Evaluation Question 1

What are some of the differences between POES and GOES that make observations from polar orbiting satellites unique? (Check the boxes for all answers that apply, and leave those that do not apply unchecked. Then click DONE.)

	a) The overlapping of POES orbits allows POES to view a given location at low latitudes more frequently than GOES.
	b) One POES can provide global coverage every 12 hours whereas GOES observes a fixed region at higher intervals.
	c) POES spacecraft are placed into sun-synchronous orbit, circling the earth once every 101 minutes and viewing a location once every 12 hours. In contrast, GOES views a fixed portion of the earth at more frequent time intervals.
	d) A microwave sensing capability onboard POES allows for observation both into and through clouds.

Discussion

One very important difference between GOES and POES is the frequency with which each system observes any given point on the earth. One POES completes 14 orbits each day, with each orbit advancing toward the west in synchronization with the sun (15 degrees per hour or 25.2 degrees per 101-minute orbit). One POES can therefore view a location at least twice each 24-hour period (once ascending from south to north, and once descending from north to south). More frequent observations are available at higher latitudes where POES orbits overlap. This overlap may result in as many as five to seven observations per day over a given location with a single satellite. Since GOES are fixed with respect to a point above the equator, viewing frequency is a function of how the particular observing instrument is designed to scan, and not its orbit.

a) is incorrect for two reasons. First, the overlapping of orbits occurs at high latitudes, but not at low latitudes. And second, even with the overlapping of POES orbits, GOES routinely observes a given area much more frequently.