Combined rigorous-generic direct orthorectification procedure for IRS-p6 sensors

The accessibility of global data, such as the digital elevation model (DEM), and the development of global visualisations allow promising new methods for minimising the distortion in the online generation of rough orthorectified products to be developed. Direct georeferencing (DG) has attracted a considerable amount of attention in the applications of pushbroom raw images in orthorectification or mono-plotting using ancillary satellite data. This study builds on recent DG studies to achieve an “orthoimage” from raw data and to determine potential mapping errors due to the DG procedure. Thus, this paper focuses on establishing a simple method for mitigating the misalignments of space-borne imageries to be used in direct orthorectification. Towards this goal, instead of image resectioning, affine transformation in different coordinate systems is employed in the orthorectification algorithm to compensate for the systematic DG errors. For a given point, the elevation corresponding to the obtained planimetric coordinate is extracted using available topographic maps and global DEMs, such as SRTM’s and ASTER’s DEMs. As a result, parameters no longer need to be updated, as in the conventional orthophoto generation methods. To evaluate the proposed procedures, experiments were conducted over three different IRS-p6 sensors in five datasets with different swath widths and tilt angles. The obtained results also demonstrate that the geographic coordinate system and a simple 2D affine transformation can efficiently correct misalignments.