chilnoise

This is a program that is intended to help with finding the correct parameters to use with chil2nc, chil2nc and loadchil. The recommended command-line options are returned on standard output. A table of values calculated from each raster is returned on standard error.

If chilnoise is applied to scanning 3-GHz data then it will use the data measured above 14 km (20 km for Singapore data) to estimate the noise levels of the Zh, Zv and cross-polar channels. These are required if noise subtraction is to be correctly performed on the parameters Zh, Zdr and Ldr. The result is of the form -polar X Y Z, as described here.

If the program is applied to scanning data that contains only Zh, then the result is an argument of the form -noise X.

If the program is applied to data that contains phi_dp, then the calibration of this parameter is estimated by finding in each ray the first group of five rays that have a variance of less than 3 degrees. This indicates the presence of signal, and provided that no heavy rain has been penetrated, the mean of the phi_dp in these gates should be zero. The actual value measured therefore provides the calibration value, returned in the form of a -PHIDPcal argument.

The program is typically applied to all the rasters in a data file, and in each of the cases above the returned value is the median of the values estimated from each raster. This way the occasional anomalous raster (caused the large differential phase shift associated with heavy rain or some instrumental problem affecting the noise levels) cannot bias the values returned.

Usage

The program is called similarly to chil2nc and friends (described here). Note because it is built on the same code it can also accept all the same options as chil2nc, but you should not use them because they may affect the numbers produced.

chilnoise
With no options, some basic usage information is returned.
chilnoise file1.dat rasterrange1 [file2.dat rasterrange2 ...] [options]
Reads the specified rasters from a set of files, where rasterrange can be a single raster number (e.g. 1), a range of rasters (e.g. 1-10) or a single hyphen to indicate all rasters in the file (-).
chilnoise -all file1.dat [file2.dat ...] [options]
Reads all rasters from the files specified.
chilnoise -date date filepattern1.dat [filepattern2.dat ...] [options]
Searches the summary files corresponding to the files that match the specified patterns for rasters recorded on the date specified (which can be of the form YYYYMMDD or YYMMDD. A file pattern can contain the wildcards * and ?.

Options

-minheight f
Only uses data above f km for estimating the noise levels.