GIS4035 - Module5a - Intro to ERDAS Imagine and Digital Data 1

This week's lab appeared simple enough but truly understanding the differences in images and the devices used to capture them as well as continuing to learn about the properties of Electromagnetic Radiation and the Electromagnetic Spectrum proved to be challenging.  This class so far has covered more subject matter material than previous courses.   The focus points of this lab were to ensure we knew how to calculate the wavelength, frequency, and energy of Electromagnetic Radiation and to learn about and how to use ERDAS Imagine to view and create images.

The first exercise was to perform simple calculations using formulas such as Maxwell's Wave Theory: The speed of light is equal to the wavelength in meters times the frequency in Hertz.  The important takeaway was the inverse relationship between wavelength and frequency.  The longer the wavelength the lower the frequency and conversely, the shorter the wavelength the higher the frequency.  The wavelength can be used to determine the spectral region/location.  

Max Planck proposed the quantum theory of electromagnetic radiation where energy is transferred in discrete packets called photons (Jensen, p. 45).   The energy Q, of a quantum measured in joules, is equal to Planck's constant multiplied by the frequency of the radiation.  The relationship between energy and wavelength is also important.  Longer wavelengths result in lower energy content.

The second exercise introduced us to ERDAS Imagine.  We learned how to open provided raster images of different types and how to display the images using the Raster Options tab.   We used different tools and techniques to view the images such as panning, zooming, fitting the image to frame or changing its scale as well as how to display multiple images.  We also viewed an Arc Coverage file which is a digital vector format file that can be found in the ERDAS Imagine default installation filepath.   The images we viewed were obtained from different devices.   One image was from an Advanced Very High Resolution Radiometer (AVHRR) and the other images were obtained using a Landsat Thematic Mapper (TM).   These images had vastly different spatial resolutions.   This exercise also had us explore the different band combinations for multispectral data.  Changing the band combination can aid in identifying different elements in the image.

The final exercise had us open a thematic single layer in ERDAS Imagine and tasked us to focus on a smaller area of the image.   Using ERDAS we were able to create a subset image which was then used to create a map in ArcMap.   While in ERDAS we also viewed the image's attribute table and added a new "Area" column that calculated the area of each classification.

Classified Subset Image of Washington State Created in ERDAS Imagine

The subject material in this lab was the challenge for me this week; understanding the concepts and properties of EMR.  Learning how to change the view or display of images, in order to aid in the interpretation of feature elements, was the fun part.