Morphological characteristics were measured for barchan dunes on Earth (2,686 dunes in 30 barchan fields) and Mars (720 dunes in 10 barchan fields) using satellite images. The data were used to (a) develop a new barchan classification system; (b) compare characteristics of barchans on Earth and Mars; and (c) assess whether barchans, in bulk, display allometric or scale‐invariant characteristics. Dimensional metrics were obtained for the width and length of barchan bodies, the width and length of barchans including the horns, and the length of each horn. Dimensionless metrics were derived for the ratios of the body width to the width between the tips of the horns (width ratio), the length of the entire barchan to the length of the body (length ratio), and the length of the longer horn to the shorter horn (symmetry ratio). The width, length, and symmetry ratios were used to classify barchans into eight types and compare the characteristics of their distributions on the two planets. From this analysis, it was established that, statistically, barchans on Earth are distinctive from those on Mars based on the morphometrics, with terrestrial barchans being, on average, of smaller size and more often symmetrical, while Martian barchans more often have convergent horns that are short relative to the central dune body and are more often asymmetrical. The analysis further reveals that barchan planform morphology can be considered scale‐invariant, and we argue that body width is the most appropriate measure representing barchan size.

Wind-blown sand concentrations decay rapidly and in an orderly manner with height above the surface. The saltation flux profiles are of interest to understand wind and sand interactions and for fundamental measurement and modeling of associated transport rates. This study compares methods to measure and represent aeolian sand flux profiles. We measured vertical flux profiles and used quality-controlled data to test power, logarithmic, and exponential functions to reproduce the profiles. These results are used in a pragmatic assessment of the efficiency of reproducing flux profiles from vertically discontinuous arrays of traps or sensors compared to profiles obtained from continuous vertical arrays of segmented traps. Our analysis corroborates previous findings demonstrating that exponential decay functions are statistically the best method to approximate flux profiles. The results are used in a novel application to compare flux profiles reproduced from vertically discontinuous arrays of devices with those obtained from continuous vertical arrays comprising nine mesh-style traps. The results indicate that discontinuous arrays of 3, 4, 5, or 6 devices deployed less than 200 mm from the surface will effectively reproduce results from the continuous array, with average errors less than 3%. Errors increase when devices are at greater heights or as the number of devices decreases. Discontinuous arrays typically do not capture creep transport which would contribute to error in our comparisons. Therefore, creep must comprise less than 3% of total aeolian sand flux, contradicting typical assumptions of 25%.

Acoustic distance sensors have a long history of use to detect subaqueous bedforms. There have been few comparable applications for aeolian bedforms such as ripples. To address this, we developed a simple and reliable apparatus comprising a pair of distance sensors, a bracket upon which they are mounted, and a base upon which the bracket can slide. Our system relies on two Senix Corporation (Hinesburg, VT, USA), ToughSonic^® model 14-TSPC-30S1-232 acoustic distance sensors: one to measure surface elevation changes (in this case, ripple morphology) and a second to measure horizontal location. The ToughSonic^® vertical resolution was 0.22 mm and the horizontal scan distance was about 0.60 m with a locational accuracy of 0.22 mm. The measurement rate was 20 Hz, but we over-sampled at 1 KHz. Signal processing involves converting volts to meters, detrending the data, and removing noise. Analysis produces ripple morphologies and migration rates that conform with independent measurements. The advantages of this system relative to terrestrial laser scanning or structure from motion are described.

Barchans represent a common dune type found on Earth and Mars. Their morphological characteristics are singular and easily recognized. Their formation is favored on relatively immobile substrates with near-unidirectional winds that sculpt the distinctive crescentic, aerodynamic morphology. Barchans often occur isolated from one another, although they can occur in organized sets or barchanoid dune fields.  Long and Sharp (1964) and Bourke and Goudie (2009) measured attributes of barchan morphology and identified four archetypal shapes based on the ratio of the length of the stoss slope to the distance between the ends of the horns.            In this study, we report findings based on measurements of 3,406 barchans: 2,686 from 20 terrestrial dune fields and 720 from 10 Martian dune fields. Barchan morphology was characterized by six metrics: body length (L1), measured from the upwind nose of the barchan to the nearest base of the slipface; total length (L2) measured to the (average) ends of the horns; body width (W1), measured on a line perpendicular to L1 and intersecting at the base of the slipface; horn-to-horn width (W2), measured perpendicular to L2 and parallel to W1; and horn lengths (H1 and H2) measured perpendicular to W1. The morphometric data were used to develop three new shape metrics as a basis for barchan shape characterization: 1) a width ratio (WR: W1/W2); 2) a length ratio (LR: L1/L2); and 3) a symmetry ratio (SR: longer horn length/shorter horn length). The barchan stereotype (Type 1) was defined as meeting three criteria: SR between 1.0–1.2, WR between 0.95-1.58 (mean value +/- one standard deviation) and LR between 0.52–0.76. Cluster analysis was used to define three additional characteristic shapes. Type 2 barchans are moderately symmetrical ( =1.47), uniform in width (  = 1.01), and elongated (  = 0.53). Type 3 barchans are moderately symmetrical (  = 1.4), with converging horns (  = 1.56), and compact (  = 0.74). Type 4 barchans are asymmetric (  = 3.46) uniform in width (  = 1.15) and average elongation (  = 0.64).            We found that, on average, terrestrial barchans are shorter, proportionately wider, and more symmetric than those on Mars. Most barchans are Type 1, 2, or 3 (26%, 32%, and 35%, respectively), and relatively few are Type 4 (8%). The distributions of types, however, is quite different for the two planets. On Earth, most barchans are Type 2 (38%) and Type 1, stereotypical barchans comprise 30% of our samples. Type 4 barchans are least common (6%). On Mars, most barchans are Type 3 (64%). The distributions of Types 1, 2, and 4 are similar. Type 1, stereotypical barchans, the least common on Mars, comprise 11% of our samples, and Types 2 and 4 each represent 13% of our samples. These results indicate that most barchans do not conform to our idealized morphological image on either Earth or Mars. In our sample, Martian barchans are larger than terrestrial, with shapes characterized largely by asymmetric, converging horns.