What Are Indices?

Опубликовано: 04 Апрель 2023
на канале: SkyWatch
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WI Series by SkyWatch Presents: What Are Indices? https://skywatch.com/

What are indices?

Indices or singularly, an index, are a way of processing satellite data that allows you to interpret a more specific measure from that image.

Some examples include the NDVI, the EVI, the MSAVI2 and the NDWI2. Although, a number of other examples exist.

On EarthCache, we currently offer those four options.

The first and most famous of the indices is the NDVI or normalized difference vegetation index.

This provides a measure of how green an image is which will tell you a lot about the chlorophyll content of any plants included in that image.

This index varies from 0-1 with 0 meaning that there is almost definitely no vegetation in that pixel and 1 indicating that there is a lot of vegetation and definitely a lot of chlorophyll content.

The second example is EVI or the enhanced vegetation index.

Because the NDVI is normalized, it suffers a lot from saturation in very green locations such as the Amazon rainforest.

The EVI accounts for this by adding a correction factor to the equation that calculates this value.

The EVI was most famously used in a study that studied the Amazon rainforest and discovered that there was seasonality to the trees, ebbing and flowing through the summer and the winter.

Which was not visible either on the ground or through the NDVI before.

Some of the other examples of indices available on EarthCache are the second modified soil adjusted vegetation index which accounts for bare earth and is much better for arid areas such as deserts or tundra.

There is also the normalized difference water index which measures water content in each pixel.

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