NATURAL SOURCE MAGNETOTELLURICS
May 2002 Section 13, Page 24
13.10 CASCADE DECIMATION OVERVIEW
For the upper three frequency bands (very high, high and medium bands), data are gathered in
time series records of 4141 points each (4096 + 45 extra points used in the decimation filter).
The data are then processed in 32 point records, for all of the data points for that level.
Decimation Total Points Data points
Level Bursts per burst processed
1 128 32 4096
2 64 32 2048
3 32 32 1024
4 16 32 512
5 8 32 256
The low frequency band acquires data on a continuous basis, and filters, decimates and
transforms the data real time. The length of the time series record depends upon the level of
decimation chosen. If the full 13 levels are selected, the number of points processed range from
256 at 0.0007 Hz to 1.061 million at 4 Hz.
Decimation levels and base frequencies for the four frequency bands are:
Low Frequency Band
Sample Rate = 16 Hz
Decimation Base Frequency Frequencies
Levels Frequency Interval Obtained
2 .25 Hz 1.5 - 4 Hz 1.5, 2, 3, 4 Hz
3 .125 .75 - 4 .75, 1. + above
4 .0625 .375 - 4 .375, .5 + above
5 .03125 .1875 - 4 .1875, .25 + above
6 .015625 .0938 - 4 .0938, .125 + above
7 .007813 .0469 - 4 .0469, .0625 + above
8 .003906 .0234 - 4 .0234, .0313 + above
9 .001953 .0117 - 4 .0117, .0156 + above
10 .0009765 .0059 - 4 .0059, .0078 + above
11 .0004882 .0029 - 4 .0029, .0039 + above
12 .0002441 .0015 - 4 .0015, .00195 + above
13 .0001221 .0007 - 4 .0007, .00098 + above
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