Singular value decomposition and wavy reflections in ground-penetrating radar images of base surge deposits

High-pass eigenimages of ground-penetrating radar (GPR) profiles were computed in order to quantify the amount of wavy reflections. These wavy reflections are caused by the presence of subsurface trains of climbing dune-forms in the base surge deposits of the Ubehebe hydrovolcanic field (Death Valley National Park, California). The profiles were collected along a flow direction radial to the Ubehebe Crater to study the lateral facies variation of the pyroclastic deposits. The reflections become increasingly less wavy moving away from the crater because the number and size of the climbing dune-forms decrease downflow. The high-pass eigenimages act as a filter discarding the highly correlated parts of the traces (i.e. those forming the flat reflections) and leaving the portions of the profiles with the wavy reflections. For this reason, the energy of the eigenimages appears to be an index of the waviness of the reflections. This index is relatively fast to compute and quantifies the decrease of the number and size of the climbing dune-forms in the deposits. (C) 2001 Elsevier Science B.V. All rights reserved.