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Berlin Environmental Atlas

01.02 Impervious Soil Coverage (Sealing of Soil Surface) (Edition 2007)

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Rule-Based Classification

Under rule-based classification, the results of spectral classification are combined with ISU data (section types) to yield degrees of impervious coverage derived at the pixel level. Figure 4 shows a schematic overview.

Figure 4
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Fig. 4: Diagram of rule-based classification

The classes and the NDVI categories were then assigned to degrees of impervious coverage. A reliable delimitation of completely vegetation-free and completely vegetation-covered areas was achieved in the NDVI categories 1 and 12 (lowest or highest NDVI values, respectively). Corresponding threshold values were derived automatically by means of reference sections.

  • NDVI Category 12 "Vegetation - Certain:"
    Under the rules, such sections were classified as 0 % impervious. This applied to all section-type categories.
  • NDVI Category 1 "Vegetation-Free - Certain:"
    Vegetation-free spaces were only considered to be 100 % impervious once they had been determined to not be neither "Sand" nor "Track Gravel."

The range of values between these NDVI limits is broken down via interval scaling into 10 additional NDVI categories of "Vegetation - Uncertain." In order to obtain a reliable assignment of degrees of vegetation and impervious coverage, they had to be interpreted differently, by section-type category or section type. Thus, a total of 3 assignment variants were established (Table 3). For each NDVI and impervious coverage category, the mean percentage value (5 %, 1 5%, ..., 95 %) was established as the conversion factor.
Recommendations from the concept study, the evaluation results of Haag 2006 and findings from aerial image interpretations and terrain inspections were incorporated. Also, results from the procedural validation process (cf. Validation) were taken into account for the iterative process optimization.

  NDVI (categories and degree of vegetation)  
Kat 1 2 3 4 5 6 7 8 9 10 11 12
% 0 5 15 25 35 45 55 65 75 85 95 100
Degree of
impervious
coverage
% 100 0 0 0 0 0 0 0 0 0 0 0 A Assignment
variant
% 100 95 85 75 65 55 45 35 25 15 5 0 B
% 100 100 100 100 100 100 0 0 0 0 0 0 C
Conversion factors for the calculation of pixel values:
Degree of impervious coverage 100 % = 1.00; 95 % = 0.95 etc.


Tab. 3: Assignment variants: Degree of vegetation - Degree of impervious coverage

The assignment variants were oriented toward certain section types, which are characterized by the spatial interconnection and the proximity of certain surface materials and types of buildings.

  • Assignment Variant A: Vegetation and pervious vegetation-free sections.
    The intermediate stages of the degrees of vegetation coverage (5 % - 95 %) were interpreted as mixed signatures of vegetation and other pervious surface types. The corresponding sections were therefore classified as pervious.
    Examples: Fallow areas, Forest, Farmland.
  • Assignment Variant B: Vegetation and impervious vegetation-free sections.
    The characteristic surface materials suggest a low share of vegetation-free pervious sections. Intermediate stages of the degrees of vegetation were therefore interpreted as mixed signatures of vegetation and impervious surfaces. The gradual increase in degree of vegetation per category thus corresponded to an adequate drop in degree of impervious coverage.
    Examples: Allotment gardens, traffic areas, block-edge buildings.
  • Assignment Variant C: Vegetation and impervious vegetation-free sections - block type "Airports".
    A variety of impervious surfaces characterized this block type. Some materials, such as concrete, showed strong spectral coincidences with sand and open soil. Such blocks indicate runways, parking areas etc. Within the airport area; green spaces were largely delimited as separate blocks. To achieve certain separation, it has proved useful to classify sections with low degrees of vegetation as completely impervious (NDVI categories 2 through 6).

At the same time, the result of the rule-based classification system of the non-built-up blocks corresponded to the final result of the satellite-image classification process. The category non-built-up impervious sections has been described in the classification with the 12 impervious coverage-degree categories, a Shade class and a Track-Gravel class.

Figure 5 shows the result of the satellite-image evaluation and the mapping results of the built-up impervious sections. Both data sets were brought together, and in conclusion, the degrees of impervious coverage were calculated (cf. Calculation of the Degrees of Impervious Coverage).

Figure 5
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Fig. 5: Result of rule-based classification

The result published via FIS-Broker as Map Impervious Soil Coverage (Edition 2007) raster dataraster-map shows the distribution of impervious coverage inside the bloc. At the same time the effect of shades in different blocs will be visible (in contrary map 01.02 shows average degrees of impervious coverage per bloc).

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