Lab 8: Spectral Signature Analysis

Goals and Objectives

The main goal of this lab is for you to gain experience on the measurement and interpretation of spectral reflectance (signatures) of various Earth surface and near surface materials captured by satellite images. In this lab, you will learn how to collect spectral signatures from remotely sensed images, graph them, and perform analysis on them to verify whether they pass the spectral separability test discussed in lectures. This is a prerequisite for image classification which will be cover in the advanced version of this class. At the end of this lab, students will be able to collect and properly analyze spectral signature curves for various Earth surface and near surface features for any multispectral remotely sensed image.

Methods

This lab was all about collecting spectral signatures on 12 different Earth surface's.  The 12 surfaces we needed to find were:

   1. Standing Water

   2. Moving water

   3. Vegetation

   4. Riparian vegetation.

   5. Crops

   6. Urban Grass

   7. Dry soil (uncultivated)

   8. Moist soil (uncultivated)

   9. Rock

   10. Asphalt highway

   11. Airport runway

   12. Concrete surface (Parking lot)

In order to do this I opened up the image that was provided and connected to Google Earth.  Connecting to Google Earth helps with finding the right surface.  It is difficult to find the right surface by just looking at the image in ERDAS.  Once I found the right surface I used the polygon drawing tool to draw in the surface area.  In order to find the spectral reflectance I had to use another tool called the signature editor.  This tool will show the spectral reflectance for each band for that surface and plot it on a graph.

Results

The image below is of the 12 different surface areas we had to draw a polygon on and collect the spectral reflectance on.  Using the Signature Editor tool we were able to have this grid of each surface we had to find.

The image below is a graph showing all of the surface areas and there respective spectral reflectance.  As you can see different surfaces have different reflectance.

Conclusion

Overall, this lab was very interesting to do.  To be able to go over other tools that we used earlier in the semester like syncing Google Earth with our image to be able to tell what kind of surface is on the image.  It was interesting to use new tools as well.  This was a great lab to do because remote sensing is all about reflectance and this lab was useful to help us be able to find different surface reflectance values.