1.1.4 Geographical Coverage
MERIS scans the Earth's surface by the so-called push-broom method. CCD arrays provide spatial sampling in the across-track direction, while the satellite's motion provides scanning in the along-track direction. The instrument's 68.5° field of view, nadir pointing, covers a swath width of 1,150 km. at a nominal altitude of 800 km.
MERIS products are available at two spatial resolutions:
· Full Resolution (FR) with a resolution at subsatellite point 300 m
· Reduced Resolution (RR) with a resolution at subsatellite point 1200 m
Product partition is performed by segments of 43.5 minutes for the MERIS RR, which consist of that part of the orbit for which the Sun zenith angle is below 80°. A MERIS RR segment corresponds to 17,400 km along track.
The MERIS FR segment corresponds to the same Sun illumination limitations as for the reduced-resolution mode; however, the acquired data is not necessarily contiguous.
For the purpose of distribution, the MERIS product is packaged in multiple of scenes of 1,150 km ×1,150 km for the reduced-resolution product; and in scenes of 575 km × 575 km or 296 km × 296 km for the full-resolution products.
RR scenes contain 71 × 71 tie points for an 1,150 km × 1,150 km image; FR-1 scenes contain 36 × 36 tie points for an 575 km × 575 km image; FR-2 scenes contain 18 × 18 tie points for an 296 km × 296 km image.
Only a part (called a “Child”) of a acquisition segment could be ordered.
MERIS's 68.5° field of view allows global coverage to be provided in two to three days, as required by oceanographic, land, and atmospheric investigations. See figure 1.5
Figure 1.7 - Global coverage