High resolution sensors in space and time for determination saltation and creep intensity

• Published in: Earth surface processes and landforms Vol. 37; no. 10; pp. 1065 - 1073
• Main Author: Schönfeldt, Hans-Jürgen
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01-08-2012; Wiley
• Subjects: aeolian; Bgi / Prodig; Geomorphology; instrumentation; methods; Methods and techniques; Physical geography; saltation; Saltiphone; webcam; Mecklenburg-West Pomerania; Germany; Aeolian features; Creep; Research technique; Experimentation; Instrumentation; Coastal environment; Aeolian transport; Saltation
• ISSN: 0197-9337; 1096-9837
• DOI: 10.1002/esp.3228

ABSTRACT
The measurement of aeolian sand transport rates at high temporal and spatial resolution is crucial for further progress in testing and developing numerical models of sand movement by wind and in the modelling of sand dunes, ripples and so on. This paper reports the development and field testing of two sand transport sensors. The first one, a webcam commonly used with personal computers, is a new device in aeolian research. The webcam frame transfer is triggered by a sonic anemometer every 0·1 second. Consecutive frames are compared and analysed in real‐time by a computer program. Changes in pixel light intensity exceeding a threshold level are recorded and interpreted as grain movements. The second sensor is a small‐sized ‘Saltiphone’‐type device made of simple loudspeakers with a diameter of 15 mm as used in MP3 players. It can be deployed as a 2 × 3 array of six such devices distributed to enable horizontal and vertical spatial sampling of the sand flux.
The devices are tested under field conditions. Both signals and the sum of microphone impacts over 15 minutes are compared to data gathered using a Guelph sand trap, and very good agreement is found. Measurements in a wind tunnel using sieved natural sand indicate that the webcam can be used to infer additional information about the grain size. As an application, the fluid and impact thresholds for aeolian sand transport are investigated in field measurements by analysing the onset and breakdown of saltation in gust and lull intervals of rising and falling wind speeds, respectively. In this way, constitutive equations for sand transport in terms of the wind speed can be tested. If viable, they can be employed to infer estimates for the thresholds by minimizing the root‐mean‐square error between measured and calculated transport data. Copyright © 2012 John Wiley & Sons, Ltd.