I'm at the ION GNSS meeting here in balmy Savannah Georgia and I've now heard from several people regarding the RAIM issue.  Here's the issue.

Pilots flying with GPS as their main navigation system or as a secondary system on selected routes must submit a RAIM (Receiver Autonomous Integrity Monitoring) report for their destination before flying.  This report defines whether GPS will meet some fairly stringent requirements for satellite  and signal availability.  The Federal Aviation Administration (FAA) is mandating this requirement.  The pilots, concerned with how they will meet this requirement asked the FAA - "how do we meet this requirement?"  The FAA responded by tasking the VOLPE center to develop a RAIM assessment tool.  This tool technically calculates RAIM, but it turns out, is not very useful to any pilot.

One pilot I talked with at the ION GNSS show said that it was too difficult to plan a route with the VOLPE tool.  Look at the tool and you'll see why.  Well, it's a good thing he was talking to us!  AGI has long been in the business of calculating access and coverage along routes - for virtually any kind of metric you can think of (no jokes here Kevin).  Here's an example:  the blue line represents a route in a mountainous area (Breckenridge I think) where there's a threat (large colorful communications jammer).  The white potato chip shaped thing is the Azimuth-Elevation mask for the jammer.  Any place below the potato chip the jammer is unable to see - above the chip - watch out. 

This route can be edited in the 3-D window to reroute around threats (or, say RAIM outages?) and reports run easily to determine RAIM outage times, etc.

I bring this point up because AGI has the technology to solve this pilots problem today.  Using our STK Engine and our components, an application can be built to make the RAIM reporting requirement a breeze and we can add the benefit of being able to give the pilot some additional valuable information!  Here's how.

Our Navigation Accuracy Library calculates RAIM (Fault Detection) and can report three types of RAIM outages for any location and time.  (En Route, Terminal and Non-Precision Approach) Our Dynamic Geometry Library comes with a waypoint propagator, useful for propagating routes of aircraft, land vehicles, whatever.  Our STK Engine provides 3-D graphing capabilities that can display routes (colored if you like) as well as coverage (a RAIM outage contour map for example).  Put these together in a single application and add some features like the following:

• Upload your own route file
• Database of predefined routes the Airline flies
• Recalculate the 'wheels up' time based on RAIM outages
• Create a handheld mobile application the pilot can use to initially assess RAIM for standard flight routes - from anywhere prior to flight.

There are many different versions of this scheme that could be put together depending on how the particular pilot or airline wanted to use the system.

There's another stick in the mud I haven't touched on yet.  The VOLPE center calculates RAIM in a specific way, using predefined vertical and horizontal alert thresholds.  I say predefined, because there is nowhere on their tool to change these.  There is no standard RAIM algorithm to use when calculating RAIM outages.  There are accepted algorithms in the literature, but nothing mandated by and interface control document (ICD).  Each GPS receiver manufacturer is free to calculate RAIM any way they choose.  AGI uses the accepted algorithms in the literature, but we allow the user/developer to define any alert threshold they like.  This provides more flexibility in calculating different RAIM outage thresholds.  AGI components are also flexible enough to be able to incorporate receiver manufacturer algorithms - with our without source code.

So, there is a great opportunity here for pilots to have a better system and a way to grow when future GPS availability requirements are enacted.  For more information on our technologies in this area, please contact me.

Technorati Tags: navigation,accuracy,utility,web tools,web service,web application,AGI,Google Earth,Space,satellite

Recently, I posted a Nog on some utilities and tools I created to help with the day-to-day engineering tasks faced when working with GPS.  Well, I've added to the mix (with help!) and put the collection in a single, easy to access place.  the tools can be accessed from the Web Apps/Services tab on the AGI developer Network: http://adn.agi.com/webServices/.

Here's a list of the GPS related tools there.  Some are repeats from the previous Nog, but I wanted to give you a complete list:

• GPS Date Calendar

The GPS Date Calendar displays a standard calendar with dates specific to the GPS community. Dates included are: GPS Week (current and full), day of week, day of year and time of week.

• GPS Navigation Accuracy

This web application calculates GPS Navigation Accuracy for the specified time interval and location of the GPS receiver. Specifically, it calculates Total System Error and Signal In Space Error and generate the appropriate reports and graphs. This application has been built using the Navigation Accuracy Library, which is part of AGI Components.

• GPS Satellite Outage Calendar

This Calendar displays historical, current and predicted GPS satellite outages based on the latest satellite outage file (SOF) produced by the United Stated Air Force. Clicking on a specific calendar date provides more information about the outage. You can also view all historical outages in a table format.

• GPS Satellite Outage Web Service

This web service allows you to connect and retrieve outage information for specific GPS PRNs, or specific time intervals, or both. Using just the PRN, a list of strings will be returned of all times that PRN has been unhealthy, based on the latest satellite outage file (SOF). Providing a start and stop time will return a list of strings denoting all PRNs that were unhealthy during that interval, with their outage times. Another service allows you to specify both the PRN and the time interval to further thin the results. The dates returned can be either Gregorian (standard date format) or Julian date format.

This example application shows how this service could be used.

• GPS Satellite Performance

GPS satellite performance is at the heart of navigation accuracy. AGI Performance Assessment Files (PAFs) and Prediction Support Files (PSFs), contain GPS satellite errors which AGI uses to calculate receiver positioning errors. This utility helps to visualize and understand those GPS satellite errors.

The following tools aren't specifically for GPS, but are just as handy in their own right. 

• Google Earth Satellite Database (Awesome tool!)

This KML network link visualizes all earth orbiting objects tracked by the United States Strategic Command (USSTRATCOM) using the satellite database processed by Analytical Graphics, Inc. using the Dynamic Geometry Library in AGI Components. All satellites are tracked in real-time and updated every 30 seconds. Please open this link using Google Earth.

• Satellite Tracker

This web application generates ground tracks on an embedded Google map, as well as ephemeris tables, for a user-selected satellite viewed from a user-defined location during a user-specified time period.

• Space Data Reporting (Web Service)

The Space Data Reporter is an example implementation of AGI’s new Dynamic Geometry Library (DGL). This suite of Web Services powered by the DGL enables users to:
- Publish ground tracks
- Derive current locations of satellites
- Calculate inter-visibility between satellites and locations on the ground
- Compute GPS dilution of precision (DOP)
- Analyze STK generated conjunction analysis (CAT)