Page 87 - Digital Analysis of Remotely Sensed Imagery

58 Cha pte r T w o

single panchromatic camera that collects data over 0.45 to 0.85 μm at
a spatial resolution of 0.8 m. The camera is able to operate in one of
three modes: spot, paint brush, and multiview. In the first mode,
strips of imagery are obtainable on either side of the satellite track in
the north-south orientation. In the second mode, the camera is tilted
to increase the standard swath width of 9.6 km (NRSA, 2007). In the
last mode the same ground is imaged 3 times at different viewing
angles to acquire a stereoscopic coverage. Lacking multispectral
bands, Cartosat-2 data are more suited to mapping than monitoring
and detection applications.

2.4.5 WorldView
This program consists of two commercial satellites, WorldView-1 and
Worldview-2. The first satellite was launched into a sun-synchronous
orbit 496 km in altitude on September 18, 2007. It has a period of
94.6 minutes with a 10:30 a.m. descending node. The payload of this
satellite is a panchromatic camera only. It captures data of a 0.50-m
nadir spatial resolution at 11 bits of quantization, covering a swath
width of 16 km (Table 2.23). This resolution degrades to 0.59 m at the
2
viewing angle of 25°. In total, 500,000 km of ground area can be sensed
by the satellite in a single day. Similar to Cartosat-2, WorldView-1
does not record multispectral data. What distinguishes WorldView-1
from other satellites is its agility in tilting the scanning mirror. It can
be tilted over a wide range of angles rapidly to retarget the ground in
order to image it stereoscopically. Another improvement of the
satellite is its geolocation capability that is accurate to 7.6 m CE90 at
nadir without ground control. This accuracy is improved further to
<3.5 m with ground control. The revisit period can be shortened to 1.7
days at 1-m ground sampling distance (GSD), or 5.9 days at 25° off
nadir. These features of WorldView-1 imagery make it suitable for
cartographic applications, defense, and national security, instead of
general land use mapping, and environmental monitoring.
The second satellite in this series, WorldView-2, is anticipated to be
launched into a sun-synchronous orbit at an altitude of 770 km in late
2008. Apart from the same one panchromatic band as WorldView-1, it
is able to capture four multispectral bands at 1.8 m. Furthermore, it will
also contain four new bands of coastal, yellow, red edge, and NIR-2
(Table 2.23) (Krebs, 2007). All data are quantized to 11 bits. The ground
swath is 16.5 km at a geospatial accuracy (CE90) of 10 to 13 m without
ground control. This accuracy improves to 5.5 m with ground control.
Revisit frequency (to 40° latitude) varies between 1.1 days at 1.0 m
GSD to 4.2 days at 0.52 m GSD. Major applications of WorldView-2
data include mapping and updating of maps at a scale up to 1:2000,
production of high accuracy DEMs, as well as other applications
similar to other very high resolution satellite data, such as agriculture
and forestry, oil and gas pipeline monitoring and exploration,
municipal and land planning, and so on.