Optimization of optical image geometric modeling, application to topography extraction and topographic change measurements using PlanetScope and SkySat imagery

Abstract:

The volume of data generated by earth observation satellites has increased tremendously over the last decades and will increase further in the coming decade thanks in particular to the launch of nanosatellites constellations. These data should open new avenues for Earth surface monitoring due highly improved spectral, spatial and temporal resolution. Many applications depends however on the accuracy of the image geometric model. The geometry of optical images, whether acquired from pushbroom or frame systems, is now commonly represented using a Rational Function Model. While the formalism has become standard, the procedures and data used to generate these models are diverse. The RFM models delivered with commercial data are generally not accurate enough for 3-D extraction or ground deformation measurements. In this study, we present a methodology for RFM optimization and demonstrate its potential for 3D reconstruction , using tri-stereo and multi-date Cubesat images provided by SkySat and PlanetScope, respectively. We use SkySat data over the Morenci Mine, Arizona, which the largest copper mine in the United States. The re-projection error after the RPCs refinement is 0.4 pix without using GCPs. Comparison with a reference DEM obtained from a LiDAR survey (1m GSD) over stable areas yields a standard deviation of the elevation differences of ~3.9 m. The comparison of the 2 DEMs allows detecting and measuring the topographic changes due to the mine activity. We assess the potential of PlanetScope data, using multi-date DOVE-C images from the Shisper glacier, located in the Karakoram Pakistan which known for its recent surge. We extracted DEMs in 2017 and 2019 before and after the surge. The reprojection error after the RPCs refinement is 0.6 pix without using GCPs. The DEMs accuracy was evaluated through comparison with the SRTM and with DEM generated from GE-1 stereo images. The standard deviation of the elevation differences in stable areas between the DOVE DEM and SRTM is ~12m, and ~7m with the GE DEM. The mass transfer due to the surge is clearly revealed form the comparison of the 2017 and 2019 DEMs. The study demonstrates that, with the proposed scheme for RPC optimization, times series of DEM extracted from SkySat and Dove images can be used to measurer topographic changes due to mining activities or ice flow.