How to Improve Satellite Image Accuracy
There are several factors contributing to the accuracy of satellite imagery: satellite positioning technology, distortion caused by variation in topography, and viewing angle (as discussed in the previous post “Satellite Imagery: Resolution vs. Accuracy”). To ensure a satellite image is ready for analysis, such as feature extraction and direct measurements, the accuracy of the raw image needs to be improved by performing orthorectification. An overview of the orthorectification process is available on a previous post “Orthorectification in a Nutshell”.
There are a few components needed to perform orthorectification on satellite imagery. First, you need the raw geometry metadata from the satellite imagery provider. The metadata contains information about the satellite’s orbital position and orientation, which is contained in the rational polynomial coefficient (RPC) file. The other component for orthorectification is a digital elevation model (DEM). Orthorectification accuracy is heavily reliant on the underlying DEM, as it better represents the topography details such as slope, elevation and terrain changes. A highly accurate DEM can better correct the geometric errors present in raw satellite imagery.
Ground Control Points
The overall image accuracy can be further improved by using ground control points (GCPs) together with the geometry data collected from the satellite. GCPs are used in the orthorectification process to match ground coordinates to pixel coordinates. It is best if the GCPs are located in open ground and have high contrast compared to the surroundings to ensure they can be visually identified in the satellite image.
We at Intermap Technologies® are passionate about geospatial technology and applications. We work with numerous industries and process data to provide location-based answers. This blog series will highlight how geospatial data processing plays an important role in imagery applications.