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EUROPEAN ENVIRONMENT AGENCY
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Figure 1: Institutional connections of the CORINE Land Cover project (see text for details)
Raw satellite images first have to be pre-processed and enhanced to
yield a geometrically correct document (satellite image map) in the
desired map projection. Digital film writers are used as output device
to produce an optimal hardcopy for visual photointerpretation.
Recently large sized, high-resolution computer printers are becoming
also a selectable alternative for output production. In the course of
interpretation, the photointerpreter draws polygons on transparent
overlay, fixed on the top of satellite image hardcopy. The
photointerpreter should consult simultaneously all available ancillary
data (topographic maps, aerial photographs, vegetation maps, land
cover and land use statistics, etc.). The polygons are coded according
to one of the items (a three-digit code) of the nomenclature. Although
display and evaluation of satellite imagery on screen of image
processing system is highly recommended to compensate for
drawbacks of using hardcopy images, it depends on availability of
appropriate facilities.
satellite image processing:
rectification, enhancement, hardcopy
photointerpretation,
field checking
digitisation of interpreted map sheets
verification
| merging adjacent map sheets |
| CORINE Land Cover database |
Figure 2: Flowchart of CORINE Land Cover mapping
Table 2:
Basic characteristics of the CORINE Land Cover database
e A Area coverage: 3,5 million km’, 23 countries (1998)
fully completed
e Method: computer assisted satellite photointerpretation
e Satellite images: LANDSAT, SPOT, etc.
e Ancillary data: topographic maps, vegetation maps,
land use and land cover statistics, etc
e Working scale: 1:100 000
e. Minimum mapping unit: 25 hectares
e Minimum linear feature width: 100 m
e Nomenclature: hierarchically structured in 3 levels: 5
classes for level-1, 15 classes for level-2 and 44 classes
for level 3
e Cartographic projection: Lambert azimuthal equal area
e X Various projections in country databases
e Implementation: national teams
e Supervision: Land Cover Technical Unit
e Overall classification reliability: better than 85%
e Geometric accuracy compared to topographic map: 100
meters RMS or better
e Mean cost: 5 ECU/km?
In the latest time however, with the rapid spread of lower cost
hardware and software systems, computer assisted
photointerpretation (CAPI) technology is more and more applied and
provides better thematic and positional accuracy.
Landsat Thematic Mapper (TM) data have been the most widely
used satellite imagery in the course of the project, because it provides
good area coverage, sufficient thematic and geometric details for a
reasonable cost. Recently, new high- resolution satellites with a
International Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998 635