Remote Sensing: Module 6 - Image Preprocessing Part 1

     This modules covers spatial enhancements and image preprocessing. The exercise introduces the USGS Global Visualization Viewer where satellite and aerial data can be browsed and downloaded. These satellite images can then be imported into ERDAS Imagine for analysis. Some of the Landsat imagery exhibits striping due to a sensor malfunction and in this lab we attempted to correct for this phenomenon with spatial enhancements. These can be performed in either ArcMap or Imagine. Edge detection, Fourier transformations, and other techniques help in getting the most out of remotely sensed data.
     Two maps below show my attempts at image enhancement. The first one is the map deliverable for the exercise. I used the Focal Analysis tool in Imagine iteratively. That is, I performed a focal analysis calculating the mean of a 3x3 kernel (excluding 0 values from the calculations) and applying those values to pixels with a value of 0. Performing this analysis to each end product of the previous analysis (using the same exact settings) results in gap closure. The image, however, is not perfect and there is a disconnect between the gap filled areas and the original data. causing it too look like an improper join. This image is a composite between the original banded image and the modified image. Other methods attempt to fill missing data by using Fourier transformations in conjunction with other filters (low pass, high pass, range/edge detect, sharpening).

Map 1: Image Enhancement Exercise Using Landsat Satellite Imagery

     The second map I created shows some of the end products of combinations of filter effects and enhancements including focal statistics, histogram adjustments, and altering raster display settings. The top left image is the original, unaltered image with gaps. The top right is the image I used in my final map above. The bottom left and bottom right images are composites using the banded image. The bottom left image uses a Fourier transformed, sharpened image. The bottom right image was made by using focal statistics (maximum) and a Fourier transformation. 

Map 2: Various Attempts at Image Enhancement Using Different Methods

     While you can perform these enhancements in ArcGIS, I predominately used ERDAS Imagine. Both programs are great but I like that I could open four views in Imagine and compare them simultaneously. Imagine also lets you preview the alterations which I found helpful.