Testing of phase speed filtering vs. frequency filtering.

Input data: hi-res cube with t_first=1998.06.18_15:36:59.0_UT, binned 2x2. The unbinned cubes are on tape MDI_3. 512 frames.

In the directory Freq_filt is the results of using a filter of fwhm=1mhz and center frequency=3mhz and distance range of 4.692 to 5.372. The rms of the central 33:96,33:96 of the mean signal is 0.55min.

In the directory Phase_filt is a result of a phase speed filtering with nu/l=13.98 and width 1.3 for the same distance range. The rms for the central region for the mean signal is 0.11min., or a factor of five smaller.

In some of the other directories Phase_filtn, n=2-4, are some other tests of phase speed filters with different widths. The column "rms after fit" refers to the residuals of a parabolic fit to the central 33:96,33:96 of the mean signal.
Directoryfilter width(microhz)rms noise (min) distance range (deg)rms after fitexec. time(min)
Phase_filt31.00.118 4.692-5.3720.102 267
Phase_filt1.30.108 4.692-5.3720.092
Phase_filt22.60.099 4.692-5.3720.079 268
Phase_filt45.20.121 4.692-5.3720.098 243
Phase_filt55.20.115 4.352-5.7120.093 352
Phase_filt62.60.132 4.896-5.1680.114 200
Phase_filt71.30.148 4.896-5.1680.136 200
Phase_filt81.00.156 4.896-5.1680.145 215