Thermal & Multispectral Analysis

The three images above all show different ways in which a remotely sensed image can be viewed in order to examine different features of interest.  In this image showing part of the coast of Ecuador, a feature that seems to be fields is visible to the lower right of the island. Each image shows the same feature, but what each band combination highlights is different.  In the true color image, the colors are what would be "expected" - vegetation is green, bare earth is grey, urban areas are tan.  The smaller rivers and streams show variation in depth based on the lightness or darkness of the brown and grey hues.  When the band combination is changed to the configuration in the upper right image, much of the vegetation stands out as bright green, but several areas, including the focus feature, show up as blue.  This highlights the moisture content of various elements in the image, including all rivers and streams, as well as areas of agriculture that are moist.  The third image shows Layer 6 - the Thermal band, in one color ramp.  The feature stands out as both an area of vegetation, and an area of relatively high moisture content because of the radiant energy produced by water in comparison to other substances.

Multispectral Analysis

This week's lab focused on learning how to read and understand histograms, and understanding how to identify spectral characteristics of various features..  We also explored various band combinations that would highlight certain features within an image.  Below are three examples.

The first feature we were to identify had a spike in Layer 4 between pixel value 12 and 18.  These low numbers indicate that the feature absorbs rather than reflects EMR, and this image clearly shows that characteristic, especially when the colors are manipulated so that the water is especially dark, contrasted with the light green vegetation and pink/red ground.

The second feature we were looking for had to satisfy two different criteria - a spike in pixel values around 200 in Layers 1-4, indicating high reflectivity, and a spike in pixel values between 9 - 11 in Layers 5 & 6.  The snow-capped mountains have this pattern.  A bright, nearly electric blue makes this feature stand out.

Variations in this water feature are highlighted by using a band pattern that allows the vegetation to remain muted.  Attention is then focused on the variations in the water, showing sediment buildup and a clear channel leading out to a larger body of water.  

Image Enhancement

This map shows an image that was enhanced using both Imagine and ArcGIS.  The first problem was to reduce the visibility of striping that occurred in the Landsat7 image.  Fourier Transform is a process that reduces the banding, although it can still be seen.  Further use of filters and adjustment of the histogram improved the contrast and detail, allowing the viewer to be able to see edges more clearly, and to be able to identify areas of vegetation, water, and urban or residential land use.