**1. Introduction**

Wind erosion of soils refers to the detachment, transport, and subsequent deposition of sedi‐ ment or surface soils by wind. This process is sometimes termed aeolian movement and is responsible for the formation and migration of dunes, soil degradation in agricultural areas, and formation of deep loess deposits in areas downwind from major sediment sources. From cross-bedding in ancient sandstones, it has been determined that aeolian movement of soils and sediments has been occurring for eons and is a natural geomorphic process. Wind erosion affects over 500 million ha of land worldwide and is responsible for emitting be‐ tween 500 and 5000 Tg of fugitive dust into the atmosphere annually [1]. These fugitive dust emissions contain a disproportional amount of soil organic carbon and plant nutrients and the winnowing and loss of these materials degrades the soil [2, 3].

Much of what we know about aeolian processes comes from wind tunnel-based investiga‐ tions. The seminal work of Ralph Bagnold was largely conducted in a stationary suctiontype wind tunnel 9 m in length [4]. Wind tunnels allow control over the wind and surface factors controlling aeolian movement and thus much more definitive investigations can be conducted in a shorter period of time than in the natural environment where these factors are highly variable in time and space. Other early aeolian researchers used wind tunnels to assess the erodibility of soil surfaces without plant residues based on the texture of the soil and relative abundance of aggregates too large to be entrained by the wind [5]. Large sta‐ tionary wind tunnels have allowed sufficiently detailed understanding of the physical proc‐ esses of aeolian movement that predictive models such as the Wind Erosion Equation [6] and the Wind Erosion Prediction System [7, 8] have been developed.

Stationary wind tunnels continue to be used for aeolian research at scales from single grain movement [9] through soil surface scale [10] to landscape scale [11]. The ability to control

© 2013 Van Pelt and Zobeck; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Van Pelt and Zobeck; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

the humidity of the atmosphere has enabled scientists to study such sensitive processes as the electrostatic interactions between particles and electrical fields generated during aeolian activities [12]. Stationary wind tunnels have also been used to study abrasion effects of wind-driven sands on building materials [13], crop plants [14], bare crusted soil surfaces [15], and soil surfaces with microphytic crusts [16] as well as to compare and calibrate in‐ strumentation for aeolian filed studies [17, 18].

Fugitive dust is perhaps the most visible product of aeolian activity and stationary wind tunnels have been used to study fugitive dust emissions from eroding soils. From wind tun‐ nel testing of crusted soils and aggregates, it has been determined that sandblasting of these otherwise non-erodible features is responsible for much of the dust generated during aeoli‐ an events [19, 20]. Soluble salts such as CaCO3 effects on dust emissions have also been in‐ vestigated in stationary wind tunnels [21] as have complex and vegetated surfaces [22] and specific soils from Death Valley, a major dust source area in North America [23]. Although stationary wind tunnels have great utility, they are limited to testing disturbed soil surfaces that have been removed from their natural setting. The development of field portable wind tunnels has greatly expanded our ability to investigate aeolian processes in the field under controlled conditions.
