JAPRS & SIS, Vol.34, Part 7, “Resource and Environmental Monitoring”, Hyderabad, India, 2002
lagoon. Nalabana Island , which was submerged
during July,1996 has been delineated in a better
way through YSI than the corresponding BBI
(figure not shown). Further, the emergent
vegetation/island vegetation (Somal Island in the
southern sector) is clearly delineated
(represented as yellow colour) and is distinct
from submerged vegetation in YSI (Fig. 2b) but
not in BBI. Therefore, .it, is- apparent «that
delineation of submerged vegetation is better in
YSI than BBI.
EERE: ET r6: OF CHILKA LAGOON DT: 29.01.1995
BENTHIC BIOMASS INDEX
——— SEE
ati ee mE aia
CHILKA LAGOON
YELLOW SUBSTANCE INDEX
IRS - 18 LISS X
00e 10-7-96.
À
Figure 2: a) Benthic Biomass Index (BBI), January
1995 b) Yellow substance Index (YSI), July
1996 of Chilka Lagoon
The area estimate for the four data sets show that
the areas covered with submerged vegetation
during January 1995, April 1995, July 1996 and
May 1998 were respectively 306.4km?, 313.9km?,
48.4km? and 151.7km?. Further, comparison of
January and April (not shown) images show an
enhancement and distinct spatial variability in the
coverage area of submerged vegetation. In
January, submerged vegetation areas were
388
confined to the periphery of the lagoon while in
April, maximum area of submerged vegetation
were observed along the north-western sector of
the lagoon. It may be mentioned here that the
increase in the area of submerged vegetation and
decrease in depth of water from January to April
are concomitant features and cause serious
inconvenience to the fishermen communities
inhabiting especially the north-western sector of
the lagoon.
The "area estimate distinctly show the large
interannual variability in the area of submerged
vegetation; the highest during April, 1995 and
lowest during July 1996. It is observed that the
growth of submerged vegetation takes place from
winter to pre-monsoon season followed by a
decay period from later part of pre-monsoon to
post- monsoon season. Despite the fact that
submerged vegétation in the lagoon undergoes
significant spatial and temporal variability
(seasonal as well as interannual), the feature
which is consistently observed throughout the
study period - is .the - presence of . submerged
vegetation along the periphery of the lagoon and
the extreme northern portion i.e. the confluence
of the riverine system with the lagoon.
3.3 Radiance Characteristics
Figure 3 presents the remotely sensed radiance
over submerged vegetation (Fig 3a) and shallow
water (Fig 3b). In both the cases, radiance values
in all the seasons are found to be maximum in
band-1 and then gradually reduce towards band-4.
However, the difference in magnitude of radiance
values are distinct with higher values in case of
vegetation "'free' :shallow ^ water" "area" and
comparatively lower values in case of submerged
vegetation. Thus, it may be inferred that presence
of submerged vegetation in a shallow water body
absorbs significant amount of radiation and
thereby" reduces'"the "reflected" radiance, ^ more
prominently in band-3 and band-4. It is also
observed that the difference in radiance values
between submerged vegetation and vegetation free
shallow water area is maximum in winter season
(January) and then it reduces with the approach of
pre-monsoon and monsoon season. This behaviour
of radiance characteristics can be attributed to the
turbidity of the lagoon water which was observed
to be lowest during winter and highest during pre-
monsoon and monsoon season (Mohanty and Pal,
2001).
