Hunting mosquitoes from space
What do you do with an orbiting scientific satellite designed to measure the state of polar ice when it's moving over the equator?
There is a fascinating map showing the places on Earth where the upcoming Cryosat-2 mission will be making detailed observations.
As you'd expect, the measurement campaign is at its most intense over the Arctic and the Antarctic. The European Space Agency satellite has been equipped with an advanced radar altimeter to measure surface heights. It will record the rates of change in land and marine ice thickness very precisely.
But gaze across the map and you'll see plenty of locations with no ice at all, where Cryosat's instrument will still be busy gathering data.
For sure, we see ice fields at low latitudes, such as in the Himalayas (5) and in the Andes (2) - but in the middle of the Pacific? And in Central Africa?
All this illustrates some routine, unsung functions of running a space mission... and some quite intriguing ones, too.
The region in the Pacific (1) includes calibration zones. To make its measurements of Arctic sea-ice thickness, Cryosat has to see both the top of the ice and the top of the water (it's then a relatively simple calculation to get to the overall volume).
The calibration zone in the Pacific is where the performance of the Cryosat instrument over water will be checked out. The squares denote areas of historically low wave height. Try to avoid getting caught in a sail boat in these places as the wind tends not to blow that strongly that often.
By looking at a flat ocean surface in these places, the Cryosat team will learn more about the internal noise of their instrument, and that means they'll be better able to interpret the radar signals during the all important science observation phases.
In general, many of the purple squares you see on land in this map indicate observations for hydrology - using Cryosat to investigate lake and river levels. The classic example here, I guess, is the Amazon (3).
Cryosat's instrument should be an excellent tool to study the behaviour of water surfaces, and several scientific groups will use the spacecraft to observe, in particular, coastal locations - places where past generations of radar instruments have struggled to get the necessary resolution.
Cryosat should see detail at below the kilometre scale, on the order of a few hundred metres.
I draw your attention though to Africa (4). Some of the data here will go into developing a tool that is about as far from ice-monitoring as you could imagine: a model to forecast the risk of malaria.
The disease blights sub-Saharan areas [PDF 1 Mb] of this continent. Of the 800,000 or so deaths that result globally from malaria each year, about 90% of them occur in Africa and the vast majority of those deaths are in children under five.
A group of Spanish scientists have been working on a project to use radar altimetry to detect the presence of mosquito breeding grounds - the puddles and ponds of water where the insects lay their eggs.
Water has a very distinct radar echo.
If this information is tied to other data-sets, such as temperature and precipitation, it might be possible to produce risk infection maps for great swathes of Africa. The authorities could then take pre-emptive measures, including targeted spraying of insecticides.
It's a very novel application for radar altimetry data; but one which Mònica Roca, who's been working on the Malarsat Project, believes has great potential:
"The footprint area of radar is very big compared to other instruments. It is more than one kilometre square with the classic altimeter, and that doesn't give you the resolution to detect little puddles. Nevertheless, you have a lot of accuracy in the differences in receive power which means although you cannot say where the ponds are, you can say they are present. It's based on how much power you receive and the shape of this echo."
Cryosat's radar will have a far better resolution than the altimeters used in the project so far, such as the one on Europe's Envisat spacecraft.
However, Cryosat's very tight orbital path over the poles means it does not see locations at lower latitudes very frequently. A lot of change can occur in the time it takes for the satellite to come back over the same spot.
But the Spanish group hope at the very least to establish the principle of their malaria mapping technique.
If they can do that, then when radar technology with Cryosat performance is put on a spacecraft with more favourable orbital characteristics, the technique could really take off.
The European Space Agency's Sentinel-1 satellite, due for launch in 2013, is expected to be just such a platform.
All of this, of course, is an aside to Cryosat's main mission - which is to make detailed measurements of the state of Arctic and Antarctic ice.
If you look at a picture of Cryosat, you'll see its radar instrument has a double antenna arrangement on the underside of the spacecraft.
When the satellite is travelling over sea ice (light green colour in the map), it needs just the one antenna. When it's travelling over the edges of the continents (dark green), it goes into "interferometric mode".
By listening to the radar echoes with an additional antenna offset from the first by about a metre, the instrument can sense much better the shape of the ice below, returning more reliable information on slopes and ridges.
This is important for the study of Greenland and Antarctica, and gives Cryosat a unique ability to discern what is happening at the edges of the ice sheets. These are the locations where some of the biggest, fastest changes have been taking place.
Keep your fingers crossed for Cryosat. Its launch on a Dnepr rocket is timed for Thursday 8 April at 1357 GMT (1457 BST; 1557 CEST). After the failure in orbit of the American Icesat platform last year, the European mission will become the only dedicated ice mapper in space.
We should get at least five years work out of it.
US President Barack Obama is promising a budget to get Icesat-2 into space by late 2015.
To really understand climate trends you must have continuous, cross-calibrated, long-term data-sets. You don't get that if you have extended periods with no satellite coverage of key parameters.