Page 67 - Digital Analysis of Remotely Sensed Imagery

40 Cha pte r T w o

resolution of 72 m and a swath width of 146 km. LISS-II has two
separate imaging sensors, LISS-IIA and LISS-IIB at a spatial resolution
of 36.25 m each. Jointly, they provide a composite swath width of
146.98 km. This first generation of sensors contains four spectral
bands, three visible and one NIR (Table 2.12).
Launched on December 28, 1995 and September 28, 1997,
respectively, IRS-1C and IRS-1D represent the second generation of
the IRS series of satellites. They were designed as follow-ons to the
first generation of IRS-1A and IRS-1B satellites, with an enhanced
resolution and capability. IRS-1C has a near-polar, sun-synchronous
orbit at an altitude of 817 km at the local north-to-south equatorial
crossing time of 10:30 a.m. (Table 2.12). The satellite completes about
14 revolutions around the Earth per day (NRSA, 1995). Each
successive orbit is shifted westward by 2820 km at the equator. There
is a distance of 117.5 km between any two adjacent paths at the
equator. It takes 24 days for the satellite to cover the Earth completely.
The payload of IRS-1C and –ID consists of three sensors: one
panchromatic (PAN) camera, one LISS-III sensor, and one Wide Field
Sensor (WiFS) (Table 2.13). All the three sensors use pushbroom
scanning to ensure a high geometric fidelity. The PAN camera can be
rotated by up to 26°, reducing the revisit period to only 5 days.
Through this rotation it is possible to acquire stereoscopic images.
Recently, the IRS program was expanded to include Resourcesat-1,
launched on October 17, 2003. This satellite followed the ground
track of the IRS-1C satellite. Its payload is similar to that of IRS-1C
and IRS-1D satellites, namely, LISS-III, LISS-IV and Advanced WiFS
(AWiFS). LISS-III is identical to that in the previous satellites. The
high resolution LISS-IV sensor operates in either of two modes:
multispectral or monospectral. In the multispectral mode, all three
visible and near-infrared (VNIR) spectral bands cover a swath width
of 23 km within a total swath of 70 km. In the monospectral or
panchromatic mode, a single band covers a full swath of 70 km at a
spatial resolution of 5.8 m. AWiFS operates in four spectral bands
(Table 2.13). Its twin cameras are tilted by 11.94° from each other, each
covering a swath of 370 km on the ground. Specifically designed for
agricultural applications and Earth resources, both images have a
nadir resolution of 56 m with a 5-day revisit period.
Closely following the design of Landsat sensors, early IRS satellite
data share a striking similarity in their properties to Landsat MSS and
TM. The designation of bandwidth of IRS-1A and IRS-1B bears a
remarkable resemblance to that of Landsat MSS imagery. Besides, the
spatial resolution (73 m) and swath width (146 km) are both very
similar to, but slightly inferior to, those of MSS. Although the spatial
resolution was halved to 36 m later, it is still coarser than the 30 m of
Landsat TM. Because of these uncompetitive features, LISS-I and
LISS-II data have found limited applications outside India. This fact
is due partly to the absence of ground stations to receive IRS data