Lab 8: Spectral Signature Analysis

Spectral Signature Analysis

Goal and Background

The main goal of Lab 8 is to gain experience in measuring and interpretating spectral signatures of various earth surfaces.

Methods

In this lab we will be creating spectral signatures of 12 common surfaces found on earths surface. These surfaces include standing water, moving water, vegetation, riparian vegetation,  crops, urban grass, dry soil, moist soil, rock, asphalt highways, airport runways, and concrete parking lots. To create spectral signature curves we find each surface, use the drawing tool to create a polygon inside that surface (Figure 1), then using the "Signature Editor" tool we can create a spectral signature of each land surface.

Figure 1  Using the polygon draw tool to create spectral signatures

 

 

 

Results

Figure 2 below shows the spectral signatures of all 12 surfaces that were collected. As you can see the majority of surfaces have similar spectral signatures in the visible spectrum. The largest difference in signatures occurr in band 5 (middle infrared). As you expect the reflectance of water starts highest in the blue and decreases across the green and red bands of the spectrum and becomes negligible across the NIR, MIR and thermal bands. You can also see that vegetation has a typical spectral signature, in that it has really high relfectance in the NIR band. The differences in reflectance between similar surfaces can be attributed to differences in color, water content, and algae content.

Figure 2  Spectral signatures of 12 common earth surface features.

 

Conclusion

In conclusion, the signatures of each surface are the most similar in the visible portion of the spectrum and have to largest difference in reflectance in the MIR portion of the spectrum. Therefore, to differentiate between surfaces it is best to use reflectances in the MIR portion.

Sources

Satellite image is from Earth Resources Observation and Science

Center, United States Geological Survey.