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The GPS Aided Geo Augmented Navigation system (GAGAN) is the SBAS implementation by the Indian government.
==GAGAN Introduction==
[[File:Isrologo.jpg|ISRO logo|150px|thumb]]


The GPS Aided Geo Augmented Navigation or GPS and Geo Augmented Navigation system (GAGAN) is the SBAS implementation by the Indian government.
In August 2001 the Airports Authority of India and the Indian Space Research Organization (ISRO) reached an agreement for the establishment of the GAGAN system.<ref>Grewal et al., ''Global positioning systems, inertial navigation, and integration'', Wiley-Interscience, 2007</ref>
<gallery widths="200px">
Image:gagan_overview.png|GAGAN overview.<ref name="GAGAN WIKI">[[Wikipedia:GPS_Aided_Geo_Augmented_Navigation|GPS Aided Geo Augmented Navigation on Wikipedia]]</ref>
</gallery>


==GAGAN Introduction==
The development plan consists of two different phases:<ref name="GAGAN_ICG8">[http://unoosa.org/pdf/icg/2013/icg-8/5.pdf ''IRNSS and GAGAN status Presentation''] S. Sayeenathan, ICG-8, DUBAI, November 2013</ref>
 
#Technology Demonstration System (TDS) with the Initial Experimental Phase (IEP);
#Final Operational phase (FOP).
 
The TDS phase was completed in August 2007 using the navigation payload of the INMARSAT 4F1 satellite. The IEP was conducted at the same time, concluding in 2009 <ref name="GAGAN RSA">[https://www.icao.int/APAC/APAC-RSO/GBASSBAS%20Implementation%20Workshop/3-7_GAGAN_Regional_Service_Availability%20(T%20Schemmp).pdf GAGAN Regional Service Availability]</ref>.
 
On 15 April 2010, an attempt to launch the first GAGAN navigation payload took place. The equipment was installed in the satellite, GSAT-4, but, unfortunately, the launch failed and the GEO satellite never reached its nominal orbit<ref>[http://www.thehindu.com/news/article398070.ece ''India’s own cryogenic rocket launch fails'']The Hindu news, 15th April 2010</ref>. In May 2011, the GSAT-8 satellite carrying a GAGAN SBAS payload was successfully launched by the Ariane-V launch vehicle of Arianespace from Kourou, French Guiana<ref>[https://www.geospatialworld.net/news/indias-gsat-8-satellite-to-help-gagan/ India’s GSAT-8 satellite to help GAGAN, Geospatial World, May 2011]</ref>. Later on 28 September 2012, another Ariane 5 rocket successfully launched the India's GSAT-10 satellite which carries the second GAGAN payload <ref>[https://www.gpsworld.com/gsat-10-gagan-satellite-launched/ GSAT-10 GAGAN Satellite Launched, GPSWorld, October 2012]</ref>.
 
GAGAN Stability tests were successfully completed in June 2013. The overall performance of the systems was reviewed by the review committee of the DGCA (Director General of Civil Aviation)<ref>[http://www.isro.gov.in/applications/satellite-navigation-programme GPS Aided Geo Augmented Navigation (GAGAN) in ISRO website]</ref>. In December 2013, the system was certified for RNP 0.1 and started APV1 operations. The Final Operational Phase (FOP) was completed in 2014.<ref name="DGCA">[http://gagan.aai.aero/gagan/content/dgca-certification DGCA certification]</ref><ref>[https://www.icao.int/APAC/APAC-RSO/GBASSBAS%20Implementation%20Workshop/1-7_System%20Development-GAGAN_final%20(M%20Rao).pdf System Development - GAGAN: GBAS/SBAS Implementation Workshop, Seoul, June 2019]</ref>


In August 2001 the [http://www.  Airports Authority of India] and the [http://www. Indian Space Research Organization (ISRO)] signed a memorandum of understanding for jointly establishing the GAGAN system.
On 21 April 2015 it was certified for approach with vertical guidance (APV1) becoming the third SBAS in the world to achieve it and the first to do so operating in the equatorial region.<ref>[https://www.icao.int/APAC/APAC-RSO/GBASSBAS%20Implementation%20Workshop/3-7_GAGAN_Regional_Service_Availability%20(T%20Schemmp).pdf GAGAN Regional Service Availability]</ref><ref name="DGCA"/>
It is being implemented in three phases:
1. Technology Demonstration System (TDS)
2. Initial Experimental Phase (IEP)
3. Final Operational phase (FOP)


The TDS phase was completed in August 2007 using the INMARSAT 4F1 Navigation payload. The Initial Experimental Phase (IEP), planned to be finished by 2009, is still under implementation due to a series of delays. The first GAGAN navigation payload was integrated into the GSAT-4 geostationary satellite. GSAT-4 was launched on 15 April 2010, however it failed to reach orbit.<ref> news</ref>
The third and last satellite (GSAT-15) was launched onboard an Ariane 5 rocket on 10 November 2015.<ref name="Ariane5">[https://www.isro.gov.in/indias-gsat-15-communication-satellite-launched-successfully India's GSAT-15 Communication Satellite Launched Successfully]</ref>


==GAGAN Architecture==
==GAGAN Architecture==
[[File:gagan_overview.png|GAGAN overview.<ref name="GAGAN WIKI">[https://en.wikipedia.org/wiki/GPS-aided_GEO_augmented_navigation GPS Aided Geo Augmented Navigation on Wikipedia]</ref>|400px|thumb]]


The main components of the GAGAN Architecture are:
The main components of the GAGAN Architecture are:<ref name="GAGAN_ICG8"/>


*Space segment: two operational GEO satellites, GSAT-8 & GSAT-9 satellites
*'''Space segment''': three operational GEO satellites<ref name="currProg"> Navigation Current Programme, Indian Space Research Organization</ref><ref name=" futProg">Forth Future Programme, Indian Space Research Organization</ref><ref name="Ariane5"/>:
**GSAT-8: Launched in March 2011.
**GSAT-10: Launched in April 2012.
**GSAT-15: Launched in November 2015.


*Ground segment:  On the ground, the GPS Data is received and processed in the 8 Indian Reference Stations (INRES), located at Delhi, Ahmedabad, Bangalore, Thiruvananthapuram, Kolkata, Guwahati, Port Blair and Jammu. The Indian Master Control Center (INMCC), located at Bangalore, processes the data from the multiple INRESs to determine the differential corrections. Information from the INMCC is sent to the Indian Land Uplink Station (INLUS) and uplinked along with the GEO navigation message to the GAGAN GEO satellite.   
*'''Ground segment''':  On the ground, the GPS data is received and processed in the 15 (of the up to 45 it can support <ref name="GAGAN FAQ">[http://gagan.aai.aero/gagan/content/faq-0 GAGAN FAQ]</ref>) Indian Reference Stations (INRES), located at Ahmedabad, Bangalore, Bhubaneswar, Kolkata, Delhi, Dibrugarh, Gaya, Goa, Guwahati, Jaisalmer, Jammu, Nagpur, Porbandar, Port Blair, Trivandrum. The Indian Master Control Center (INMCC) composed by two operational sites located in Bangalore and Delhi, processes the data from the INRESs to compute the differential corrections and the estimate of its level of integrity. The SBAS message generated by the two INMCC is uplinked to the GEO satellites through its corresponding Indian Land Uplink Station (INLUS)<ref name="GAGAN_RESULTS">[http://www.icao.int/APAC/Meetings/2012_ISTF_1/IP02_India%20AI.4%20-%20Presentation.ppt C.L.Indi (GAGAN), Surendra Sunda (GAGAN), Airports Authority of India, "GAGAN - Ionospheric data collection and analysis over Indian region - Recent results", First Meeting of ionospheric Studies Task Force (ISTF/1) 27th -29th  Feb 2012]</ref><ref name="GAGAN RSA"/>.
*'''User segment''': GAGAN-enabled GPS receivers, with the same technology as [[WAAS Receivers]], capable to use the GAGAN Signal-in-Space (SIS). User equipment for civil aviation shall be certified against several standards (see article [[SBAS Standards]]).


*User segment: GAGAN-enabled GPS Receivers, with the same technology as WAAS Receivers, capable to use the GAGAN Signal-in-Space (SIS). User equipment for civil aviation shall be certified against several standards (see SBAS standards).
The company Raytheon was awarded in 2009 with the contract to modernize the Indian air navigation system. Raytheon was responsible for building the Ground Stations being supplied by some ground equipment by ISRO.<ref>[https://insidegnss.com/isro-extends-raytheon-contract-for-gagan-gps-augmentation-system/ ''ISRO Extends Raytheon Contract for GAGAN GPS Augmentation System''] Inside GNSS News July 2009</ref>
 
Raytheon company was awarded in 20?? of the contract to build the GAGAN sytem. (ref Inside)


==GAGAN Signals and Performances==
==GAGAN Signals and Performances==
[[File:GAGANperformance.jpg|GAGAN performance<ref name="GAGAN FAQ"/>. Real time monitoring can be accessed [http://gagan.aai.aero/gagan/content/apv-1-rnp-01-services here].|400px|thumb]]


The GAGAN GEO satellite will downlink navigation data via L1 and L5 WAAS signals, with Global Positioning System (GPS) type modulation. L1 and L5 WAAS signals were obtained from the United States Air Force and U.S Department of Defense on November 2001 and March 2005. <ref name="GAGAN WIKI"/>
The GAGAN GEO satellites broadcast SBAS navigation data using L1 and L5 signals (this latter still under development), with Global Positioning System (GPS) type modulation<ref name="GAGAN WIKI"/>.
 
The specification of the SBAS message data format is contained in the [http://www.icao.org ICAO] SARPS Appendix B for the aspects related with the signal in space, as well as in the RTCA MOPS DO-229 for the minimum performance requirements applicable to the airborne SBAS receiver equipment.  The format of the messages is thoroughly explained in the article [[The EGNOS SBAS Message Format Explained]]. (See the article [[SBAS Fundamentals]] for more information.)
GAGAN augments the GPS system with integrity and corrections to make the GPS system a trusted navigational aid.  It will be built to support the integrity required for APV I phases of flight, and to meet the [[SBAS Fundamentals|performance requirements]] of international civil aviation regulatory bodies.


==GAGAN Development==
GAGAN is designed to achieve a [[SBAS Fundamentals|performance]] level of<ref name="GAGAN FAQ"/>:
*APV 1.0 over the Indian land mass.
*RNP 0.1 over the oceanic region, within the Indian Flight Information Region (FIR).


GAGAN is primarily meant for civil aviation. GAGAN is planned to get into operation by the year 2014. The goal is to provide navigation system to safety-to-life operations over the Indian airspace and in the adjoining area. Once GAGAN is operational, it should improve air safety over India and aircraft will be able to make precision approaches within the coverage area. There are 449 airports and airstrips in the country, but only 34 have instrument landing systems (ILSs) installed. <ref name="GAGAN WIKI"/>
On December 30, 2013 the GAGAN system was certified to RNP0.1 service level by the Director General of Civil Aviation (DGCA) and on 21 April 2015 it was certified for approach with vertical guidance (APV1) (both have been renewed for up to 18 July 2022) <ref name="DGCA"/>. This means, as of this date, aircraft equipped with SBAS receivers will be able to use GAGAN SiS in Indian airspace for en route navigation and approach operations with vertical guidance. The GAGAN signal availability filled the gap between [[EGNOS General Introduction|EGNOS]] and [[MSAS General Introduction|MSAS]] coverage areas.<ref>[http://gpsworld.com/gagan-certified-for-aviation-in-india/ GAGAN Certified for Aviation in India], GPS World, GPS Staff, January 13, 2014</ref><ref>[http://www.insidegnss.com India Certifies GAGAN for En Route and NPA Flight Operations], Inside GNSS, January 14, 2014</ref><ref name="GAGAN FAQ"/>
------
Ionospheric issues: One of the main concerns about an SBAS implementation in India is the ionospheric behavior at these latitudes.  The ionosphere near the geomagnetic equator has physical process and features that rarely, if ever, affect mid-latitudes.  These include the Appleton geomagnetic anomaly, plasma bubbles, and scintillation. India is in fact iunder the geomagnetic equator.


Current SBAS in the mid magnetic latitudes provide a precision guidance for the single frequency users [11].  The ionospheric phenomena mentioned above and typically found at the equatorial latitudes would significantly challenge SBAS approaches currently used in these mid magnetic latitudes for precision guidance.  The peak large scale features could cause positioning inaccuracies to standard SBAS that may exceed the precision approach alert limits.  Even when such extreme features are not present, the possibility of unobserved small scale features makes it difficult for an SBAS system to ensure integrity compatible with the precision approach alert limits.
==Ionospheric issues==


One of the main concerns about an SBAS implementation in India is the [[Ionospheric Delay|ionospheric]] behavior at these latitudes, as India is located in the equatorial ionospheric anomaly belt.  The ionosphere near the geomagnetic equator has physical process and features that rarely affect mid-latitudes.  These include the Appleton geomagnetic anomaly, plasma bubbles, and scintillations.


Free from adverse ionospheric effects, current SBAS in the mid magnetic latitudes provide vertical guidance for the single frequency users. The ionosphere equatorial anomaly and the ionospheric phenomena typically found at equatorial latitudes, produce large spatial gradients and temporal gradients in the [[Ionospheric Delay|ionospheric delay]].  This significantly challenges SBAS to meet the stringent requirements associated to precision guidance. The macroscopic effects (equatorial anomaly) are not well approximated with the 5 x 5 degree grid thin shell model specified in the current [[SBAS Standards]]. Also, the microscopic phenomena (plasma bubbles) cause sharp gradients during a short period of time (less than 5 minutes). If these small scale features are not observed or alerted by the SBAS system, it would make difficult to ensure integrity compatible with the precision approach alert limits. Finally, the user equipment and the reference stations of the SBAS system might suffer from tracking and noise problems because of scintillation, which is a particularly likely problem in equatorial latitudes depending on the season and day time. All these problems are under study by several groups and different approaches for an SBAS implementation in equatorial magnetic regions have been presented.<ref >Doherty, Patricia et al., "Ionospheric Effects on Low-Latitude Space Based Augmentation Systems", proceedings of ION GPS, Portland, OR, September 2002. </ref><ref > Lejeune, R. et al., "Adequacy of the SBAS Ionospheric Grid Concept for Precision Approach in the Equatorial Region", proceedings of ION GPS, Portland, OR, September 2002.</ref><ref> Wu, S. et al., "A Single Frequency Approach to Mitigation of Ionospheric Depletion Events for SBAS in Equatorial Regions", ION GNSS 2006.</ref><ref> Cormier, D., et al., "Providing Precision Approach SBAS Service and Integrity in Equatorial Regions," Proceedings ION GPS/GNSS 2003, Portland, OR, September 2003. </ref><ref> Shukla, A.K., et al,‘’Two-Shell Ionospheric Model for Indian Region: A Novel Approach’’ IEEE Transactions on Geoscience and Remote Sensing,  Aug. 2009 Volume: 47 Issue:8,Pages 2407 – 2412</ref>


==Notes==
In order to cope with the ionospheric perturbations at the equatorial level, the GAGAN system makes use of the ISRO GIVE Model – Multi Layer Data Fusion (IGM-MLDF). The model ensures that the broadcast GIVEs have a sufficiently high level of integrity so that the user ionosphere vertical errors (UIVEs) computed by user receivers will bound their vertical ionosphere errors with a very high probability. The algorithm provides the delay and the confidence values for the user, resulting in improved accuracy and availability. <ref>[http://www.insidegnss.com/node/4788 GAGAN — India’s SBAS]</ref>
<references group="footnotes"/>


==References==
==References==

Latest revision as of 10:47, 22 June 2021


Other SBASOther SBAS
Title GAGAN
Edited by GMV
Level Basic
Year of Publication 2011
Logo GMV.png

The GPS Aided Geo Augmented Navigation system (GAGAN) is the SBAS implementation by the Indian government.

GAGAN Introduction

ISRO logo

In August 2001 the Airports Authority of India and the Indian Space Research Organization (ISRO) reached an agreement for the establishment of the GAGAN system.[1]

The development plan consists of two different phases:[2]

  1. Technology Demonstration System (TDS) with the Initial Experimental Phase (IEP);
  2. Final Operational phase (FOP).

The TDS phase was completed in August 2007 using the navigation payload of the INMARSAT 4F1 satellite. The IEP was conducted at the same time, concluding in 2009 [3].

On 15 April 2010, an attempt to launch the first GAGAN navigation payload took place. The equipment was installed in the satellite, GSAT-4, but, unfortunately, the launch failed and the GEO satellite never reached its nominal orbit[4]. In May 2011, the GSAT-8 satellite carrying a GAGAN SBAS payload was successfully launched by the Ariane-V launch vehicle of Arianespace from Kourou, French Guiana[5]. Later on 28 September 2012, another Ariane 5 rocket successfully launched the India's GSAT-10 satellite which carries the second GAGAN payload [6].

GAGAN Stability tests were successfully completed in June 2013. The overall performance of the systems was reviewed by the review committee of the DGCA (Director General of Civil Aviation)[7]. In December 2013, the system was certified for RNP 0.1 and started APV1 operations. The Final Operational Phase (FOP) was completed in 2014.[8][9]

On 21 April 2015 it was certified for approach with vertical guidance (APV1) becoming the third SBAS in the world to achieve it and the first to do so operating in the equatorial region.[10][8]

The third and last satellite (GSAT-15) was launched onboard an Ariane 5 rocket on 10 November 2015.[11]

GAGAN Architecture

GAGAN overview.[12]

The main components of the GAGAN Architecture are:[2]

  • Space segment: three operational GEO satellites[13][14][11]:
    • GSAT-8: Launched in March 2011.
    • GSAT-10: Launched in April 2012.
    • GSAT-15: Launched in November 2015.
  • Ground segment: On the ground, the GPS data is received and processed in the 15 (of the up to 45 it can support [15]) Indian Reference Stations (INRES), located at Ahmedabad, Bangalore, Bhubaneswar, Kolkata, Delhi, Dibrugarh, Gaya, Goa, Guwahati, Jaisalmer, Jammu, Nagpur, Porbandar, Port Blair, Trivandrum. The Indian Master Control Center (INMCC) composed by two operational sites located in Bangalore and Delhi, processes the data from the INRESs to compute the differential corrections and the estimate of its level of integrity. The SBAS message generated by the two INMCC is uplinked to the GEO satellites through its corresponding Indian Land Uplink Station (INLUS)[16][3].
  • User segment: GAGAN-enabled GPS receivers, with the same technology as WAAS Receivers, capable to use the GAGAN Signal-in-Space (SIS). User equipment for civil aviation shall be certified against several standards (see article SBAS Standards).

The company Raytheon was awarded in 2009 with the contract to modernize the Indian air navigation system. Raytheon was responsible for building the Ground Stations being supplied by some ground equipment by ISRO.[17]

GAGAN Signals and Performances

GAGAN performance[15]. Real time monitoring can be accessed here.

The GAGAN GEO satellites broadcast SBAS navigation data using L1 and L5 signals (this latter still under development), with Global Positioning System (GPS) type modulation[12]. The specification of the SBAS message data format is contained in the ICAO SARPS Appendix B for the aspects related with the signal in space, as well as in the RTCA MOPS DO-229 for the minimum performance requirements applicable to the airborne SBAS receiver equipment. The format of the messages is thoroughly explained in the article The EGNOS SBAS Message Format Explained. (See the article SBAS Fundamentals for more information.)

GAGAN is designed to achieve a performance level of[15]:

  • APV 1.0 over the Indian land mass.
  • RNP 0.1 over the oceanic region, within the Indian Flight Information Region (FIR).

On December 30, 2013 the GAGAN system was certified to RNP0.1 service level by the Director General of Civil Aviation (DGCA) and on 21 April 2015 it was certified for approach with vertical guidance (APV1) (both have been renewed for up to 18 July 2022) [8]. This means, as of this date, aircraft equipped with SBAS receivers will be able to use GAGAN SiS in Indian airspace for en route navigation and approach operations with vertical guidance. The GAGAN signal availability filled the gap between EGNOS and MSAS coverage areas.[18][19][15]

Ionospheric issues

One of the main concerns about an SBAS implementation in India is the ionospheric behavior at these latitudes, as India is located in the equatorial ionospheric anomaly belt. The ionosphere near the geomagnetic equator has physical process and features that rarely affect mid-latitudes. These include the Appleton geomagnetic anomaly, plasma bubbles, and scintillations.

Free from adverse ionospheric effects, current SBAS in the mid magnetic latitudes provide vertical guidance for the single frequency users. The ionosphere equatorial anomaly and the ionospheric phenomena typically found at equatorial latitudes, produce large spatial gradients and temporal gradients in the ionospheric delay. This significantly challenges SBAS to meet the stringent requirements associated to precision guidance. The macroscopic effects (equatorial anomaly) are not well approximated with the 5 x 5 degree grid thin shell model specified in the current SBAS Standards. Also, the microscopic phenomena (plasma bubbles) cause sharp gradients during a short period of time (less than 5 minutes). If these small scale features are not observed or alerted by the SBAS system, it would make difficult to ensure integrity compatible with the precision approach alert limits. Finally, the user equipment and the reference stations of the SBAS system might suffer from tracking and noise problems because of scintillation, which is a particularly likely problem in equatorial latitudes depending on the season and day time. All these problems are under study by several groups and different approaches for an SBAS implementation in equatorial magnetic regions have been presented.[20][21][22][23][24]

In order to cope with the ionospheric perturbations at the equatorial level, the GAGAN system makes use of the ISRO GIVE Model – Multi Layer Data Fusion (IGM-MLDF). The model ensures that the broadcast GIVEs have a sufficiently high level of integrity so that the user ionosphere vertical errors (UIVEs) computed by user receivers will bound their vertical ionosphere errors with a very high probability. The algorithm provides the delay and the confidence values for the user, resulting in improved accuracy and availability. [25]

References

  1. ^ Grewal et al., Global positioning systems, inertial navigation, and integration, Wiley-Interscience, 2007
  2. ^ a b IRNSS and GAGAN status Presentation S. Sayeenathan, ICG-8, DUBAI, November 2013
  3. ^ a b GAGAN Regional Service Availability
  4. ^ India’s own cryogenic rocket launch failsThe Hindu news, 15th April 2010
  5. ^ India’s GSAT-8 satellite to help GAGAN, Geospatial World, May 2011
  6. ^ GSAT-10 GAGAN Satellite Launched, GPSWorld, October 2012
  7. ^ GPS Aided Geo Augmented Navigation (GAGAN) in ISRO website
  8. ^ a b c DGCA certification
  9. ^ System Development - GAGAN: GBAS/SBAS Implementation Workshop, Seoul, June 2019
  10. ^ GAGAN Regional Service Availability
  11. ^ a b India's GSAT-15 Communication Satellite Launched Successfully
  12. ^ a b GPS Aided Geo Augmented Navigation on Wikipedia
  13. ^ Navigation Current Programme, Indian Space Research Organization
  14. ^ Forth Future Programme, Indian Space Research Organization
  15. ^ a b c d GAGAN FAQ
  16. ^ C.L.Indi (GAGAN), Surendra Sunda (GAGAN), Airports Authority of India, "GAGAN - Ionospheric data collection and analysis over Indian region - Recent results", First Meeting of ionospheric Studies Task Force (ISTF/1) 27th -29th Feb 2012
  17. ^ ISRO Extends Raytheon Contract for GAGAN GPS Augmentation System Inside GNSS News July 2009
  18. ^ GAGAN Certified for Aviation in India, GPS World, GPS Staff, January 13, 2014
  19. ^ India Certifies GAGAN for En Route and NPA Flight Operations, Inside GNSS, January 14, 2014
  20. ^ Doherty, Patricia et al., "Ionospheric Effects on Low-Latitude Space Based Augmentation Systems", proceedings of ION GPS, Portland, OR, September 2002.
  21. ^ Lejeune, R. et al., "Adequacy of the SBAS Ionospheric Grid Concept for Precision Approach in the Equatorial Region", proceedings of ION GPS, Portland, OR, September 2002.
  22. ^ Wu, S. et al., "A Single Frequency Approach to Mitigation of Ionospheric Depletion Events for SBAS in Equatorial Regions", ION GNSS 2006.
  23. ^ Cormier, D., et al., "Providing Precision Approach SBAS Service and Integrity in Equatorial Regions," Proceedings ION GPS/GNSS 2003, Portland, OR, September 2003.
  24. ^ Shukla, A.K., et al,‘’Two-Shell Ionospheric Model for Indian Region: A Novel Approach’’ IEEE Transactions on Geoscience and Remote Sensing, Aug. 2009 Volume: 47 Issue:8,Pages 2407 – 2412
  25. ^ GAGAN — India’s SBAS
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