Using RapidEye 5-meter Imagery for Vegetation Analysis
In this short piece, the Apollo Mapping team would like to introduce you to the value offered by RapidEye's 5-meter medium resolution satellite imagery with its 5 spectral bands. The RapidEye constellation of 5 satellites offers daily revisit time to every location on the planet with a huge footprint that is 40-km wide. The data is priced extremely competitively with a base price of $1.28 per square kilometer – academics do receive discounts on this price – for all 5 spectral bands. RapidEye adds a fifth band, the red edge, to the 'traditional' multispectral set of blue, green, red and near-infrared (NIR). The red edge has been found to be particularly useful when studying vegetative health and stress.
For the animation below, we calculated a Red Edge Normalized Difference Index (NDVI) to show the health of vegetation when this RapdiEye data was collected over San Luis Valley in Colorado. A NDVI can reveal patterns of plant health that may not be apparent in natural color imagery. The scientific rationale behind a NDVI is predicated on the presence of chlorophyll in healthy plant vegetation. In a vigorous, healthy plant, chlorophyll is busy absorbing the sun's energy in the red band and converting this into the sugars it needs to grow and thrive. This same chlorophyll reflects most of the sun's energy that falls in the NIR spectrum. As such, a healthy plant has a high ratio between NIR and red reflectance that can be detected by satellites such as RapidEye. A Red Edge NDVI is calculated with RapidEye data like this:
Red Edge NDVI = (Band 4 – Band 3) / (Band 4 + Band 3)
Once this value is calculated for every pixel, you can create a colorized image where healthy vegetation is red (typically a value of ~0.35 for Red Edge NDVI); less healthy vegetation is orange to yellow; and the rest of the colors represent human-made features, bare soil and water. The results of this calculation are in the animation below; and it clearly shows areas of less healthy vegetation in these pivot agriculture fields. With this spectral information, farmers can improve precision agricultural techniques. It is not uncommon to find 6 or more images collected over the growing season in key agricultural zones making RapidEye the ideal solution for precisions agriculture.
If you would like to find out more about using RapidEye for your academic, agricultural or any vegetation study, let us know at email@example.com or (303) 993-3863.
An animation showing 5-meter RapidEye imagery over the San Luis Valley, Colorado. The first slide is in natural color, while the second slide shows a Red Edge NDVI calculation. (Image Courtesy: RapidEye). Please click the image to see the animation.