Worksheet to Chapter 6 - Teacher Instructions

Image Classification -
Compare a Satellite Image with a Classification

Objectives:

Satellite images are often classified for further analysis and interpretations. During this process the different colour and structure information of the image data is clustered and categorised. Each pixel and area can be assigned to a specific land cover class or type.

Didactical comment:

• The worksheet 'Image classification' helps the students understand classification procedures with help of the satellite image example of the area of Düsseldorf, Germany. The students should compile a legend by assigning the correct colour to the different land cover classes in the given table. In addition, the students have to estimate the area percentage of each legend class.
• Advantages and possible applications of true colour satellite images and classified images are developed by the students in the second step.

Solution to the worksheet 'Image Classification'

1. Please compile the legend by adding the right colour to the 10 land cover classes. Following colours are given: yellow - light green - medium red - blue - lime green - dark red - grey - light red - dark green - medium green
2. Estimate the area percentage of each land cover class (be sure not to exceed 100% in total)

   Legend class	Colour	Area percentage
   High degree of sealing (> 80%)	Dark red	9%
   Medium degree of sealing (40 - 80%)	Medium red	33%
   Low degree of sealing (< 40%)	Light red
   Waste deposit sites, gravel-pits, building sites	Grey	-
   Agricultural land	Yellow	16%
   Grassland and pasture	Lime green	7%
   Coniferous forest	Dark green	13%
   Mixed forest	Medium green
   Deciduous forest	Light green
   Water bodies	Blue	6%

3. Name reasons why a classification is useful.
   • Image classification categorises all pixels in an image into land cover classes or themes.
   • Classified images are more valuable for regional planners, researchers etc.
   • They can be used for inventory monitoring and other land use applications.
4. True colour satellite image or classified image? Name advantages and disadvantages of true colour and classified satellite images and where they are most useful.

   True colour satellite images	Classified satellite images
   + the natural colours can provide information about the actual state of vegetation and seasonal changes	- classified images do not distinguish between seasons
   - high information density, no distinction between important and unimportant information	+ only important land use classes or themes visible on a classified imaged
   	- these images are generalised and lack information
   - a clearly assignment of colour and land cover type is not possible	+ each pixel can be assigned to a land cover class with its colour
   	+ (infra)structures and cities are immediately distinguishable
   + general overview over an area	+ very useful for regional/ environmental planning and monitoring
   	+ land cover inventory
   	+ change detection