# Sensor-Level Mosaic of Multistrip KOMPSAT-3 Level 1R Products
## 1 Introduction  
High-resolution satellite images provide detailed geospatial information with a high geospatial resolution up to 30-80 cm over the area of interest, even located in inaccessible areas. There are many operating satellites such as Ziyuan-3 (2.1 m), KOMPSAT-2 (1 m), Gaofen-2 (0.8 m), TripleSat (0.8 m), EROS B (0.7 m), KOMPSAT-3 (0.7 m), Pleiades 1A/1B (0.7 m), SuperView 1-4 (0.5 m), GeoEye-1 (0.46 m), WorldView-1/2 (0.46 m) and WorldView 3 (0.31 m), etc. [1]. The satellites operate at low altitudes, such as 500,700 km, to achieve a high geospatial resolution of the data. In addition, the satellite cameras are specially designed by increasing the focal length up to around 10 m using a few aspherical mirrors. For example, WorldView-2, Pleiades-HR, and KOMPSAT-3 have focal lengths of 13.311, 12.905, and 8.562 m, respectively. As a trade-off for the low altitude and long focal lengths, the high-resolution satellite data show a relatively narrow field of view compared to the mid- or low-resolution satellite data. WorldView-3, Pleiades-HR, and KOMPSAT-3, for example, have swath widths of13.1, 20, and 16.8 km, respectively. Note that mid-/low-resolution satellite data have dozens or hundreds of kilometers of swath width. These high-resolution satellite cameras frequently use a combination of shorter CCD (Charge-Coupled Device) lines with a slight overlap to increase the swath width [2; 3; 4; 5; 6]. As examples, IKONOS, Quickbird, KOMPSAT-3 have three, six, and two overlapping PAN CCD lines, respectively, with shifts in the CCD lines in the scan direction. The merge of each sub-scene from CCD lines is carried out with precise camera calibration information. Each sub-scene is processed considering the sensor alignment, ephemeris effects, and terrain elevations to be merged for a single scene covering a larger swath [2; 5]. After the sub-scene merging process, high-resolution satellite data are provided in different processing levels. For example, Maxar provides WorldView data in system-ready, view-ready, and map-ready categories. System-ready imagery allows users to perform custom photogrammetric processes such as digital surface model (DSM) generation and orthorectification using the custom data. View-ready imagery data are products already photogrammetrically processed and designed for users interested in remote sensing applications. Map-ready is a base map that has been orthomosaicked. Level 1R and 1G KOMPSAT-3 data from the Korea Aerospace Research Institute are also available. Level 1R is a product that has been corrected for radiometric and sensor distortions. Level 1G is the product corrected for geometric distortions, including optical distortions and terrain effects, and finally projected to a universal transverse mercator coordinate system. Many satellite data, including WorldView System-ready and KOMPSAT-3 products, are usually delivered in a single image. This is true when the target area is small enough to be located in an archived image region or a new collection less than the swath width is requested. However, in some cases where the area of interest is large and located crossing over the archived images, users are delivered with a bundle of satellite images. Then, the users have to carry out a photogrammetric process for each data bundle to meet their application purposes. Typical photogrammetric processes with the bundle of images delivered include orthorectification and mosaics to create a complete image map. The orthorectification requires accurate sensor modeling information such as physical model or rational polynomial coefficients (RPCs) and DSM of the target area. In advance of the orthorectification and mosaic, users should carry out bias compensation of the original sensor model information using ground controls to meet mapping requirements [7]. Then, each image is orthorectified for the DSM and the resulting orthoimages are mosaicked for an image map. There have been many studies for high-resolution satellite image mosaics in the ground coordinates [8; 9; 10; 11; 12].