Improved Regression-Based Component-Substitution Pansharpening of Worldview-2/3 Data Through Automatic Realignment of Spectrometers

This work presents a pre-processing patch to automatically realign the multispectral (MS) spectrometers of WorldView-2 or WorldView-3. Once the resampled bands have been accurately overlaid onto the Pan image, established component substitution pansharpening algorithms can recover their original top performance, which had been diminished in the passage from a 4-band (a unique MS spectrometer) to an 8-band setup (two separate MS spectrometers). The misalignment arises because the three instruments onboard Worldview-2 (four on WorldView-3) - namely, old MS, new MS, and Pan - share the same optics and thus cannot have parallel optical axes. Consequently, they image the same swath area from different positions along the orbit. Local height changes (hills, buildings, trees, etc.) originate local shifts among the datasets. The three images can be accurately aligned only if the digital elevation surface model is exactly known. The proposed alignment procedure is fully automated and does not require any additional or ancillary information, but relies on the unimodality of the MS and Pan sensors.