JA:土地表面

A priori and a posteriori systems

In an a priori classification system the classes are abstractions of the types actually occurring. The approach is based upon definition of classes before any data collection actually takes place. This means that all possible combinations of diagnostic criteria must be dealt with beforehand in the classification. The main advantage is that classes are standardized independent of the area and the means used. The disadvantage, however, is that this method is rigid, as some of the field samples may not be easily assignable to one of the pre-defined classes.

A posteriori classification differs fundamentally by its direct approach and its freedom from preconceived notions. The approach is based upon definition of classes after clustering similarity or dissimilarity of the field samples collected. The advantage of this type of classification is its flexibility and adaptability compared to the implicit rigidity of the a priori classification. The a posteriori approach implies a minimum of generalization. This type of classification better fits the collected field observations in a specific area. At the same time, however, because an a posteriori classification depends on the specific area described and is adapted to local conditions, it is unable to define standardized classes. Clustering of samples to define the classes can only be done after data collection, and the relevance of certain criteria in a certain area may be limited when used elsewhere or in ecologically quite different regions.

NLCD92 - National Land Cover Database

National Land Cover Database (NLCD) is a land cover classification scheme that has been applied consistently across all 50 United States and Puerto Rico. NLCD is based primarily on Landsat satellite data.

LCCS - Land Cover Classification System

The Land Cover Classification System (LCCS) is the result of an initiative to take a first step towards an internationally agreed reference base for land cover. The objectives of the Africover Programme of the Environment and Natural Resources Service (SDRN), FAO, are to develop an approach for conceptualizing, defining and classifying land cover.

Definition: Land cover is the observed (bio)physical cover on the earth's surface.

One of the basic principles adopted in the new approach is that a given land cover class is defined by the combination of a set of independent diagnostic attributes, the so-called classifiers. There are 83 main classifiers (Type A), 13 Type B, 19 Type C, 3 Type D, 7 Type E, 10 Type F, 2 Type G (numbers are not approved).

The creation of the land cover class is given by the combination of a set of pre-defined pure land cover classifiers. This set of classifiers is different for each of the eight main land cover types. E.g. trees can have classifier A1 or A3; shrubs can have A2 or A4; B1 stands for large to medium sized fields or height 7-2m or Dunes.

The main criteria is the uppermost canopy layer. This means that the dominant layer goes from Tree canopy to Shrub to Herbaceous/Forbs/Graminoids.

The user can describe up to three layers of stratification (including the main layer) for Terrestrial Vegetation (A12) and up to two layers in Aquatic or Regularly Flooded Vegetation (A24). "Tree Savannah" is clearly defined by two main elements: a Herbaceous vegetation layer and a Sparse Trees layer. Thus, the Stratification of the two elements Herbaceous and Tree layer is crucial for the definition of this class. "Closed Forest" is clearly defined by the element of a Closed Trees layer. Limitations have been introduced for this class in the use of Stratification. All limitations in use of Stratification are built into the software application.

It is crucial where the classifier (e.g. trees) appears, in the main layer or second or third layer.

Examples for results of LCCS-Code in main type A12. Natural and Semi-Natural Vegetation:

• A3.A10 - Closed forest
• A3.A10.B2.C1.D1.E2 - Broadleaved dedicious forest
• A3.A10.B2.C1.D1.E2.F2.F5.F7.G2 - Multi-layered broadleaved dedicious forest
• this combinations have a completely different meaning in other main types