The coordinated ESA–NASA flight activities and orbital ground track of CryoSat on 17 April. The straight red and black thick line indicates CryoSat's ground track and the colour changes where the measurement mode switches to pass over the steep ice sheet margin. The dark green straight line shows the 15 April CryoSat track, with the yellow line indicating the NASA P-3 aircraft underflight. The white line shows the paths taken by the Twin Otter carrying the ASIRAS instrument and the green lines show the AWI aircraft carrying the electromagnetic sensor, which take measurements of the area for comparison.