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Imaging of Togo, West Africa, with Side-Looking Airborne Radar (SLAR) in 1977 provided the data required for the production of semicontrolled radar mosaics at a scale of 1:200,000. These mosaics revealed significant errors in the existing geologic and topographic maps of Togo. The mosaics also served as a base for the generation of a new geologic map of Togo. The use of two opposing radar "look" directions helped in making numerous revisions, such as identifying previously unknown structural features, age relationships, refinement of unit boundaries, and the repositioning of structural features and lithologic units. Positional errors in some cases involved relocation of points by as much as 12 km and reorientation of major faults by as much as 22°. Although the value of radar's synoptic view and low illumination angle for detecting geologic features has been clearly demonstrated, the utilization of a SLAR mosaic for rectifying the location and orientation of geologic features has not received sufficient attention.
Geologic mapping of Togo was initiated as early as 1905, and sporadic but continuing revisions occurred through 1973. The fact that numerous investigators with diverse interests have participated in subsequent mapping, without apparent rectification of major errors in position and orientation, suggests that errors on earlier maps were incorporated into more recent versions. That this is the case is emphasized by the lack of congruence of major, topographically expressed rock units and structures in recently published, small-scale maps with their well-defined counterparts on the radar mosaics. Furthermore, it suggests the seriousness of the error of geologic-map revision utilizing a previously published map as a base without verification of its geometric fidelity.
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