FAPAR (The Fraction of Absorbed Photosynthetically Active Radiation)
//VERSION=3 (auto-converted from 2)
var degToRad = Math.PI / 180;
function evaluatePixelOrig(samples) {
var sample = samples[0];
var b03_norm = normalize(sample.B03, 0, 0.253061520471542);
var b04_norm = normalize(sample.B04, 0, 0.290393577911328);
var b05_norm = normalize(sample.B05, 0, 0.305398915248555);
var b06_norm = normalize(sample.B06, 0.006637972542253, 0.608900395797889);
var b07_norm = normalize(sample.B07, 0.013972727018939, 0.753827384322927);
var b8a_norm = normalize(sample.B8A, 0.026690138082061, 0.782011770669178);
var b11_norm = normalize(sample.B11, 0.016388074192258, 0.493761397883092);
var b12_norm = normalize(sample.B12, 0, 0.493025984460231);
var viewZen_norm = normalize(Math.cos(sample.viewZenithMean * degToRad), 0.918595400582046, 1);
var sunZen_norm = normalize(Math.cos(sample.sunZenithAngles * degToRad), 0.342022871159208, 0.936206429175402);
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 fapar = denormalize(l2, 0.000153013463222, 0.977135096979553);
return {
default: [fapar]
}
}
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 =
- 0.887068364040280
+ 0.268714454733421 * b03_norm
- 0.205473108029835 * b04_norm
+ 0.281765694196018 * b05_norm
+ 1.337443412255980 * b06_norm
+ 0.390319212938497 * b07_norm
- 3.612714342203350 * b8a_norm
+ 0.222530960987244 * b11_norm
+ 0.821790549667255 * b12_norm
- 0.093664567310731 * viewZen_norm
+ 0.019290146147447 * sunZen_norm
+ 0.037364446377188 * 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 =
+ 0.320126471197199
- 0.248998054599707 * b03_norm
- 0.571461305473124 * b04_norm
- 0.369957603466673 * b05_norm
+ 0.246031694650909 * b06_norm
+ 0.332536215252841 * b07_norm
+ 0.438269896208887 * b8a_norm
+ 0.819000551890450 * b11_norm
- 0.934931499059310 * b12_norm
+ 0.082716247651866 * viewZen_norm
- 0.286978634108328 * sunZen_norm
- 0.035890968351662 * 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 =
+ 0.610523702500117
- 0.164063575315880 * b03_norm
- 0.126303285737763 * b04_norm
- 0.253670784366822 * b05_norm
- 0.321162835049381 * b06_norm
+ 0.067082287973580 * b07_norm
+ 2.029832288655260 * b8a_norm
- 0.023141228827722 * b11_norm
- 0.553176625657559 * b12_norm
+ 0.059285451897783 * viewZen_norm
- 0.034334454541432 * sunZen_norm
- 0.031776704097009 * 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 =
- 0.379156190833946
+ 0.130240753003835 * b03_norm
+ 0.236781035723321 * b04_norm
+ 0.131811664093253 * b05_norm
- 0.250181799267664 * b06_norm
- 0.011364149953286 * b07_norm
- 1.857573214633520 * b8a_norm
- 0.146860751013916 * b11_norm
+ 0.528008831372352 * b12_norm
- 0.046230769098303 * viewZen_norm
- 0.034509608392235 * sunZen_norm
+ 0.031884395036004 * 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 =
+ 1.353023396690570
- 0.029929946166941 * b03_norm
+ 0.795804414040809 * b04_norm
+ 0.348025317624568 * b05_norm
+ 0.943567007518504 * b06_norm
- 0.276341670431501 * b07_norm
- 2.946594180142590 * b8a_norm
+ 0.289483073507500 * b11_norm
+ 1.044006950440180 * b12_norm
- 0.000413031960419 * viewZen_norm
+ 0.403331114840215 * sunZen_norm
+ 0.068427130526696 * relAzim_norm;
return tansig(sum);
}
function layer2(neuron1, neuron2, neuron3, neuron4, neuron5) {
var sum =
- 0.336431283973339
+ 2.126038811064490 * neuron1
- 0.632044932794919 * neuron2
+ 5.598995787206250 * neuron3
+ 1.770444140578970 * neuron4
- 0.267879583604849 * 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;
}
function setup() {
return {
input: [{
bands: [
"B03",
"B04",
"B05",
"B06",
"B07",
"B8A",
"B11",
"B12",
"viewZenithMean",
"viewAzimuthMean",
"sunZenithAngles",
"sunAzimuthAngles"
]
}],
output: [
{
id: "default",
sampleType: "AUTO",
bands: 1
}
]
}
}
function evaluatePixel(sample, scene, metadata, customData, outputMetadata) {
const result = evaluatePixelOrig([sample], [scene], metadata, customData, outputMetadata);
return result[Object.keys(result)[0]];
}Evaluate and Visualize
General description of the script
FAPAR is the fraction of incoming solar radiation absorbed for photosynthesis by a photosynthetic organism (live leaves).
Note that the FAPAR 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
FAPAR visualization of Rome. Acquired on 8.10.2017.
