Water-bodies Mapping and Reservoir sedimentation

Bharath Reddy K Scientist/Engineer - SC

Water Resources Informatics Division National Remote Sensing Centre

02-Aug-2018

Water-body mapping using Remote Sensing

All the forms of water have very distinct signature in much of the electromagnetic spectrum.

These distinctive characteristics of water in visible, infrared and microwave regions of electromagnetic spectrum helps in the identification, extraction and mapping of water-bodies.

Absorption of water in vapour, liquid and solid states(green,red and blue)

Spectral Signature

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Water body reflectance in different spectral bands

Natural Colour composite Near Infra Red (NIR)

Blue Green Red

Monitoring the Surface Extent of Water Bodies

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The best wavelength region for discriminating land from pure water is in the near-infrared and middle-infrared from 740 - 2,500 nm. In the near- and middle-infrared regions, water bodies appear very dark, even black, because they absorb almost all of the incident radiant flux, especially when the water is deep and pure and contains little suspended sediment or organic matter.

Reference: Remote Sensing of the Environment, John R. Jensen (2007) Second Edition Pearson Prentice Hall

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Examples of Absorption of Near-Infrared Radiant Flux by Water and Sunglint

Black and white infrared photograph of water bodies in Florida

Black and white photograph with sun-glint

Water with sunglint

Water

Reference: Remote Sensing of the Environment, John R. Jensen (2007) Second Edition Pearson Prentice Hall

Effect of Sediment, Aquatic Vegetation & Turbidity of Multi-spectral images

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Case 1: Relatively clear water pond with little or no aquatic vegetation.

Case 2: Relatively clear water pond with substantial aquatic vegetation.

Case 3: Farm pond with turbid water and moderate aquatic vegetation.

Case 4: Pond inundated with aquatic vegetation and sediment build-up.

Microwave Remote Sensing its advantages and limitations in Water bodies mapping and monitoring

Imaging and Non Imaging sensors, basin differences

All weather observation capability

Very sensitive to water/moisture because it di-electric constant

The back-scattering is very sensitive to the top layer of vegetation because of the shorter wave length of C band.

Hence shallow water bodies with vegetation cover has degraded area estimate compared to that other waterbodies.

Reservoir Sedimentation and Capacity Loss Estimation

Many reservoirs built at a huge investment are under going rapid silting and loss of storage results in reduction of economic life of reservoir

Study on Indian reservoirs show that annual siltation rate is 1.5 to 3 times the designed rate

Types of sediment loads

Reduction in the storage capacity beyond a limit prevents the reservoir from fulfilling the purpose for which it is designed. Periodic capacity surveys of the reservoir help to assess the rate of sedimentation and reduction in storage capacity.

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Multi-date satellite data set of Hirakud reservoir during 2005-06

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Multi-date water spread of Hirakud reservoir

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Multi-date water spread of Hirakud reservoir

Contours of water spread of Hirakud reservoir derived from satellite data

Elevation-Water spread area of Hirakud reservoir derived from satellite data

Elevation-Capacity of Hirakud reservoir derived from satellite data

THANK YOU