GNSS/GPS Update

Eric Gakstatteregakstatter@questex.com

GPS World magazinePresented July 14, 2009

ESRI International User ConferenceSan Diego, CA©Copyright 2009

GNSS/GPS Current EventsUnited States

-GAO report on GPS-SVN 49 report-SBAS (WAAS)-NDGPS

International

-Solar Cycle 24-GLONASS-Galileo-SBAS (EGNOS/MSAS/GAGAN)

GAO Report on GPS health

Government Accountability Office- In April 2009, released a report

entitled..“Global Positioning System

Significant Challenges in Sustaining and Upgrading

Widely Used Capabilities”. -Full report available at:

http://gao.gov/products/GAO-09-325

GAO Report on GPS health

• Currently, there are 31 healthy satellites. The DoD is only committed to a 24-satellite constellation.

• A number of satellites are well-beyond their design life.

• Delays in new satellite development have raised concerns about the medium/long-term health of GPS.

GAO Report on GPS health

GAO Report on GPS health

Is there a legitimate concern?

-For consumer GPS users, very minimal.

-For GIS and survey GPS users, there’s a legitimate concern.

GAO Report on GPS health

Why be concerned?-GIS and survey GPS receivers are

“satellite-hungry”. They need satellite signals to perform well.

-Even a drop of 2-3 GPS satellites will affect performance. A drop of 4-5 satellites would be very significant.

-Field productivity would be significantly reduced.

GAO Report on GPS healthWhat to Do?

-Monitor constellation status. http://www.navcen.uscg.gov/navinfo/Gps/ActiveNanu.aspx

-If the constellation is reduced by 2-3 satellites, utilize mission planning software.

-Survey receivers utilizing GLONASS (in addition to GPS) will likely not be affected.

-GIS (mapping-grade) receivers generally don’t utilize GLONASS.

GAO Report on GPS healthFurther comments

-Three older satellites are available to return to service and are tested every six months.

-Full GAO report available at:http://gao.gov/products/GAO-09-325

-Univ. of New Brunswick analysis of GLONASS compensating for a loss of GPS satellites. http://sidt.gpsworld.com/System+Design+and+Test+News

SVN 49 Report

SVN 49 (PRN01) Report

SVN 49 Report

• The 7th (of 8) Block IIR-M satellite was launched March 24, 2009. It hasn’t been declared healthy.

• SVN 49 includes a unique L5 demonstration payload to secure the L5 frequency with ITU.

• L5 payload is interfering with the normal operation of the IIR-M satellite.

SVN 49 Report – cont.

Ionospheric refraction corrected pseudoranges Relative to a “best fit” orbit determined early in the test program Roughly a 4+ meter spread from 10 to 80 degrees

SVN 49 Report – cont.

• Design flaw essentially means it will never perform as well as the previous IIR-M satellites, but likely still falls within contract specification.

• Department of Defense is investigating possible “patches” and seeking user community input.

• There is no plan to declare SVN-49 healthy in the immediate future.

Solar Cycle 24

Solar Cycle 24 Report

Solar Cycle 24Solar Cycle 24

-On May 8, 2009, the National Oceanic and Atmospheric Administration’s (NOAA) Solar Cycle 24 Prediction Panel (consisting of 12 international experts) released a statement revising their predictions for Solar Cycle 24.

-You can read the press release here…http://www.noaanews.noaa.gov/

stories2009/20090508_solarstorm.html

Solar Cycle 24Solar Cycle 24 will be the weakest solar cycle since

1928.

Solar Cycle 24

Why do we care?-11 year cycle. -Geomagnetic storm activity

affects GPS receivers by altering the density of the electrons in the ionosphere. The density of electrons is referred to as the Total Electron Content (TEC).

-Real-time TEC can be viewed at:http://iono.jpl.nasa.gov//

latest_rti_global.html

Solar Cycle 24

Why do we care?-GPS L1 (single frequency)

receivers rely on a rough TEC model to estimate the ionospheric delay.

-DGPS (real-time or pp) largely mitigates the delay.

-Dual frequency receivers can more precisely mitigate the TEC.

-A dynamically changing TEC is very difficult to model.

Solar Cycle 24

Why do we care?-GPS L1 receivers are affected

the most by a dynamic TEC.-Sunspot count isn’t necessarily

an indicator of geomagnetic activity and therefore the low Sunspot Number Prediction isn’t an indicator that GPS will be affected less than Solar Cycle 23.

-In practical terms, a TEC value of 1 = ~15cm of GPS L1 error.

Solar Cycle 24

How bad can it get?-During the late October 2003

geomagnetic event, simulations showed that L1 DGPS accuracy reached 18 meters (95% horizontal) and L1 WAAS accuracy reached 25 meters (95% horizontal).

-Extreme events can last for several days.

Solar Cycle 24

What to do?-Sign up to receive email alerts

at:https://pss.swpc.noaa.gov/

LoginWebForm.aspx?ReturnUrl=%2fproductsubscriptionservice%2fMainMenuWebForm.aspx

-Don’t operate mission-critical GPS L1 receivers during predicted periods of geomagnetic storm activity.

-Geomagnetic storms affecting GPS typically occur 1-2 years after the solar cycle peak.

GPS Modernization

GPS Modernization

GPS Modernization

GPS Launch Schedule-Last Block IIR-M satellite launch

scheduled for August/September.

-First Block IIF satellite launch delayed until Spring 2010 at earliest. Introduces L5 signal.

GLONASS status

GLONASS status-Russian GNSS

GLONASS status

-Currently 18 operational satellites, effectively adding 3-6 observables in addition to GPS.

-Six more planned to launch by end of 2009.

-Still considered an augmentation for high precision users until GLONASS quality reaches GPS.

Galileo status

Galileo status-European GNSS

Galileo status

• European Union Transport funding the initial 3.4B Euro development with public funds.

• Planned 30 satellite constellation.• Two Galileo test satellites in orbit.• June 16, 2009. Contract signed to launch

the first four operational Galileo satellites (two at a time) by the end of 2010.

• Full constellation is proposed to be 2013.

SBAS

SBAS status-Satellite-Based

Augmentation System

GPS SBAS systems

• WAAS – Covers North America, AK, HI• EGNOS – Covers most of Europe and

Northern Africa. Not officially operational for aviation users be usable for ground users.

• MSAS – Covers region around Japan.• GAGAN – Covers India. Not operational

yet. Limited availability for ground users.• OmniSTAR – World-wide coverage.

Subscription-based.

Worldwide SBAS Coverage Map

Courtesy: Geneq, Inc.

DGPS – Radio beacon corrections

• Used internationally for marine navigation.

• Used in the US for marine navigation and inland applications such as transportation, mapping, etc. Referred to as NDGPS.

• The correction is free. Requires a “beacon receiver” to use.

• NDGPS budget is under intense scrutiny.

Current US DGPS coverage

Eric GakstatterContact Information:

egakstatter@questex.com

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