loadchil

loadchil is a `mex' file that reads Chilbolton data directly into matlab. A mex file is basically compiled C code that can be dynamically linked in to the matlab process when the function it provides is called from within matlab. This gives it a distinct speed advantage over a program written in the interpreted matlab language. The processing options are shared with chil2a, chil2nc and loadchil. Additional options are given below. To run you will need the mex file to be in your matlab path. The compiled mex file has the name loadchil.mex*, where the `*' is a suffix denoting the operating system, such as sol for Solaris or glx for Linux (glibc 2.x). Within matlab the function can be called either in its functional form, e.g.

loadchil('6134new.dat', '4', '-coords', 'Zcal', '5');
or in its command-line form, e.g.
loadchil 6134new.dat 4 -coords -Zcal 5;

Arrays read into matlab

The radar parameters that can be read in are

Zh
Radar reflectivity (in dBZ) using horizontal polarisation.
Zdr
Differential reflectivity (in dB).
Ldr
Linear depolarisation ratio (in dB).
phi_dp
Differential phase shift (degrees).
v
Radial velocity (in m/s) measured at horizontal polarisation, where positive indicates towards the radar.
v1, v2
CAMRa measures two velocities: v1 is the velocity measured using only horizontally-polarised pulses, and v2 is that measured using both horizontally- and vertically-polarised pulses. Both are in m/s. The folding velocity of v2 is twice that of v1.
width
Doppler spectral width (in m/s).
sigma_v
Standard deviation of the raw (usually 64-pulse) mean velocities (in m/s). This parameter is calculated from v in cloud data when some averaging is applied.
x
Distance of each pixel east of Chilbolton, in km. Only set for scanning data when the -coords option is selected.
y
Distance of each pixel north of Chilbolton, in km. Only set for scanning data when the -coords option is selected.
z
Distance of each pixel above the height of Chilbolton, in km. This takes no account of the curvature of the earth. Only set for scanning data when the -coords option is selected.
r
Distance of each pixel from Chilbolton along the ground. Only set for scanning data when the -coords option is selected.

Vectors read into matlab

range
The range to the centre of each gate in kilometres.
elev
The elevation angle of each ray in degrees.
azim
The azimuth angle of each ray in degrees clockwise from due west.
utc
The time of each ray in decimal hours UTC.
full_date
The date of each ray in the form YYYYMMDD.
nez
The noise-equivalent reflectivity at 1 km (in dBZ) for each ray. This parameter is only calculated if the -process or -oscillator options are selected. If the data is calibrated using the -Zcal option then this parameter is calibrated also.

Scalars read into matlab

Note that the writing of many of these scalars can be suppressed by employing the -basicsonly option.

latitude, longitude, altitude
The longitude (degrees N), latitude (degrees E) and altitude (m) of the radar site. Currently this is correct only for the Chilbolton site.
file, raster, scan
The file (tape), raster and scan numbers of the last raster.
system, freq
The system ID (0=unknown, 1=CAMRa, 2=Rabelais, 3=Galileo, 4=Singapore) and frequency (GHz) of the radar that took the data.
start_sec, start_min, start_hour, day, month, year
The second, minute, hour, day, month and year of the start of the last raster that was loaded. These are present only because they were produced by the previous program used to load scanning data.
sweepm
The sweep mode in `universal radar format' (0=calibration scan, 1=PPI, 2=coplane, 3=RHI, 4=vertical, 5=dwell, 6=manual, 7=idle).
drange
Range gate spacing in kilometres.
min_gate, max_gate
The minimum and maximum gates in clock units (only useful if you want to perform your own range correction).
range_offset
The range offset that has been applied to the data, in kilometres.

Additional options

-basicsonly
Suppress the non-essential scalars that tend to clutter up the matlab workspace (day, month, year, file, raster, scan, latitude, longitude, altitude, start_hour, start_min, start_sec, min_gate, max_gate).
-coords
Output extra coordinate matrices x, y, z and r. These enable the data to be plotted easily, e.g. for an PPI:
pcolor(x,y,Zh); shading flat

Or an RHI:

pcolor(r,z,Zh); shading flat