RADARDECODE

NAME

SYNOPSIS

DESCRIPTION

radardecode is a filter to decode radar data. The overlap save algorithm from THE FAST FOURIER TRANSFORM AND ITS APPLICATIONS (Brigham 1988 pg.212) is used. The input data is read from standard input (as a pipe), unpacked, transformed to the frequency domain, conjugated and then multiplied by the transformed code, transformed back to the time domain, and then the complex points are written to standard out as two 4 byte floating point numbers.

radardecode on startup will first allocate the buffers it needs and then it prepares the pn code. The program /usr/loca/bin/comppncode will be run to generate the pn code to use for decoding.

The input data can be ri, cbr, or unpacked data (depending on the -m option). The program will only process one polarization at a time.

If ri data is input, then the header must have been already be stripped off (see stripVme(1l). If the ri data had two polarizations, then one of them must be stripped off before inputting it to this program.

If cbr data is input then all polarizations are input to the program and the -p option is used to tell the number of polarizations input, and which polarization should be decoded.

For unpacked data, the input should be complex floating point numbers (one polarization only).

A number of shell scripts under ~phil/datatk/astro/rdrN have been written to drive the radardecode program (see radarranging(1l)).  

OPTIONS

-b

bits
 The number of bits the data was sampled at. It can be 1,2,4,8 or 12. The default is 12 bits. cbr and unpacked data ignore this value.

-c

codelen
 The codelen for the pn code that was used.  The default is a codelength of 2047.

-l

fftlength
 This is the length of the transform to use for decoding. The default fft length is 32k.

-n

numcodes
 The number of codes of length codelen to decode. The program will decode the data until the this many codes have been decoded or the end of the input data stream is hit (whichever comes first). The default value is 100000000 codes.

-o

offset Offset to add to the input data. The ri two's complement packing of the sampled data goes from -m to (m-1). To give zero dc bias you would normally add .5 to the input data so the positive and negative numbers are symmetric about zero. This value will not be added to the pn code that is input. The default is to add no value to the input data.

-p

numPol polToUse For cbr data this specifies the number of polarizations in the input data and which polarization to use on output. The default is numPol == 2 and polToUse == 1.

-q

 Run quietly.  Do not output how many ffts have been done so far. The default is to output to stderr how many ffts have been done (every 50 ffts).

-r

Remove DC. If this option is selected then the mean will be computed and removed for each fftlength complex points. The default is to not remove DC.

-s

samplesPerBaud This can be any integer number >= 1. It will duplicate each baud in the code by this value before decoding. The default value is 1.

-m

ri cbr unpacked The type of data input. The default is the ri. If cbr is selected, then the -p option should be used to specify the polarization info. The default value is ri.

-t

Print the times for each fft to stderr complex multiply, fft--> time domain, and output. The default is to not output this information.

-f

freqShift Shift the frequency in the decoding process (in case there was an ephemeris error). This is no yet implemented.

EXAMPLES

The examples below show different ways of calling radardecode

Assume the data is from the ri and is on disc. The headers have already been stripped off. The data is 2 bit packed, one polarization, with a codelength of 8191. Add .5 to the input data and don't printout the time for each fft. Since the number of codes were not given, the program will decode until the end of file is hit or 100000000 codes have been decoded.

 radardecode -b 2 -c 8191 -l 131072 -o .5 < infile > outfile

Assume the data is ri 8 bit data on disc, two polarizations, with the headers already removed. You want to decode the 1st (oc) polarization. The code is 2047 long and the decode fft length is 256k

 selectpnts -b 4 -f 1 -s 2 | \ # remove 2nd pol
 radardecode -b 8 -c 2047 -l 262144  -o .5 

Decode cbr data, 2 polarizations, 2 samples/baud, and keep the 1st polarization. The codelength is 64k-1. The output data will have 65535*2 range bins.

 radardecode -m cbr -p 2 1  -c 65535 -l 262144 < infile > outfile 

FILES

~phil/util/filters/radardecode.c location of source code
/usr/S2local/bin/radardecode       executable for sun
~phil/datatk/astro/rdrN/main_decode.sc  shell scripts to drive radardecode.
/usr/local/bin/comppncode        program to compute pncodes for sun.

SEE ALSO

comppncode(1l),radarranging(1l)

Index

NAME

SYNOPSIS

DESCRIPTION

OPTIONS

EXAMPLES

FILES

SEE ALSO