Page 70 - Digital Analysis of Remotely Sensed Imagery

42 Cha pte r T w o

outside India, apart from the one in Norman, Oklahoma (Bakker,
1998). No established data vendors are selling IRS data.
Starting from the second generation of satellites, the IRS data
underwent significant improvements in their quality, with stereo
viewing capability added and revisit period shortened. The type of
data acquired has been diversified to include very coarse resolution
imagery for regional studies, and the spatial resolution of multispectral
bands has been refined to less than 10 m. These moderate resolution
data are able to fulfill the traditional applications (mainly natural
resources mapping) similar to those of Landsat MSS and TM data.
LISS-III data with a 23.7 m spatial resolution can complement data
from the aging Landsat 5 TM sensor. However, high resolution IRS
data will stimulate new applications. In particular, the 5.8-m resolution
PAN imagery with stereo capabilities is ideal for applications that
require spatial detail, and the coarse WiFS data are suited to monitor
vegetation over broad areas. Not only has IRS data quality been
enhanced, but also the means of data distribution and delivery has
been diversified. It is now possible to purchase IRS data from lead
data supply agencies, such as Space Imaging in the United States via
its Web site.

2.3.4 ASTER Data
The Earth Observing Satellites (EOS) program jointly initiated by
the United States and other countries heralded a new era in
spaceborne remote sensing. It triggered one of the three trends in
remote sensing data acquisition, namely, multiple sensors aboard a
single platform, each of which is designed to obtain data intended
for specialized applications, and all of which complement each
other. In this largest and most ambitious mission ever undertaken,
the flagship satellite is the Terra spacecraft launched on December
18, 1999. It has a sun-synchronous circular orbit, crossing the
equator at 10:30 a.m. local time (descending node). Terra has a polar
orbit 705 km in altitude. Its orbital path follows closely that of
Landsat 7 to ensure data continuity. Terra was later complemented
by another satellite, Aqua, launched on May 4, 2002. It crosses the
equator at 1:30 p.m.
The payload of the Terra satellite includes five state-of-the-art
sensors, each designed for a specific domain of applications
(Table 2.14). These sensors are called ASTER, MODIS, Clouds and
the Earth’s Radiant Energy System (CERES), Multiangle Imaging
Spectroradiometer (MISR), and Measurements of Pollution in the
Troposphere (MOPITT). The diverse data collected by these sensors
are excellent in studying the Earth’s radiation balance, including
the effect of heavier cloud cover on the amounts of solar radiation
absorbed by the planet, human-induced land cover and land use
changes, glacier volume, properties of the mid to upper atmosphere,
and the effects of volcanic activity on the atmosphere (JPL, 2004).