Module 4 - Spatial Enhancement, Multispectral Data and Band Indices

In this week's lab, we encountered four tools that will be key in helping identify different features during image analysis: Histogram Analysis, Image Grayscale Analysis, Multi-spectral Band Experiments/Analysis, and Image Brightness Analysis. To practice this, we were tasked with finding features that fit certain criteria using the aforementioned methods. Furthermore, once those features were selected, we needed to choose multispectral band combinations that helped distinguish these features on the map. Below are the maps generated for each of those features.

Figure 1- Identification of water features. 

Feature 1: WATER

For identifying the feature in Layer_4, there is a spike between pixel values of 12 and 18. This is quite straightforward: the larger the feature, the larger the spike in the histogram due to the high concentration of pixels at that brightness level. Additionally, the fact that it is on the left side of the histogram indicates that these are dark features. The large dark body of water explains this spectral signature in the histogram. 

To highlight this feature in the image, the chosen filter was False Color Infrared (bands 4/3/2). This is because water appears dark, creating a stark contrast with the surrounding vegetation. Another acceptable band combination would have been False Natural Color (bands 5/4/3), where the dark blue water would be greatly contrasted against its green surroundings.

Figure 2 - Identification of Snow on the Mountaintops

Feature 2 : SNOW: 

The features that represent both A) a small spike in layers 1-4 around pixel value 200, and B) a large spike between pixel values 9 and 11 in Layer_5 and Layer_6, were deduced to be snow on the mountaintops.

The small spike in layers 1-4 around pixel value 200 represents a small amount of pixels at a high brightness level on the left side of the histogram. These correspond to the small caps of bright snow on the mountaintop. As for the large spikes between values 9 and 11, these represent the dark areas of the mountain surrounding the snow, which outnumber the amount of snow on the mountaintop.

To highlight this feature, the TM True Color combination of bands 3/2/1 was used, as the bright white snow highly contrasted with its dark mountain top surroundings.

Figure 3- Identification of varying water depth. 

Feature 3: Varying Water Depths

To represent the gradient in color of water in relation to its depth, the shallower the water, the lighter the color, and the more noticeable the changes in brightness. Once the water becomes deeper, which is the case for the vast majority of the water features in this image, the bands remain the same color as they correspond to those darker values.

To highlight these features, a custom band combination of 5/2/1, where one can distinctly see the depth dependent gradient from the lighter to the darker water features, was selected.  This combination also somewhat neutralized features surrounding the water and contrasted them at the same time.