Roger Bland's Log for November 4, 2001
Webb Sources from Day 245, 2001
( logbook )
Today I have one complete day of data from Pioneer Seamount to work with. The day is day-of-the-year 245(Sept. 2, I think). The files are r0124400.18m r0124506.27m r0124512.36m r0124518.45m r0124502.21m* r0124508.30m r0124514.39m r0124520.48m r0124504.24m* r0124510.33m r0124516.42m r0124522.51m (The first one has the day number wrong by one, in the file name and internally, too. It will eventually be replaced by a corrected file.) The files contain 2 hours of digitizings at 1000 Hz, four channels, 16 bits, interleaved.

The files were read in by (IDL), and two files written. A file named like r0124400.18b (ending in 'b') contains the starting day number, then an array of 7,376,896 integers representing the four channels formed into a horizontal beam (added, then divided by four).

This same program carries out the first stage of analysis for the Webb sources. The signal idat(7376896) is multiplied, point-by-point, by an array representing the signal f(t) = sin(2pft), where f = 260 Hz is the central frequency of the signal from the Webb sources. This mixing generates sum and difference frequencies. The difference is then selected by an averaging process where lblk samples are added together, having the effect of a low-pass filter. (lblk = 512 for the work done today, corresponding to a time of 0.512 seconds.) This results in an array of "filtered" data, 14408 samples for one 2-hour file. The files are named like 40124400.18w (ending in "w", for "Webb").

To plot the data, the routine reads in one 2-hour time series, calculates a time vector for plotting, and plots the whole series. Blowups can be done easily by hand with IDL, eg

	IDL> plot1day
	input file: r0124425.00w : 
	infile:   /usr/data/bland/pioneer/2001/r0124425.00w
	day0,lblk,nblk =        244.01316         512      172896
	IDL> restore
	IDL> plot,yd,websig,xrange=[244.1905,244.1920]
To see an entire day at once, the program merges the 12 files for a single day into a file named like r0124425.00w (The '25' in the our position distinguishes it from a 2-hour file.) The progrm reads the day signal (172896 samples long, each representing 0.512 sec) into memory for plotting, and calculates the time vector.