Book reviews

Computing Procurement: Guidelines and Procedures Henry Norton OUP1988

Acquiring Computer Systems and Services Publisher: Theodore Goddard, London EC1A 4EJ, 1988     

Book reviews

This study used four near-real-time multispectral Systeme pour l'Observation de la Terre (SPOT) high-resolution visible (HRV ) images to establish land cover and forest classes of relevance to slash-and-burn agriculture. The study was conducted in 1.43 million ha of the Alternative to Slash-and-Burn (ASB) global benchmark research area for Africa selected as representative of the entire Congolese basin of Central Africa and located in Southern Cameroon. The land cover and forest classes mapped have different impacts on global phenomena as well as their own management challenges and include slash-and-burn dominant farmlands, C hromolenea orodata dominant short-fallows, Imperata cylindrica dominant weeds, long-fallows or regenerated forests, raphia palm-dominant lowlands, permanently flooded swamp forests, and primary and secondary forests. In order to map these distinct and complex classes the study proposes and implements a piecemeal approach to classification involving stratification of the image into several distinct discrete subsets of forest corridors, lowlands, and uplands. The approach involves the use of image texture indicators in conjunction with groundtruth data to divide the image into discrete subsets, performing unsupervised classification on these discrete subsets, masking problem classes and reclassifying them, editing certain spectrally inseparable areas, adopting post-classification strategies, and finally mosaicking the discrete subsets into one seamless image. This approach led to an overall mapping accuracy of 82.4% with individual classes mapped at accuracies above 72.9% (user's), and above 66.7% (producer's).     

Book reviews

A laboratory experiment was conducted to determine the spectral characteristics of different types of sediment under suspension in water and to select an optimal wavelength for the quantification of suspended sediment concentration and secchi depth (water clarity) in the Tawa reservoir, using the Indian Remote Sensing Satellite-1A Linear Imaging Self Scanning Scanner-I (IRS-1A LISS-I) data. It was noted that the correlation between suspended sediment concentration and reflected radiance varied with colour, mineral composition of sediment and grain size. The clay minerals of low specific gravity had a larger value of reflected radiance than those from high specific gravity non-clay minerals. The laboratory results indicated that an algorithm to quantify suspended sediment concentration and secchi depth in the reservoir can be developed from reflected radiance received by the satellite. For this purpose the Tawa reservoir on the Tawa river of the Narmada basin in Central India was selected. Tawa reservoir water samples were collected on 20 October, 1988 concurrent with an IRS-1A overpass. The secchi depth, pH, and conductivity measurements were made at all the sampling points. The samples were analysed to determine the concentration of total suspended matter, grain size and mineralogy. A positive functional relation exists between the concentration of suspended solids and the visible wavelength bands 1, 2 and 3 (0.45 to 0.68 mu m). On the other hand, the secchi depth of water increases with the decrease in reflected radiance. It has been observed that concentration, mineralogy and grain size of the suspended solids are the main factors which influence the reflected radiance.