Module 3: Intro to ERDAS Imagine and Digital Data

 Module 3: Intro to ERDAS Imagine and Digital Data

In this weeks lab we learned about how to calculate the Electromagnetic Radiation (EMR) and understanding how EMR transmits/travels through the landscape. Also, in this weeks lab we learned how to use ERDAS Imagine and why one would use it. Lastly, in this weeks lab we learned how different passive and active sensors can present their data in ERDAS Imagine.

It is important to note that EMR energy comes from the sun and is a continuous spectrum of energy. Also, EMR has different wavelengths and frequencies that range from a longer wavelength equals a lower frequency to a shorter wavelength equals a higher frequency. Nowadays the equations to know the frequency and wavelengths are done automatically through the remote sensors. We did learn how to do basic equations called Maxwell’s wave theory: C = λν and Planck Relation: Q = hν. The Maxwell's wave theory is the relationship between the wavelength and frequency of the EMR. The Planck Relations is the amount of energy is inversely related to the wavelength of the light. This means that the shorter the wavelength, the greater the energy of each photon of the light. Being able to understand how the remote sensors interpret the data can help with the GIS analyst knowing what EMR energy is being collected.

I have been using remote sensing machines for awhile but I have always used ArcGIS Pro after the data was processed. This weeks lab showed another way to look at data and that is ERDAS Imagine. This was supposed to help us understand how to look at large-data sets from remote sensors. First we learned how to put in Raster data into the data layer. The raster layers can be raw/multiple layer continuous data, single layer panchromatic continuous data, or categorical/single layer thematic data. This is important because the raster data is meant for many different sensors. Also, when presenting the Raster Options and make sure to use the correct Display As tab. They are True Color, Pseudo Color, Grayscale, and Relief. In the lab we used Pseudo Color because it displays thematic images by associated each class value a color or single layer. Another tab we need to click on is Multiple and click on the Multiple Independent Files because it brings in files, individually, as separate layers that can be arranged or deleted separately from the other files in the Viewer. Lastly, click OK button and it will present your data on the page. Many of the other features are the same as ArcGIS Pro when zooming in and out as well as clicking on the different tabs to get information you may need to understand the data.

While being in ERDAS Imagine you can create an image that can be put into ArcGIS Pro. The way this is done is by opening the data imagine you want onto the layer. Since much of this data has a lot of information you will want to only take a portion of the image out. This is done by clicking on the Home tab and hit the button next to Inquire tab until you see Inquire Box. When it opens up you can change the size of the box and have that as the boundary. In the Raster tab, under the Geometry group, you will expand Subset and Chip menu, and select Create Subset Image. Then you will press the From Inquire Box button to set the appropriate area. Lastly, under the Output File navigate to your Output folder and name the file. Also, in this image we needed to get the Area of the different classification categories. This was done by right clicking on the layer I wanted and clicking Display Attribute Table and it will show up on the bottom of the screen. Then you will click on the Table tab and hit the Add Area tab. It will then show up and you can pick different ways of presenting the data but we chose hectares. The image below is how I presented the data in ArcGIS Pro.

Lastly, in this weeks lab was looking at the layer information, spatial resolution, and radiometric resolution. To see the layer information make sure to click on the layer you want and click on the Metadata tab. It will present a lot of data starting with File Info: which shows the basic information about the imagine including file type and file path. Next it is Layer Info: which shows the width and height in pixels, Type (if it continuous or thematic), and Data Type (how the pixel data is stored). Also, this is where you find the radiometric resolution that is usually expressed as a bit number (Unsigned 8-bit). Next tab is Statistics Info: which shows the min and max of the pixel darkness (min) or brightness (max). Also, shows the mean, median, and mode which the values are the measures of the average brightness of all pixels in the layer. Whereas the standard deviation  represents how close most of the pixels fall to the mean value. Next tab shows Map Info (Pixel Center): which shows provides the spatial coordinates of the corners of the image in the projection and the height and width of each pixel in the image. The last tab is Projection Info: tells you how the data is being projected and if it is not geo-rectified it will be blank in this portion. Knowing how to read the metadata can help understand how the data was collected and if it was projected correctly.