Remote sensing satellites use two types of orbits:
|The map shows the coverage of the TOPEX/Poseidon
radar altimeter, but all polar orbiting
satellites would show a similar geometry. TOPEX
has a 10 day repeat cycle, with 127 compete orbits. Each
orbit has an ascending (odd numbers) and a descending
(even numbers) portion, numbered from 1 to 254. The
coverage of all 254 passes is indicated with the gray
color, with the first eight highlighted.
Note the lack of coverage for high latitudes in both hemispheres, determined by the orbit's inclination.
Track width is the area directly beneath the satellite ("nadir") and on either side which is imaged on each pass. Greater track width allows greater coverage, but the geometric distortion at the edges of the track increases because of the earth's curvature. If track width is decreased for greater geometric precision, more orbits will be required for complete global coverage, which decreases the time between coverage.
Each orbit of a polar orbiting satellite will have an "ascending" pass when the satellite moves northward toward the equator and then into the northern hemisphere, and then a descending pass on the other side of the word when then satellite moves southward. Because of the geometry, one of the passes will occur during daylight hours and the other will be during the night because it occurs on the opposite side of the earth with a very short delay.
Last revision 1/17/2018