Exporting MODIS imagery in Google Earth Engine & Pixel colours

Question

I am attempting to detect fires using MODIS thermal anomaly data (MODIS/006/MYD14A1) on Corsica island, and the code I am using below produces a suitable fire mask. I am a bit inexperienced with this, and am unsure what the different pixel colours correspond to (any information relating to pixel colours online is evading me).

Also, when I attempt to export the image to drive I am getting an error message in the Tasks tab: Error: Image.clipToBoundsAndScale, argument 'input': Invalid type. Expected type: Image. Actual type: ImageCollection.

var site = ee.Geometry.Point(9.41, 42.81);
var aoi = ee.Geometry.Rectangle(9.317758730652592, 42.86545558133746, 9.504869631531498, 42.77429487610457);
Map.centerObject(aoi, 11);

// Mid Fire period
var midStart =ee.Date('2017-08-08');
var midEnd =ee.Date('2017-08-24');

//MODIS images of the site, 
var midfireimage = ee.ImageCollection('MODIS/006/MYD14A1')
                    .filterBounds(site)
                    .filterDate(midStart,midEnd);

Map.addLayer(midfireimage, {bands: ['MaxFRP', 'FireMask', 'FireMask'], min:0.0, max:6000}, 'Fire Mask');

Export.image.toDrive({
  image:midfireimage.select('MaxFRP', 'FireMask', 'FireMask'), 
  region:aoi, 
  description: 'MidFire',
  folder: 'Corsica_Fire', 
  scale:30});

Answer 1

I assume you picked the map visualization up from the EE catalog example. I find that one a bit strange. Interpreting the colors when visualizing these bands is indeed difficult. I would simply visualize MaxFRP instead.

Your error when exporting is because you are trying to export an ee.ImageCollection. midfireimage is not a single image, but a collection of images. You will want to reduce it into a single image. You have a lot of options on how you want to do that - it all depends on what you want to achieve. Look into the docs for ee.ImageCollection. Methods like min(), max(), median(), mean(), mosaic(), qualityMosaic(), and reduce() will do the trick.

var site = ee.Geometry.Point(9.41, 42.81)
var aoi = ee.Geometry.Rectangle(9.317758730652592, 42.86545558133746, 9.504869631531498, 42.77429487610457)
Map.centerObject(aoi, 11)

// Mid Fire period
var midStart = ee.Date('2017-08-08')
var midEnd = ee.Date('2017-08-24')

//MODIS images of the site, 
var midfireimage = ee.ImageCollection('MODIS/006/MYD14A1')
  .filterBounds(site)
  .filterDate(midStart, midEnd)
  .qualityMosaic('MaxFRP') 

Map.addLayer(midfireimage, {
  bands: ['MaxFRP'], 
  min: 0,
  max: 4000,
  palette: 'yellow, orange, red'
}, 'Fire Mask')

Export.image.toDrive({
  image: midfireimage.select('MaxFRP', 'FireMask', 'FireMask'),
  region: aoi,
  description: 'MidFire',
  folder: 'Corsica_Fire',
  scale: 30
})

https://code.earthengine.google.com/8392d41098c925c27440afdbf87d5092