25 May 2011 NDVI

It was another warm and sunny day today. The breeze is the only thing that is cooling us down now. Just a couple of weeks ago the wind was cold and uncomfortable. Work is moving very well for my last week here. We are getting alot accomplished and everyone is busy. I worked on cutting in the last of the carbon dating collars today. These will be used later in the season to find out how old the carbon is in the soil at various sites. After doing that I worked with Elizabeth to capture the NDVI data. What is NDVI? I'm glad you asked!

NDVI stands for the Normalized Difference Vegetation Index. It is a tool that measures the greenness of an area and helps to put a quantitative view of that greenness. This measures the infrared and the visible light that is reflected from plant leaves. The numbers change with the amount of chlorophyll in the green leaves of vegetation. Healthy plants reflect less red light and therefore have a higher NDVI. The number can go from a negative 1 to a positive 1. So the closer you are to 1 the more healthy plants you have and the more green you measure. You can just look at an area and say it is green. That statement doesn't have any meaning to someone who can't see the area. The NDVI helps to give a number to an area that is the same throughout the world.

If I take a photo of a plot in our experiment with a regular camera it will look like a normal picture. But with the NDVI camera the photo will come out looking like a dark picture that nobody would want! However, when you run this photo through the NDVI program on the computer it shows the green areas in a pink shade. The other colors are places that have not turned green yet.

The program then changes the photo once more to almost a black and white, very unreal looking photo. From this black and white shot, the program can determine an NDVI number. This is the number that tells you how much green is there. This technology was developed in 1973 and is used extensively today by many organizations including NASA. NASA uses this information to track crops and changes in the growing patterns around our country and the world. At time they can see where water is increasing or decreasing, where disease may have affected vegetation, and how different types of vegetation are changing.

Dr. Natali will use this data to determine how green the plots are during the year, and how different the warming side is from the non-warming side. Later there may also be measurements to show the difference between the drying and non-drying areas. The photos in this journal show different plots during September of last year and May of this year. During September we see lots of green in the plants. This is when the tundra has really taken off and is growing well. May is a time when things have not yet bloomed and green is still showing up on the plants. The September NDVI = .487, which is good. The May NDVI = .112, which is much lower and reflects the plants when they have not greened up yet. How high do you think this area can go? What would the NDVI be in the middle of the winter? Think about it!