Something amuck in GPS ? ? ?

The following are GPS NOTAMS (Notice to Airmen) pertaining to GPS availability ...

ZJX NAV GPS IS UNRELIABLE AND MAY BE UNAVAILABLE WITHIN A CIRCLE RADIUS OF 370 NM AND CENTERED AT 304906N/0802811W OR LOCATION ALSO KNOWN AS 105.25 DEGREE RADIAL 52.1 NM FROM THE SSI VOR AT FL400; DECREASING IN AREA WITH A DECREASE IN ALTITUDE TO A CIRCLE WITH A RADIUS OF 325 NM AT FL250; A CIRCLE WITH A RADIUS OF 260 NM AT 10,000 FEET MSL AND A CIRCLE WITH A RADIUS OF 215 NM AT 4000 FT AGL 0000-0245 DLY WEF 1102160000-1102210245

ZAB NAV GPS IS UNRELIABLE AND MAY BE UNAVAILABLE WITHIN A CIRCLE WITH A RADIUS OF 375 NM AND CENTERED AT 333807N/1063425W OR LOCATION ALSO KNOWN AS 58.9 DEGREES AND 41.3 NM FROM THE TCS VOR AT FL400; DECREASING IN AREA WITH A DECREASE IN ALTITUDE TO A CIRCLE WITH A RADIUS OF 325 NM AT FL250; A CIRCLE WITH A RADIUS OF 240 NM AT 10,000 FT MSL AND A CIRCLE WITH A RADIUS OF 235 NM AT 4000 FT AGL. 0400-1200 DLY WEF 1102080400-1102111200

The first is in reference to the circles on the East Coast of the United States, and the second over the vicinity of the White Sands Missile Range in New Mexico.

Now remember, GPS is a Space-based navigation system which shouldn't be limited to ground-based systems line-of-sight requirements.

The East Coast area specifies:
* a 370 nautical mile radius at FL400 (40,000 feet)
* a 325 nautical mile radius at FL250 (25,000 feet)
* a 260 nautical mile radius at 10,000 feet
* a 215 nautical mile radius at 4,000 feet above ground level.

The White Sands area specifies:
* a 375 nautical mile radius at FL400 (40,000 feet)
* a 325 nautical mile radius at FL250 (25,000 feet)
* a 240 nautical mile radius at 10,000 feet
* a 235 nautical mile radius at 4,000 feet above ground level.

Also depicted in the image are:
+ the locations of the reports of dead birds, manatees and other animals.
+ the locations of earthquakes (yellow and orange dots)
+ the locations of Yellowstone, Mt. St. Helens, Long Valley Caldera, and the New Madrid Seizmic Zone, and the forecast location of a potential earthquake with its forecast window set to close on the 8th of February.
+ Also plotted are the Kings Bay Submarine Base, Kennedy Launch Complex 39-A, Holloman AFB, and the Trinity Nuclear Test Site (historic marker); and two laser tests one at NASA's Goldsboro, Maryland, and the other at Apache Point Observatory in New Mexico.

The "normal" ground based line-of-sight data for ...
40,000 feet is 246.6 nautical miles, for
25,000 feet is 195.24 nautical miles, for
10,000 feet is 124.19 nautical miles, and for
4,000 feet is 79.67 nautical miles.

The East Coast area line-of-sight corresponds to:
* a 370 nautical mile radius approximately 90,000 feet, a diffence of 50,000 feet.
* a 325 nautical mile radius approximately 70,000 feet, a differnce of 45,000 feet.
* a 260 nautical mile radius approximately 45,000 feet, a differnce of 35,000 feet.
* a 215 nautical mile radius approximately 30,000 feet, a diffence of 26,000 feet.

The White Sands area line-of-sight corresponds to:
* a 375 nautical mile radius approximately 93,000 feet, a difference of 53,000 feet.
* a 325 nautical mile radius approximately 70,000 feet, a diffence of 45,000 feet.
* a 240 nautical mile radius at approximately 38,000 feet, a difference of 28,000 feet.
* a 235 nautical mile radius at approximately 36,000 feet, a diffence of 32,000 feet.

So using "normal" line-of-sight calculations we have a variance of between 53,000 feet and 26,000 feet in elevation above what should be line-of-sight.

For example if you have an E-3C AWACS plane flying at 35,000 feet, it would be able to detect another aircraft flying at 65,000 feet approximately 389 nautical miles away; or if you had an SR-71Blackbird flying at 100,000 feet it would be able to detect a radio signal coming from a ground-level transmitter also 389 nautical miles away.

The other interesting aspect is look at the time data in the NOTAM .... 0000-0245 DLY WEF 1102160000-1102210245 (0000UTC - 0245 UTC Daily, from February 6, 2011 at 0000 UTC until February 21, 2011 at 0245UTC) for the East Coast, and .... 0400-1200 DLY WEF 1102080400-1102111200 (0400 UTC - 1200 UTC Daily from February 8, 2011 at 0400 UTC until February 11, 2011 at 1200 UTC).

Something is very, very hinky here .... because "normally" at any given time, my hand-held GPS unit is capable of receiving data-signals from between six to eleven satellites, and only a six-satellite constellation is necessary to provide position fix information.