Google Earth Engine:遮盖云并在不同传感器的图像集合上映射功能 [英] Google Earth Engine: mask clouds and map a function over an image collection of different sensors
问题描述
我想将1985年至今的所有Landsat传感器整合到Google Earth Engine中,去除云层并计算NBR索引的时间序列.作为GEE的新用户,我具有以下特点:
I want to combine all the Landsat sensors from 1985 up today in Google Earth Engine, remove the clouds and calculate the time-series of the NBR index. As a new GEE user I have the following:
// find all data and filter them by date
var lst5 = ee.ImageCollection('LANDSAT/LT5_SR').filterDate('1984-10-01', '2011-10-01');
var lst7 = ee.ImageCollection('LANDSAT/LE7_SR').filterDate('2011-10-01', '2013-04-07');
var lst8 = ee.ImageCollection('LANDSAT/LC8_SR').filterDate('2013-04-07', '2018-05-01');
var lst7_08 = ee.ImageCollection('LANDSAT/LE7_SR').filterDate('2007-12-01', '2008-02-01');
var lst7_92 = ee.ImageCollection('LANDSAT/LT4_SR').filterDate('1992-01-02', '1992-04-01');
// Combine all landsat data, 1985 through 2015
var everything = ee.ImageCollection(lst5.merge(lst7));
everything = everything.merge(lst8);
everything = everything.merge(lst7_08);
everything = everything.merge(lst7_92);
var alltogether = ee.ImageCollection(everything.filterDate('1984-01-01', '2018-05-01'));
From this point, I do not know how to remove the clouds and calculate the NBR index (NBR index here) for every image in my final collection.
有人可以帮助我吗?
谢谢.
我认为我需要在集合上映射一个normalizedDifference
函数以获得NBR索引,但是我不确定如何使用不同的传感器对我的集合进行此操作.
I think that I need to map a normalizedDifference
function over my collection in order to get the NBR index but I am not sure how to do this for my collection with the different sensors.
推荐答案
您在这里进行了很多工作,但是我想这就是您想要的.您应该非常仔细地检查此内容,以确保其行为符合预期:
You've got quite a lot going on here, but here's what I think you want. You should check this very carefully to ensure it's behaving as intended:
// Function to cloud mask Landsat 8.
var maskL8SR = function(image) {
// Bits 3 and 5 are cloud shadow and cloud, respectively.
var cloudShadowBitMask = ee.Number(2).pow(3).int();
var cloudsBitMask = ee.Number(2).pow(5).int();
// Get the QA band.
var qa = image.select('pixel_qa');
// Both flags should be set to zero, indicating clear conditions.
var mask = qa.bitwiseAnd(cloudShadowBitMask).eq(0).and(
qa.bitwiseAnd(cloudsBitMask).eq(0));
return image
// Scale the data to reflectance and temperature.
.select(['B5', 'B7'], ['NIR', 'SWIR']).multiply(0.0001)
.addBands(image.select(['B11'], ['Thermal']).multiply(0.1))
.updateMask(mask);
};
// Function to cloud mask Landsats 5-7
var maskL57SR = function(image) {
var qa = image.select('pixel_qa');
// Second bit must be zero, meaning none to low cloud confidence.
var mask1 = qa.bitwiseAnd(ee.Number(2).pow(7).int()).eq(0).and(
qa.bitwiseAnd(ee.Number(2).pow(3).int()).lte(0)); // cloud shadow
// This gets rid of irritating fixed-pattern noise at the edge of the images.
var mask2 = image.select('B.*').gt(0).reduce('min');
return image
.select(['B4', 'B7'], ['NIR', 'SWIR']).multiply(0.0001)
.addBands(image.select(['B6'], ['Thermal']).multiply(0.1))
.updateMask(mask1.and(mask2));
};
// find all data and filter them by date
var lst5 = ee.ImageCollection('LANDSAT/LT05/C01/T1_SR')
.filterDate('1984-10-01', '2011-10-01')
.map(maskL57SR)
var lst7 = ee.ImageCollection('LANDSAT/LE07/C01/T1_SR')
.filterDate('2011-10-01', '2013-04-07')
.map(maskL57SR)
var lst8 = ee.ImageCollection('LANDSAT/LC08/C01/T1_SR')
.filterDate('2013-04-07', '2018-05-01')
.map(maskL8SR)
var lst7_08 = ee.ImageCollection('LANDSAT/LE07/C01/T1_SR')
.filterDate('2007-12-01', '2008-02-01')
.map(maskL57SR)
var lst7_92 = ee.ImageCollection('LANDSAT/LT04/C01/T1_SR')
.filterDate('1992-01-02', '1992-04-01')
.map(maskL57SR)
// Combine all landsat data, 1985 through 2015
var everything = ee.ImageCollection(lst5.merge(lst7));
everything = everything.merge(lst8);
everything = everything.merge(lst7_08);
everything = everything.merge(lst7_92);
// NBR:
var nbrFunction = function(image) {
image = ee.Image(image)
return image.addBands(image.expression(
'(nir - 0.0001 * swir * thermal) / ' +
'(nir + 0.0001 * swir * thermal)', {
nir: image.select(['NIR']),
swir: image.select(['SWIR']),
thermal: image.select(['Thermal'])
}).rename('NBR').clamp(-1, 1));
};
everything = everything.map(nbrFunction);
var check = ee.Image(everything.first());
Map.centerObject(check);
Map.addLayer(check);
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