Orthoimage Generation by GÖKTÜRK-1: A Test Case in Rome

The paper presents a first evaluation of the potentialities of the imagery acquired by the GÖKTÜRK-1 satellite for the generation of orthoimages. Starting from a stereo pair captured over Rome (Italy), two orthoimages were generated with the Free and Open Source Software DATE developed at the Geodesy and Geomatics Division, Sapienza University of Rome. The two orthoimages were compared to a map of Rome at 1:2000 scale: only translations in the East and North directions were detected as geolocation errors, compliant with the expected geolocation accuracy of GÖKTÜRK-1 (CE90 of 10 m with no Ground Control Points). Specifically, an East bias of approximately -8 m was found for both the orthoimages, whereas a North bias of 1 m was detected for the quasi nadiral image and a much higher North bias of -7 m was observed for the second image, displaying an off-nadir angle of about 25 degrees. These geolocation errors can be in principle corrected using just one Ground Control Point, enabling the production of orthophoto maps at 1:5000 scale from GÖKTÜRK-1 pseudo-nadiral imagery.