Small satellites keep up their oil watch
The Gulf oil slick is a situation where access to satellite data is absolutely essential to the strategy for dealing with the problem.
Leaving aside the maritime communications and navigation for a moment, it is the fleet of international Earth observers flying over the region that are providing the day-by-day update on the scale and movement of the spill.
As is normal in such cases, signatories to the International Charter [on] Space and Major Disasters have made their satellites available to the US authorities, to provide them with the space-borne data they need to manage the crisis.
In this instance, that means the National Oceanic and Atmospheric Administration (Noaa), and the USGS - the US Geological Survey.
Indeed, it was the USGS that triggered the charter on this occasion on behalf of the US Coast Guard. It was the 17th activation of 2010. There have been two further activations since the Deepwater Horizon rig caught fire on 21 April (GMT).
It's not clear how much oil has gushed free. It's at least 23 million litres, more than half the amount the Exxon Valdez tanker spilled in Alaska in 1989; Noaa and other experts believe it's actually substantially more than that.
Radar satellites like Europe's mighty Envisat platform have been especially useful in tracking the spill. Radar sees through cloud and works day and night.
More than that though, the presence of oil in the water works to flatten the surface somewhat and radar can sense this effect.
It was data from Envisat this week which suggested the oil had now entered the so-called Loop Current, a powerful conveyor belt that flows clockwise around the Gulf of Mexico towards Florida. The obvious worry here is that the pollution could now travel much further afield, even up around Florida and up the eastern seaboard.
This is not to say satellites that view the Earth at other wavelengths, in the infrared and optical, have not been playing their part.
The UK's contribution in this area has, in large part, been exercised through the Disaster Monitoring Constellation (DMC) which is managed from Guildford.
The DMC consists of six small imaging satellites that see the planet at resolutions between 4m and 32m, across an ultra-wide 600km-plus swath.
The constellation's strength is its fast return over one location. Clouds permitting, the sextet can build a map the size of Europe in just five days.
The DMC knows the Gulf region very well, having provided important flooding data in the aftermath of Hurricane Katrina in 2005.
Its cameras are particularly well suited to see changes in vegetation. After all, that is the "day job", if you like, for these satellites. When they're not on disaster duty, they perform a lot of "precision agriculture", mapping crop growth to advise farmers where exactly in their fields they should be applying fertilisers.
The USGS has asked if the DMC satellites can continue to image the Gulf region in the weeks ahead to see where oil comes ashore. The brown ooze from the spill has already started to coat the marsh grasses of Louisiana's and Mississippi's wetlands.
DMC images collected over the coming days will be compared with the "reference data" held in the archives to determine the locations of pollution hot-spots, the places where urgent clean-up is required.
Dave Hodgson is the managing director of DMC International Imaging Ltd (DMCii), which operates the constellation:
"We're tracking the slick but we're also imaging a lot of the coastline. Because we know what the vegetation looks like normally, we will see changes straightaway. What usually happens is that our data gets digitised into Geographical Information Systems layers, and then they go to all sorts of agencies and departments. We image in strips. On each orbit, we can take an image of somewhere between about 600km and 3,000km. For example, we can image an area the size of the UK and part of northern France every time we pass over, which is once every five days with a single satellite. With five satellites, you can image that area every day."
The Gulf situation could go on for some time. I notice a top BP executive was quoted on one of the American TV networks on Friday as saying that in the worst-case scenario, the leak could continue for months, until a new well being drilled to cap the flow permanently could be finished.
The DMC consists of satellites belonging to the UK, Spain, Algeria, China and Nigeria; a Turkish satellite is no longer operational after finishing its mission.
The constellation will be boosted at the end of the year by the addition of a seventh platform, NigeriaSat-X. NX, as it's sometimes called, is set to fly in October. And it'll be joined on its Dnepr rocket by an even more capable machine for Nigeria called NigeriaSat-2.
This also will do some DMC work.
All the spacecraft come out of the small satellite specialist Surrey Satellite Technology Limited (SSTL).
The company is not resting on its laurels, however, and is looking to push the capability of its next generation of platforms.
The aim is to develop a small radar satellite within the next few years.
That's a challenge because you need a lot of power to operate a radar instrument. Access to kilowatts is not a problem if you're an eight-tonne behemoth like Envisat; it is a big problem if you're a 100kg, 60cm cube like a DMC satellite.
The interesting news out of SSTL is that its engineers think they now know how to make a small radar satellite.
Watch this space.
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