Figure 1-8.—Data coverage on successive orbits of a polar-orbiting satellite.

Figure 1-8.—Data coverage on successive orbits of a polar-orbiting satellite. polar-orbiting satellites circle the earth at a much lower altitude (about 850 km), they have the advantage of photographing clouds directly beneath them at relatively high resolution. Although nearly every environmental satellite provides both infrared and visual imagery, polar-orbiting satellites are better suited to gathering imagery from the high-latitude and polar regions. They also provide imagery as they cross the equatorial regions. This makes them extremely well suited for oceanographic applications where slow changes in water temperature are adequately tracked by only two or four images a day. The width of the usable image from a polar- orbiting satellite is a function of the satellite’s altitude. The average swath width is about 2700 km (1500 nmi). Polar-orbiting environmental satellite orbits are planned so that the usable image area overlaps slightly. Figure 1-7 shows a typical TIROS-N satellite, while figure 1-8 shows the area covered by usable imagery on successive orbits of a polar-orbiting satellite. As of this writing, NOAA 12 (TIROS-ND) and NOAA 14 (TIROS-NJ) are the two fully operational polar-orbiting satellites in the TIROS-N series. A new series of polar-orbiting satellites will be launched by the spring of 1998, and will be referred to as NOAA- POES (NOAA-Polar-orbiting Operational Environmental Satellite). Table 1-1 compares various characteristics between geostationary and polar- orbiting satellites. Table 1-1.—Geostationary Versus Polar-orbiting Characteristics 1-7