Remote Sensing Lab 6

Goal and Background - The goal of this lab is to practice geometric correction. There are two types of geometric correction; Image-to-map rectification and Image-to-image registration. These are both used in the program Erdas Imagine 2013.

Methods and Results - We first took an image of Chicago from 2000 that was distorted and we wanted to correct the image and we first took a topographic image of the Chicago area and brought it into Erdas with the distorted satellite image. Using image-to-map rectification we will be able to correct this image. We opened up the Geometric Correction tool and selected a first order polynomial model with a nearest neighbor resampling method. Since this is a first order polynomial model we only need three ground control points or GCPs, but we should always do more than the minimum, so we'll use four. The image below (fig 1) shows the four GCPs. We then perform the Geometric Correction and our output image is no longer distorted.

fig 1

In the second part of the lab we use a severely distorted image of a region in Sierra Leone in 1991. For this image we will be using the image-to-image registration method. Since this is more distorted than the pervious image we will be using a third order polynomial model with a bilinear interpolation resampling method. Since this is a third order polynomial it is more complex and will require at least ten GCPs, therefore we will use twelve to be on the safe side. The image below (fig 2) shows the twelve GCPs. We then perform the Geometric Correction and our output image is no longer distorted.

fig 2

Sources - All satellite images provided by Cyril Wilson.