Lab 5: Spectral Reflectance Signature Analysis & Resource Monitoring

Introduction & Goal

The goals of this lab is to gain experience on the interpretation of spectral reflectance signatures of multiple surface features on Earth. The data is captured by satellite images to be used in performing monitoring and basic delineations of Earth's Resources. Including monitoring the health of vegetation and soils utilizing remote sensing band ratio techniques. This lab post is intended for future reference and documentation of the correct image classification skills, and includes collecting spectral reflectance signatures from remotely sensed images, graph them, and perform analysis on them by the end of this lab.

Methods

By using a Landsat ETM + image that covers the Chippewa Valley area and other regions of WI and MN, we will gather and analyze the spectral reflectance signatures of various Earth surface features. Twelve materials and surfaces from the image had data collected including spectral reflectance signatures in Erdas, although spectral signatures can be efficiently collected in the filed named spectroradiometer as well. These surfaces include standing water, moving water, deciduous forest, evergreen forest, riparian vegetation, crops, dry soil (uncultivated), moist soil (un cultivated), rock, asphalt highway, airport runway, and concrete surfaces. Additionally, similar techniques were used to perform simple band ratio to monitor the health of vegetation and soils and will implement the normalized difference vegetation index (NDVI) on the image.

Results

Figure 1: Signature Mean Plot for Standing Water

The spectral channel that has the highest reflectance for standing water is the blue band (521 um). The spectral channel with the lowest reflectance for standing water is red (263 um).

Figure 2: Signature Mean Plot for all Earth surface features.

When looking at the graph containing all twelve spectral signatures, there appears to be three trends that generally dominate the plot: water, vegetation, and soil/rock/land. Standing water has a higher reflectance than moving water, potentially caused by other “sitting” particles/pollutants in the water compared to moving water. Vegetation features are relatively similar; however, crops have a higher red band and infrared channel compared to forest or wetland forest vegetation with more tree cover. This suggests that the crops are not as healthy as other types of vegetation in the area. Asphalt & Dry soil for land/rock trends dominates in the green spectrum/near-IR channel due to its high reflectance, because it does not absorb radiation unlike moist soil.

Figure 3: Signature Mean Plot for Soil Types

Due to the inverse relationship between soil moisture (and soil organic matter) and reflectance, it can be seen that the spectral channel that varies the most is the red band.

Figure 4: Signature Mean Plot for Deciduous Forest

The reason the deciduous forest displayed the highest and lowest reflectance at the spectral channels listed above (red highest, Green lowest) is because of the high reflectivity of plant health. The vegetation response to being close to red-infrared boundary shows the chlorophyll content and for this particular forest, there is a lot of red (and blue) light absorption. Lower absorption of the two chlorophyll bands would show reflectance of more green light.

Figure 5: Vegetation abundance map generated in ArcGIS Pro

In areas that are purple, there is likely very little vegetation, which therefore, includes features such as water bodies, buildings, roads, and areas where there are industrial/worked agricultural fields/areas.

In areas that are purple, there is likely very little vegetation, which therefore includes features such as water bodies, buildings, roads, and areas where there are industrial/worked agricultural fields/areas.

Figure 6: ArcGIS Pro  Map for Spatial Distribution of Ferrous Minerals

Based on the image, the red areas show the high distribution of ferrous minerals in the Chippewa and Eau Claire counties. Due to the nature of iron oxides and their presence in wetland soil science, I notice that there is a high presence in wooded and areas surrounding/with water (green tone).

Data and information provided by the UW-Eau Claire Geography + Anthropology Department

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