Analyzing Spectral Signatures in Imagine

D. Meyerdmeyer@usgs.gov

E. Woodwoodec@usgs.gov

Concept: Spectral Signatures• Locate 5 examples of the following land

cover types and plot them:– conifer forest– mixed forest– water– agriculture (fields with crops)– agriculture (“bare” fields)– dense urban– open urban

RGB: decomposing images

RGB red green blueClass Red Green Blue

Tomato Bright Very dark Very dark

Background Very dark Kinda dark Medium

Green pepper Kinda dark Medium Very dark

Yellow pepper Very bright Kinda bright Very dark

Orange pepper Very bright Kinda dark Very dark

Garlic Very bright Very bright Very bright

Bowl Medium Medium Medium

RGB: spectral signaturesClass Red Green Blue

Tomato Bright Very dark Very dark

Background Very dark Kinda dark Medium

Green pepper Kinda dark Medium Very dark

Yellow pepper Very bright Kinda bright Very dark

Orange pepper Very bright Kinda dark Very dark

Garlic Very bright Very bright Very bright

Bowl Medium Medium Medium

Bright

Very bright

Kinda bright

Medium

Kinda dark

Dark

Very dark

Red Green Blue

Vegetation color (“spectra”)

Tools• Identify spectral signatures of different land

cover types using tools within Imagine: – Signature editor• Alarm feature• Signature editor statistics

– Areas of interest (AOI’s)• AOI tool

To do:• Using the “inquire” tool, locate 5 examples

of the 7 land cover types (5 different locations each)

• Make a spectral plot of each cover type (5 curves per plot)

• Determine how easy or hard it might be to identify each of the different cover types.

Locate example cover types• Open germtm.img in a viewer, display

bands 5,4,3 as red,green,blue • Using Inquire Cursor, type in file coordinates (make sure project is “file”, not “map”) and locate: x=185, y=480 (conifer forest)

Locate example cover types• Zoom into Selected Area – Note conifers

are darker, redder than mixed forests.

Make a plot of each cover type• From the viewer menu, select AOI > Tools (the AOI tools

icon window should appear). Click on the “create polygon AOI” icon. Draw a polygon around the “conifers” & double click to close.

Make a plot of each cover type (con’t)

• Click on “Classifier” in the ERDAS Imagine bar, and then click on “Signature Editor” (the “Signature Editor” window should appear).

• Click the polygon to select it (should be outlined with a rectangle when selected.

Make a plot of each cover type

• In signature editor, click on the “create polygon” icon

• Right click on the color field of the signature and make it “dark green”

• Label the class “conifer1”

Make a plot of each cover type (con’t)• To make plots in the Signature Editor, use

the “Display Mean Plot Window”– You can make multiple plots by selecting

multiple signatures ,using the multi-plot icon.

Make a plot of each cover type (con’t)• Repeat for each cover type, color

appropriately, • Can you tell where there might be problems discriminating different cover types??

Make a plot of each cover type (con’t)• Uses the image alarm in the signature editor to

locate best guesses of where the class might be in the image.

Make a plot of each cover type (con’t)

• To save the AOI polygons, select “File -> Save -> Save AOI layers as …”, type in the file name “germtm.aoi”, navigate to the results folder and click “okay”.

Make a plot of each cover type (con’t)• To manipulate the layers in the viewer (the 3-color

image itself, the AOI polygons, or the “Alarm mask” generated above), right-click on the image..