gee_landsatTools.txt

// Functions used to collect a mosaic of all Landsat images over a specified area
// and within a certain number of days from the maximum flood extent image.
exports.getLandsat = function(id, gfd, cloudCover, deltaDays){

  // Prep the Landsat data by filtering flood dates
  // LANDSAT 8 - Filter Landsat 8 OLI Products by Flood Events Boundaries and Dates
  function filterFloodEventsL8 (roi, filterDate){
    var imageCollection = ee.ImageCollection("LANDSAT/LC08/C01/T1_SR").filterBounds(roi)
                          .filterDate(filterDate, filterDate.advance(deltaDays, "day"))
                          .filterMetadata("CLOUD_COVER", "less_than", cloudCover)
    return imageCollection
  }

  // LANDSAT 7 - Filter Landsat 7 ETM Products by Flood Events Boundaries and Dates
  function filterFloodEventsL7 (roi, filterDate){
    var imageCollection = ee.ImageCollection("LANDSAT/LE07/C01/T1_SR").filterBounds(roi)
                        .filterDate(filterDate, filterDate.advance(deltaDays, "day"))
                        .filterMetadata("CLOUD_COVER", "less_than", cloudCover)
    return imageCollection
  }

  // LANDSAT 5 - Filter Landsat 5 TM Products by Flood Events Boundaries and Dates
  function filterFloodEventsL5 (roi, filterDate){
    var imageCollection = ee.ImageCollection("LANDSAT/LT05/C01/T1_SR").filterBounds(roi)
                        .filterDate(filterDate, filterDate.advance(deltaDays, "day"))
                        .filterMetadata("CLOUD_COVER", "less_than", cloudCover)
    return imageCollection
  }

  // DFO Fusion Table and extract important variables
  var dfoEvents = ee.FeatureCollection("projects/global-flood-db/dfo-polygons/dec-03-2019");
  var dfoPoly = ee.Feature(dfoEvents.filterMetadata('ID','equals',id).first()).geometry()
  var img = ee.Image(gfd.filterMetadata("Index", "equals", id).first()).select("flooded").clip(dfoPoly)
  var ft = img.updateMask(img).reduceToVectors({scale: 1000, maxPixels: 10e13})
                    .map(function(f){return f.simplify(10000)})

  // Variables for filter landsat series of functions
  var maxDate = ee.Date(img.get('maxImgDate'))

  // Filter for Landsat 8 images
  var l8 = filterFloodEventsL8(ft, maxDate).select(["B2", "B3", "B4", "B5", "B6", "B7", "pixel_qa"],
                                                ["B1", "B2", "B3", "B4", "B5", "B7", "pixel_qa"]);
  // print("Landsat 8 OLI Collection", l8);

  // Filter for Landsat 7 Images
  var l7 = filterFloodEventsL7(ft, maxDate).select(["B1", "B2", "B3", "B4", "B5", "B7", "pixel_qa"]);
  //print("Landsat 7 ETM Collection", l7);

  // Filter for Landsat 5 images
  var l5 = filterFloodEventsL5(ft, maxDate).select(["B1", "B2", "B3", "B4", "B5", "B7", "pixel_qa"]);
  //print("Landsat 5 TM Collection", l5);

  // print("getLandsat() retrieved the following number of images:",
  //       ee.String("Landsat 8: ").cat(ee.String(l8.size())),
  //       ee.String("Landsat 7: ").cat(ee.String(l7.size())),
  //       ee.String("Landsat 5: ").cat(ee.String(l5.size())));

  return ee.ImageCollection(l8.merge(l7).merge(l5));
};

// Mask clouds based on FMask band where clouds = 4; cloud shadows = 2
exports.maskClouds = function(imgColl) {
  var output = imgColl.map(function(img){
    var cloud_pixel_qa = img.select('pixel_qa').bitwiseAnd(32).eq(0)
    var cloud_shadow_pixel_qa = img.select('pixel_qa').bitwiseAnd(8).eq(0)
    var imageSansCloudandShadow = img.updateMask(cloud_pixel_qa.and(cloud_shadow_pixel_qa))
    var clear = ee.Image.constant(1).updateMask(cloud_pixel_qa.and(cloud_shadow_pixel_qa)).rename(['clear'])
    var obs = ee.Image.constant(1).rename(['observation'])
    return ee.Image(imageSansCloudandShadow.addBands(clear).addBands(obs))
  });
  return output;
};