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.
Table 1.2 Average revisit frequency per 35-day orbit cycle as a function of latitude and incidence angle variation to illustrate ASAR revisit time capability (only for descending path)
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." 184.108.40.206.