If the time is prefixed by an A , data are from an ascending arc traveling from bottom right to top left. Conversly an arc time prefixed by a D descends from top right to bottom left. As data take around 2-4 hours to reach SOS from the satellite, some data on the map may not correspond to the date indicated at the top of the chart. Points on adjacent tracks are around 100 minutes apart. Ice extent coverage plots may be supplied on request for both areas.
Every image map produced is accompanied by a text summary.
Summaries are generated from review of up to 11 seconds of altimeter data, covering around 75km. The median values in the data stream are recorded and output to a text file. In the case of the Daily service all valid 11 second records are written to a file which can be examined the following day via the user's dedicated WWW page. Wave period and direction are measured 250km to the right of the altimeter track. It is important to point out that the instrument on its own cannot distinguish direction, only orientation, i.e. a 180 degree ambiguity.