| IRECI Algorithm Specification | |
The Inverted Red-Edge
Chlorophyll Index algorithm incorporates the
reflectance in four bands to estimate canopy chlorophyll content
(Guyot and Baret, 1988; Clevers et al., 2000)
The 'red edge' is the name given to the abrupt reflectance change
in the 680 � 740 nm region of vegetation spectra that is
caused by the combined effects of strong chlorophyll absorption and
leaf internal scattering.
Increases in the amount of chlorophyll visible to the sensor,
either through an increase in leaf chlorophyll content, or Leaf
Area Index (LAI), result in a broadening of a major chlorophyll
absorption feature centred around 680 nm.
The effect is to cause a movement of the point of maximum slope,
termed the red edge position (REP).
The position of the red edge has been used as an indicator of
stress and senescence of vegetation (Collins1978, Horler et al.
1983, Rock et al. 1988, Boochs et al. 1990, Jago and Curran
1995)
The IRECI results from the following (Sensor-dependent)
equation:
IRECI = (IR_factor * near_IR - red1_factor * red1) /
(red2_factor * red2 / red3_factor * red3)
For Sentinel-2 the formula is:
(B7 - B4) / (B5 / B6), where (Central
wavelength/Bandwidth): B7 = 783 nm (15 nm), B6 = 740 nm (15 nm), B5
= 705 nm (15 nm), B4 = 665 nm (30 nm)
Also the processor computes an additional flags band called 'ireci_flags' with the following bit coding:
| Bit Position | Description |
|---|---|
| Bit 0 | The computed value for IRECI is NAN or is Infinite |
| Bit 1 | The computed value for IRECI is less than -1 (minus one) |
| Bit 2 | The computed value for IRECI is greater than 1 (one) |