Lab 8: Spectral Reflectance

Goals and Objectives

Within this lab, spectral reflectance from satellite images were measured and interpreted. Spectral signatures were collected from a provided image, then later graphed. Analysis was performed on the verified their spectral separability within the signature mean plots.

Methods

To begin the lab, the provided image was opened within Erdas. To collect spectral signatures, the Drawing tab was clicked, followed by the Polygon function. Once this was activated, a polygon is drawn around the desired surface type. From here the Raster tab is clicked. Next, the Supervised button is clicked and the Signature Editor is selected. Now, the Signature Editor is opened. Within the window, a new signature is added by clicking the Create New Signature form AOI button. Once the signature row appears, the Signature Name and color is able to be changed.

The collection of the standing water polygon, with its spectral curve

Next the Signature Mean Plot can be observed by pressing the Display Mean Plot Window button. The background color of the graph can be edited by selecting Edit, followed by Chart Options. Here a lighter color can be selected within the dropdown box. For this lab, the first surface type analyzed was Standing Water. The Signature Mean Plot looks as followed.

Signature mean plot of standing water

Throughout the rest of the lab, eleven other surface types were analyzed. All signature mean plots were gathered through the same processed previously used, however they were gathered within the same Signature Editor window.  The eleven other signature plots appeared as followed.

Signature mean plot of moving water

Signature mean plot of vegetation

Signature mean plot of riparian vegetation

Signature mean plot of crops

Signature mean plot of urban grass

Signature mean plot of dry soil

Signature mean plot of moist soil

Signature mean plot of rock

Signature mean plot of asphalt highway

Signature mean plot of airport runway

Signature mean plot of concrete surface (parking lot)

After all of these spectral signatures were collected, the Switch Between Single and Multiple Signature Mode was clicked within on of the Spectral Mean Plot windows. This allows you to observe all spectral signatures at once. Here, you can analyze similarities between the objects reflectance. The table below indicates which band wavelength had the highest and lowest reflectance for all surfaces.

Signature	Material/Surface	Highest (µm)	Lowest (µm)
1	Standing water	0.45	0.63 and 10.40
2	Moving water	0.45	10.40
3	Vegetation	0.77	10.40
4	Riparian vegetation	0.77	0.63 and 10.40
5	Crops	0.77	0.63 and 10.40
6	Urban grass	0.77	0.63 and 10.40
7	Dry soil	1.55	0.63
8	Moist soil	0.45	10.40
9	Rock	0.45	10.40
10	Asphalt highway	1.55	0.77
11	Airport runway	0.63 and 1.55	0.77
12	Concrete surface (Parking lot)	0.45	0.77

Results

The spectral curves of all twelve surfaces collected