Spectral Signature Analysis and Resource Monitoring

Goals and Background

           The main goal of this lab is to gain experience in the measurement and interpretation of spectral reflectance of a number of earth surfaces. From there, basic monitoring of earth resources using different bands will be completed. Erdas Imagine will be used to  collect, graph and analyze the spectral signatures of the earth surfaces using there spectral signatures. Additionally, the health of vegetation and soil will be explored by using a simple band ratio technique.

Methods

         A personal folder was created prior to the start of lab 8, in order to ensure that the data was saved in the correct spot throughout the lab. Part 1 involved spectral signature analysis. A Landsat ETM+ was used that covered the Eau Claire Area and other regions around Eau Claire to analyze the spectral signatures of certain earth surface features and near surface features. The images used were from the year 2000. The spectral reflectance of 12 materials and man made surfaces will be looked at.

1. Standing Water
2. Moving Water
3. Deciduous forest
4. Evergreen Forest
5. Riparian Vegetation
6. Crops
7. Dry Soil
8. Moist Soil
9. Rock
10. Asphalt Highway
11. Airport Runway
12. Concrete Surface

          Erdas was opened and the image of Eau Claire and surrounding areas was opened. From there under the home tab, the drawing tool was selected and the polygon tool from inside the drawing tool was selected. A polygon was made on Lake Wissota to get the spectral reflectance of standing water. Next, by clicking on raster and then supervised and signature editor, the signature editor is opened. The class one label was switched to standing water, and the rest were changed to there correct label as they were completed. By clicking on the display mean plot window at the top, the user can see what the spectral plot looks like for the area inside the polygon that was made on Lake Wissota. The same process for collecting the spectral signatures for surface 1 is used for surfaces 2 through 12. All of the signatures are going to be displayed in one signature mean plot window, in an effort to get a good idea of how the features vary. The scale chart to fit current signatures button can be used to fit all the different signatures in one frame. The chart background color was changed to white in an effort to increase visibility on the graph, from there the values were recorded and accessed.

        Part 2 involves resource monitoring. This is done by performing a band ratio to view the health of vegetation and soils. The band ratio is normalized by the normalized difference vegetation index (NDVI), and the equation is shown below.

NDVI= (NIR-Red)/(NIR+Red)

       With a fresh Erdas opened, a viewer was added and the second image provided in the lab was added. From there, by clicking on raster, then unsupervised, then NDVI, the indices interface will be opened. A folder name (NVDI) was added to the lab 8 folder in the personal drive and the output was saved there. Be sure the sensor reads 'landsat 7 multispectral,' and that the function is the NDVI. After completion the image is viewed and the vegetation is documented. A map was generated from this tool and it is displayed below by figure 6.

       Section 2 of Part 2 is to perform the same steps as listed above for section 1 of part 2, though the goal now is to monitor the spatial distribution of iron contents in soils with Eau Claire and Chippewa counties. The equation used is displayed below.

Ferrous Mineral= (MIR)/(NIR)

       Be sure to change the select function to ferrous minerals this time so the tool outputs the target variable. A map of the ferrous minerals is displayed below by figure 5. The band values are displayed below for further discussion in the results section.

Band 1 (Blue): 0.45-0.52

Band 2 (Green): 0.52-0.60

Band 3 (Red): 0.63- 0.69

Band 4 (NIR): 0.77-0.90

Band 5 (Short-Wave Infrared): 1.55-1.75

Band 6: (Thermal Infrared): 10.40-12.50

Results

        Figure 1 below shows the first step of the lab, it shows how a polygon was drawn on standing water, and the table to the left shows how the values were displayed. The signature mean plot for the standing water is displayed on the right.

Figure 1

            Figure 2 below shows the signature editor in use in Erdas. It displays the values for the red, green and blue bands.

Figure 2

         Figure 3 below displays the signature mean plot of each of the surface and near surface features in the lab. This is an effective display because it shows the values all next to each other which makes the results meaningful because it is easy to note the differences.

Figure 3

         Figure 4 below displays the distribution of ferrous minerals in Eau Claire and Chippewa Counties. The distribution of more minerals is certainly centered to the west. This would make sense because there is less tree cover, and soil that has been more eroded and had time to form minerals. 

Figure 4

         Figure 5 is a map that displays the areas of heavy vegetation in the areas of Eau Claire and Chippewa Counties. The entire eastern side is covered in thick vegetation, mainly in the northeast corner. Whereas in a line to the southwest of lake Wissota there is a good amount of land that does not have vegetation on it.

Figure 5

Sources

Satellite image is from Earth Resources Observation and Science Center, United States Geological Survey.