GEE中的Landsat数据

1. Landsat collection structure

The USGS produces data in 3 tiers (categories) for each satellite:

• Tier 1 (T1) - Data that meets geometric and radiometric quality requirements
• Tier 2 (T2) - Data that doesn’t meet the Tier 1 requirements
• Real Time (RT) - Data that hasn’t yet been evaluated (it takes as much as a month).

ID	Description
LANDSAT/LC08/C01/T1_RT	Landsat 8, Collection 1, Tier 1 + Real Time
LANDSAT/LC08/C01/T1	Landsat 8, Collection 1, Tier 1 only
LANDSAT/LC08/C01/T2	Landsat 8, Collection 1, Tier 2 only

ID	Description
LANDSAT/LC08/C01/T1_RT_TOA	Landsat 8, Collection 1, Tier 1 + Real Time, TOA
LANDSAT/LC08/C01/T1_TOA	Landsat 8, Collection 1, Tier 1 only, TOA
LANDSAT/LC08/C01/T1_SR	Landsat 8, Collection 1, Tier 1 only, SR
LANDSAT/LC08/C01/T2_TOA	Landsat 8, Collection 1, Tier 2 only, TOA
LANDSAT/LC08/C01/T2_SR	Landsat 8, Collection 1, Tier 2 only, SR

These data exist for Landsat 4, 5, 7, and 8. Replace ‘LC08’ in the above collection definitions with IDs from the following table to retrieve collections for the various satellites.

ID	Description
LT04	Landsat 4, Thematic Mapper ™
LT05	Landsat 5, Thematic Mapper ™
LE07	Landsat 7, Enhanced Thematic Mapper Plus (ETM+)
LC08	Landsat 8, Operational Land Imager (OLI)

2.At-sensor radiance and TOA reflectance

• "raw" 中包含带有数字（DN）的图像，这些数字表示缩放后的辐射度。The conversion of DNs to at-sensor radiance is a linear transformation using coefficients stored in scene metadata (Chander et al. 2009). ee.Algorithms.Landsat.calibratedRadiance() 方法执行此转换。

• 转换为TOA反射率是一种线性转换，说明了太阳高度和季节性变化的地球与太阳之间的距离。 TOA转换由ee.Algorithms.Landsat.TOA()方法处理。 TOA方法将热带转换为亮度温度。See Chander et al. (2009) (or this USGS site for Landsat 8) for more information about computing TOA reflectance or brightness temperature.

// Load a raw Landsat scene and display it.
var raw = ee.Image('LANDSAT/LC08/C01/T1/LC08_044034_20140318');
Map.centerObject(raw, 10);
Map.addLayer(raw, {bands: ['B4', 'B3', 'B2'], min: 6000, max: 12000}, 'raw');

// Convert the raw data to radiance.
var radiance = ee.Algorithms.Landsat.calibratedRadiance(raw);
Map.addLayer(radiance, {bands: ['B4', 'B3', 'B2'], max: 90}, 'radiance');

// Convert the raw data to top-of-atmosphere reflectance.
var toa = ee.Algorithms.Landsat.TOA(raw);

Map.addLayer(toa, {bands: ['B4', 'B3', 'B2'], max: 0.2}, 'toa reflectance');

3. Surface reflectance

• Conversion to surface reflectance generally requires some sort of atmospheric compensation. USGS uses the LEDAPS software (Schmidt et al. 2013) to convert raw Landsat data to surface reflectance. LEDAPS requires a variety of atmospheric inputs to constrain an atmospheric model. These include outputs of a 6S model run, a DEM, total column ozone, National Centers for Environmental Prediction (NCEP) modeled surface pressure, temperature and water vapor (Kalnay et al. 1996).

• You can access pre-computed surface reflectance images directly from the SR collections. For example, to load a Landsat 7 surface reflectance image, use:

var srImage = ee.Image('LANDSAT/LE07/C01/T1_SR/LE07_044034_19990707');

The surface reflectance datasets for Collection 1 Landsat 4 through 7 are:

var surfaceReflectanceL4 = ee.ImageCollection('LANDSAT/LT04/C01/T1_SR');
var surfaceReflectanceL5 = ee.ImageCollection('LANDSAT/LT05/C01/T1_SR');
var surfaceReflectanceL7 = ee.ImageCollection('LANDSAT/LE07/C01/T1_SR');

筛选 Landsat 8 数据

var gt = ee.ImageCollection('LANDSAT/LC08/C01/T1_SR')
	.filterDate('2020-01-01', '2020-09-17')
	.filterBounds(guanting);
print('gt',gt);

4. Simple cloud score

// Load a cloudy Landsat scene and display it. 加载一景有云的影像
var cloudy_scene = ee.Image('LANDSAT/LC08/C01/T1_TOA/LC08_044034_20140926');
Map.centerObject(cloudy_scene);
Map.addLayer(cloudy_scene, {bands: ['B4', 'B3', 'B2'], max: 0.4}, 'TOA', false);

// Add a cloud score band.  It is automatically called 'cloud'.
var scored = ee.Algorithms.Landsat.simpleCloudScore(cloudy_scene);

// Create a mask from the cloud score and combine it with the image mask.
var mask = scored.select(['cloud']).lte(20);

// Apply the mask to the image and display the result.
var masked = cloudy_scene.updateMask(mask);
Map.addLayer(masked, {bands: ['B4', 'B3', 'B2'], max: 0.4}, 'masked');

// Load a Landsat 8 composite and set the SENSOR_ID property.
var mosaic = ee.Image(ee.ImageCollection('LANDSAT/LC8_L1T_8DAY_TOA').first())
  .set('SENSOR_ID', 'OLI_TIRS');

// Cloud score the mosaic and display the result.
var scored_mosaic = ee.Algorithms.Landsat.simpleCloudScore(mosaic);
Map.addLayer(scored_mosaic, {bands: ['B4', 'B3', 'B2'], max: 0.4},
    'TOA mosaic', false);