Bengt Lundén

Vanishing seagrass (Zostera marina, L.) in Swedish coastal waters.

Abstract Along the Swedish Skagerrak coast eelgrass (Zostera marina) is a dominant phanerogam on shallow soft bottoms. Eelgrass meadows are important biotopes for many crustacean and fish species being either migratory or stationary. During the 1980s, inventories of the shallow coastal areas with eelgrass have been carried out along the Swedish west coast as a basis for coastal zone management. In the present study we revisited 2000 ha of eelgrass meadows in 5 coastal regions along 200 km of the Skagerrak coast. The inventory was made with the same methods (aquascope) as during the 1980s, but increasing the mapping accuracy by using a Global Positioning System (GPS). The results from this study show that the areal extension of Zostera marina has decreased 58% in 10–15 years with great regional variations. The decline was mainly restricted to the shallow parts of the meadow. The causes and ecological consequences are discussed.

Assessment of vegetation indexes useful for browse (forage) prediction in semi-arid rangelands

Considerable significance is placed on the mapping and monitoring of degraded areas in semi-arid regions of the world, including Botswana. Degraded areas include those suffering from bush encroachment, believed to result from heavy cattle grazing over a number of years. However, certain bush encroachment species have been found to be relatively nutrient-rich. The present work considers the extent to which a series of quantified layers through mainly bush encroachment canopies can be identified using conventional and newly derived vegetation indexes and transforms based on Thematic Mapper (TM) imagery. Field work involved the stratification of green biomass into firstly the herbaceous cover layer; secondly the 0.3-1.5 m browse layer; then the 1.5-2.5 m browse layer; and finally the >2.5 m browse layer. Biomass measurements from these layers were statistically associated with conventional vegetation indexes and transforms such as the Normalized Difference Vegetation Index (NDVI), brightness and greenness values, and relatively newly derived darkening indexes involving the mid-infrared bands. When green biomass and transformed pixel data were averaged per classified vegetation unit, weak negative correlations emerged between grass biomass and the transformed pixel data and no significant correlations developed with the woody biomass (browse) layers. However, when point data were used in the analyses, results showed that most indexes and the brightness transform were significantly correlated with the lower browse layer. Only the darkening indexes and brightness function were sensitive to the browse layers individually and the browse plus grass layers. This work shows the limitations of conventional indexes such as the NDVI in terms of browse and herbaceous layer assessment. New indexes for forage assessment based on relationships between the mid-infrared bands, such as those found in the new MODIS TERRA platform, are urgently required for semi-arid areas.

Assessment of shoreline changes in the western side of Zanzibar channel using satellite remote sensing

The present study uses a satellite remote sensing approach for assessing coastal sediment dynamics in the western side of the Zanzibar channel, Tanzania. Four Landsat images (1986, 1998, 1999 and 2000) were used for the study. Investigation of the four images revealed that the Ruvu delta north of the river mouth has been growing rapidly, especially between 1986 and 1998, with an annual northward linear growth rate of about 133 m year−1 and an annual areal growth rate of about 1 km2 every 3 years. The study identified a palaeo-shoreline feature that is parallel to the present shoreline and located about 1.9 km inland from the present shoreline. An important sediment contributor to river Ruvu is derived from the Uluguru Mountains, a tropical mountainous area located about 200 km from the coastline of the Tanzania mainland. The working hypothesis is that either the observed growth of the delta occurred at a gradual rate between 1986 and 1998 or it was mainly an episodic event related to the extreme rainfall events such as the 1997/98 El Niño–Southern Oscillation (ENSO) event, which was associated with extreme rainfall and widespread landslides.

Sediment sources, sediment transfer in a small Lesotho catchment. A pilot study of the spatial distribution of erosion features and their variation with time and climate

Abstract This study focuses on the erosion and transportation processes and their evidence in landforms and sediments in a small drainage basin in SW Lesotho. The spatial distribution of erosion features was mapped by air-photo interpretation and is discussed in relation to other areas in Lesotho. As described in previous literature, the study area has very active gully erosion. The most active gully erosion occurred during the 1951 to 1961 period which was characterized by high rainfall rates. The relations between gully erosion and surface erosion by wash and rill vary from period to period. If a threshold is reached, gullies are the most important sediment source, otherwise they are equal to or less important than other processes.

Analytically processed Landsat TM images for visual geological interpretation in the northern Scandinavian Caledonides

Abstract The best results for lithogical mapping and mineral exploration using remote sensing have hitherto been achieved in areas with arid or semi-arid climates, residual soils and with little or no vegetation cover. This study concerns the applicability of Landsat TM data for lithological mapping in a part of the northernmost Scandinavian Caledonides, dominated by bare rock but with frequent occurrence of vegetation-covered glacial deposits. In order to efficiently use existing image enhancement methods, e.g., principal component analysis and ratios, it is important to concentrate, as far is possible, on the spectral characteristics of the bedrock within the areas to be interpreted. The statistics for the processed images are then concentrated on bare rock and spectrally similar objects like soils. Various methods for image enhancement for geological purposes are discussed, and procedures for the removal of picture elements influenced by vegetation, water, clouds, snow and deep shadows are described.

Mapping of Colophospermum mopane using Landsat Tm in eastern Botswana

ABSTRACT The spatial distribution of a tree species, Colophospermum mopane is mapped at its southern limits in eastern Botswana. Its relationship with soil type distribution is also investigated. Methods applied in the exercise used the possibilities of integrated applications of geographic information systems and remote sensing to detect and delineate spectral classes of C. mopane and of soils. Landsat TM data for the wet and dry seasons were analysed and interpreted for soil and vegetation classification. Supervised classification of the wet season (19/04/93) image was carried out using land use/cover classes derived from Colour infrared (CIR) aerial photographs, flown during the wet season (April, 1996) over the study area. Classification of the dry season (19/10/84) image on the other hand was based on the existing Food and Agricultural Organisation (FAO) soil maps of the same area. Results show that CIR photographs can be reliably used in selecting training areas for the classification of Landsat TM imagery. Secondly, results also indicate that Landsat TM can be used to map the distribution pattern of mopane. The methods applied in this study and the tools used prove that the much needed inventorying of vegetation in Botswana can be carried out using remote sensing. Lastly, the study shows that spectral classes of soil and vegetation have a positive relationship.

Satellite remote sensing for monitoring of vanishing seagrass in Swedish coastal waters

Conventional field mapping has shown that the important eelgrass biotope on the shallow sea bottoms of the Swedish West Coast has decreased 58% in the last 10–15 years, with great regional variations. This study investigates the possibility to map and monitor eelgrass meadows using satellite remote sensing. The test, using Landsat TM data from two dates, clearly indicates the potential of the technique, but further studies are needed before it is fully operational.

Satellite Image Enhancement For Rock Type Separation

Landsat TM data have been used for lithological mapping in a part of the northernmost Scandinavian Caledomdes, dominated by bare rock but with frequent occurrence of vegetation-covered glacial deposits. In order to efficiently use existing image enhancement methods, e.g. principal component analysis, it is important to concentrate on the spectral characteristics of the bedrock. Various image enhancement methods for geological mapping are discussed, and procedures for removal of pixels influenced by ve etation, water, clouds, snow and deep shadows are descried.

Analysis of satellite–derived surface temperatures in relation to land cover and topography

Satellite–derived surface temperatures Knowledge of the surface temperature of the Earth is of great importance for a correct para– meterization of several important energy and mass transport phenomena. The land surface– atmosphere interaction–is one of the most uncertain aspects in global climate models. Because of the difficulties measuring the true surface temperature – the ‘skin’ temperature – with traditional contact thermometry, there have been rapid ad– vances in radiation–based infrared thermometry techniques. As the exchange processes of interest, sensible and latent heat fluxes, are often studied at regional scales there is a growing need for using remote–sensing techniques with thermal infrared sensors on aircraft and satellites. This quantitative analysis in the field of thermal remote–sensing, requires knowledge of object emissivities and, especially for satellite remote–sensing, a knowledge of the influence of the atmosphere.

Digital Elevation Data, Landsat TM and Magnetic Data for Visualization of Geomorphological and Geological Features

The main objective of this study is to develop methods for optimizing and merging different types of digital data for visual interpretation of geological lineaments and geomorphology. Two test areas with different topographic variability were selected in the Scandinavian mountain region. Different methods for enhancement based on convolution, both directional and non-directional, were applied on elevation data to detect subtle structural features. An excellent product for visual interpretation of lineaments is the artificial stereo pairs, using raw elevation data for the topography and spatially enhanced elevation data as background. The best spatial enhancement of Landsat TM images was achieved by unsharp masking and adaptive contrast stretch. To visualize the topography when analyzing satellite imagery, artificial stereo pairs were created using elevation data with Landsat TM data as background. Using synthetic stereo pairs solely based on magnetic data it was possible to find subtle magnetic anomalies. Also, together with elevation data, artificial stereo pairs were created with magnetic data as background color. This product allows interpretation of the relationship between topographic lineaments and magnetic anomalies. The image products presented here will not replace traditional maps and mapping methods; however, used as supplementary tools they may increase the understanding of many various geological and geomorphological phenomena. The techniques can provide some of the useful products needed for a complete environmental site characterizations.