.R

Calculate a new parameter (param) for a scan (scan) or polar volume (pvol)

calculate_param(x, ...)

# S3 method for class 'pvol'
calculate_param(x, ...)

# S3 method for class 'ppi'
calculate_param(x, ...)

# S3 method for class 'scan'
calculate_param(x, ...)

Arguments

x

A pvol or scan object.

...

An expression defining the new scan parameter in terms of existing scan parameters.

Value

An object of the same class as x, either a pvol or scan.

Details

Calculates a new scan parameter (param) from a combination of existing scan parameters. Useful for calculating quantities that are defined in terms of other basic radar moments, like linear reflectivity eta, depolarization ratio (Kilambi et al. 2018), or for applying clutter corrections (CCORH) to uncorrected reflectivity moments (TH) as TH + CCORH.

For the expression to work it is important that the operation can be vectorized. For example the base ifelse function is not vectorized, in these cases alternatives can be used (e.g. dplyr::if_else).

Also note that some functions do not operate on a matrix or param object. One example is the dplyr::if_else function. A workaround is calling the c() function on a parameter to convert it to a vector (e.g. c(DBZH), see examples).

Methods (by class)

  • calculate_param(pvol): Calculate a new parameter (param) for all scans in a polar volume (pvol).

  • calculate_param(ppi): Calculate a new parameter (param) for a plan position indicator (ppi).

  • calculate_param(scan): Calculate a new parameter (param) for a scan (scan).

References

  • Kilambi A, Fabry F, Meunier V (2018) A simple and effective method for separating meteorological from nonmeteorological targets using dual-polarization data. Journal of Atmospheric and Oceanic Technology 35, pp. 1415–1424. doi:10.1175/JTECH-D-17-0175.1

See also

Examples

# Locate and read the polar volume example file
pvolfile <- system.file("extdata", "volume.h5", package = "bioRad")
pvol <- read_pvolfile(pvolfile)

# Calculate linear reflectivity ETA from reflectivity factor DBZH
radar_wavelength <- pvol$attributes$how$wavelength
pvol <- calculate_param(pvol, ETA = dbz_to_eta(DBZH, radar_wavelength))
#> Error in eval(nn <- (calc[[i]]), x$params): object 'radar_wavelength' not found

# Add depolarization ratio (DR) as a scan parameter (see Kilambi 2018)
pvol <- calculate_param(pvol, DR = 10 * log10((ZDR + 1 - 2 * ZDR^0.5 * RHOHV) /
  (ZDR + 1 + 2 * ZDR^0.5 * RHOHV)))

# The function also works on scan and ppi objects
calculate_param(example_scan, DR = 10 * log10((ZDR + 1 - 2 * ZDR^0.5 * RHOHV) /
  (ZDR + 1 + 2 * ZDR^0.5 * RHOHV)))
#>                   Polar scan (class scan)
#> 
#>      parameters:  DBZH VRADH RHOHV ZDR PHIDP DR 
#> elevation angle:  0.5 deg
#>            dims:  480 bins x 360 rays

# set all reflectivity  values to NA when correlation coefficient > 0.95
# (indicating precipitation)
if (require(dplyr, quietly = TRUE)) {
  calculate_param(pvol,
    DBZH=if_else(c(RHOHV)>.95, NA, c(DBZH)) )
}
#> 
#> Attaching package: ‘dplyr’
#> The following objects are masked from ‘package:stats’:
#> 
#>     filter, lag
#> The following objects are masked from ‘package:base’:
#> 
#>     intersect, setdiff, setequal, union
#>                Polar volume (class pvol)
#> 
#>      # scans:  3 
#>        radar:  seang 
#>       source:  WMO:02606,RAD:SE50,PLC:Angelholm,NOD:seang,ORG:82,CTY:643,CMT:Swedish radar 
#> nominal time:  2015-10-18 18:00:00 
#> 

# it also works for ppis
ppi <- project_as_ppi(example_scan)
calculate_param(ppi, exp(DBZH))
#>                Plan position indicator (class ppi)
#> 
#>   parameters:  DBZH VRADH RHOHV ZDR PHIDP exp(DBZH) 
#>         dims:  201 x 201 pixels
#>