Geometric Correction

Introduction:

When remotely sensed images are collected, certain factors can cause the location of the pixels to be different from their actual locations on the earth’s surface. This distortion is fixed through geometric correction. Geometric correction is a process of image transformation using known locations on the earth’s surface called ground control points.

Methods:

The first method I used to correct an image was “image-to-map rectification. I used a  USGS 7.5 minute Digital Raster Graphic topo map to correct a multispectral satellite image. I recorded points at corresponding locations in both images, using easily identifiable landmarks like levees or intersections. After four of thee points were collected polynomial transformation was calculated to correct the multispectral image.

The second method I used to correct an image was “image to image registration”. When correcting the second image, a second image with the same extent was used.  The second image already had ground control points recorded, so I needed to find their locations on the second image to record their locations on the image. After 10 points were recorded, a 3^rd order polynomial transformation was performed.

Figure 1: The results of the second image correction.

Results:

Geometric correction allowed for non-corrected images to be used. It will be an extremely useful skill to know as a remote sensing professional, and I’m sure it will be used often.