**3.3 Third-party mission data**

From the available third-party mission data sets, we selected for demonstration four pairs of multi-sensor images of TerraSAR-X and WorldView-2 [27].

TerraSAR-X is a German radar satellite launched in June 2007, followed by its TanDEM-X twin in 2010. Both operate in X-band and are side-looking SAR instruments that offer a wide selection of operating modes and product generation options [7]. TerraSAR-X has a revisit cycle of 11 days on the Earth's equator. We selected high-resolution spotlight mode images because they provide the highestresolution data of the target areas. As for the product generation options, we took enhanced ellipsoid corrected (EEC) and radiometrically enhanced (RE) data. Finally, we took horizontally polarized (HH) or vertically polarized (VV) images, as this option is most frequently used. The images have a pixel spacing of 1.25 m and a resolution of 2.9 m with WGS-84 map projection. The average size of the images is 8000 rows × 9600 columns.

In contrast, WorldView-2 provides a single panchromatic band and eight multispectral bands. It was launched in October 2009 to become a DigitalGlobe satellite. The revisit period of the satellite is about 3 days on the Earth's equator [28]. The resolution for the panchromatic band is 0.46 m and for multispectral bands is 1.87 m. The map projection of WorldView-2 is, again, WGS-84, and the size of these images (on average) for panchromatic images is 47,000 × 37,000 pixels (rows × columns) and for multispectral images is 11,000 × 9000 pixels (rows × columns).
