ABSTRACT

Rupam, K.; Ferrer, V.A., and Ramachandran, K.K., 2020. Bathymetry estimation using multispectral imagery over an inland water body – Vembanad Lake, Kerala, India. In: Sheela Nair, L.; Prakash, T.N.; Padmalal, D., and Kumar Seelam, J. (eds.), Oceanic and Coastal Processes of the Indian Seas. Journal of Coastal Research, Special Issue No. 89, pp. 126-131. Coconut Creek (Florida), ISSN 0749-0208.

The biological and biophysical characteristics of the nearshore and inland (estuarine) water bodies are mainly dependent on their bathymetry which also drives the coastal/estuarine hydrodynamics and other nearshore processes. The study of bathymetry in inland navigational backwaters of the coastal regions gain further importance due to the periodical dredging activities undertaken to maintain the required draft for navigation. The carrying capacity of the lakes gets affected due to sedimentation from the river inflow gradually altering the bathymetry. Conventional bathymetric soundings are highly time consuming and man power intensive which can be successfully augmented and made faster through remote sensing (RS) methods. The RS method can provide better spatial data compared to point-based measurements and also have the advantage of capturing temporal information. The present study explores the feasibility of retrieving bathymetry using satellite based remote sensing techniques for an inland coastal water body, aiming to provide synoptic inexpensive method for estimating and updating bathymetry data making it handy for coastal research and management. The study has been attempted in Vembanad Lake in Kerala, southwest coast of India. The ratio of the blue (450 - 515 nm) to the green (525 - 605 nm) wavelength of the Landsat satellite images as proposed by Stumpf was applied to generate the linear relationship between the reflectance and field measured depth information. The Kochi to Alappuzha National Waterway No. 3 bathymetry chart of the year 2005 is used as the in situ information for generating a site specific linear regression model which yielded a significant correlation coefficient of 0.753 (N = 707). The regression equation has been applied to generate the Satellite optical reflectance derived bathymetry map for the southern part of Vembanad Lake. The bathymetry obtained through this model has been validated with a set of independent depth sounding values (r2 = 0.92; N = 66). By and large the Stumpf model has been found helpful in recreating water depth using multispectral images in clear waters that permit proper light penetration. However, the present study has shown the potential of its application even in the inland water bodies where the light penetration is affected by a high concentration of suspended sediments and floating vegetation (water hyacinth).

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