radcart4 −− interpolate airborne or ground-based Doppler radar data to a Cartesian grid
radcart4 lon0 dx xsize lat0 dy ysize alt0 dz zsize [reftime svx svy]
Radcart4 reads a Candis file on the standard input consisting of a volume of radar data from one or more radars. A Candis file is written to the standard output with these data interpolated to a rectangular Cartesian grid. Corrections are made for the earth’s curvature. Positions are adjusted for storm propagation to a specified time if the optional command line arguments reftime, svx, and svy are supplied. The reference time, reftime, should be in kiloseconds and the storm propagation velocity components should be in meters per second. If these arguments are not given, the assumed propagation velocity is zero. Interpolation of the ray to the Cartesian grid is made after corrections for the storm velocity and the curvature of the earth are made. The actual interpolation is made taking the corrected position of each gate and distributing the values to all eight corners of the box by a weighting system based upon how close the gate is to each corner.
The first 9 arguments define the grid. Lon0, lat0, and alt0 define the lower southwest corner of the grid in degrees (longitude and latitude) and kilometers (altitude). Dx, dy, and dz define the grid interval in kilometers. Xsize, ysize, and zsize define the size of the domain in kilometers. The number of grid points in the x dimension is calculated from nx = xsize/dx + 1.5, with similar calculations in the y and z directions.
The input file must meet certain requirements. Each variable slice must contain data associated with a single ray. Certain assumptions are made about the names of input fields. These are easily changed by editing the source file before compilation. The assumed names are all located in defines near the beginning of the program. Default names of required input fields for each variable slice are "vr" (radial velocity in meters per second), "dbz" (reflectivity in dBZ), "lon" (longitude of radar in degrees), "lat" (latitude of radar in degrees), "alt" (altitude of radar in kilometers), "time" (time in kiloseconds), "az" (azimuth angle of the ray in degrees), and "el" (elevation of the ray in degrees). The first two fields are assumed to be one-dimensional with index field "range" (radar range in kilometers). The other fields are scalar. Note that "lon", "lat", and "alt" are not normally supplied for every ray for ground-based radars. These need to be somehow created (using, say, cdfmath) before applying radcart4.
The output static slice contains the three index fields x, y, and z. All one-dimensional fields with range as the dimension are interpolated to the Cartesian grid. All other fields are dropped.
Additional Cartesian fields resulting from computations on input fields are added to the output. These fields are vx, vy, vz, ux0, uy0, seu, sev, sewp, magu, magv, magwp, dmagu, dmagv, deu, dev, gx, gy, and avgtime, and are created to help in subsequent dual and triple Doppler synthesis. (More on these later -- this man page is still under construction.)
raduf(1), raduffix(1), rtape(1), hrdrad(1)