Spatial accuracy of orthorectified IKONOS imagery and historical aerial photographs across five sites in China

High-resolution ((1 m) satellite imagery and archival World War II era (WW2) aerial photographs are currently available to support high-resolution long-term change measurements at sites across China. A major limitation to these measurements is the spatial accuracy with which this imagery can be orthorectified and co-registered. We orthorectified IKONOS 1 m resolution GEO-format imagery and WW2 aerial photographs across five 100 km 2 rural sites in China with terrain ranging from flat to hilly to mountainous. Ground control points (GCPs) were collected uniformly across 100 km 2 IKONOS scenes using a differential Global Positioning Systems (GPS) field campaign. WW2 aerial photos were co-registered to orthorectified IKONOS imagery using bundle block adjustment and rational function models. GCP precision, terrain relief and the number and distribution of GCPs significantly influenced image orthor-ectification accuracy. Root mean square errors (RMSEs) at GCPs for IKONOS imagery were ,2.0 m (0.9–2.0 m) for all sites except the most heterogeneous site (Sichuan Province, 2.6 m), meeting 1:12 000 to 1:4800 US National Map Accuracy Standards and equalling IKONOS Precision and Pro format accuracy standards. RMSEs for WW2 aerial photos ranged from 0.2 to 3.5 m at GCPs and from 4.4 to 6.2 m at independent checkpoints (ICPs), meeting minimum requirements for high-resolution change detection.