In This Space
The movement of sand dunes is usually a slow one, but it affects in important ways the life of local populations and the design and maintainance of infrastructures. It has impact on cultivated lands, houses, irrigation canals, artesian wells of oases and pipeline routes. Deserts are characterised by severe climate and remote locations; summertime temperatures are very high with high daily and seasonal thermal excursions (1). Moreover winds affect the changing shape of those territories influencing human stettlements and activities.
Surveys of dunes and estimation of their migration rates have a crucial role for public autorities, populations and economic actors active in such environment. Climate change impacts are expected to be an important factor which will affect the rate of sand dunes movements. The shape, movements and interaction of dunes depends mainly on the amount of sand and the yearly winds, but also on high temperatures, droughts and the slope of the topography (2).
The dune erodibility and erosivity, governed by several environmental conditions, such as dust storms and meteorological factors, are important variables for modeling and forecasting sand dunes shape and changes (2). It is possible to slow down the movements of dunes building infrastructures which affect wind path and strenght; vegetation restoration could play a role as well.
The migration of dunes measurements are normally performed by combining surface mapping with aerial and satellite imagery, GPS and ground-based lidar measurements (3) Remote sensing technologies provide data for large scale monitoring mapping, and to analyse linear infrastructures, such as pipelines, roads and rails: the combination of radar satellite data with other types of satellite data and ground measurement generates the best results. After the identification and map of sand dunes from satellite imagery, different images are subtracted to identify the frontier movement of sand dunes during temporal separation; dunes dimension calculation serve to derive the rate of movement, as well as minimum, maximum and average values (4). Radar monitoring is based on the fact that pipelines and other infrastructural elements work as reflectors for the radar signal sent by the satellite. On the basis of this result, it is also possible to investigate archived data to obtain "backward monitoring analysis".
Research indices based on Landsat images used in a study of sand encroachment are the Normalized Difference Vegetation Index, the Tasseled Cap Wetness Indicator, the Land Surface Temperature, and the Normalised Difference Sand Index elaborated by A.M. Fadhil in a study on sand dunes monitoring in Iraq (5). Other useful satellite derived information are those about land use and land coverage, which play an important role in forecasting the impact of sand movements on local environment and economy: this, together with meteorological data, represents crucial information for adaptation and future developmen.
(1) R. Kumar, M. S. Gunjiyal, N. Sinha, Design Challenges and Technological Advancement: A Case Study of Pipeline Through Sand Dunes (in Thar Desert)
(2) A.C. Sparavigna 2013, A study of moving sand dunes by means of satellite images.
(3) USGS, Monitoring and Analysis of Sand Dune Movement and Growth on the Navajo Nation
(4) Gadhiry M., Koch B., Developing a monitoring system for sand dunes migration in Dakhla Oasis, Western Desert, Egypt.
(5) A. M. Farhil Sand dunes monitoring using remote sensing and GIS techniques for some sites in Iraq.
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