IRAF Help page for: PSERIES


PSERIES (Jan93)               grasp.grtools              PSERIES (Jan93)



NAME
    pseries -- Calculate the Power Spectra of a GONG time series image.
    
    
USAGE
    pseries input output
    
    
PARAMETERS
    
    input
        Input image list.
    
    output
        Output image list.
    
    type_output = "gong"
        Output data type.
        
        "fft"
            Complex FFT: (band1 = real part,  band2 = imaginary part).
        
        "power"
            Power/Phase: (band1 = power,  band2 = phase).
        
        "gong"
            Power/Phase in GONG power spectrum format.
    
    window = "none"
        Type of window to be  used  on  the  data  before  transforming.
        Five  of  the  most  commonly  used windows are available.  (N =
        number of points)
        
        "bartlett"
                            |j - 0.5*N|
                 w(j) = 1 - |---------|
                            |  0.5*N  |
            
        
        "hamming"
            
                 w(j) = 0.54 - 0.46*cos(2*pi*j/(N-1))
        
        
        "hanning"
            
                 w(j) = 0.5 * [1. - cos(2*pi*j/"(N-1))]
            
        
        "parzen"
                            |j - 0.5*(N-1)|
                 w(j) = 1 - |-------------|
                            |  0.5*(N+1)  |
            
        
        "welch"
                                             2
                             /j - 0.5*(N-1)\
                 w(j) = 1 - < ------------- >
                             \  0.5*(N+1)  /
            
    
    gapfill = yes
        Use gap-filled data.
    
    
DESCRIPTION
    
    PSERIES computes the 1-dimensional FFT of the  input  image  line(s)
    and  writes  the  result  to the corresponding line(s) of the output
    image according to type_output.  The task  assumes  that  the  input
    image  data  is  the  complex  time  series  of  spherical  harmonic 
    coefficients stored in GONG format. That is, a 3-d image where  band
    1 contains the REAL part and band 2 contains the IMAGINARY part.
    
    The  task  expects to find the following header keywords in addition
    to a GONG MWCS:
       L_VALUE - The spherical harmonic degree L of the input image.
       MTYPE   - "even" or "all"
    
    If type_output = "fft" or "power", the output image will  be  either
    the complex FFT or power spectrum, with no special reformatting.
    
    If  type_output  =  "gong",  the output image will be reformatted to
    GONG power spectra: 3-d images where band1 = power, band2  =  phase.
    The  columns will be the frequency bins, and each line will hold the
    power spectrum of a specific  spherical  harmonic  "m":  line[1]  =>
    m=-L, line[naxis2] => m=L, for even m's only.
    
    The   input  image  lines  are  windowed  according  to  window  and 
    zero-padded to the  next  power  of  two  (if  necessary)  prior  to
    transforming.
    
    If  gapfill  =  YES,  the task will use all the data (i.e., assuming
    that some type of gap filling algorithm has been previously  applied
    to  the  time series).  If gapfill = NO, then each line of the input
    image will be multiplied by the observing window (stored in the last
    line  of  that  image) to set any gap filled data to zero before the
    FFT is done.
    
    
    
EXAMPLES
    
    1.  To calculate the GONG power spectrum of an image:
    
      gr> pseries imageA imageB
    
    
    2.  To calculate the power spectrum but not have the  standard  GONG
    output format:
    
      gr> pseries imageA imageB type=power
    
    
TIME REQUIREMENTS
    
    The  following  timings  are  for a Sun 3/60 (with disk) using 68881
    binaries, and a Sun 4/370.  The task was used  to  FFT  a  512x127x2
    GONG image (i.e., an l=250 time series of 8.5 hours duration).
    
                Image  Size                CPU Time
                                           (seconds)
                ------------------------------------------------
                                    Sun 3/60          Sun 4/370
    
                  512x127x2            35.5              5.01
    
    
    
BUGS
    
    No renormalization is done if a window is used.
    
    
SEE ALSO
    pseries, ptox, xtop

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