Page 76 - Digital Analysis of Remotely Sensed Imagery

48 Cha pte r T w o

Panchromatic images are acquired along the satellite track with a
base-to-height ratio of 1:0. In this forward-nadir-backward stereo
mode, a swath width of 35 km on the ground is covered at a spatial
resolution of 2.5 m (JAXA, 2004). This width rises to 70 km in the
nadir-only viewing mode. Through pointing the telescope sideway,
the normal revisit period of 46 days can be reduced to up to two days.
Stereoscopic PRISM data can be used to construct highly accurate
DEMs and to produce topographic maps of the world at a scale
<1:25,000.
AVNIR-2 is a visible and NIR imaging radiometer of four
multispectral bands at a spatial resolution of 10 m at nadir (Table 2.17).
In this position a strip of 70 km is scanned along track. The sensor can
be tilted cross track by up to 44° away from the nadir position either
way for quickly monitoring natural disasters, such as earthquakes,
fires, volcanic eruptions, and oil spills. However, the primary
applications of AVNIR-2 data are mapping of land covers and
environmental monitoring at the regional scale, very similar to Landsat
TM and SPOT data.
PALSAR is an L-band (1.27-GHz) sensor designed to succeed the
Synthetic Aperture Radar (SAR) sensor aboard the Japanese Earth
Resources Satellite-1 (JERS-1) satellite (refer to Sec. 2.6.1 for more
details) with improved functionality. This sensor is able to operate in
either high resolution mode or the ScanSAR mode. The former mode
is able to generate images at a spatial resolution of 10 m at a swath
width of 70 km. This conventional mode is intended for detailed
regional observations and repeat-pass interferometry. In the second
mode a swath width of about 250 to 350 km, depending upon the
number of scans, is covered. This mode extends the swath width of
conventional SAR images by three- to fivefolds, a feature particularly
useful for monitoring sea-ice extent and rainforests.

2.4 Very High Spatial Resolution Data
About a decade ago spaceborne remote sensing experienced another
trend, namely, the advent of very high spatial resolution satellite
imagery. Their spatial resolution is so fine that it is comparable to
that of airborne photographs. A few successful satellite programs
have recorded images with a spatial resolution on the order of meters
and submeters. So far more than twelve of them have become
available for digital analysis (Table 2.18). The majority of these
sensors record only a panchromatic band that is intended mostly for
cartographic mapping, even though environmental monitoring is
possible with the data. Acquisition of multispectral bands that are
usually numbered four for the purpose of detection is not the primary
objective for these satellites. Of these systems, some have been in
existence for nearly a decade, and others are still in the pipeline, to