Experimental Log: Roger Bland, January 1-3, 2002
Finishing up RAFOS detection
ifremer on RAFOS
17:40 Tuesday January 1, 2002. I am just finishing up the job
of making all the plots necessary to see RAFOS signals, and imagining
how they will show up on these plots. I am trying to get completely tuned
up on a file with no RAFOS signal, to enhance my objectivity. All I
have left to do is to display the result of the quadrature
cross-correlation detection, and to decide how much noise and how much
signal I expect to see.
Based on some pretty primitive reasoning, I expect the rms value of
the product of a random signal of bandwidth f1 with another random signal
of bandwidth f2 (f1 is greater than f2), as shown in the figure, to be
rmsprod = rms1 * rms2 * (T1/T2) * (T2/T)1/2 * (1/2)
(6:11 Thursday January 3, 2001)
Here T1 and T2 are the periods corresponding to
f1 and f2, and T is the length of the time
series. For the test signal r0124506.27w the rms is 17.56, and for the
RAFOS quadrature replicas the rms is 0.707 . Also T = 80 sec, and
(roughly) f1 = 8 Hz, f2 = 1.5 Hz. This gives
rmsprod (predicted) = 0.419
The detection scheme which I am using consists of (a) multiplying the
RAFOS-band signal by a replica and averaging the values in the
resulting vector; (b) doing the same for the 90-degree-out-of-phase
replica; (c) and adding these two numbers in quadrature (program rafdet.pro). This should
give a number averaging to the value calculated above, and peaking for
a RAFOS signal at roughly (give or take a couple of factor of two)
the amplitude (in original digitization units) of the RAFOS signal.
Here is the resulting signal, for
r0124506.27m. The rms of the signal is equal to 0.687, in fine
agreement with the 0.419 predicted above.
It is time to look at this signal for a day's data (plotting program p20101a.pro):
9:35 It is encouraging to see large signals showing up where we
expect them. I have to go and do other things for a while.
But, here is a list of things to do next.
- Look at each large peak, and categorize their shapes or other
features which might separate good signals and noise.
- Proceed with automation of this analysis.
- Make a few more pages like this one.
- Determine the times of the peaks.
- Calculate the size of the signal expected.