An evaluation of ultralight aircraft capability for remote sensing applications in West Africa

Abstract

An ultralight aircraft was used to make concurrent, near continuous measurements and to acquire spectral responses in several wavelengths over various ground features: water bodies (river and irrigation channels), geomorphological features (sand banks, levees, iron crust), aquatic vegetation (rice and spontaneous aquatic vegetation) and stubbles (millet and sorghum). The experiment was performed in Mali, along the Niger river. The airborne instrumentation made it possible to collect simultaneously spectral responses in the MSS and SPOT bands, flying height by laser rangefinder and colour video tapes of the area over-flown. Five profiles, several kilometres long, were obtained at heights above the ground varying from 20 to 75 m. Along each profile spectral data and flying height were scanned every 0-1 s and recorded on the audio channel of a videotape, after multiplexing and analogue-to-digital conversion. The preliminary data analysis suggest a very high potential for ultralight aircraft in remote sensing applications.     

FACILITATED TRANSPORT OF CARBON DIOXIDE: A REVIEW

The effect of reversible chemical reaction upon the diffusion of carbon dioxide in thin liquid film membranes is reviewed. Particular emphasis is placed upon the hydration reaction of CO₂ and catalysis thereof. Theoretical analysis is developed for equilibrium, near-equilibrium and near-diffusion regimes. The important effects of weak acid buffers, proteins and amines upon CO₂ transport are also discussed, as well as the significance of diffusion potentials, particularly in the case of protein systems. Results of experimental investigations of facilitated CO₂ transport are reviewed, as well as general aspects of CO₂ transport in biological systems and absorbers.     

Cover photograph Use of LANDSAT-RBV data for the assessment of flooded areas for rice production forecasting in West Africa

Land degradation is difficult to assess in arid rangelands because of short-term variations in rainfall, landscape diversity and the problems of sampling very large areas. This paper shows how vegetation cover index values derived from multi-temporal remotely-sensed data can be used in association with spatial models of grazing impact on landscapes to identify grazing-induced land degradation. The method assumes that grazing effects decrease with distance from water and that temporary grazing impacts largely disappear as vegetation responds to major rainfalls. Grazing gradients (i.e., systematic changes in vegetation cover with distance from water) which remain indicate long term damage. Simple grazing gradients involve changes in average cover with distance from water and include normal, inverse and composite types, complex grazing gradients show systematic changes in cover variance with distance from water and develop where soil and runoff are being redistributed. Although complex grazing gradients may involve little change in total cover with distance from water, they are symptomatic of a reduction in the proportion of forage present. The ability to recognize grazing gradients may greatly simplify range assessment procedures and may also improve satellite image based procedures for determining erosion risk.     

A spatialized APAR for heterogeneous pixels

The importance of APAR models for the study of biomass production from space requires an analysis of their performances on natural mixed pixels. This is the objective of present study which gives quantitative values for the role of heterogeneity on the APAR assessment from space. These results show that the accuracy of the APAR as currently computed from satellite data cannot be considered as acceptable. Wegive a new APAR model adapted to heterogeneous pixels.     

Screening tests of free radical scavengers for preventing sun-accelerated cutaneous ageing

Free radical formation has been shown to occur in UV-irradiated skin and a large body of evidence suggests that these reactive agents are responsible for sun-accelerated cutaneous ageing. The paper describes two tests for screening free radical scavengers potentially capable of inhibiting photo-induced skin alterations. They are based on analysis of thiobarbituric acid-reactive materials either in an acellular model in vitro or in the epidermis of rose bengal-sensitized mice after white light irradiation. The tests were illustrated with silymarin, a potent vegetable free radical scavenger.