The Global Positioning System: A Shared National Asset (1995)
Chapter: Accuracy and Integrity
use of GPS for the precision delivery of cargo by parachute or paraglider. For this application, GPS must be capable of providing steering commands to a reefing system to steer the parachute or paraglider to the desired landing point.
Combat search and rescue is another important function for which the use of GPS is increasing. Although GPS is already used for navigation by helicopters and other aircraft involved in combat search and rescue, it also will be used in the future to determine the exact location of downed aircrew members. By combining GPS with space-based communications capabilities, individuals can be found quickly, saving lives, time, and money. Communications capabilities would allow the location of aircraft, helicopters, and tanks to be monitored in real time, reducing casualties by friendly fire. Further, if GPS and communications capabilities are combined with guidance systems, unmanned aerial vehicles could be used for surveillance of target areas.
Tables 2-1 through 2-3 represent an extensive list of the military's positioning and navigation applications and their requirements.
Challenges to Full GPS Utilization
Accuracy and Integrity
The shaded cells in Tables 2-1 through 2-3 point out positioning and navigation requirements that cannot be met with the current 16 meter (SEP) specified accuracy8, or 8-meter (CEP) derived accuracy9, of the GPS PPS (Precise Positioning Service). Presumably, many of these requirements are currently being met by other guidance systems, such as highly accurate inertial navigation systems and terminal seekers, and other radionavigation systems, such as the microwave landing system. If these applications were to rely on GPS alone in the future, their accuracy requirements could only be met with some form of DGPS or a significantly improved PPS.
Some of the aviation applications listed in Table 2-1 also have specified integrity requirements. These requirements cannot be met with the PPS as currently configured.
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8 |
SEP, or spherical error probable, represents an accuracy that is achievable 50 percent of the time in all three dimensions (latitude, longitude, and altitude). PPS accuracy is normally represented in this manner. The 2 drms PPS specified accuracy value is 21 meters SEP, as shown in Figure C-7 in Appendix C. |
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9 |
CEP, or circular error probable, represents an accuracy that is achievable 50 percent of the time in two dimensions (latitude and longitude). Most military accuracy requirements are defined in this manner. CEP, and other positioning accuracy definitions are discussed in greater detail in Appendix D. |
Table 2-1 Military Aviation and Precision-Guided Munitions Applications and Requirementsa
|
|
Application |
Accuracy |
Integrity |
|
Resistance to RF Interference |
|
|
|
|
1 minus PHE times PMDb |
Time to Alarm |
|
|
Aviationb |
Low-level Navigation and Air Drop |
50.0 m (2 drms) |
0.999 |
10 sec |
High |
|
|
Non-precision Sea App/Landings |
12.0m (2 drms) |
0.999 |
10 sec |
High |
|
|
Precision App/Landings Unprepared Surface |
12.5m (2 drms) |
0.999 |
6 sec |
High |
|
|
Precision Sea App/Landings |
0.6m (2 drms) |
0.999 |
6 sec |
High |
|
|
Amphibious and Anti-submarine Warfare |
50.0 m CEP |
Not specified |
Not specified |
High |
|
|
Anti-air Warfare |
18.1 m CEP |
Not specified |
Not specified |
High |
|
|
Conventional Bombing |
37.5 m CEP |
Not specified |
Not specified |
High |
|
|
Nuclear Bombing |
75.0 m CEP |
Not specified |
Not specified |
High |
|
|
Close Air Support/Interdiction |
9.0 m CEP |
Not specified |
Not specified |
High |
|
|
Electronic Warfare |
22.5 m CEP |
Not specified |
Not specified |
High |
|
|
Command, Control & Communications |
37.5 m CEP |
Not specified |
Not specified |
High |
|
|
Air Refueling |
370.0 m CEP |
Not specified |
Not specified |
High |
|
|
Mine Warfare |
16.0 m CEP |
Not specified |
Not specified |
High |
|
|
Reconnaissance |
18.1 m CEP |
Not specified |
Not specified |
High |
|
|
Magnetic and Gravity Survey |
20.0 m CEP |
Not specified |
Not specified |
High |
|
|
Search & Rescue and Medical Evacuation |
125.0 m CEP |
Not specified |
Not specified |
High |
|
|
Mapping |
50.0 m CEP |
Not specified |
Not specified |
High |
|
Precision-guided Munitions |
Precision-guided Munitions |
3.0 m CEP |
Not specified |
Not specified |
High |
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a. Availability and continuity of service requirements are not specified for military aviation and precision-guided munitions applications. b. This measure relates the probability that a hazardously misleading error will occur (PHE) and the probability that this error will go undetected (PMD). c. Peacetime requirements for the en route through Category I approach and landing phases of flight are identical to FAA requirements. |
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Table 2-2 Naval Applications and Requirementsa
|
|
Application |
Accuracy |
Resistance to RF Interference |
|
En route Navigation |
Pilotage & Coastal Waters |
72.0 m CEP |
High |
|
|
Inland Waters |
25.0 m CEP |
High |
|
|
Open Waters |
2400.0 m CEP |
High |
|
|
Rendezvous |
380.0 m CEP |
High |
|
|
Harbor |
8.0 m CEP |
High |
|
Mine Warfare |
Swept Channel Navigation & Defensive Mining |
16.0 m CEP |
High |
|
|
Offensive Mining |
50.0 m CEP |
High |
|
|
Anti-mine Countermeasures |
<5.0 m CEP |
High |
|
|
Geodetic Reference Guide (WGS-84) |
128.0 m CEP |
High |
|
Special Warfare |
Airdrop |
20.0 m CEP |
High |
|
|
Small Craft |
50.0 m CEP |
High |
|
|
Combat Swimming |
1.0 m CEP |
High |
|
|
Land Warfare & Insertion/Extraction |
1.0 m CEP |
High |
|
|
Task Group Operations |
72.0 m CEP |
High |
|
Amphibious |
Beach Surveys |
185.0 m CEP |
High |
|
Warfare |
Landing Craft |
50.0 m CEP |
High |
|
|
Artillery & Reconnaissance |
<6.0 m CEP |
High |
|
Surveying |
Hydrographic |
<5.0 m (2 drms)b |
High |
|
|
Ocean & Geophysical Deep Ocean |
90.0 m (2 drms) |
High |
|
|
Oceanographic |
100.0 m (2 drms) |
High |
|
a. Availability, integrity, and continuity of service requirements are not specified for naval applications. b. This requirement can currently be met with data post-processing. |
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