Abstract
Optical and infrared remote sensing may provide first-order clues for the identification of potential impact structures on the Earth. Despite the free availability of at least optical image data at highest resolution, research has shown that remote sensing analysis always remains inconclusive and extensive groundwork is needed for the confirmation of the impact origin of such structures. Commonly, optical image data and digital terrain models have been employed mainly for such remote sensing studies of impact structures. With the advent of imaging radar data, a few excursions have been made to also employ radar datasets. Despite its long use, capabilities of imaging radar for studying surface and subsurface structures have not been exploited quantitatively when applied for the identification and description of such features due to the inherent complexity of backscatter processes. In this work, we make use of higher-level derived radar datasets in order to gain clearer qualitative insights that help to describe and identify potential impact structures. We make use of high-resolution data products from the ALOS PALSAR-1 and ALOS PALSAR-2 L-band sensors to describe the heavily eroded Oasis impact structure located in the Libyan Desert. While amplitude radar data with single polarization have usually been utilized to accompany the suite of remote sensing datasets when interpreting impact structures in the past, we conclude that the integration of amplitude data with HH/HV/HH–HV polarization modes in standard and, in particular, in Ultra-Fine mode, as well as entropy–alpha decomposition data, significantly helps to identify and discriminate surface units based on their consolidation. Based on the overarching structural pattern, we determined the diameter of the eroded Oasis structure at 15.6 ± 0.5 km.Graphical .
Highlights
Introduction and backgroundRemote sensing data analyses have advanced to an important and commonly utilized tool for the surface investigation and characterization of potential or already confirmed impact structures (e.g., Garvin et al 1992; Wagner et al 2002; Koeberl 2004; Koeberl et al 2005a, b; Buchner and Schmieder 2007; Folco et al 2010, 2011; Schmieder et al 2008, 2013; Reimold and Koeberl 2014)
While most large bolide impacts, bar very low-angle impacts, produce quasi-circular crater forms when impacting on planetary surfaces, not all circular features are caused by impacts
We aim to demonstrate the considerable potential by using SAR imaging for single-amplitude analysis of L-band SAR and for making use of (1) multi-temporal/polarization amplitude and (2) polarimetric signatures that are acquired through multiple SAR imaging passes
Summary
Remote sensing data analyses have advanced to an important and commonly utilized tool for the surface investigation and characterization of potential or already confirmed impact structures (e.g., Garvin et al 1992; Wagner et al 2002; Koeberl 2004; Koeberl et al 2005a, b; Buchner and Schmieder 2007; Folco et al 2010, 2011; Schmieder et al 2008, 2013; Reimold and Koeberl 2014). On the usually densely cratered and vegetation-free surfaces of other terrestrial planets, the forward argumentation is sometimes reversed and usually convincing arguments need to be found against an impact origin (e.g., van Gasselt et al 2007; Michaelski and Bleacher 2013) Even there, this might cause considerable debate despite the usually simple stratigraphic target environment and availability of super-resolution image data down to submeter scale from recent sensors on the Mars or Lunar Reconnaissance Orbiters
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