Using Satellites To Monitor Weather
Chris - The moon is our biggest natural satellite, but you work on artificial satellites. What is involved in making a satellite and getting it up there?
Maggie - The main thing I notice is lots of paperwork, because one of the difficulties in launching things into space is that you want it to succeed. You can't just go out and tinker with it, or if you do, it costs an awful lot of money like with the Hubble Space Telescope. What you're trying to do is make something bound not to fail. To do this you build in lots of redundancy. Also, rather than going for cutting edge technology, you try and use existing technology that is well known and established. Usually a consortium of people will get together. For example, I'm working on a project now with people from the James Webb Space Telescope, which is organised by NASA but this is a sub-system that's put together by ESA, the European Space Agency. We're building a detection system. One of the exciting things about these projects is that they work on a global scale. There are scientists all over the world working on the James Webb Space Telescope. What we'll do is build an instrument and put it through very rigorous tests.
Chris - What's it going to detect?
Maggie - The one on the James Webb is looking for infra-red and is looking out into space. Another system I'm working on looks at Earth rather than space. This is designed to look at wind speeds through the atmosphere.
Chris - How on earth do you see the wind because it's invisible?
Maggie - That's one of the beauties of the system. It uses the Doppler effect. This is just like ambulances get louder as they are going past. What we're actually doing is shining a laser beam through the Earth's atmosphere and it works in a similar way to RADAR. It's called LIDAR, because it's like a light RADAR. We pulse a UV beam and it bounces of particles in the atmosphere. As it bounces off particles, the light scatters and we pick up the return beam. This return beam is fair fainter than the one we send out. By looking at the Doppler shift, you can see a change in the wavelength and work out how the particle is travelling in the Earth's atmosphere. By looking at the time of the return, you can see whether it's close to the Earth's surface or high up in the atmosphere. For instance, if people fly kites close to the ground, it will travel at one speed. If you lengthen the string and it goes higher, the wind speed changes quite rapidly. This gives us a 3-D view of winds through the atmosphere.
Chris - I was just going to say, does it look at just one altitude, but presumably not. You can look at a whole lot of different heights.
Maggie - That's it. Just like with RADAR, you can look at different signals coming from different points in time. This means that you can look right from the ground where you get a ground return, which is the strongest signal, and then look at particles throughout the atmosphere.
Chris - How is this actually useful though? Do we know if this translates into better weather forecasts for example?
Maggie - Yes. It does two things. It does local short-term weather forecasting and so hopefully we can send this information to Michael Fish to get a better weather forecast for the future. It's also looking at long-term climate prediction. For instance we talk about global warming, but there are many models associated with global warming. You need data in order to verify them. This mission is set up to give global coverage of wind speeds through the atmosphere, and thereby able to verify these climate change models. So it's short term and long term data that we're getting.
Chris - So you're designing this probe. It then goes aboard a satellite and gets carried into space. When it gets up there, how does it actually get powered? How do these things actually work?
Maggie - It depends on what sort of orbit you're going into. Once it gets there, it's deployed and is contacted by telemetry, which sends signals to the satellite. The signals ask the satellite to deploy its solar panels. You can get some satellites which are powered by nuclear energy, but the sort of satellite we're setting up is actually solar.
Chris - And they never end up in the dark? Do they always have a supply of sunlight, or do they have batteries to back them up?
Maggie - They generally have batteries to back them up, especially during the launch when there's a period before the solar panels are deployed. Depending on the sort of orbit you put it in, you can tilt your solar panels so they're always facing towards the sun.