Over the coming months we are going to use all the detailed data gathered in the field to guide our analysis of thousands of satellite images which have been acquired over the ice sheet surface during the last two decades.
A few satellites are particularly useful to us. One of these is The European Space Agency’s Sentinel-2A, which carries an optical sensor and was only launched late last summer. Sentinel-2A offers a 10-metre ground resolution in the visible parts of the spectrum (think red, green, blue – what your eyes can see) and re-visits the same place on Earth at least every couple of weeks.
The last time Sentinel-2A went whizzing over our field site was on Monday 11 July, less than 24 hours before the first field team put in to camp. In the picture below we can see there are no large patches of snow left, just lots of bare ice, with lots of darker patches which could contain algae, black carbon, mineral dust, cryoconite …
The scale of the ice sheet surface that the team are camping on is intimidating. The ridges to the north-west of the camp could be several metres high, whilst to the south there are crevasse fields and supraglacial streams which rush water down-glacier into vast, tumbling moulins. Our biggest tents for the labs and cooking, which are about 7 metres in diameter, might just appear on the next Sentinel-2A image in a couple of weeks as two tiny orange specks amidst a sea of white and gray – we’ll have to wait and see!
In the meantime these 10-metre images are invaluable in letting the field team know where they should focus sampling. They are currently staking out an Ice Surface Observatory somewhere close to the suggested one marked in the picture above. In this ISO they will take a variety of measurements of algae, black carbon and surface albedo.
The ISO will be at least 500 m by 500 m, which is about the spatial resolution of two other important satellite sensors: MODIS on NASA’s Terra, which has 500 m resolution, and the OLCI on ESA’s new Sentinel-3A satellite. MODIS has been gathering data over the ice sheet every day since 2000 whilst OLCI went into orbit earlier this year and will also give daily data but with even more information about changes in reflectivity in the visible and thermal parts of the spectrum than MODIS.
We’ll be using all this satellite data over the coming months and years to understand exactly how the processes we are studying at our field camp up-scale to the rest of south-west Greenland and the whole ice sheet. The field measurements are going to be essential to interpreting what the satellites are telling us!
Research Associate on BLACK and BLOOM. I work on upscaling our field measurements to ice-sheet-wide scales using satellite data and regional climate models.