Temporal analysis - burned area

[pierre.markuse]

A little tweaked for nicer visuals:

function setup (dss) {
  // get all bands for display and analysis
  setInputComponents([dss.B02,dss.B03,dss.B04,dss.B05,dss.B08,dss.B12]);
  // return as RGB
  setOutputComponentCount(3);
}

function stretch(val, min, max) {return (val - min) / (max - min);}

function filterScenes (scenes, inputMetadata) {  
return scenes.filter(function (scene) {
// set dates for pre-and-post fire analysis
var allowedDates = ["2017-05-15","2017-06-24"]; // Knysna fires
// format scene date timestamp to match allowed dates 
var sceneDateStr = dateformat(scene.date);
if (allowedDates.indexOf(sceneDateStr)!= -1) return true;
else return false;
  });
}

// Normalized Burn Ration calculation
function calcNBR(sample) {
  var denom = sample.B08+sample.B12;
  var nbrval = ((denom!=0) ? (sample.B08-sample.B12) / denom : 0.0);
  return nbrval;
}

function dateformat(d){  
  var dd = d.getDate();
  var mm = d.getMonth()+1;
  var yyyy = d.getFullYear();
  if(dd<10){dd='0'+dd}
  if(mm<10){mm='0'+mm}
  var isodate = yyyy+'-'+mm+'-'+dd;
  return isodate;
}

function evaluatePixel(samples,scenes) {  
  var nbrpre = 0;
  var nbrpost = 0;  
  
  // get pre-fire image
  nbrpre = calcNBR(samples[1]);
  // get post-fire image
  nbrpost = calcNBR(samples[0]);  
  // get difference 
  var dnbr = nbrpre - nbrpost;
  // set output display layers
  var stretchMin = 0.05;
  var stretchMax = 1.00;
  var NaturalColors = [stretch(2.8 * samples[0].B04 + 0.1 * samples[0].B05, stretchMin, stretchMax), stretch(2.8 * samples[0].B03 + 0.15 * samples[0].B08, stretchMin, stretchMax), stretch(2.8 * samples[0].B02, stretchMin, stretchMax)];  
  var burnModerate = [stretch(2.8 * samples[0].B04 + 0.1 * samples[0].B05, stretchMin, stretchMax)+0.5, stretch(2.8 * samples[0].B03 + 0.15 * samples[0].B08, stretchMin, stretchMax)+0.5, stretch(2.8 * samples[0].B02, stretchMin, stretchMax)];  
  var burnSevere = [stretch(2.8 * samples[0].B04 + 0.1 * samples[0].B05, stretchMin, stretchMax)+0.5, stretch(2.8 * samples[0].B03 + 0.15 * samples[0].B08, stretchMin, stretchMax), stretch(2.8 * samples[0].B02, stretchMin, stretchMax)];
  return (dnbr < 0.27 ?
  NaturalColors : (dnbr < 0.66 ?
  burnModerate : burnSevere)
  );
  
}

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