Dan Kennedy and Cindy Banyon
The most sensitive screening test in the ASRG SETI project is also the fastest.
It is the CoolEdit spectral display with an FFT size of 16,384 and the vertical
zoom to maximum.
CoolEdit and the data file both load quickly. It takes a minute or two to generate the spectrogram graphic. Then a smooth scrolling from bottom to top, and another from top to bottom (after selecting the entire range to get a reverse color scheme) reveals lots of signals that are otherwise invisible. Many PCs have to be set to 256 colors for the scrolling to work smoothly.
Using this method, it is possible to see dozens of artifacts and a lot of interesting areas that have suspicious signal formations.
This whole process takes 10 minutes and can detect more detail than SETIEasy. In fact, when SETIEasy is set to detect signals this small, it continuously triggers on the interferences and artifacts, requiring the loading of the file into CoolEdit, anyway, to go through the Interference Checklist on the signals.
Manual analyses in MathCAD, Speakeasy, or Matlab are actually more sensitive to signals, but are not useful for a data file screening search because of the level of operator involvement required.
The normal color scheme shows the signals best in the high noise areas. The reverse color scheme from selecting the entire time range shows the signals best in the low noise upper frequencies.
With this process it is possible to quickly spot about 20 terrestrial signal artifacts in the two displays below. (Most of these are obviously terrestrial in origin because they have no frequency drift.)
Another thing that this process does is expose some very subtle features that I do not believe would be easy to extract mathematically. The following graph has a couple signal that have opposite drifts. It is very difficult to see them here. But when the graph is slowly scrolling they are very obvious. I invite you to try this this signal file at http://monroe.pharm.uky.edu/seti/e102800_0011_5.wav
The signals I am referring to a centered vertically below. Another image shows the same with some lines I added as references.
The lines here are above and below the signals that can be seen in the first image of these two. Still, the signals are very subtle and only become obvious during scrolling.
This scrolling method is used by the navy in the SONAR waterfall displays. They scroll through time instead of through frequency, but the motion gives the same increased sensitivity for the human eye.
The bottom of these two is the 62nd harmonic of the power line hum. The signal above it is harder. It has a reverse slope but the drift rate is very similar. I will try a couple dechirps and some MathCAD to see if I can identify it better.
A million point FFT in the first two minutes hints at these signals at 3722 and 3737 Hz.
- Dan