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 RVI?
The Ratio Vegetation Index (RVI) algorithm is the simplest ratio-based one. This is the most widely calculated vegetation index, although you rarely hear of it as a vegetation index. A common practice in remote sensing is the use of band ratios (e.g. the ratio of NIR to RED) to eliminate various effects such as irradiance (topography) and transmittance (atmospheric effects).
RVI processed images are created using the following formula:
RVI = NIR/R
where NIR = pixel values from the infrared band and R = pixel values from the red band. Each pixel will have a value between 0 and 255. The resulting image will be displayed in grayscales, where lower values are darker and higher values are lighter.
The RVI is particularly good for detecting vegetated versus non-vegetated soil, as vegetated soil would appear much lighter, while non-vegetated soil shows as darker areas.
How to obtain RVI 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 RVI 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: