[GIS] Do clouds reflect NIR/Red bands

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When using Landsat 8 imagery to calculate NDVI, will the NIR and Red bands be affected by cloud cover?

In other words, will clouds produce a wrong NDVI calculation?

Best Answer

Yes, it affects the values of NDVI, and it may not give the desired results sometimes. Information from Wikipedia: Normalized Difference Vegetation Index provides some details about the effects of cloud and snow as follows:

clouds and snow tend to be rather bright in the red (as well as other visible wavelengths) and quite dark in the near-infrared

Which implies based on mathematical equation of NDVI applied on dense forest:

It can be seen from its mathematical definition that the NDVI of an area containing a dense vegetation canopy will tend to positive values (say 0.3 to 0.8) while clouds and snow fields will be characterized by negative values of this index.

You can read the above article to get more information about the effects of clouds on NDVI.

Related Solutions

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

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.

[GIS] NDVI analysis of LANDSAT 8 imagery in QGIS

Using Dark Object Subtraction (DOS) can provide a a quick way to correct for atmospheric effects, which may be sufficient for preparing multispectral data for spectral indices such as NDVI. However, it will not be as accurate as using Landsat Surface Reflectance High Level Data Products for Landsat 8 that is generated from the L8SR algorithm. The L8SR is available through earthexplorer and you can download the data you need, and then calculate NDVI more accurately.

Since you are using Semi-Automatic Classification Plugin (SCP) for QGIS, there is an interesting research done to compare DOS1 Correction with USGS High Level Data Products of the Landsat 8 Surface Reflectance titled: Landsat 8 Surface Reflectance: a Comparison of DOS1 Correction and USGS High Level Data Products.

You can test the difference by comparing the NDVI calculated using raw data DN values of Landsat 8 before conversion to surface reflectance, using DOS1, and using L8SR High Level Data and see difference.

Best Answer

Related Solutions

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

[GIS] NDVI analysis of LANDSAT 8 imagery in QGIS

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