The calculation resultsalso showed that besides the relativeground clearance, the ratios ofthicknessandcamber of wingprofilehavesignificantinfluence on the aerodynamicsof WIGs.
For GPS, this is an enormous issue because it turns out that the clocks on the satellites drift by almost 40, 000 nanoseconds per day relative to the clocks on the ground because they are high above the earth's surface (and therefore in a weaker gravitational field) and are moving fast relative to the ground.
Thus, a spy plane could not be completely invisible if it were to be used for espionage or, indeed, flown at all, since its pilots would need to know its position relative to the ground.