R. S. Dwivedi

Spectral behaviour of salt-affected soils

Abstract For mapping and monitoring the spatial distribution of salt-alTected soils using remote sensing data, a thorough understanding of their spectral behaviour is of paramount importance. The spectral behaviour of a few typical salt-affected soils of the Indo-Gangetic alluvial plain was studied by taking ground-based spectral measurements with the Exotech radiometer (model 100 BX) and measurements made by the thematic mapper (TM) onboard Landsat-5. Salt-alTected soils, in general, showed relatively higher spectral response in the visible and near-infrared regions of the spectrum as compared to normal cultivated soils. Further, strongly saline-sodic soils were found to have higher spectral response as compared to moderately saline-sodic soils. The vegetation cover modifies the overall spectral response pattern of salt-affected soils especially in the green and red spectral bands. In addition, variation in the Sun elevation angle and moisture content were also found to modify the observed spectral respo...

Evaluation of various digital image processing techniques for detection of coastal wetlands using ERS-1 SAR data

One of the problems associated with synthetic aperture radar (SAR) data analysis is the presence of random noise or speckle SAR data, being achromatic in nature, which offers very limited scope for the detection and delineation of various terrain features. ERS-1 SAR data for the coastal region of West Bengal, India were processed (a) to suppress the random noise using various filters, (b) to generate the intensity, hue and saturation (IHS) transform from temporal SAR data, and (c) to study the synergism of SAR data with optical sensor data. The results indicate that the Gamma MSP filter with a 5 5 pixel kernel size has been the most efficient in suppressing the noise and concurrently improving the image contrast. The IHS transform of temporal SAR data made it easier to discriminate between various wetland categories. This was also the case with hybrid image generated by the Indian Remote Sensing Satellite (IRS-1B) Linear Imaging and Self-scanning Sensor (LISS-II) data when compared to SAR data alone.

Mapping and monitoring of degraded lands in part of Jaunpur district of Uttar Pradesh using temporal spaceborne multispectral data

Apart from soil erosion by wind and water, the major land degradation processes operating in irrigated commands in arid and semi-arid regions are waterlogging and subsequent salinization/alkalinization. Remote sensing data have been used successfully in studies of the spatial extent, magnitude and temporal behaviour of lands affected by such processes. In this work we interpreted Landsat Multispectral Scanner images acquired during 1975 and Landsat Thematic Mapper data acquired during 1993, in conjunction with ancillary information and adequate ground data, to derive information on the extent and spatial distribution of various degraded lands, namely salt-affected soils, waterlogged areas and eroded lands in part of the Jaunpur district of Uttar Pradesh. The results indicate a significant shrinkage in the spatial extent of salt-affected soils (of the order of 49.76%) over the period 1975 to 1993. A similar trend was observed in the temporal behaviour of waterlogged areas, but an increase (6.45%) was found in the spatial extent of eroded lands. The methodology employed and the observations made are described here in detail.

Inventory of salt-affected soils and waterlogged areas: A remote sensing approach

Waterlogging and subsequent salinization and/or alkalization are the major land degradation processes in irrigated agricultural lands of arid and semiarid regions. The use of spaceborne multispectral data has been shown to have potential for deriving information on the nature, extent, spatial distribution and magnitude of various degraded lands. Indian Remote Sensing Satellite (IRS-1B) Linear Imaging Self-scanning Sensor (LISS-I) and Landsat Thematic Mapper (TM) data in the form of standard false colour composite (FCC) prints at 1 100000 scale covering Nagarjunsagar Left Bank canal command area in Andhra Pradesh, southern India, have been used to delineate waterlogged areas and salt-affected soils through a systematic visual interpretation approach. Waterlogged areas are estimated at 1380ha whereas salt-affected soils of mostly saline-sodic nature cover 6830ha of the command area. The methodology used and results are described in detail.

Monitoring the spatial extent of coastal wetlands using ERS-1 SAR data

Being highly dynamic by nature due to their changing hydrological regime and to the encroachment of urbanization, inductrialization and changing patterns in agriculture, reliable and timely information about the extent, nature, spatial distribution and temporal behaviour of wetlands is a prerequisite for their effective management. Optical remote sensing data have been used extensively to generate such information. In this study the European Remote Sensing (ERS-1) Synthetic Aperture Radar (SAR) data collected during April 1993 were used to study the temporal behaviour of the coastal wetlands of the Sunderban delta of West Bengal, India. Account was also taken of the Landsat MSS data of 1973. Shrinkage in the wetlands on the periphery of Calcutta due to the encroachment of urbanization and the development of new islands in the active coastal zone have been observed over a period of 20 years.

Mapping wetlands of the Sundaban Delta and it's environs using ERS-1 SAR data

Wetlands play an important role in bio-geochemical cycling, flood control and recharging of aquifers. They serve as a major source and net sink of carbon and a potential site for aquaculture and the breeding of waterfowls. The wetlands of Sundarban and its adjoining areas support a variety of flora and fauna and they are currently being used for fish culture. Precise information of their nature, extent and spatial distribution is a pre-requisite for their optimal utilization. Being a coastal region, the cloud-free optical remote sensing data for the area is not very often available. Synthetic aperture radar, which has the ability to penetrate cloud, permits regular and repetitive observation of the wetlands. A study was made to evaluate the potential of the ERS-1 SAR data for delineating wetlands in part of the Sundarban delta and its adjoining areas of West Bengal. ERS-1 SAR data was analysed/interpreted in conjunction with optical data, i.e., Indian Remote Sensing Satellite (IRS-1B) data, acquired simul...

Mapping the magnitude of sodicity in part of the Indo-Gangetic plains of Uttar Pradesh, Northern India using Landsat-TM data

Abstract The standard false colour composite (FCC) print made from bands 2, 3 and 4 of Landsat-TM data at 1:50 000 scale covering part of the Indo-Gangetic plain was interpreted visually following a systematic visual interpretation approach. Based on image elements and their correlation with the ground features, two categories, namely moderately and strongly sodic soils, could be delineated. On Landsat-TM FCC print strongly sodic soils appear as bright white patches with fine texture, while moderately sodic soils are manifested as dull white to strong brown. The delineation thus made, would help the execution of a reclamation programme for sodic soils at district level.

Delineation of salt-affected soils and waterlogged areas in the Indo-Gangetic plains using IRS-1C LISS-III data

Waterlogging and subsequent salinization and/alkalinization is the major land degradation problem in irrigated commands in the arid and semi-arid regions. The Linear Imaging Self-scanning Sensor (LISS-III) digital data acquired by the Indian Remote Sensing Satellite (IRS-1C) over part of the Indo-gangetic plains are digitally analysed for delineating salt-affected and waterlogged areas on a IBM RS-6000 system. A comparison with the IRS-1B LISS-II data, with comparable spectral bands and acquired very close to LISS-III data, reveals a relatively poor overall classification accuracy achieved from this data as compared to LISS-II data. This may be attributed to higher intra-class spectral variations resulting from high spatial resolution LISS-III data. The classifiers capable of exploiting the spectral variations in spatial domain, like segmentation, textural analysis, etc., need to be used for exploiting the full potential of IRS-1C LISS-III data for mapping salt-affected soils and other degraded lands.

Cover: Land‐use/land‐cover change analysis in part of Ethiopia using Landsat Thematic Mapper data

Land cover and human or natural alterations of land cover play a major role in global-scale patterns of climate and biogeochemistry of the Earth’s systems. Landuse and land-cover changes have a direct impact on land management practices, economic health and social processes of concern at the national and global level (Ojima et al. 1994). Global assessment of changes in physical characteristics of land cover is therefore a fundamental input for models of global climate and terrestrial hydrology (Lambin and Strahler 1994). Several researchers have attempted to use digital satellite sensor data to address the land-use and land-cover change detection problem (Fung 1990, Lambin and Strahler 1994, Heo and FitzHugh 2000, Rogan et al. 2003). Several procedures including comparison of land-cover classifications, multi-data classification, image differencing/ratioing, vegetation index differencing, principal component analysis and change vector analysis have been employed for land-use and land-cover change detection (Singh 1989). We report here a study that was carried out (i) to derive information on spatial distribution of land use/land cover in part of Ethiopia, and (ii) to study its temporal behaviour during the period 1994 and 1997 using Landsat Thematic Mapper (TM) data. With a geographical area of 1883 km, the test site is bound by geo-coordinates 6u089 to 6u489 N and 37u249 to 37u429 E and forms part of Chencha Wareda and adjoining areas of Gamo Awraja, Gamo Geofa Kifle Hafer, Ethiopia. Landsat TM digital data acquired on 2 January 1994 and 11 February 1997 were used. Ethiopian Mapping Agency topographical sheets at 1 : 50 000 scale and published relevant report and maps were also referred to. The methodology involves radiometric normalization, geo-referencing, digital analysis and accuracy estimation. Radiometric normalization of Landsat TM data of 1994 and 1997 was carried out by converting DN values into radiance values using calibration coefficients provided by Markham and Barker (1986). For georeferencing the Landsat TM digital data, available 1 : 50 000 scale topographic maps were scanned on a Contex FSS-800 system and were rectified for scanning error. The output, thus generated, was taken as a reference for geo-referencing the Landsat TM data of 1994 by using ground control points on a Silicon Graphics Octane Work station using ERDAS/IMAGINE version 8.3 software. The Landsat TM data of 1997 was subsequently co-registered to Landsat TM data acquired in 1994 using an image-to-image registration tool. For deriving information on land use and land cover, spectrally homogeneous classes were initially made from Landsat TM data of 1997 using an unsupervised classification algorithm. Based on the results of unsupervised classification and ground data, a cluster of pixels representing various land-use and land-cover categories were selected as training sets

The inventory and monitoring of eroded lands using remote sensing data

Abstract In order to prevent soil loss and protect fertile lands from soil erosion, precise information on the nature, extent and magnitude of soil erosion is a prerequisite. In the study reported here, Landsat MSS, TM and Indian Remote Sensing Satellite (IRS-1A) Linear Imaging Self-scanning Sensor (LISS-II) data have been visually interpreted to derive qualitative information on both eroded lands and shifting cultivation areas. Three categories of eroded lands, namely (i) nil to slight, (ii) moderate, and (iii) severe to very severe were delineated. Opticalcum-digital enlargement of LISS-II data helped to pick up small pockets of eroded lands and shifting cultivation areas that were not discernible at a 1 :250 000 scale. Temporal variation observed in the extent and distribution of eroded lands is also discussed in detail.