Cumulative sum of thermal anomalies in Earth Engine

Question

I am writing a short script that will be used to chart thermal anomalies (FIRMS) by year for a given boundary.

The following code will achieve this...

var  now = new Date()

// IMPORT MODIS ACTIVE FIRE TIME SERIES
var FIRMS = ee.ImageCollection('FIRMS')
  .select('T21').filterDate('2019-01-01',now)
  
// ISOLATE AREA OF INTEREST
var Leon = SE_Counties.filterMetadata('NAME','equals','Leon')
print(Leon)

// TIME SERIES CHART
var options = {
    title: 'MODIS Thermal Anomalies for Leon County, FL',
    fontSize: 12,
    hAxis: {},
    vAxis: {title: 'Pixel Count', viewWindow: {min: 0}},
    //legend: {position: 'none'},
};
   
var chart = ui.Chart.image.doySeriesByYear(FIRMS, 'T21', Leon, ee.Reducer.count(), 1000).setOptions(options);
print(chart)

However I am also interested in plotting thermal anomalies cumulatively like this..

I checked out this example (Iterating over an ImageCollection) but I couldn't figure out how to customize the code to work with my data.

What would be a solution for this?

Answer 1

Not sure if this is going to work for large imageCollections but iterating of the dates and creating a new sum for each date might work:

var cummulative = dates.map(function(d){
  
  var selectedImages = FIRMS.filterDate('2018-12-31', d)
  
  var sumPeriod = selectedImages.reduce(ee.Reducer.sum())

  var sumArea = ee.Dictionary(ee.Algorithms.If(sumPeriod.bandNames(), 
              sumPeriod.reduceRegion(ee.Reducer.sum(),Leon, 300), {'T21_sum':0}))
  
  return ee.Feature(null, sumArea).set('date', d)
})
print(cummulative, 'cummulative')

https://code.earthengine.google.com/cddeedb7de9be393d5df78ea2b68729b