Ronald G. Blom

Detection of subsurface features in SEASAT radar images of Means Valley, Mojave Desert, California

Igneous dikes buried beneath as much as 2 m of alluvium in the Mojave Desert of California were detected by the SEASAT L-band (23.5-cm wavelength) synthetic-aperture radar (SAR) in 1978. The roughness and dihedral configuration of the dikes are favorable to generation of strong radar echos. The soil-moisture levels in 1978 were likely below the critical 1% level. The other permissive conditions for radar penetration of a fine-grained and thin alluvial cover are present. Our findings suggest that subsurface features with potential tectonic or geomorphic significance may be revealed in other orbital radar images of semiarid terrains.

Southern Arabian Desert Trade Routes, Frankincense, Myrrh, and the Ubar Legend

A location that likely inspired some elements of legendary accounts of the “lost city” of Ubar has been found at the edge of the Arabian Peninsula’s Empty Quarter at the village of Ash Shisr in modern day Oman. The site consists of the remains of a central fortress surrounding a well. Artifacts from as far away as Persia, Rome, and Greece are found, indicating a long period of far-flung trade through this isolated desert location. More recent work in Oman and Yemen indicates this fortress is the easternmost remains of a series of desert caravansaries that supported incense trade. Legend was that Ubar perished in a sandstorm as divine punishment for wicked living. Actually, much of the fortress collapsed into the sinkhole that hosted the well, perhaps undermined by ground water withdrawal used to irrigate the surrounding oasis. Less fanciful interpretation of legendary and other accounts clearly indicates “Ubar” was actually a region—the “Land of the Iobaritae” identified by Ptolemy. Desert trade was probably abandoned because of three primary factors: frankincense diminished in importance with the conversion of the Roman Empire to Christianity, desert ground-water levels continued to fall and the oases dried up, and reliable sea transportation was developed. The archaeological site was located, and its importance recognized, by an unusual combination of historical research and application of space technology in support of traditional archaeology. The site was known earlier but its significance unappreciated, as it was never studied in adequate detail. The archaeological importance of the site is supported through regional context provided by carefully enhanced Landsat Thematic Mapper (TM) and other satellite imagery that shows a discontinuous network of trails that converge at Shisr. Some of these trails are demonstrably old as they pass beneath sand dunes 100 m tall. Thus the desert environment can preserve ancient evidence of human occupation detectable in remote sensing data. Image analysis further shows no evidence of major undocumented sites in this desert region (e.g. the “Ubar” of legend). The interdisciplinary nature of this work demonstrates the significant and still underutilized potential of using remote sensing and GIS technology in support of traditional archaeology.