I am sitting in my backyard listening to a jet fighter somewhere overhead, easily identified by the earth-shattering noise as it breaks the speed of sound, sending air molecules flying in all directions.  At the same time, I am watching a shiny blob dancing around the foliage a few metres from me, making no sound at all.  By moving my wrist rapidly, I can make it can fly soundlessly across the landscape at astonishing speeds.  It is the light reflected from my watch.  It’s even more fun if I use a laser pointer with a batman image, but that is probably illegal.

The astonishing speed comes from something called group velocity.  Imagine an event deep within the earth that creates a signal that reaches the surface, an earthquake if you like.  The signal travels out from the source and reaches the closest point (A) the quickest, but reaches its neighbouring location (B) moments later.  An observer in the sky watches this happen and describes an event that travels amazingly quickly between point A and B, when no such actual event occurred.  The signals were coming from deep within the earth to two separate points and not travelling across the surface.

All sorts of dispersion events can create this apparent group velocity and can give the false appearance of travel faster than the speed of light.  A seismic interpreter works with seismic reflection data that has undergone an amazing amount of signal processing.  All sorts of interference issues are dealt with mathematically as geophysicists try to eliminate known sources of spurious data.  Diffraction and refraction energy needs to be eliminated as does surface noise, all without degrading the reflected energy from the earth’s layers.

Even the reflection energy that is detected needs to be dealt with. Spurious events need eliminating; like pegleg multiples between coal beds, and water bottom multiples and bottom simulating reflectors (BSRs) offshore.  All of this comes with the assumption that we have got everything completely accounted for in our processing, but interpreters working in tricky areas know for sure that they don’t and need to be constantly aware of spurious signal.  Signal lensing issues through unrecognized velocity events, for example are mostly ignored.

So, what is all this carry on about problematic signals observed by US fighter pilots?  They are flying at high speed, through disturbed air and reporting spurious signals.  Now, my first observation is that these signals (or reflections) travel at high speed, changing direction rapidly and make no sound.  Hmmm, I wonder what they could be? A digital camera image has a lot of signal processing involved.

An object moving quickly through the atmosphere will disturb air molecules and will make noise. Some advanced being may be able to create noiseless travel, but is that at all likely?  Signals like holograms can certainly do that, but not solid objects.

Next, it seems to be happening only in America and these events are only observed by fighter pilots.  Real objects travelling at immense speeds would be more likely to be spotted by the much greater number of commercial flights with their many more excellent observers.  They would also be more likely to be spotted by ground dwellers with telescopes, radar and other fancy devices.  Yes, we do have a few reported ground instances of UFOs, but none of the images look at all convincing.

So, why would fighter pilots be seeing these phenomena?  Probably something to do with the fancy signal processing they do when accounting for their own rapid, contorted movements, while observing reflections bouncing off clouds, lensing through distorted air pockets etc.  I imagine fighter pilots’ brains get a bit scrambled as well after such movements.  I know what I feel like coming off a roller coaster.

So is my best defense to suggest that aliens have fiddled with my seismic time data when I get my depth prognosis wrong, or do I accept that I just don’t understand all the ins and outs of seismic signal processing yet?