Why do I need Earth observation data processing?
While our eyes only detect a fraction of all light available, satellite sensors can actually capture – and send back – much more information. Furthermore, this information is relayed back to us in a format quite different from the photographs we are used to. For each band, satellites capture the spectral reflectance of the area within a specific narrow band of the light spectrum.
True-colour composite images use the red, green, and blue bands gathered by satellites to mimic the range of vision for the human eye, showing us images closer to what we would expect to see in a normal photograph.
Satellites also capture information in the non-visible part of the light spectrum. Different features: rock, bare soil, vegetation, burned ground, snow, sediment-rich water, etc. all have different reflectance properties in each band. This a called a 'spectral signature'.
To highlight specific features, one or more of the RGB bands can be substituted for another, such as infrared, or near infrared, which are not visible to the human eye. These images are referred to as false-colour images.
Additionally, to better discriminate between features and highlight changes in time, mathematical models can be applied to the data to produce a new kind of processed image. These are referred to as indexes.
When should I use IPVI?
IPVI stands for Infrared Percentage Vegetation Index. The IPVI algorithm was first described by Crippen (1990).
IPVI processed images are created using the following formula:
IPVI = NIR/(NIR + R)
where NIR = pixel values from the infrared band and R = pixel values from the red band. It is functionally equivalent to NDVI and RVI, but it only ranges in value from 0.0 - 1.0. It eliminates one mathematical operation per image pixel which is important for the rapid processing of large amounts of data. The resulting image will be displayed in grayscales, where lower values are darker and higher values are lighter.
Looking at the results of the infrared percentage vegetation index, lower values are mainly generated from clouds, water, and snow — which have high reflectance in the red band but low values in the near-infrared band, as well as barren areas, mostly rock, sand, and bare soil. Moderate values represent shrubs and grassland, while very high values indicate temperate and tropical rainforests.
How to obtain IPVI data using EarthCache
Note: If you do not have an account, you can sign up for one here.
To obtain a true-colour image using EarthCache, simply select IPVI processing as an output when creating or editing a pipeline through the dashboard.
To obtain a true-colour image using code, you can create or edit a pipeline using the following parameters: