[GIS] How to remove clouds with the cf_mask.tif file provided from landsat 8 surface reflectance data

arcgis-desktopcloud coverlandsat 8ndvi

I just downloaded my first group of landsat 8 surface reflectance data files. In this package contains sr bands 1-7 (I hope to use some of these to create an NDVI) as well as numerous files called: sr_cloud, cf_mask, and cf_mask_conf (all tif files). I am using arcgis.

I am assuming that these files are utilised to help remove cloud coverage from the images. However, I have never dealt with any of these types of files (srcloud, cfmask, etc.) and I have no idea regarding how they work or how to use them to effectively remove clouds. Does anyone have any experience working with these kinds of files and know how I may effectively use to remove clouds?

Best Answer

The cf_mask file identifies cloud (Pixel value 4), cloud shadow (2), snow (3), and water (1) pixels. Assuming you only want "clear land" pixels (0) you can use the Con tool with the following options

Input Conditional raster = "cfmask.tif"
Expression = "Value = 0"
Input true raster = "<surface reflectance layer>"

Use the composite bands tool to make a multi-band raster which can be used instead of an individual layer for RGB plotting.

The sr_cloud layer provides information about the atmospheric correction needed on the scene.

You mention you want to use the surface reflectance layers to generate NDVI, this can be done pre-delivery by the USGS if you use the ESPA interface, https://espa.cr.usgs.gov.

Related Solutions

[GIS] Mask clouds in LandSat 8 surface refletance image

The Surface Reflectance products contain a band called 'cfmask' and 'cfmask_conf'. The documentation tells you that all pixels labelled 4 in the first band are clouds. If you just want to mask clouds from your NDVI calculation you just have to update the image mask. If you want to do an ImageCollection you simply have to .map it as a function.

An example image from the alps with only clouds masked from the NDVI as well as an NDVI time-series from the region. The great thing about the EarthEngine is that instead of the NDVI mean you can also look at the NDVI time-series for selected areas.

// single image
var lt8 = ee.Image('LANDSAT/LC8_SR/LC81930272016103')

var lt8_ndvi = lt8
  .normalizedDifference(['B4', 'B5'])  // calculate NDVI
  .updateMask(lt8.select(['cfmask']).neq(4))  // mask everything labeled 'cloud'

// Map.centerObject(lt8_ndvi, 10)
Map.addLayer(lt8_ndvi, {}, "LC81930272016103 NDVI cloud masked", 0)

// image collection
var lt8_ic = ee.ImageCollection('LANDSAT/LC8_SR')
  .filterBounds(aoi)  // filter to area-of-interest
  .filterDate(ee.Date("2016-01-01"),ee.Date("2016-12-31"))  // filter to 2016

var lt8_ndvi_ic = lt8_ic
  .map(function(img){  // add cloud free NDVI to all images
  return img.addBands(img.normalizedDifference(['B4', 'B5'])).updateMask(img.select(['cfmask']).neq(4))
  });

print(lt8_ndvi_ic)

Map.centerObject(testPoint, 10)
var ndvi_viz = {min:-0.8, max:0.3, palette:'000000,00FF00'};
Map.addLayer(lt8_ndvi_ic.select('nd').mean(), ndvi_viz, "LT8 2016 NDVI mean")

// NDVI time-series chart
// Create and print the chart.
print(ui.Chart.image.series(lt8_ndvi_ic.select('nd'), testPoint, ee.Reducer.mean(), 30));

Best Answer

Related Solutions

[GIS] Mask clouds in LandSat 8 surface refletance image

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