Remote Sensing: Lab 8 : Spectral Signature Analysis

Spectral Signature Analysis

Introduction

The goal of this lab was to obtain experience through hands on experience with the interpretation of spectral signatures of different materials on the Earth's surface. In the following lab, I used aerial photographs to collect spectral signatures and analyzed their reflectance with signature plot means to determine variations among different spectral channels and how they relate to different surfaces on our planet.

Methods

I was presented a list of 12 spectral signatures to collect and analyze. AOI's were collected for each signature using the drawing tool and then used with the supervised signature editor (Located under Raster options). Each of the 12 spectral signature was viewed on a signature plot mean separately and then all at once for comparison (Figure 13). The signature plot means were viewed and analyzed to come up with an idea of which surfaces were similar and those that were not. Comparing the bands also showed which bands are good indicators of different types of Earth surface materials. The figures below show all 12 signature plot means and then all of them on one graph.

Results

Highest and Lowest Reflectance

1. Moving Water: Highest = Band 1 (0.433 µm – 0.453 µm) Lowest = Band 4 (0.630 µm – 0.680 µm)

Vegetation: Highest = Band 4 (0.630 µm – 0.680 µm) Lowest = Band 3 (0.525–0.600) and 6 (1.560–1.660)

Riparian Vegetation: Highest = Band 4 (0.630 µm – 0.680 µm) Lowest = Band 3 (0.525–0.600) and 6 (1.560–1.660)

Crops: Highest = Band 4(0.630 µm – 0.680 µm) Lowest = Band 3 (0.525–0.600) and 6 (1.560–1.660)

Urban Grassland: Highest = Band 4(0.630 µm – 0.680 µm) Lowest = Band 3 (0.525–0.600) and 6 (1.560–1.660)

Dry Soil: Highest = Bands 4(0.630 µm – 0.680 µm) and 5(0.845–0.885) Lowest = Band 3 (0.525–0.600) and 6 (1.560–1.660)

Moist Soil: Highest = Band 1(0.433 µm – 0.453 µm) and 5(0.845–0.885) Lowest = Band 6 (1.560–1.660)

Rock: Highest = Band 5(0.845–0.885) Lowest = Band 1(0.845–0.885)

Highway: Highest = Band 5(0.845–0.885) Lowest = Band 4 (0.630 µm – 0.680 µm)

Runway: Highest = Bands 3(0.525–0.600) and 5 (0.845–0.885) Lowest = Band 4 (0.630 µm – 0.680 µm)

Concrete Surface: Highest = Band 1(0.433 µm – 0.453 µm) Lowest = Band 4 (0.630 µm – 0.680 µm)

Signature Mean Plots for all Signatures

Figure 1

Signature Plot Mean for Standing Water. The NIR and MIR has low reflectance because water absorbs a lot of NIR and MIR in turn reducing reflectance. The reflectance is high in the blue green spectrum.

Figure 2

Signature Plot Mean for Moving Water. The variations between moving water and standing water can be explained through the specular and diffuse reflection. Standing water will have more specular reflection because it is a smoother surface. Moving water will have more diffuse reflection because of the rough surface of moving water, which reflects light in all directions.

Figure 3

Signature Plot Mean for Vegetation

Figure 4

Signature Plot Mean for Riparian Vegetation

Figure 5

Signature Plot Mean for Crops

Figure 6

Signature Plot Mean for Urban Grassland

Figure 7

Signature Plot Mean for Dry Soil. Band 4 is higher here than moist soil. This is because dry soil has less water to absorb NIR, therefore more is reflected.

Figure 8

Signature Plot Mean for Wet Soil. Band 4 is lower here because water in the soil absorbs more NIR, causing lower reflectance than dry soil, which has less moisture content.