Editing Wide Area Augmentation System (section)

{{short description|System that enhances the accuracy of GPS receivers}}
{{redirect|WAAS|other uses of the acronym "WAAS"|WAAS (disambiguation)}}
{{Infobox navigation satellite system
|name = Wide Area Augmentation System (WAAS)
|image = File:Waas-logo.svg
|image_caption = 
|country = United States
|type = 
|status = Operational
|operator = [[Federal Aviation Administration|FAA]]
|coverage = United States, Canada, Mexico
|precision = {{convert|1.0|m|ft}}<ref name="WAAS_NSTB_PAN_Report_Jul06"/>
|satellites_nominal = <!-- 33 -->
|satellites_current = 3
|first_launch = {{start date and age|2003}}
|last_launch = 
|launch_total = 
|regime = [[Geostationary orbit|GEO]] (uses communication satellites)
|orbit_height = <!--20,180&nbsp;km (12,540 mi)-->
}}
{{Geodesy}}

[[File:FAA WAAS System Overview.jpg|thumb|right|WAAS system overview]]

The '''Wide Area Augmentation System''' ('''WAAS''') is an [[air navigation]] aid developed by the [[Federal Aviation Administration]] to [[GNSS augmentation|augment]] the [[Global Positioning System]] (GPS), with the goal of improving its accuracy, integrity, and availability. Essentially, WAAS is intended to enable aircraft to rely on GPS for all phases of flight, including approaches with vertical guidance to any airport within its coverage area. It may be further enhanced with the [[local-area augmentation system]] (LAAS) also known by the preferred ICAO term ''ground-based augmentation system'' (GBAS) in critical areas.

WAAS uses a network of ground-based reference stations, in [[North America]] and [[Hawaii]], to measure small variations in the GPS satellites' signals in the [[western hemisphere]]. Measurements from the reference stations are routed to master stations, which queue the received deviation correction (DC) and send the correction messages to geostationary WAAS satellites in a timely manner (every 5 seconds or better). Those satellites broadcast the correction messages back to Earth, where WAAS-enabled GPS receivers use the corrections while computing their positions to improve accuracy.

The [[International Civil Aviation Organization]] (ICAO) calls this type of system a [[GNSS augmentation|satellite-based augmentation system]] (SBAS). Europe and Asia are developing their own SBASs: the Indian [[GPS-aided GEO augmented navigation|GPS aided GEO augmented navigation]] (GAGAN), the [[European Geostationary Navigation Overlay Service]] (EGNOS), the Japanese [[Multi-functional Satellite Augmentation System]] (MSAS) and the Russian [[System for Differential Corrections and Monitoring]] (SDCM), respectively. Commercial systems include [[StarFire (navigation system)|StarFire]], [[OmniSTAR]], and [[Hemisphere GNSS|Atlas]].
[[File:SBAS Service Areas.png|right|thumb|SBAS Service Areas]]