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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 km2
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
1st 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,Ycheck the check points coordinates measured on control dataset and X,Ydata 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
RMSEX,Y (m) 0.389 0.607 0.495 0.838 0.453 0.465
AFTER BIAS REMOVAL
RMSEX,Y (m) 0.522 0.381 0.578 0.6455 0.453 0.465
HR RESIDUALS
Data source Pleiades B1 Geoeye-1 LSO
RMSEXY (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 RMSEY ≠ StDEVY indicating a systematic error in Y axis • Geoeye-1 data have the bigger RMSEXY 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.
