Scanning the Sea from Space
Chris - Building an instrument to fly on board a satellite is a feat of precision engineering. It's got to be robust enough to withstand the launch, sophisticated enough to produce new science and - since you can't easily call out a repairman - very reliable.
Since a huge amount of environmental science now takes place onboard satellites, Planet Earth Podcast presenter Sue Nelson visited RAL Space at the Rutherford Appleton Laboratory in Oxfordshire. There she met Earth observation scientist Hugh Mortimer to find out how they ensure their space-based equipment is accurate...
Hugh - The Rutherford Appleton Laboratory has been sending instruments into space to measure sea surface temperature since the early '80s. That gives us a continual data record of temperatures which we can then use to identify trends within the climate and we can use then look at different aspects such as climate change and how the sea is warming up.
Sue - Now you're involved in an instrument that's going to fly on board a satellite for this.
Hugh - The instrument that we are calibrating is a large European Space Agency project. Within the next few years, it will be launched and operational and it will be providing data for the scientific community both for operational purposes, so for the Met Office for providing weather forecasts, because essentially, the temperature of the ocean really drives the weather that we get in Europe.
The other thing that we're trying to do is then use this data to look at climate change and climate records. So the instruments that we're developing and building here, we're then calibrating before it gets launched into space and therefore, we know precisely how accurate that instrument is at measuring sea surface [temperature]. We've just walked into the molecular spectroscopy facility and within this facility we have the ways and means of calibrating ground based instrumentation. We use spectrometers primarily to look at the differences in how light interacts with materials around us, both solid, liquids and gases. What we're doing is then using that information to give us, essentially, data on how much gas is present or the equalities of that particular gas. Here, in this laboratory we also have something called the SISTeR instrument, which is the Scanning Infrared Sea Surface Temperature Radiometer.
Sue - And SISTeR actually goes on board a ship doesn't it, the Queen Mary II.
Hugh - We're very privileged to have this collaboration with Cunard where we're able to put our instruments on the side of these really prestigious beautiful ships, where we can measure sea surface temperature in exactly the same way that the satellites measure sea surface temperature. From this we can then take the instrument that we know very well, that we've calibrated at the labs and then cross compare the sea surface temperatures as the satellite passes overhead of the Queen Mary II.
Sue - And how accurate have they been?
Hugh - About 10 milli Kelvin which is pretty accurate.
Sue - So, where do we go to see your instrument?
Hugh - Okay, we can go through to this laboratory over here.
Sue - Through another door here.
Hugh - And now we're in the heart of the spectroscopy facility itself. So, what we're looking at are two very high resolution spectrometers, one is used for measuring solid phase materials; aerosols, dust and the other one - a much higher resolution spectrometer - is about half a tonne of equipment, that's used to measure gases. We look at pure concentrations of materials such as methane, carbon dioxide, water vapour and then we can look at how the light interacts with those materials, those gases, to actually change the light as it passes through. So, the instrument in space looks at specific wavelengths of light. The spectrometers can break down those bands even further. Essentially they can look at different wave lengths across the spectrum. The wavelengths that the radiometer will be looking at, both the radiometer in space and the radiometer on SISTeR, they will be looking at very specific wavelengths while these instruments are able to measure different components, not only temperature but also how that radiation is affected by the gases and the materials it interacts with.
Sue - And the spectrometer is sort of like - I always think of it as like the work horse for space science and astronomy...
Hugh - Yeah, that's right. They really underpin a lot of the knowledge that we have about the world around us. It allows us to see in depth where our eyes can't view, essentially. They allow us to probe the interaction between radiation and the gases that you can't see with your eyes. Because these instruments work in the infra red, they get to understand the impact of how light absorbs thermal radiation and then how it emits thermal radiation. So essentially looking at the climate change effect, the climate greenhouse gases and how that thermal radiation is actually stored and then emitted in different wave lengths.
Chris - Hugh Mortimer from RAL Space. And you can hear a longer version of that report from Sue Nelson on the Planet Earth podcast. Follow the link on our website or find it at Planet Earth Online.