In this monthly feature, we span the globe and examine Our Changing Landscape with time series of medium resolution RapidEye satellite imagery. The RapidEye archive dates back to late 2008 and already contains more than 3 billion square kilometers of data. This month, we travel to the Midwest and look at changes in crop development over rural Logan County, Illinois.

The RapidEye Constellation

RapidEye is a constellation of five 5-meter medium resolution satellites each offering five spectral bands of information. The RapidEye constellation offers a daily revisit time to every location on the planet with a huge footprint that is 77-km wide. The data is priced competitively with a base price of $1.28 per square kilometer for all five spectral bands – academics do receive discounts. RapidEye adds a fifth band, the red edge, to the ‘traditional’ multispectral set of blue, green, red and near-infrared (NIR). The additional spectral data available in the red edge band allows users to extract more useful land ‘information’ than can be from traditional 4-band imagery sources. When RapidEye imagery is ordered as a Level 3A Orthorectified product, images from multiple dates are extremely well registered, making it the ideal data source for Our Changing Landscape.

The Growing Season in Logan County, Illinois

The Midwest is home to some of the richest soils and agricultural lands of the entire world, let along the United States. Each spring, farmers ready the fields for the summer crops that are to be grown and harvested to feed local livestock and hungry Americans! Having completed my undergraduate degree at the University of Illinois, I’ve seen my fair share of corn and soybean fields which is the inspiration for this month’s Our Changing Landscape.

In the animation below, we focus on a rural section of Logan County which is home to some of Illinois’ most productive corn and soybean fields. In Illinois, corn and soybean planting usually starts in April or May and continues through early June with harvests starting in mid-September and ending in mid to late-November. During the growing season, spring fields start barren or covered with a thin layer of dead vegetation, they are tilled, planted and crops fill in the rows from there, until they are harvested in the Fall. One way to track the development of crops through the growing season, also referred to as their phenological development, is with an index that is derived from multi-band satellite imagery. The red-edge normalized difference vegetation index (or red-edge NDVI) measures both the amount of vegetation and its health in a location. Therefore, it is an effective imagery-based tool to track plant growth throughout the growing season. For more information about the red-edge NDVI and how it is calculated, you can refer to this previous newsletter article.

In the animation, we used seven RapidEye images to track crop development in Logan County, with data spanning the 2010 growing season from: 3/29, 5/28, 6/16, 7/2, 8/15, 9/12 and 10/17. A red-edge NDVI was calculated for each date and then a similar color scheme was applied to each of these NDVI layers. The color scheme had five classes:

• Human-made structures, dead vegetation, bare soil and water – NDVI from -1 to 0.2; colored in red
• Light vegetation – NDVI from 0.2 to 0.275; colored in yellow
• Moderate vegetation 1 – NDVI from 0.275 to 0.35; colored in the lightest green
• Moderate vegetation 2 – NDVI from 0.35 to 0.45; colored in medium green
• Densest vegetation – NDVI from 0.45 to 1; colored in the darkest green

If you would like to find out more about using RapidEye for your academic studies, engineering projects or any landscape analysis, let us know at sales@apollomapping.com or (303) 993-3863.