Contents lists available at ScienceDirect Remote Sensing of Environment journal homepage: www.elsevier.com/locate/rse Comparison of remote sensing observations of planetary wind streaks A.L. Cohen-Zada a, ⁎ , S. Maman b , D.G. Blumberg a a Department of Geography and Environmental Development, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel b Homeland Security Institute, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel ARTICLE INFO Edited by Jing M. Chen Keywords: Wind streaks Radar images Optical images Aeolian Venus ABSTRACT Wind streaks are common aeolian features observed on terrestrial planets. They were frst identifed on Mars; thus, the associated terminology is based on Mars-related observations usually describing surface patterns with distinct albedos. However, terms related to refected tones are only relevant to past knowledge for Mars, and not necessarily suitable for description of radar-visible streaks located on Venus, Titan, or Earth. Furthermore, the sensor type used to observe wind streaks can infuence the subsequent data analysis. The purpose of this study was to examine the efects of sensor type on wind streak identifcation and interpretation. Six case studies featuring wind streaks on Earth were performed, using imaging by both radar and optical sensors. The results indicate that wind streak identifcation is constrained to a specifc combination of sensor settings appropriate for the local surface properties. Only half the optically visible wind streaks considered in this study were also radar- visible, but all the wind streaks observable in the radar images also appeared in the optical images. Furthermore, “bright” and “dark” (refectance and backscatter) are relative terms and should be used with caution. These results suggest that the Venusian wind streak database is most likely far from complete and that many more streaks exist. 1. Introduction Of the countless geomorphological features observed on planetary surfaces, particularly of aeolian origin, wind streaks are among the most abundant. “Wind streak” is a general term for a variety of aeolian features that, when observed from above, appear as distinctive albedo surface patterns. They are known to occur by the thousands on Mars, Venus, and Earth (Cohen-Zada et al., 2016; Greeley et al., 1995; Thomas et al., 1981). Recently, dark wind streaks were identifed on the surface of Pluto (Stern et al., 2015; Telfer et al., 2018), and it is likely that dark wind streaks appear on Titan and possibly Triton (Sagan and Chyba, 1990; Porco et al., 2005; Malaska et al., 2016). As with all aeolian features, wind streaks result from interactions between the at- mosphere and planetary surface, and can indicate past and present climatic processes. However, as opposed to other common aeolian bedforms such as dunes (Hayward et al., 2014), wind streaks are globally distributed and serve as leading indicators of the prevailing wind directions near the surfaces of planetary bodies other than Earth. For almost four decades, wind streaks have been used to estimate the atmospheric global circulation on Mars and Venus (Fenton and Richardson, 2001; Greeley et al., 1993; Greeley et al., 1994; Veverka et al., 1981). Although the application of wind streaks in planetary research for climatic purposes is supported by a recent terrestrial study (Cohen-Zada et al., 2017), techniques for wind streak interpretation in remote sen- sing images are still lacking. The geomorphological manifestations of wind streaks are diverse. These streaks can have signifcant topo- graphical expressions or consist only of thin layers of deposited (or eroded) surface material. In some cases, the formation of diferent types of dunes and ripples relative to an obstacle is responsible for wind streak visibility (e.g., in the lee of a crater). In other cases, the com- positional contrast between the streak and its surroundings facilitate observation. Nonetheless, the outcome is the same in each situation (i.e., a change occurs in the surface albedo) (Greeley and Iversen, 1985). The surface albedo is frequently used to describe the geomorpho- logical nature of wind streaks. Previous research proposed that bright wind streaks in optical images are depositional, while dark wind streaks are erosional (Thomas et al., 1981; Thomas et al., 1984; Veverka, 1975; Veverka et al., 1978). Further examinations showed that not only do other possibilities exist on Mars (Edgett and Malin, 2000), but that radar-visible wind streaks on Venus cannot be discussed in the same manner (Greeley et al., 1992). Exclusive information about aeolian features can be obtained from radar imagery. However, the responses of radar to aeolian features are not fully understood, and also depend on both the incidence and look angles relative to the bedform orientation https://doi.org/10.1016/j.rse.2019.111342 Received 14 March 2019; Received in revised form 20 July 2019; Accepted 21 July 2019 ⁎ Corresponding author. E-mail address: avivlee@post.bgu.ac.il (A.L. Cohen-Zada). Remote Sensing of Environment 232 (2019) 111342 0034-4257/ © 2019 Elsevier Inc. All rights reserved. T