Having no prior experience with raster files besides my previous introductory GIS courses, the first lab assignment for Remote Sensing had me a little nervous. The chapter assignments for Module 1 and Module 2 were detailed and lengthy but necessary to provide the background information needed to have an understanding of the history of remote sensing and the technology behind it. Module 2's focus was on aerial photography. In Exercise 1 we were tasked to interpret the tone and texture of a provided aerial photograph. Tone is the brightness or darkness of an area. We had to identify five areas on the image that depicted variations in tone ranging from very light to very dark. I realized my mapping skills were a bit rusty but was able to convert identified tone areas to a feature shapefile. Identifying five varying areas of texture proved to be more difficult as this interpretation seemed more subjective. Knowing where this aerial photograph was taken might have aided my interpretation. Variations in texture were on a scale from very fine to very coarse with "mottled" being the middle of the range. Hopefully as the course progresses my interpretation skills will improve.
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| Exercise 1 - Tone and Texture Interpretation |
Exercise 2 had us examine another aerial photograph and identify different features/objects in the photograph using four different elements of image interpretation (shape/size, pattern, shadow and association). We had to identify three different objects in the image for each criteria, except association which required two. Some features were easily found, while others were identified by more carefully studying the image, especially when using the shadow element. Noting the angle of the shadow and also applying the element of patterns. For example, at first glance I thought long stick like objects were light/lamposts but after looking at the shadows and noticing a repeating pattern I realized these sticks were utility/transmission line poles. This exercise was my favorite part of the lab because I began to see how the different elements could be used individually as well as combined to aid in the visual interpretation of an image.
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| Exercise 2 - Features Identified Using Elements of Image Interpretation |
In Exercise 3 we were tasked with comparing a True Color image of an area with a False Color Infrared image of the same area. This exercise proved to be the most difficult for me. I identified five different features to compare between the two images. I tried to understand which colors were being absorbed and which colors were being reflected. Some of the color differences of my selected features did not make sense to me. What appeared as a field in the True Color image appeared as water in the False CIR image. Also, some areas that appeared white in the True Color image appeared as blue water features in the False CIR image while other white areas remained white. Again, having an idea of the location of these images would have aided in the visual interpretation of the two raster files. It could also be that the images were taken at different times, possibly months apart, and this would explain why the True Color image showed a feature as a field while the same area in the False image appeared as water. Possibly during construction of the area the field had originally been a water retention area. Some areas that appeared as water (blue) in the False image that did not appear as water in the True image may have changed due to a flow release from a nearby power plant or industrial facility. I realized after this exercise how important it is to know your study area when possible.
I am looking forward to learning about remote sensing technology and how to best use it in GIS applications.
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