Remote Sensing Lab 8

The main goal of this lab is to look at spectral reflectance signatures of different earth surfaces captured by satellite sensors. This lab had three parts to it. First it showed how to get the spectral signatures of its features from an image . Then I learned how to graph those signatures which allows you to compare them to each other. The final part of the lab is all about taking those graphed signatures and interpreting them to try and determine what kind of land feature they are representative of. These spectral signatures can be used for many purposes. One of the biggest is for keeping track of crop health in agriculture. It makes the growing process much less expensive for large farm and is much more efficient. Instead of paying many workers to go out into the fields to check on the crops they can use satellite images to look at the health of the crops.In farming they can track many things about the crops. Moisture content of the soil and plants, health of the plants, if there is a weed invasion, how old the plants are, and how much organic matter is in the soil are all things that can be tracked for farmers.

How do you find a spectral reflectance signature? It is pretty easy to do and very straight forward. You take your aerial of satellite photo and use the drawing tool in Erdas Imagine. You select the polygon tool which allows you create a shape on the image. This shape is the area that the spectral signature is going to correspond with. In the case of a farm they would create the shape just around their field or a section of a field they are interested in and this will show the signature.

Once you have taken the spectral signature of an area you can and should graph it to see it in an easy to read way. All the signature is is a line graph on top of the blue, green, red, near infrared and middle infrared bands. It shows the amount of reflectance inside each of the bands and based on the amounts in the different bands you can get a pretty good idea of what kind of feature is in that area.

Figuring out what the spectral signatures are representing is the interpretation aspect of this lab. Roads, parking lots, lakes, rivers, farm fields, forest and all other types of land cover and features have different unique signatures. Knowing what the signatures look like for these features allows us to be able to better interpret aerial images. Sometimes this can be challenging however. There are so many different kinds of plants and vegetation and sometimes the spectral signatures look very similar for multiple kinds of vegetation. This is where hyper spectral sensors and images should be used. Hyper spectral sensors are much more sensitive and collect many more kinds of data. These extra kinds of data can be the key in finding the very small differences in signatures that are very similar. Being able to gather read and map spectral signatures is a very valuable skill.

 

This is multiple scpectral signatures for various kinds of landcover and features.

Sources:
Erdas Imagine 2013