P141 3D GPR DATA ACQUISITION AND THE INFLUENCE OF POSITIONING ERRORS ON IMAGE QUALITY Summary J. GROENENBOOM J. VAN DER KRUK and J.H. ZEEMAN Delft University of Technology Applied Earth Sciences Mijnbouwstraat 120 2628 RX Delft The Netherlands Two 3D GPR data sets have been acquired over the same test site. The first data set was recorded manually. Positioning errors caused discontinuous behaviour of the measurements along the crossline direction. After application of a migration algorithm we observe that the image quality is distorted. The second data set was acquired with an automated measurement frame with high positioning accuracy. The