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ndvi_uncertainty

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Nov 4, 2019
Nov 4, 2019
Oct 10, 2017

Normalized difference vegetation index with uncertainty

Show script or download{:target="_blank"} it.

{% highlight javascript %} {% include_relative script.js %} {% endhighlight %}

Evaluate and visualize

Basic information

  • Bands used to calculate NDVI index: B4, B8
  • Bands used by the script: B2, B3, B4, B8

General description

This script allows you to visually interpret how the normalized density vegetation index (NDVI) [1] is affected by the uncertainties in detector reflectances of the L1C products.

Since NDVI is defined as a ratio of difference over sum of bands 8 and 4 (near infrared and red):
N D V I := Index ( B 8 , B 4 ) = B 8 B 4 B 8 + B 4 .

the uncertainty propagation [3] gives us the uncertainty of the index itself as

Δ N D V I := B 8 2 Δ B 4 2 + B 4 2 Δ B 8 2 2 B 4 B 8 Δ B 4 B 8 ( B 8 + B 4 ) 2 .

where Δ B 4 and Δ B 8 are uncertainties of red and near infrared bands respectively (reported by ESA to be 0.02 and 0.03). We left out the mixed part Δ B 4 B 8 as if the two uncertainties were not correlated.

The script encodes the uncertainty with darkness, as can be seen in following figure [2]
Color map of the NDVI uncertainty script from [2][1]

Description of representative images

NDVI with uncertainty of Madrid. Acquired on 10.26.2019.

NDVI of Rome

References

[1] Wikipedia, Normalized Difference Vegetation Index . Accessed on October 4th 2017.
[2] Sentinel-Hub, Ad hoc testing of algorithms globally. Accessed October 10th 2017.
[3] Wikipedia, Propagation of uncertainty. Accessed October 10th 2017.