huong dan su dung tien xu ly anh ve tinh bang ILWIS

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Pre-processing imagery Joan Looijen TOPICS • • • • • • • • 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 OLI? J Looijen VNREDSAT • Which band combinations (RGB) would you select to create a FC based on VNREDSat imagery? J Looijen VNREDSat Similar to? J Looijen EXERCISE FC • Creation and use of a false colour composite & DEM J Looijen NDVI J Looijen 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 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 ... 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... • • • • • • • • Why land cover mapping? Land cover classification Data requirements Pre-processing imagery (FC & NDVI) Image classification Data collection Land cover mapping Accuracy assessment... 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
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