High-frequency measurements of aeolian saltation flux: Field-based methodology and applications

TL;DR

This paper introduces a new field methodology to measure high-frequency saltation flux in aeolian processes, enabling better understanding of wind-driven sand transport fluctuations.

Contribution

It develops a calibration-based approach to generate 25 Hz saltation flux time series from particle counts, improving short-term flux measurements.

Findings

Method successfully calibrates HF particle counts to LF flux measurements.

Enables analysis of saltation dynamics at millisecond to daily scales.

Facilitates coupling of flux data with high-frequency wind measurements.

Abstract

Aeolian transport of sand and dust is driven by turbulent winds that fluctuate over a broad range of temporal and spatial scales. However, commonly used aeolian transport models do not explicitly account for such fluctuations, likely contributing to substantial discrepancies between models and measurements. Underlying this problem is the absence of accurate sand flux measurements at the short time scales at which wind speed fluctuates. Here, we draw on extensive field measurements of aeolian saltation to develop a methodology for generating high-frequency (25 Hz) time series of total (vertically-integrated) saltation flux, namely by calibrating high-frequency (HF) particle counts to low-frequency (LF) flux measurements. The methodology follows four steps: (1) fit exponential curves to vertical profiles of saltation flux from LF saltation traps, (2) determine empirical calibration factors through comparison of LF exponential fits to HF number counts over concurrent time intervals, (3) apply these calibration factors to subsamples of the saltation count time series to obtain HF height-specific saltation fluxes, and (4) aggregate the calibrated HF height-specific saltation fluxes into estimates of total saltation fluxes. When coupled to high-frequency measurements of wind velocity, this methodology offers new opportunities for understanding how aeolian saltation dynamics respond to variability in driving winds over time scales from tens of milliseconds to days.