Red edge position index (REPO)

//
// Red Edge Position - 4PLI, based on Gholizadeh et al. 2016 (abbrv. REP)
//
// General formula: 700+40*((670nm+780nm/2)-700nm/(740nm-700nm)
//
// URL https://www.indexdatabase.de/db/i-single.php?id=196
// Article: https://www.mdpi.com/1999-4907/7/10/226

let index = 700 + 40 * ((((B04 + B07) / 2) - B05) / (B06 - B05));
let min = 690;
let max = 725;
let zero = 707.5;

// colorBlend will return a color when the index is between min and max and white when it is less than min.
// To see black when it is more than max, uncomment the last line of colorBlend.
// The min/max values were computed automatically based on paper visualization, feel free to change them to tweak the displayed range.
// An arbitrary diverging color map is used. To tweak the value of the break in the color map, change the variable 'zero'.

let underflow_color = [1, 1, 1];
let low_color = [255 / 255, 0 / 255, 0 / 255];
let high_color = [0 / 255, 255 / 255, 0 / 255];
let zero_color = [255 / 255, 255 / 255, 0 / 255];
let overflow_color = [0, 0, 0];

return colorBlend(index, [min, min, zero, max],
	[
		underflow_color,
		low_color,
		zero_color, // divergent step at zero
		high_color,
		//overflow_color // uncomment to see overflows
	]);

Evaluate and Visualize

• Copernicus Browser
• EO Browser

General description of the script

The red edge position index is sensitive to changes in chlorophyll concentrations, as higher chlorophyll concentrations absorb longer wavelengths. It is calculated as: 700+40*((670nm+780nm/2)-700nm/(740nm-700nm)

Description of representative images

Visualization of the REPO index above Italy.

Credits

The script is based on Gholizadeh et al., 2016. It is described in the Index database as well.