I'll let one of our mathmaticians answer that one. When you get to a certain point in life, you remember the results but not the derivation, especially in statistics. I believe that the basic problem is that each sensor picks up some random noise along with the signal. So when you add up the signal from N sensors you also add up N sets of random noise. When random noise signals are added they get bigger by square root of N. The signal gets bigger by N so signal-to-noise improves N/(square root of N). I don't know the answer in Winquake. Doug Dick Webb wrote: > > How does the square root of N fit in? What is the rest of the > equation. Also, do you know if is it possible to sum inputs in > Winquake. Our export the Winquake data into, say Excel, and sum it results > there. > > Dick > > At 09:22 PM 06/29/2000 -0700, you wrote: > > >Dick Webb wrote: > > > > > > PSN'ers, > > > > > > I have a question about noise reduction. I have 3 short period > > > seismometers. If I place them several hundred feet apart can I sum the > > > signals and expect that local noise will be cancelled? Local noise could > > > be due to trees, water, wind, local traffic, etc.. Since the seismometers > > > are not closely spaced, the signals would arrive at each seismometer out of > > > phase with respect to the other seismometers. Regional signals would tend > > > not to be cancelled out due to their longer period. Is this hypothesis > > > correct, or is it a sand castle in front of a wave? > > > > > > Dick > > > > > > >Arrays of sensors are routine in exploration geophysics. A string of > >say 12 geophones are laid in a line to form an array. Reflection > >signals, which come pretty much straight up in petroleum surveys, hit > >all the phones at the same time and sum. Surface waves, noise, and > >shallow refractions come in horizontally or at an angle and may cancel > >or at least not stack. The arrarys are often designed to form spatial > >filters. > > > >So, the short answer is using three sensors will improve your ability to > >see stuff coming from the bowels of the earth. However, the signal to > >noise improvement is square root of N, so the improvement may not be > >worth the effort. > > > >Doug > >__________________________________________________________ > > > >Public Seismic Network Mailing List (PSN-L) > > > >To leave this list email PSN-L-REQUEST@.............. with > >the body of the message (first line only): unsubscribe > >See http://www.seismicnet.com/maillist.html for more information. > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with > the body of the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. -- Doug Crice http://www.georadar.com 19623 Via Escuela Drive phone 408-867-3792 Saratoga, California 95070 USA fax 408-867-4900 __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>