1.1.4 Geophysical Coverage

Figure 1.15 ERS-1 image Aug. 30, 1992 Mt. Spurr, Southern Alaska (Copyright ESA, 1992)

The orbit selected for ENVISAT will provide a 35-day repeat cycle, the same as the ERS-2 mission. Since the orbit track spacing varies with latitude (the orbit track spacing at 60° latitude is half that at the equator), the density of observations and/or revisit rate is significantly greater at higher latitudes than at the equator. The flexible swath positioning in Image Mode greatly increases the potential temporal coverage frequency compared to ERS. Coverage is also affected by the different swath widths of IS1 to IS7. Table 1.2 below shows the repeat coverage capability as a function of latitude and incidence angle variation (note: only for descending tracks). If there are no incidence angle constraints, average revisit will be 7 days at the equator, improving to nearly every 2 days at 70° latitude.

ASAR will operate simultaneously with the other ENVISAT instruments. Figure1.16 below shows the swath positioning of ASAR together with AATSR and MERIS coverage. Overlap with AATSR is seen to be quite limited, but ASAR IS1 to IS5 and most of Wide Swath/Global Monitoring Mode coverage falls within the MERIS cover.

Figure 1.16 Comparative simultaneous coverage of ASAR Image (red), Wide Swath - Global (orange), AATSR (violet) and MERIS (yellow).

The ENVISAT Swath and Orbit Visualisation (ESOV) software provides visualisation of the ENVISAT orbits, instrument swaths and ground station visibility. It is a free tool available to any user involved in ENVISAT data acquisition planning.

For an in-depth discussion on wide area coverage, see the section "Wide Area Coverage and Frequency of Coverage." 1.1.5.3.