Mashups are great - even if that word is getting kind of old now.  It's the idea that's really cool.  Like the tinkers who grab bits and pieces from junkyards and make something really cool, today's programmer's search the Internet and find gold nuggets that can be pieced together and brought to life in a new way.  So, I wanted to tinker a little bit.  I decided to combine the navigation accuracy component library (that I'm so fond of) with the STK 4DX embedded technology and some near real time data I found at the National Oceanic and Atmospheric (NOAA) web site.  This NOAA data consists of slant range total electron count (TEC) data for GPS satellites - and this is important is your a civilian GPS user.  The largest error for civilian users is caused by the ionosphere, so it pays to watch what it's doing.  I also found a graphing package called Zedgraph that will help with plotting any necessary data.

Ok, so what can you do with slant range TEC data, NavAccLib, DGL,  4DX and Zedgraph?  Well grab a Nog and let's take a look.

First, I created a Windows Application from Visual Studio and started designing the GUI - nothing too difficult, just enough to get the job done.

ok, maybe I added a few extra things that aren't absolutely necessary, but I get carried away.

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InsideGNSS:

On Wednesday (April 16), a U.S. Air Force team successfully launched the Communication/Navigation Outage Forecasting System (C/NOFS), an experimental satellite designed to monitor the ionosphere and predict conditions that would disturb radio communications, including GNSS signals.

This satellite carries a GPS receiver specifically designed for this mission:

The C/NOFS Occultation Receiver for Ionospheric Sensing and Specification (CORISS) is a dual-frequency GPS receiver that measures line-of-sight total electron count (TEC), on-board scintillation indices and spectra, stratospheric temperature profiles, and high rate scintillation products.

The ionosphere is the biggest cause of errors for single-frequency GPS users - if you have to ask if you are one - you probably are.  But ionospheric effects also affect dual-frequency users, typically the military.  Even though a dual frequency measurement can eliminate the ionospheric delay caused by ionized electrons, it can't get away from scintillation - the scattering of the GPS signals through a turbulent ionosphere.  

I talked with Joe Kunches, the Chief  of Operations at the Space Weather Prediction Center, and he explained scintillation to me this way:

Imagine you're shining a flashlight through a tub of still water onto a dark rock.  You can see how the light bends a little as it enters the water, but the beam is still clear and visible on the rock.  Now imagine the water sloshing around.  The beam on the rock is now just small specks and moving patches of light - that is scintillation - the bouncing of the GPS signal through a turbulent ionosphere.  So turbulent that your receiver can't lock up on the signal.

As we get closer to Solar Max, ionospheric errors and scintillation will increase, because the sun becomes more active and sloshes the ionosphere around more.

Again from InsideGNSS:

As the Earth enters a period of increasing solar activity, the effects of phenomena such as sunspots on L-band GNSS user equipment is drawing an increasing amount of attention. An article by Joe Kunches in the November/December 2007 issue of Inside GNSS highlighted the effects of space weather on GNSS and the efforts of the National Oceanic and Atmospheric Administration (NOAA) Space Weather Prediction Center (SWPC) to aid the GNSS community in dealing with these effects.

Joe has invited me to speak at the upcoming Space Weather Workshop in Boulder on May 2nd.  I'll be presenting some of the work I've done integrating their near real time total electron count data into our tools.  I'll be showing a sample application I built that shows the near real time navigation error over the continental United States.  The navigation error at each grid point includes satellite ephemeris and clock errors as well as ionospheric errors calculated from the data available from NOAA.  The data NOAA provides is very useful, but it's derived from one perspective only: that of looking from the ground to space.  This new C/NOFS satellite  will help us measure from a different perspective - from outside of the tub - opening a whole new category of analysis and extending our ionospheric prediction capabilities.

Technorati Tags: agi,navigation accuracy,terrain,3D globe,fabric,cloud computing,space symposium,ice cream,monte carlo,basketball

Next week (April 7-10, 2008) the National Space Symposium is being held at the Broadmoor in Colorado Springs. As always, AGI will be there with all of our traditions - ice cream, Monte Carlo night (!) and basketballs! We'll also have something that you may have thought didn't exist - navigation accuracy analysis on terrain.

Yes!

By now, I'm sure you're aware that navigation analysis is not that easy - it takes a lot of data, thousands of calculations and there are many variables that need to be taken into account - including your surrounding terrain. Terrain affects your visibility to satellites, reducing the number of satellites you can track and decreasing your receiver's position accuracy.

Using a combination of our 4DX technology our Navigation Accuracy Library, our Terrain Analysis Library and our Dynamic Geometry Library, I've created an application that not only calculates your navigation error over terrain, but also displays it on a 3D globe.

The majority of engineers and analysts have known that terrain is very important to getting reliable navigation accuracy - but now the less geeky crowd is starting to become aware of it as well. And this group is big. So it's important to reiterate what has been done in the past, lest the newcomers start to re-invent the wheel. There's no sense in paying to create a technology that already exists, when you can get a validated and verified solution now and start working on the real problem! By the way, this application also calculates global accuracy and runs on a fabric of 20 computers in the cloud.

This application will be running at our booth (#402), alongside many other applications representing areas such as

• Space Superiority
• Space Exploration
• Space Mission Design and Operations
• Missile Defense

and many others. Stop by if your in the area. Contact me if you need a guest pass - I'd be happy to meet and show you around!

-Ted

The GPS error budget is a lot like your home monthly budget.  At home you have to pay for gas, electricity, cable, phones, food, Internet, garbage ... - sheesh! I could go on and on.  You add up how much you spend each month then see how painful the final total is.

GPS on the other hand is a somewhat less taxing provider; at least in the number of items that must be paid.  The GPS error budget lists the errors that you have to account for when calculating your receiver's position.  Some of these errors can be estimated, thereby reducing their affect (like coupons for your food budget), and others must just be paid outright (like the phones, cable, gas, etc)

For GPS the different errors are usually binned into different categories, such as Signal-In-Space (SIS), Atmosphere, Receiver, etc.  As you might expect, there are some differences of opinion as to which error goes into which category.  That doesn't matter for what we're discussing here though.  So, here's a typical error budget for GPS:

Note that the Ionospheric error results from mis-modeling by the receiver.  Also, some receiver's model tropospheric errors, others do not.  Caveat emptor.

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