>mrvdl: Merged Day l-nu Diagram Image (Power)

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Produce the L-nu diagrams from the power spectra.

• Sample vdl image

Dimensionally, the x-axis is the spherical harmonic degree, L, and the y-axis is frequency. The FITS header keyword CD1_1, gives the conversion factor (microHz/pixels) for the y-axis.

Steps involved:
1. Calculate the power spectra of a GONG time series image with pseries.
   lpar pseries
 (type_output = "gong")         Output data type (fft|power|gong)
         (pad = "none")         Zero padding (none|1st|2nd)
      (debias = yes)            Debias time series prior to FFT
 (use_gapfill = yes)            Used gap-filled data?
    (do_phase = no)             Output phase spectra
      (window = "none")         Window (bartlett|hamming|hanning|parzen|welch|n

   output
        mrvdpYYMMDDd[000-200]

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