Accuracy and Quality Comparison of Orthorectified High Resolution Satellite Images Panagiotis AGRAFIOTIS , Andreas GEORGOPOULOS Laboratory of Photogrammetry, School of Rural and Surveying Engineering, National Technical University of Athens [email protected] [email protected] SCOPE Accuracy and quality assessment of orthorectified high resolution satellite imagery from the Pleiades 1B and the Geoeye-1 data through : •Radiometric quality assessment •Comparative evaluation of their quantitative and qualitative properties Investigation of the advantages and limits of the Pleiades B1 Imagery for producing Large Scale Orthophotos (LSO) STUDY AREA Greece Cyclades The small island of Antiparos Area ≈35000 km 2 METHODOLOGY Data Pleiades B1 Geoeye 1 GCPs 4 5 Check Pts 6 10 RMSE (m) 0.045 0.160 GPS measurments Pansharpening HSV for Pleiades data and HCS for Geoeye data Photogrammetric georeference (LPS and Photomod 5) DEM extraction Orthophoto production TEST DATASET • Pleiades B1 stereopair (0.50m GSD) from April 2013 • Two adjacent GeoEye-1 stereopairs (0.50m GSD) from December 2011 • Aerial orthophoto (LSO) provided from Ktimatologio S.A. (Hellenic Cadastre) (0.50m GSD) from 2007 CONTROL DATASET Aerial orthophoto (VLSO) provided from Hellenic National Cadastre & Mapping Agency S.A. (NCMA S.A) (0.25m GSD) from August 2012 Independent measurements for checking horizontal accuracy of orthoimages 1 st degree polynomial RPC refinement + = 16 GCPs distributed evenly on the island area GPS observations Fast static method GCPs mean uncertainty of 0.010 m GCP Check Point Pleiades Distribution Automatic procedure for Pleiades B1, semi-automatic for Geoeye-1 GCPs used for transferring the scale and real elevation values 10 m elevation interval Bilinear Convolution GSD 0.50 m Orthorectification of all stereopair’s images for DEM checking Check Points measured on VLSO Distributed according to JRC Guidelines for Best Practice and Quality Checking of Ortho Imagery and NSSDA standards Areas with different terrain relief and land cover included 25 Check Points for Pleiades B1 26 Check Points for Geoeye-1 and LSO Check Points Distribution QUALITY AND ACCURACY ASSESSMENT IMAGE QUALITY ASSESSMENT Pleiades B1 Geoeye-1 LSO Visual inspection of orthophotos for errors and/or image defects Geoeye-1 image : • Abrupt change of brightness and contrast • Many regions presented extremely dark/light tones, predominantly on the buildings and along the roads • Radiometric saturation of certain regions is especially prominent Pleiades B1 image : • Presents much more information and clearer forms • Is much darker than LSO and Geoeye-1 imagery SPATIAL ACCURACY where, d is the deviation n the number of check points X,Y check the check points coordinates measured on control dataset and X,Y data the points coordinates measured on test dataset RESIDUALS ΔΧ ΔΥ Data source Pleiades B1 Geoeye-1 LSO Pleiades B1 Geoeye-1 LSO Check Pts 25 26 26 25 26 26 StDEV (m) 0.374 0.388 0.467 0.658 0.415 0.423 RMSE X,Y (m) 0.389 0.607 0.495 0.838 0.453 0.465 AFTER BIAS REMOVAL RMSE X,Y (m) 0.522 0.381 0.578 0.6455 0.453 0.465 HR RESIDUALS Data source Pleiades B1 Geoeye-1 LSO RMSE XY (m) 0.646 0.866 0.649 The BIAS is estimated by the formula: Where, σ is the random error • In LSO and Geoeye-1 RMSE Y ≠ StDEV Y indicating a systematic error in Y axis • Geoeye-1 data have the bigger RMSE XY possibly due to bad image quality leading to erroneous GCPs measurements • Pleiades B1 orthoimage has almost the same external accuracy as the orthoimage from aerial imagery (LSO from Ktimatologio S.A.) • All data are adequate for producing LSO, according to JRC and NSSDA accuracy standards Panchromatic GSD 0.50m Multispectral GSD 2.00m Pansharpened GSD 0.50m CONCLUSION Metric and radiometric comparisons proved that the Pleiades B1 high resolution satellite imagery is capable of producing highly accurate and reliable Large Scale Orthophotos (LSO) for mapping and GIS applications having clear advantage against similar products.