## Appendix A Overview of the SkySat and PlanetScope Push-Frame Imaging System  
### SkySat  
The SkySat constellation consists of 14 individual nano-satellites with a size of 60 \(\times\) 60 \(\times\) 95 cm and a weight of approximately \(\sim\)110 kg. These satellites operate in the same sun synchronous orbit at an altitude of \(\sim\)500 km, offering a sub-daily revisit capability. They are equipped with a Cassegrain telescope with a focal length of 3.6 m, and a focal plane consisting of three 5.5 megapixel CMOS imaging detectors. Each detector consists of five distinct bands arranged vertically along-track with a size of 2560 \(\times\) 2160 pixels and a pixel size of 6.35 \(\upmu\)m: the upper half of each detector is used for panchromatic band (450-900 nm), and the lower half is used for four multi-spectral bands (blue: 150-515 nm; green: 515-595 nm; red: 506-695 nm; near infra-red: 740-900 nm) [2; 47]. A schematic of the focal plane layout (arrangement) is shown in Figure 2.  
The SkySat system can provide images and videos with a spatial resolution of less than one meter. For the video product, only the panchromatic band of the central detector (Figure 2a) records videos with 30 to 120 frames per second. For the imagery product, larger areas can be covered using a push-frame imaging mode, where the three detectors acquire a continuous strip of single frame images named as \"scene\", resulting in overlap along-track between consecutive scenes of the same detector and across-track overlap between different detectors Figure 2b). The swath width of SkySat image data is \(\sim\)6.6 km on the ground, which corresponds to -74,834 pixels in the across-track direction (Figure 2b). The ground sampling distance (GSD) at the nadir of the SkySat-1 and Skysat-2 is 0.86 m for panchromatic bands and 1.1 m for multispectral-bands. As for the new generation of SkySat satellites (i.e., SkySat-3 to SkySat-14), they have a resolution of 0.65 m and 0.81 m in the Panchromatic and the Multi-spectral bands, respectively. SkySat system is agile enough to acquire data in stereo mode similar to the present Very High Resolution (VHR) mission of Ikonos, Spot or WorldView. The pointing angle can be triggered in a range of \(\pm\)40\({}^{\circ}\) (i.e., a convergence angle of 20\({}^{\circ}\)-40\({}^{\circ}\)). A significant advantage of SkySat is the aptitude to acquire up to three images for an area, taken from the same orbit at along-track forward-, nadir-and backward-view of the sensor. Such image triplets acquisition mode is denoted as tri-stereo mode [48], which is similar to the Pleiades mission [26; 49; 50]. Planet has three SkySat imagery products that can be used for 3D extraction, referred to as L1A All Frames, L1A Fast Track and Basic L1B [2]. L1A All Frames includes all frames collected as panchromatic Level 1A with a ground sampling at nadir \(\sim\)0.9, within this level we have all frames acquired by each detectors at a high overlapping sequence. This level is delivered with the physical camera model and interpleaded RPCs derived from the physical parameters of each satellite (i.e., solved using the terrain-independent approach, Figure 1). L1A Fast Track, includes all the panchromatic scenes that match the footprints of the composite L1 Bs (2560 \(\times\) 1080 pixels, Figure 2b) with a GSD of 0.9 m at nadir, delivered with RPCs derived from the satellite telemetry. As with the Basic L1B level, the panchromatic and multi-spectral scenes are co-registered and fused using a super-resolution algorithm with a single panchromatic scene, called \"Panchromatic anchor frame\". The \"Panchromatic anchor frame\" scenes are chosen in a manner to have roughly an overlap in the along-track direction, as well as an across-track overlap between detector 2 and detectors 1 and 3 (cf. Figure 2b for an overview).