583
sacrifice the swath coverage. If we wish to monitor certain dynamic events on the
ground (e.g. natural disasters), we need to have high revisit frequency and thus have
to opt for moderate spatial resolution sensors. For example IRS AWiFS sensor has
coarse resolution of 56 m but has a large swath (370 km) and a revisit time of 3–5
days. IKONOS has a very high spatial resolution of 1 m but it has its swath restricted
to only 11 km.
Figure 19.2 explains the impact of the spatial resolution on the quality of the
image. Figure 19.2a shows the images of the same ground area, taken by sensors of
different spatial resolutions (56–5.8 m). The area shown in the image is the coastal
town of Hazira, Surat district of Gujarat state, western coast of India. The images
shown in Fig. 19.2a are the AWIFS image (56 m), Landsat TM (30 m), LISS-III
(23 m) and LISS-IV (5.8 m). We can see as the spatial resolution increases from 56
to 5.8 m, the sharpness of the image increases and we can see finer details. We cannot zoom a given image beyond a certain limit in order to see much more details,
instead we need to use images with higher spatial resolution. Figure 19.2b shows
the LISS-IV image (same as in 19.2a) and the zoomed LISS-IV image of its small
portion and Cartosat-1+ LISS-IV merged image (2.5 m effective resolution) of the
corresponding area. One can see that the zooming of the LIS-IV image has led to
blurring (Fig. 19.2b) and does not help in extracting further details from the image.
Whereas, much larger details are seen in the corresponding 2.5 m (cartsat-1 +
LISS-IV merged) image. Jetties and the industrial installations/constructions can be
clearly seen at the coast, adjacent to the red mangrove patch in the 2.5 m image
which is not clearly seen in LISS-IV (5.8 m) image.
The level of information extraction (in terms of the details) and the scale of maps
which can be prepared from the satellite images depend on the spatial resolution
(Ajai 2004). Global/Regional level maps (1:1–5 million scale) on various themes
such as land use/land cover, geomorphology, vegetation, water, mangroves etc. can
be prepared from satellite images having 200 m–1 km spatial resolution. National/
state level mapping (1:250,000 scale) will require satellite images with 70–100 m
resolution. Maps on 1:50,000/25,000 scale can be prepared using satellite images of
(20–40 m)/(10–15 m) spatial resolution. Whereas detailed level thematic mapping
on 1:4,000–10,000 scale will require satellite data of 0.5–5 m spatial resolution
(Ajai 2004).
19.5 Mangrove Inventory
One of the basic information required for conservation and management of mangrove ecosystem is the spatial inventory of mangrove cover, its type and canopy
density. The physical conditions and harsh environment prevailing in and around the
Fig. 19.2 (continued) resolution of 2.5 m. Zooming of LISS IV image has led to blurring and does
not provide any further. Much more details are seen in the corresponding 2.5 m image. Jetties and
industrial installations/built up area are clearly seen near the coast, adjacent to the red mangrove patch
19 Mangrove Inventory, Monitoring, and Health Assessment
sacrifice the swath coverage. If we wish to monitor certain dynamic events on the
ground (e.g. natural disasters), we need to have high revisit frequency and thus have
to opt for moderate spatial resolution sensors. For example IRS AWiFS sensor has
coarse resolution of 56 m but has a large swath (370 km) and a revisit time of 3–5
days. IKONOS has a very high spatial resolution of 1 m but it has its swath restricted
to only 11 km.
Figure 19.2 explains the impact of the spatial resolution on the quality of the
image. Figure 19.2a shows the images of the same ground area, taken by sensors of
different spatial resolutions (56–5.8 m). The area shown in the image is the coastal
town of Hazira, Surat district of Gujarat state, western coast of India. The images
shown in Fig. 19.2a are the AWIFS image (56 m), Landsat TM (30 m), LISS-III
(23 m) and LISS-IV (5.8 m). We can see as the spatial resolution increases from 56
to 5.8 m, the sharpness of the image increases and we can see finer details. We cannot zoom a given image beyond a certain limit in order to see much more details,
instead we need to use images with higher spatial resolution. Figure 19.2b shows
the LISS-IV image (same as in 19.2a) and the zoomed LISS-IV image of its small
portion and Cartosat-1+ LISS-IV merged image (2.5 m effective resolution) of the
corresponding area. One can see that the zooming of the LIS-IV image has led to
blurring (Fig. 19.2b) and does not help in extracting further details from the image.
Whereas, much larger details are seen in the corresponding 2.5 m (cartsat-1 +
LISS-IV merged) image. Jetties and the industrial installations/constructions can be
clearly seen at the coast, adjacent to the red mangrove patch in the 2.5 m image
which is not clearly seen in LISS-IV (5.8 m) image.
The level of information extraction (in terms of the details) and the scale of maps
which can be prepared from the satellite images depend on the spatial resolution
(Ajai 2004). Global/Regional level maps (1:1–5 million scale) on various themes
such as land use/land cover, geomorphology, vegetation, water, mangroves etc. can
be prepared from satellite images having 200 m–1 km spatial resolution. National/
state level mapping (1:250,000 scale) will require satellite images with 70–100 m
resolution. Maps on 1:50,000/25,000 scale can be prepared using satellite images of
(20–40 m)/(10–15 m) spatial resolution. Whereas detailed level thematic mapping
on 1:4,000–10,000 scale will require satellite data of 0.5–5 m spatial resolution
(Ajai 2004).
19.5 Mangrove Inventory
One of the basic information required for conservation and management of mangrove ecosystem is the spatial inventory of mangrove cover, its type and canopy
density. The physical conditions and harsh environment prevailing in and around the
Fig. 19.2 (continued) resolution of 2.5 m. Zooming of LISS IV image has led to blurring and does
not provide any further. Much more details are seen in the corresponding 2.5 m image. Jetties and
industrial installations/built up area are clearly seen near the coast, adjacent to the red mangrove patch
19 Mangrove Inventory, Monitoring, and Health Assessment