Leading GPS Software Suggests Superior Augmented GPS Service At WTC During 9/11 Attacks
"Factors that can degrade the GPS signal and thus affect accuracy include the following: Number of satellites visible - The more satellites a GPS receiver can "see," the better the accuracy; Satellite geometry/shading - This refers to the relative position of the satellites at any given time. Ideal satellite geometry exists when the satellites are located at wide angles relative to each other. Poor geometry results when the satellites are located in a line or in a tight grouping."
The period of fourteen-fifteen visible GPS/WAAS satellites from the coordinates of the WTC (40° 42? 42? N, 74° 0? 45? W) occupied only 14.5% of the hours between sunrise and sunset on September 11, 2001. It was during this brief period of virtually maximum GPS/WAAS satellite visibility from the WTC that the aircraft attacks at the WTC unfolded.