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1.1.4 Geophysical Coverage

The RA-2 and MWR are Nadir-pointing instruments in continuous operation around the whole orbit. This provides global along-track sampling up to the latitude limit of 81.5 degrees N/S.


The RA telemetry provides 18 range measurements per second which corresponds to an along-track sampling interval of about 400m. Over the ocean it is common to average 20 of these measurements to give a sampling interval of 1.1 seconds or about 8km. The Altimeter is essentially a 1-dimensional instrument: the concept of a swath-width does not apply.


Across-track sampling is determined by the Orbit pattern. ENVISAT will operate with a 35 day exact repeat cycle of 501 orbits with an inclination of 98.5 degrees. This gives an across-track sampling of 80km at the equator. The across-track spacing reduces at higher latitude. This orbit pattern has sub-cycles of 3 days and 17 days, providing global coverage, with correspondingly coarser sampling, at these intervals.


An example of the coverage provided by the RA2 over the Mediterranean region is shown in Figure1.10 .




The MWR is also a nadir-viewing instrument which provides continuous along-track sampling. Again the concept of a swath-width is not applicable. The field of view has a 20km diameter at the Earth's surface and the measurement represents an average over this footprint. The global across-track sampling is as described for the RA above.



Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry