Temporally extrapolating object-based threshold for updating urban extents from nighttime light data

This study proposed an object-based method to estimate the relationship of optimal thresholds in different The Defense Meteorological Satellite Program/Operational Linescan System (DMSP/OLS) nighttime light (NTL) images for the purpose of mapping large-scale urban dynamics. In the method, the optimal threshold for an urban object was predicted by delineating the reference threshold and relating it to that in a target year through object-based normalization. The process of threshold normalization assumed the stability or proportional change of NTL intensity over time for pseudo invariant pixels. A test in China to extend the thresholds derived for F152000 NTL data to F152005 and F182010 NTL images showed that the proposed method successfully connect thresholds between years. The estimated threshold was highly correlated with the one derived from the reference urban area, with R
²
of 0.96 and 0.90 and RMSE of 2.9 and 4.9 for 2005 and 2010, respectively. At the object level, R
²
and RMSE of the estimated vs. reference urban areas were 0.91 and 14 pixels and 0.85 and 30 pixels for 2005 and 2010, respectively. At provincial level, R
²
was 0.92 and 0.87 and RMSE was 316 and 451 pixels for 2005 and 2010, respectively.