on January 1, 2023

Plot a range of values of a NDVI calculated in Google Earth Engine

Hiking & Activities

Unlocking the Secrets of Green: Plotting NDVI Ranges in Google Earth Engine

Ever wondered how scientists keep tabs on the health of our planet’s greenery from space? A big part of it involves something called the Normalized Difference Vegetation Index, or NDVI for short. Think of it as a report card for plants, telling us how much healthy vegetation is in a specific area. And one of the coolest tools for crunching these numbers? Google Earth Engine (GEE). It’s like having a super-powered geospatial lab right at your fingertips.

NDVI basically works by looking at how plants reflect light. Healthy plants are like expert bouncers, soaking up red light but bouncing back near-infrared light. By comparing these two, we get an NDVI score. Simple, right?

So, how do we actually see what’s going on with these NDVI scores in Google Earth Engine? Well, it’s not just about getting a single number. It’s about understanding the range of values. Are most of the plants super healthy? Or are we seeing a lot of stressed-out vegetation? Plotting these ranges gives us the bigger picture.

Here’s the lowdown on how to plot those NDVI ranges in GEE:

  • Grab the Right Data: First, you need satellite images. Landsat and Sentinel are popular choices. Think of them as our eyes in the sky. You’ll want to filter these images to get rid of cloudy ones and focus on the specific area and time you’re interested in. Nobody wants to analyze a bunch of clouds!
  • Do the NDVI Math: This is where the magic happens. GEE lets you use a simple formula: (NIR – Red) / (NIR + Red). Don’t worry, you don’t have to do it by hand! GEE does the heavy lifting, turning those satellite images into NDVI maps.
  • Zoom In on Your Area: Next, define the region you want to study. This could be your backyard, a national park, or even an entire country. Just draw a shape on the map in GEE, and you’re good to go.
  • Get the Stats: Now, let’s get some numbers! GEE can calculate all sorts of stats for your region, like the minimum, maximum, average, and median NDVI values. This gives you a sense of the spread of vegetation health.
  • Make it Visual: This is where the plotting comes in. GEE has built-in charting tools that let you visualize those NDVI ranges. You can create box plots to see the distribution, histograms to see how many pixels fall into each NDVI range, or even time series charts to see how things change over time.

    • Imagine you’re looking at a forest. A box plot might show you that most of the trees have high NDVI values, indicating a healthy forest. But if you see a wide range, with some very low NDVI values, that might be a sign of trouble – maybe some trees are stressed or diseased.

    Here’s a tiny taste of code to give you an idea:

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