[SAC-HELP] problem with interpolation

[maria manakou]

Hello,

I face some problem when applying the command "interpolate delta XX" in some noise data. 

I have some 1-hour noise data recorded in CMG-5 guralp sensors and I want to interpolate them for further processing in SAC software. The raw *.cgf files (the format of the CMG-5 sensors) have already transformed to *.sac files through Scream V4.4 software provided by Guralp.

The *.sac data (un-interpolated data) have delta 0.01sec and I want to interpolate them to delta 0.05sec. I use the following commands in my SAC 8/8/2001 V. 00.59.44 (Copyright 1995) software which runs in Fedora 9.0:

r *.sac
qdp off
rmean
rtrend
p1
interpolate delta 0.05
w change .sac .inter

When I plot the un-interpolated (*.sac) and interpolated data (*.inter) to see if the interpolation works ok (Fig. 1 in the attach file) the result seems ok, but when I zoom in different time windows the result is not at all good! Specific spikes in my un-interpolated noise data seem to "move" in time in the interpolated data as you can see in the attach doc file. This "moving" seems to happen after some time (e.g. in fig. 2 the coincidence of specific spikes between un-interpolated and interpolated data is very good, but this does not happen for the rest time windows,fig. 3-5).

I cannot understand why this happen.
If someone has faced this problem again and have any idea, please let me know.

Best Regards,
maria manakou



 
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