Carrying a Synthetic Aperture Radar (SAR), the images that Sentinel-1 will provide are particularly well suited for applications based on mapping sea ice. High-resolution ice charts, monitoring icebergs and forecasting ice conditions are examples of important application areas that are expected to benefit greatly from Sentinel-1, which is being developed by ESA in support of GMES (Global Monitoring for Environment and Security).
Developing the mission to meet the users' needs in a variety of application areas is of utmost importance. A major challenge for Sentinel-1 is to ensure that the satellite will yield data with the quality and timeliness that users truly need. It is not surprising therefore, that airborne campaigns play an important role in helping with the design of these missions as the experiments carried out simulate satellite data long before the actual launch of the mission.
"ESA is putting a tremendous effort into the design and implementation of the Sentinel-1 mission," says Malcolm Davidson, Sentinel-1 Mission Scientist. "While this effort might be invisible to future users of Sentinel-1 products, it is critical that we validate the modes of operation and quality of data products ahead of launch. The IceSAR campaign is allowing us to simulate Sentinel-1 radar images over ice well before launch in 2011, and better prepare for the mission."
Now one week into the IceSAR campaign, a few surprises are being revealed. Unexpectedly, there is a lack of ice – even where the campaign is being carried out near Longyearbyen in Svalbard, which is way above and Arctic Circle and only 10 degrees from the North Pole.
"It is unusual to have so little sea ice at this time of year," commented sea ice expert Wolfgang Dierking from the Alfred Wegner Institute (AWI), who is leading a team investigating better methods of characterising sea ice and the impact it has on climate. "This illustrates the importance mapping sea ice extent and conditions from space. In addition to the operational needs for high-resolution ice charts, in support of shipping for instance, we know that sea ice plays a major role in climate forecasting as it both acts as a blanket of insulation between the water and the atmosphere and, unlike open water, strongly reflects incident sunlight. Consistent information on sea ice conditions over large areas and over long time periods are required – which is exactly what the Sentinel-1 mission will bring."
A big help in locating sea ice has come from the radar satellite images from current SAR missions such as Envisat. Such 'radar maps' are now available operationally through the internet and provide a synoptic view of ice conditions around Svalbard. During campaign activities they are an integral part of the planning meeting held each morning with all the campaign participants.
The campaign will last about three weeks, but one week in and the first successful airborne acquisitions have already been made and processed on site. Irene Hajnsek from the German Space Agency DLR said that, "What impresses me most is the variety and clarity of the different sea ice structures visible in the radar images. The dual-polarisation C-band images we collected a few days ago and closely mimic those of the future Sentinel-1 mission show an amazing variety of different ice floes. The different shapes and sizes are clearly distinguished in the images because of their texture, and using both polarisations at the same time through the roughness shows up as colour. It is quite a challenge to collect and process data over flight legs of 150 km or more, but looking at these images I know we are on the right track."
The IceSAR participants include teams from the Alfred Wegner Institute, the Microwave and Radar Institute from the German Space Agency DLR and ESA, and despite the numbingly cold conditions the campaign will continue with a number of other airborne flights over sea ice in the coming days.
Malcolm Davidson | alfa
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