Remote sensing signature of geological structures inferred on landsat imagery of Afikpo area Southeastern Nigeria

Satellite remote sensing has contributed immensely to the interpretation of linear features and other geological structures. In the study area, lineaments mapped were linear and planar features on satellite imageries that are expression of fractures, or faults within the subsurface.  Image lines of different contrast may extend from a few centimetres to several of metres in length. The Landsat imagery used has a spatial resolution of 30 x 30 m, and eleven spectral bands covering the visible and thermal region of electromagnetic spectrum. Four spectral bands were selected and used for the purpose of structural mapping namely; thermal infra-red band (Band 11), 11.5 to 12.51 µm; Short-wave infrared (Band 6), 1.57 – 1.65 µm; near Infrared (Band 5) 0.85 to 0.88 µm and Red (Band 4) 0.64 – 0.67 µm. Lineaments extracted from the digital satellite scene are concentrated mostly on the sandstone belt in the North-East close to Amasiri area. A total of 116 lineaments were generated. Seven thematic maps were produced; digital elevation model (DEM) was used to create surface features maps, shaded relief and slope while the regional lineament map was digitized from the enhanced colour composites of Landsat ETM (bands 7, 5 and 2) image using ARCGIS 10.0 software for visual extraction and delineation of geological structures which were also ground-truth. The area indicates major NE – SW to minor E – W orientation of lineaments. The lineament density identified indicates regional lineaments are of great importance as indexes for groundwater exploration, mineralization targets, rocks quarrying and structural interpretation.  Key words: Landsat imagery, geological structures, linear trends, ground-truth, Afikpo area Southeastern Nigeria.