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Alluvial fans constitute important recorders of tectonic and climatic signals. Thus, determining the age of alluvial
deposits is a common and pivotal component in many quantitative studies of recent tectonic activity, past climatic
variations and landscape evolution processes. In this study we build on the established relation between surface age and
surface roughness and examine the use of radar backscatter data as a calibrated proxy for constraining the age of alluvial
surfaces in such environments.
This study was conducted in the hyper-arid environment of the southern Arava rift valley north of the Gulf of Aqaba.
ALOS-PALSAR L-Band dual-polarized (i.e., HH, HV) data with different incidence angles (24°, 38°) and resolutions
(6.25m, 12.5m) were examined for 11 alluvial surfaces, for which surface ages ranging from 5-160 ka were previously
determined. As expected, radar backscatter in such low-relief hyper-arid desert environments responded primarily to SR
at pixel-scales and below. Nonetheless, measured backscatter values for single pixels were found to be unsuitable proxies
for surface age because of the natural variability in SR across alluvial units of a given age. Instead, we found the
statistical properties of radar pixel populations within a given unit to be the most effective proxies for surface age. Our
results show that the mean backscatter value within representativeROI’s (region of interest) provided the best predictor
for surface age: Lower mean backscatter values correlated well with older and smoother alluvial surfaces. The HHpolarized
image with ~38° incidence angle and 6.25 m/pixel resolution allowed the best separation of surface ages. This
radar-based approach allows us to quantitatively constrain the age of alluvial surfaces in the studied region at comparable
uncertainty to that of “conventional” surface dating techniques commonly used.
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