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SBAS Fundamentals

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FundamentalsFundamentals
Title SBAS Fundamentals
Author(s) GMV
Level Basic
Year of Publication 2011
Logo GMV.png


A [Satellite-based Augmentation System (SBAS) is a civil aviation safety-critical system that supports wide-area or regional augmentation – even continental scale - through the use of geostationary (GEO) satellites which broadcast the augmentation information[1][2]. A SBAS augments primary GNSS constellation(s) by providing GEO ranging, integrity and correction information. While the main goal of SBAS is to provide integrity assurance, it also increases the accuracy with position errors below 1 metre (1 sigma).

The ground infrastructure includes the accurately-surveyed sensor stations which receive the data from the primary GNSS satellites and a Central Processing Facility (CPF) which computes integrity, corrections and GEO ranging data forming the SBAS signal-in-space (SIS). The SBAS GEO satellites relay the SIS to the SBAS users which determine their position and time information. For this, they use measurements and satellite positions both from the primary GNSS constellation(s) and the SBAS GEO satellites and apply the SBAS correction data and its integrity.

The augmentation information provided by SBAS covers corrections and integrity for satellite position errors, satellite clock – time - errors and errors induced by the estimation of the delay of the signal while crossing the ionosphere. For the errors induced by the estimation of the delay caused by the troposphere and its integrity, the user applies a tropospheric delay model.


SBAS Performances

The SBAS performances are defined with respect to the level of service that the system is designed to. The main source for SBAS performances comes from civil aviation navigation safety requirements and they are different for each civil aviation operation (see Table ICAO GNSS performances requirements [3]).

Typical Operation Horizontal Accuracy (95%) Vertical Accuracy (95%) Integrity Time-To-Alert (TTA) Horizontal Alert Limit (HAL) Vertical Alert Limit (HAL) Continuity Availability
Initial Intermediate Nonprecision approaches & Departure 220 m (720 ft) N/A 1 –1x10-7/h 10 s 556 m (0.3 NM) N/A 1 – 1x10-4/h to 1 – 1x10-8/h 0.99 to 0.99999
Approach operations with vertical guidance (APV-I) 16.0 m (52 ft) 20 m (66 ft) 1 – 2x10-7 (per approach) 10 s 40 m (130 ft) 50 m (164 ft) 1 – 8x10-6/15s 0.99 to 0.99999


Notes


References

  1. ^ Cite error: Invalid <ref> tag; no text was provided for refs named GNSS Aug
  2. ^ Cite error: Invalid <ref> tag; no text was provided for refs named Kaplan
  3. ^ ICAO Standards and Recommended Practices, Annex 10, Volume 1 Radio Navigation Aids, July 2006