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2nd May 2010
GPS - Where in the World Are We?
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Where in the world am I? We're looking at the science of the Global Positioning System, or GPS, this week. We find out how satellites can tell you your location, as well as communicate with the bossy little box that tells you which way to drive. We discover the potential for "spoofing" GPS with a false location, and how this might be the future of cyber-terrorism as well as explore the cosmic reference frame that the satellites themselves rely on. In Kitchen Science, we get back to basics and locate ourselves using a map and compass! Plus, the first amphibian genome helps to fill the vertebrate family tree, we meet the colourful fish that shine a light on evolution and find out how a technique developed to study eye disease can help find art forgeries.
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News
An analysis of the genome of the Western Clawed Frog, Xenopus tropicalis. was published in the journal Science this week, marking the very first amphibian genome sequenced...
A group of colourful fish living on Caribbean coral reefs have shed light on how species evolve in the oceans.
A technique developed to take three dimensional, real time images of the retina is also useful for detecting evidence of fraud in paintings, according to research published in the journal Accounts of Chemical Research this month...
The world is still losing biodiversity at an alarming rate despite world leaders promising in 2002 to cut the rate of loss by 2010. That’s the stark warning from a paper published in the journal Science this week by a large team of international researchers.
Questions

Will an increase in GPS tech mean more satellites?
More people using GPS won't require more satellites, just like more radio listeners doesn't mean you need more radio transmitters, or more bums on seats in an auditorium doesn't mean you need more members in an orchestra. However, there will soon be more positioning systems, when the Galileo constellation launches. Galileo is an EU/ESA project to enhance and back up GPS.

How popular is GPS for finding your car keys or remote control?
I've not heard about GPS isn't the best technology for this sort of application, as it doesn't penetrate too well inside buildings.
However, there could well be domestic applications of GPS that we're just not aware of! Please let us know if you know of any...

Can divers use GPS whilst underwater to navigate through the water?
We put this to Professor Todd Humphreys:
Todd - Divers can't use GPS. It’s because the high radio frequencies used for GPS just bounce off the surface of water. And so, divers will have to resort to other means - sonar or other techniques - for navigating beneath the water surface.
Ben - Helen, you're a regular diver. How do you find out where you are?
Helen - Well, we have used GPS when I've been doing things like underwater surveys. What you can do is tie the GPS to a buoy on the surface and drag it along behind you. Then you can download basically where you've been. You can track your path and match that up with what you were looking at when you were underwater.

Why do we use satellites for positioning instead of ground based methods?
We put this to Professor Todd Humphreys:
Todd - Well in fact, the early systems were ground based. There was the LORAN (LOng RAnge Navigation) system developed around the second World War that worked faithfully for many years and is still in use in some parts of the world. The trouble is that GPS enjoys great advantages over these ground based systems. It’s got global coverage and its signals aren’t distorted by the local topography. So it’s just been a question of success. GPS has line of sight global signals.

Can the US limit GPS?
We put this to Professor Todd Humphreys:
Todd - Well, it’s important to recognize that the US has a strong incentive to ensure that GPS is reliable, and that’s because a good deal of the world economy depends critically on GPS, especially for timing. So, any military initiated or US initiated denial of civilian GPS would most likely be a surgical pinpoint denial in some military area of operations. It’s possible but it’s very unlikely because the US has such a strong incentive to make sure everybody understands GPS can be counted on.
Ben - As a blanket thing doesn’t civilian GPS only work up to a certain altitude?
Todd - Well yes. Civilian GPS receivers are required to carry inside themselves certain checks against going too fast and going too high so that in the case that they were strapped to some intercontinental ballistic missile, they would fail to work. So that’s one way that the US is trying to prevent unauthorised use of GPS in a various purposes.
Ben - But obviously, assuming we’re not strapped to an intercontinental ballistic missile, we can still use it to find out where we are to go treasure hunting and to make sure we know where we are on a map.
Todd - That’s right. All of those good activities!
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Interviews
The Lancet has published a study into the benefits of looking at your genome to help personalise your medicine. Dr. Euan Ashley from Stanford University School of Medicine joined us to explain more...
How does the GPS in your car actually work? And what does the future hold for GPS? Meera went to meet Dr Chaz Dixon and Colin Lee to find out more.
Professor Todd Humphreys explains how it may be possible to intentionally fool your GPS into thinking you're somewhere else...
Chopo Ma explains the Cosmic Positioning System used to locate our satellites...
QotW
If you're driving towards a radio mast - does the music you're listening to get doppler shifted? Would there be a difference in the tone or tempo?
Alternatives being LORAN and DECCA, still used in places around the world. Has advantages and disadvantages over GPS, but requires training to use. Th...
- 1st May 10
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