The Elginfield Infrasound Array (ELFO)
Interesting (non-meteoric) Events detected by ELFO
Observations of the Space Shuttle Discovery of July 4th, 2006
The launch of the space shuttle produces regularly observed signals at ELFO. We typically record the airwave from the launch/rocket ascent 1-2 hours after liftoff.
As an example, the Space Shuttle Discovery was launched from NASA's Kennedy Space Center on July 4 th, 2006, at 14:38 EDT.
The infrasonic airwaves produced by the Space Shuttle launch were observed at ELFO as shown below.
Above - The airwave record of the shuttle launch as seen from the Northwestern element of the array.
Below - Array processing of the signal across the array, bandpassed between 0.3 - 1.5 Hz. The top panel shows the f-statistic correlating the signal in 30 sec data windows across the array; the higher the f-stat the more correlated the signal and the more probable it is a coherent signal (rather than noise). The 2nd panel shows the apparent velocity of the signal across the array (trace velocity) - the higher the trace velocity the steeper is the arriving wavetrain. The third plot from the top shows the apparent backazimuth of the direction producing the highest f-statistic in any particular 30 sec window. The beginning of the near constant azimuth at 20:05 UT marks the start of the shuttle wavetrain (which ends near 20:20 UT). The lower panel shows the bandpassed signals at the centre element.
Below: Map showing the range of backazimuths for the signal from ELFO showing that much of the signal results from the early ascednt of the shuttle, very likely when it crosses into the stratosphere (around 30 km altitude) off the coast of Florida.