FCOVER (Fraction of green Vegetation Cover)
//VERSION=3
function setup() {
return {
input: [{
bands: [
"B03",
"B04",
"B05",
"B06",
"B07",
"B8A",
"B11",
"B12",
"viewZenithMean",
"viewAzimuthMean",
"sunZenithAngles",
"sunAzimuthAngles"
]
}],
output: [
{
id: "default",
sampleType: "AUTO",
bands: 1
}
]
}
}
var degToRad = Math.PI / 180;
function evaluatePixel(sample) {
var b03_norm = normalize(sample.B03, 0, 0.253061520472);
var b04_norm = normalize(sample.B04, 0, 0.290393577911);
var b05_norm = normalize(sample.B05, 0, 0.305398915249);
var b06_norm = normalize(sample.B06, 0.00663797254225, 0.608900395798);
var b07_norm = normalize(sample.B07, 0.0139727270189, 0.753827384323);
var b8a_norm = normalize(sample.B8A, 0.0266901380821, 0.782011770669);
var b11_norm = normalize(sample.B11, 0.0163880741923, 0.493761397883);
var b12_norm = normalize(sample.B12, 0, 0.49302598446);
var viewZen_norm = normalize(Math.cos(sample.viewZenithMean * degToRad), 0.918595400582, 0.999999999991);
var sunZen_norm = normalize(Math.cos(sample.sunZenithAngles * degToRad), 0.342022871159, 0.936206429175);
var relAzim_norm = Math.cos((sample.sunAzimuthAngles - sample.viewAzimuthMean) * degToRad)
var n1 = neuron1(b03_norm,b04_norm,b05_norm,b06_norm,b07_norm,b8a_norm,b11_norm,b12_norm, viewZen_norm,sunZen_norm,relAzim_norm);
var n2 = neuron2(b03_norm,b04_norm,b05_norm,b06_norm,b07_norm,b8a_norm,b11_norm,b12_norm, viewZen_norm,sunZen_norm,relAzim_norm);
var n3 = neuron3(b03_norm,b04_norm,b05_norm,b06_norm,b07_norm,b8a_norm,b11_norm,b12_norm, viewZen_norm,sunZen_norm,relAzim_norm);
var n4 = neuron4(b03_norm,b04_norm,b05_norm,b06_norm,b07_norm,b8a_norm,b11_norm,b12_norm, viewZen_norm,sunZen_norm,relAzim_norm);
var n5 = neuron5(b03_norm,b04_norm,b05_norm,b06_norm,b07_norm,b8a_norm,b11_norm,b12_norm, viewZen_norm,sunZen_norm,relAzim_norm);
var l2 = layer2(n1, n2, n3, n4, n5);
var fcover = denormalize(l2, 0.000181230723879, 0.999638214715);
return {default: [fcover]}
}
function neuron1(b03_norm,b04_norm,b05_norm,b06_norm,b07_norm,b8a_norm,b11_norm,b12_norm, viewZen_norm,sunZen_norm,relAzim_norm) {
var sum =
- 1.45261652206
- 0.156854264841 * b03_norm
+ 0.124234528462 * b04_norm
+ 0.235625516229 * b05_norm
- 1.8323910258 * b06_norm
- 0.217188969888 * b07_norm
+ 5.06933958064 * b8a_norm
- 0.887578008155 * b11_norm
- 1.0808468167 * b12_norm
- 0.0323167041864 * viewZen_norm
- 0.224476137359 * sunZen_norm
- 0.195523962947 * relAzim_norm;
return tansig(sum);
}
function neuron2(b03_norm,b04_norm,b05_norm,b06_norm,b07_norm,b8a_norm,b11_norm,b12_norm, viewZen_norm,sunZen_norm,relAzim_norm) {
var sum =
- 1.70417477557
- 0.220824927842 * b03_norm
+ 1.28595395487 * b04_norm
+ 0.703139486363 * b05_norm
- 1.34481216665 * b06_norm
- 1.96881267559 * b07_norm
- 1.45444681639 * b8a_norm
+ 1.02737560043 * b11_norm
- 0.12494641532 * b12_norm
+ 0.0802762437265 * viewZen_norm
- 0.198705918577 * sunZen_norm
+ 0.108527100527 * relAzim_norm;
return tansig(sum);
}
function neuron3(b03_norm,b04_norm,b05_norm,b06_norm,b07_norm,b8a_norm,b11_norm,b12_norm, viewZen_norm,sunZen_norm,relAzim_norm) {
var sum =
+ 1.02168965849
- 0.409688743281 * b03_norm
+ 1.08858884766 * b04_norm
+ 0.36284522554 * b05_norm
+ 0.0369390509705 * b06_norm
- 0.348012590003 * b07_norm
- 2.0035261881 * b8a_norm
+ 0.0410357601757 * b11_norm
+ 1.22373853174 * b12_norm
+ -0.0124082778287 * viewZen_norm
- 0.282223364524 * sunZen_norm
+ 0.0994993117557 * relAzim_norm;
return tansig(sum);
}
function neuron4(b03_norm,b04_norm,b05_norm,b06_norm,b07_norm,b8a_norm,b11_norm,b12_norm, viewZen_norm,sunZen_norm,relAzim_norm) {
var sum =
- 0.498002810205
- 0.188970957866 * b03_norm
- 0.0358621840833 * b04_norm
+ 0.00551248528107 * b05_norm
+ 1.35391570802 * b06_norm
- 0.739689896116 * b07_norm
- 2.21719530107 * b8a_norm
+ 0.313216124198 * b11_norm
+ 1.5020168915 * b12_norm
+ 1.21530490195 * viewZen_norm
- 0.421938358618 * sunZen_norm
+ 1.48852484547 * relAzim_norm;
return tansig(sum);
}
function neuron5(b03_norm,b04_norm,b05_norm,b06_norm,b07_norm,b8a_norm,b11_norm,b12_norm, viewZen_norm,sunZen_norm,relAzim_norm) {
var sum =
- 3.88922154789
+ 2.49293993709 * b03_norm
- 4.40511331388 * b04_norm
- 1.91062012624 * b05_norm
- 0.703174115575 * b06_norm
- 0.215104721138 * b07_norm
- 0.972151494818 * b8a_norm
- 0.930752241278 * b11_norm
+ 1.2143441876 * b12_norm
- 0.521665460192 * viewZen_norm
- 0.445755955598 * sunZen_norm
+ 0.344111873777 * relAzim_norm;
return tansig(sum);
}
function layer2(neuron1, neuron2, neuron3, neuron4, neuron5) {
var sum =
- 0.0967998147811
+ 0.23080586765 * neuron1
- 0.333655484884 * neuron2
- 0.499418292325 * neuron3
+ 0.0472484396749 * neuron4
- 0.0798516540739 * neuron5;
return sum;
}
function normalize(unnormalized, min, max) {
return 2 * (unnormalized - min) / (max - min) - 1;
}
function denormalize(normalized, min, max) {
return 0.5 * (normalized + 1) * (max - min) + min;
}
function tansig(input) {
return 2 / (1 + Math.exp(-2 * input)) - 1;
}Evaluate and Visualize
General description of the script
The Fraction of Vegetation Cover (FCover) corresponds to the fraction of ground covered by green vegetation. Practically, it quantifies the spatial extent of the vegetation. Because it is independent from the illumination direction and it is sensitive to the vegetation amount, FCover is a very good candidate for the replacement of classical vegetation indices for the monitoring of ecosystems.
Note that the FCOVER script is as implemented in SNAP but without input and output validation! Input/output values which are suspect are not reported or changed. Most values, however, do not fall under this category. Visualized as an interval from 0-1. This can be adjusted in the evaluatePixel method.
Description of representative images
FCOVER visualization of Emmeloord, Flevoland, The Netherlands. Acquired on 18.11.2020.
