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Pre-processing imagery
Joan Looijen


TOPICS
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Why land cover mapping?
Land cover classification
Data requirements
Pre-processing imagery
(FC & NDVI)
Image classification
Data collection
Land cover mapping
Accuracy assessment

J. Looijen


PRE-PROCESSING IMAGES

• This phase includes the standard operations of

geometric correction, image referencing, image
enhancement and, if needed, the application of filters

• All data are georeferenced to UTM WGS 84,
Zone 48 N

J. Looijen


COLOUR COMPOSITES

• Besides geo-referencing and radiometric

corrections we need to make sure that the objects
of interest can be distinguished

• The spectral information stored in the separate

bands can be integrated by combining them into a
colour composite

• Many combinations of bands are possible
• The spectral information is combined by displaying
each individual band in one of the three primary
colours: red, green and blue.
J. Looijen


ELECTRO-MAGNETIC SPECTRUM

J. Looijen


REFLECTION CURVES VEGETATION

• If in land cover classification and mapping you will

mainly concentrate on the mapping of vegetation
cover, including agricultural fields, you have to select
those band combinations that give you the ideal
reflectance

• This differs per satellite image.

J. Looijen


FALSE COLOUR COMPOSITES

• Human eye cannot see the high reflection in the near
infrared and middle infrared radiation

• Since the human eye is very sensitive for different

shades of red, the infrared band is displayed in red.

• False Color Composite (FCC):
 the red color is assigned to the near-infrared band,
 the green color to the red visible band and
 the blue color to the green visible band.

J. Looijen


REFLECTANCE CURVES - SENSORS

J. Looijen


FC LANDSAT

• Which band combinations (RGB) would you

select to create a FC based on Landsat TM 5?

• Which band combinations (RGB) would you

select to create a FC based on Landsat 8 OLI?

J. Looijen


VNREDSAT 1

• Which band combinations (RGB) would you select
to create a FC based on VNREDSat 1 imagery?

J. Looijen

VNREDSat 1

Similar to?

J. Looijen


EXERCISE FC

• Creation and use of a false colour composite & DEM

J. Looijen


NDVI

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RATIO IMAGES

• Ratio images are often useful for discriminating
differences in spectral variations

• Which spectral ratio to use depends upon the

particular reflectance characteristics of the features
involved and the purpose of the land cover map

• For example a near-infrared / red ratio image might

be useful for differentiating between areas of
stressed and non-stressed
 Drought
 Pollution

J. Looijen


NDVI

• If you would like to know the presence and

condition of the green vegetation, preparation of a
Normalized Difference Vegetation Index (NDVI)
maybe useful

• The NDVI is calculated as:
NDVI = (NIR — VIS)/(NIR + VIS)

• NDVI values range from -1 to 1

J. Looijen


NDVI
How would you estimate the NDVI values for:
 No vegetation (bare soil, rocks):
 Dense green vegetation:
 Water , clouds, snow:

J. Looijen


EXERCISE

• Creation of a NDVI

J. Looijen