Multitemporal burnt area analysis

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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)
  );
  
}

Evaluate and visualize

• Sentinel Playground

  General description of the script

The script takes two pre-defined dates as an input (in filterScenes) and calculates changes of the normalised burn ratio index. See the discussion here.

Author of the script

Designed by FC Basson and improved by @Pierre_Markuse and visually

Description of representative images

Burned area analysis applied to the South African coast.