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IAPRS & SIS, Vol.34, Part 7, “Resource and Environmental Monitoring”, Hyderabad, India, 2002 
Table -I Spectral Characteristics of the four bands of IRS-1B 
  
  
  
  
  
  
  
  
LISS-1 
Band 1 2 3 4 
Central 485 555 650 815 
Wavelength (nm) 
Bandwidth (nm) 70 70 60 90 
Saturation Radiance, 16.888 | 17:564] 16645 16.972 
(mw em“ sr” um”) 
  
  
  
  
41 
It may be mentioned that the usefulness of the 
LISS-1 bands in studying the benthic biomass, 
yellow substance index etc. have been tested in 
the estuaries by Sudarshana er al. (1993). 
Therefore, the present study aims to use IRS 1B 
LISS-1 data with synchronous field observations 
to achieve the following objectives: 
(1) To quantify the area of submerged 
vegetation in Chilka lagoon in the 
time-space continuum. 
(ii) To study the radiance characteristics 
of submerged vegetation and its 
seasonal variability. 
2. DATA AND METHODOLOGY 
IRS-1B LISS-I (Linear Imaging Self Scanning 
Sensor) data (Path/row-20/54) for January 1995, 
April 1995,July 1996 and May 1998 along with 
synchronous field observations have been used in 
the present study. The satellite data were 
procured from the National Remote Sensing 
Agency Data Centre (NDC), Hyderabad. These 
data were geometrically rectified with the help of 
survey of India toposheet (1:250000) taking 
ground control point for positional accuracy and 
the image of Chilka lagoon was extracted from 
the full scene. The digital image analyses were 
accomplished using PC-based image analysis 
system with ERDAS software and IBM RS 6000 
image analysis system with EASI/PACE software, 
respectively available at the Training and 
Educational Activities Group, National Remote 
Sensing Agency (NRSA), Hyderabad and Regional 
Remote. . Sensing: . Service... Centre . (RRSSC), 
Kharagpur. 
Benthic biomass and yellow substance indices 
were computed following Sudarshana et al. 
(1993), 
Benthic Biomass Index: 
BBI = -0.3876 + 1.3338 log band-1 radiance 
Yellow Substance Index: 
YSI 2 -0.899 (band -1) — 0.429(band -2) 
+ 0.076(band-3) + 0.041 (band —4) 
387 
3. RESULTS AND DISCUSSION 
3.1 General Features 
Chilka is a shallow lagoon with an average depth 
of 1.7 m. Northern sector is observed to be the 
shallowest (0.20-1.73m) followed by central 
(0.70-2.80m) and southern (1.20-3.25m) sectors. 
Secchi depth is observed to be maximum in the 
southern sector while it is minimum in the 
northern sector. Salinity in the lagoon is observed 
to vary from almost fresh water (0.2°/00) in the 
northern sector to moderately high (22°/00) in the 
central sector. In addition to the spatial 
variability, the physico-chemical parameters show 
significant seasonal variability and are believed 
to be responsible for spatio-temporal variability 
of weed growth and decay. It is observed that 
Potamogeton pectinatus and Najas foveolata are 
ubiquitous and dominate over other species. 
Earlier Patnaik (1973) also reported that 
Potamogeton pectinatus (75.16%) was the most 
important weed of the lake followed Najas 
foveolata (14.23%) and Halophila ovata (7.12%). 
Spatial distribution of other species of submerged 
macrophytes are observed to be highly location 
specific. In the shallow and less saline (0.2-10.8 
9/90) northern sector, the species of submerged 
vegetation which are seen  abundantly are 
Potamogeton nodosus, Hydrilla verticillata, 
Vallisneria spiralis and Ceratophyllum demersum. 
In the moderately deep and relatively more saline 
(4-22°/00) central sector, the abundantly occurring 
species of submerged vegetation are Ruppia 
maritima, Gracilaria confervoidess, Halophila 
ovalis, Halophila beccarii and Gracilaria 
lichenoides. In the deeper and moderate saline 
(7.2-12°/00) southern sector, the. species of 
submerged vegetation occurring abundantly are 
also almost same as in the central sector. 
However, it has been observed that occurrence of 
the above species and their salinity tolerance 
varies from one season to the other. 
3.2 Characteristics of Submerged Vegetation 
Figures 2(a) and 2(b) respectively represents the 
Benthic Biomass Index (BBI) and Yellow 
Substance Index (YSI) of Chilka lagoon for 
January 1995 and July 1996. The red and yellow 
colour represent the areas of submerged 
vegetation in January 1995 (Fig. 2a). The red 
colour represents the areas of thick submerged 
vegetation while the yellow colour represents the 
sparse submerged vegetation. Figure-2b 
represents the YSI and delineates the submerged 
vegetation also July 1996 correspond to the 
period when the area of submerged vegetation was 
lowest (48.4 km?). The red colour in the Figure- 
2b represents the submerged vegetation. Thus, it 
can be stated that the submerged vegetation 
during July were mostly confined to the periphery 
of the lagoon and thick vegetated areas were 
along the north-western and southern sector of the