Global wavelength survey of Martian bedforms: methods and preliminary results

The mechanism/s responsible for sediment entrainment by wind and bedform migration on Mars are a matter of debate [1]. Martian large ripples (LRs) migrate under present-day low pressure conditions and have been interpreted has fluid/wind drag ripples [2] or as bedforms formed by aeolian saltation [3]. An important constraint to this debate is the relation between bedform wavelength and atmospheric density (as a function of elevation). This dataset was later complemented by the measurement of bedform wavelengths in other 11 areas [2]. Lapotre el al. [2] proposed that the fluid drag theory fits the measured wavelength vs. atmospheric density relation, a view not shared by Lorenz [1, Fig. 2].

To try to address this divergence, we will present a new method that allows the automatic mapping and morphometric characterization of bedforms (LRs to TARs) using HiRISE imagery. It consists in a windowed multiscale spectral approach, followed by a supervised classification stage using neural networks. This method can accurately identify the bedforms (overall accuracy of 94%) and provide precise wavelength measurements within a ±12% confidence interval. The surveyed bedforms have crests spaced between 1 and 100 m, and include large ripples, megaripples and TARs.

We will review and compare previous datasets and studies with our measurements. The main objective is to re-evaluate how well the wind drag hypothesis can predict bedforms’ spacing on Mars, and for this purpose we employ an improved measurement approach that allows the mapping of entire dune fields. Furthermore, we significantly increased the number of mapped areas and extended the range of sampled elevations.

Preliminary results of this ongoing effort will be presented at the conference.

 

[1] Lorenz, R.D. (2020). Martian Ripples Making a Splash. J. Geophys. Res. Planets 125, 12–15.

[2] Lapotre, M.G.A., Ewing, R.C., Lamb, M.P., Fischer, W.W., Grotzinger, J.P., Rubin, D.M., Lewis, K.W., Ballard, M.J., Day, M., Gupta, S., et al. (2016). Large wind ripples on Mars: A record of atmospheric evolution. Science (80). 353, 55–58.

[3] Sullivan, R., Kok, J.F., Katra, I., and Yizhaq, H. (2020). A Broad Continuum of Aeolian Impact Ripple Morphologies on Mars is Enabled by Low Wind Dynamic Pressures. J. Geophys. Res. Planets 125, 1–39.

[4] Lorenz, R.D., Bridges, N.T., Rosenthal, A.A., and Donkor, E. (2014). Elevation dependence of bedform wavelength on Tharsis Montes, Mars: Atmospheric density as a controlling parameter. Icarus 230, 77–80.