Leaflet | Map data © OpenStreetMap contributors, CC-BY-SA, Imagery © Mapbox, Map data © OpenStreetMap contributors, Length of green season computed and visualized from Landsat using Google Earth Engine
Zoom control is at upper left. Adjust transparency with this slider, to see road map underneath.
Then this slider allows you to see aerial map underneath.
This map differs from many satellite views. It is generated from a time series, and shows, as a first draft, average length of green season from 2017-18 for each Landsat pixel.
Green growing plants reflect a lot of near-infrared radiation, and they absorb red. The ratio, called normalized difference vegetation index (NDVI), is an indicator of the work of photosynthesis. Landsat, which passes over every 16 days, can measure NDVI over each quarter acre pixel when there are no clouds.
The colors on the map represent the number of days in the year that NDVI is observed to be over a threshold, in this case .33 (NDVI is usually between 0 and 1). Where the underlying map shows through, there are no observations above the threshold.
How long is the soil foodweb getting fed by carbohydrates from the roots of green and growing plants? When soil life is not being fed, it may starve or go dormant, and the work of growing and maintaining soil structure and aggregation is not being done. This has major implications for water quality, erosion, and soil health.
Length of green season is about soil health principles over time. As you can see from the map, management has major influence!