5. Qualité de la carte : discussion et perspectives
5.4. Contrôle qualité de la cartographie
Le contrôle qualité de la cartographie passe en revue l’ensemble des facteurs ayant trait à l’acquisition par télédétection, à l’observation et au recueil de données de terrain, au processus d’interprétation, enfin à la qualité du produit cartographique final (Foster-Smith et al., 2006).
Les trois zones intertidale, subtidale et des faibles fonds intermédiaires étant relativement différentes en ce qui concerne la mise en œuvre des levés et de l’interprétation, elles sont traitées séparément ci-dessous.
Littoral area
Ground truthing
- Sampling technique: Most techniques appropriate, some not appropriate Boundary positioned on field with DGPS waypoints.
Granulometry estimated by sight for sedimentary substrats.
- Positional accuracy: high (differential GPS)
Sample density: medium (every class in the map sampled) Processing: medium (qualitative informations)
- Vintage: high (data collected in the year of edition of the map)
Remote sensing
- Techniques used: medium (Techniques moderately appropriate). While photo-interpretation in coastal orthophotographs associated with Lidar altimetric data is the optimal method for mapping littoral rocky shores, this technique is less adapted for mapping littoral sedimentary shores.
- Coverage: high (excellent coverage). Mapping area very heterogeneous. But coastal orthophotographs covers 100% of the area and Lidar altimetric data cover more than 50% of the area.
- Positional accuracy: high. Coastal orthophotographs are made by National Geographical Institute, they are the spatial reference in France for coastal area. Topographic LIDAR positional accuracy is better than 5 meters.
- Standards: medium (standards for material, internal standards for the use in REBENT strategy)
Interpretation
- Method: medium (evidence of expert interpretation but not accompanied by accuracy/error matrices) - Level of classification: medium (classification in EUNIS levels 4 and 5)
Cartographic product
- Scale: high (maximal scale for restitution: 1:10000)
- Resolution: high (map resolution is lower than resolution of data collected). Resolution of orthophotographs is 0.5 meters, that of Lidar digital elevation model is 2 meters.
Sublittoral area
Ground truthing
- Sampling technique: high (Techniques comprehensive and appropriates). Granulometry sampling with shipek grab. Biological sampling with Hamon grab (3 samples per point).
- Positional accuracy: high (digital GPS)
- Sample density: medium (every class in the map sampled) - Processing: high (qualitative et quantitative data)
- Techniques combo: high (optimum combination between delimitation of habitats with side scan sonar mosaic and identification by grain size, biological and video analyses).
- Level of classification: high (classification in EUNIS level 5)
Cartographic product
- Scale: high (Maximal scale for restitution: 1:10000)
- Resolution: high (Map lower resolution than data collected). Side scan sonar mosaic resolution is 50 centimeters.
Shallow water area
Ground truthing
- Sampling technique: low (Techniques not appropriates). Some points for validation of macro-algae on infralittoral rocks. Granulometry estimated by sight for sedimentary substrats, few ground truthing points. Some points have grain size analyses.
- Positional accuracy: medium (GPS Positioning)
- Sample density: medium (every class in the map sampled) - Processing: low (samples labelled with limited informations)
- Vintage: 3 (Data collected in the 3 years before map establishment)
Remote sensing
- Techniques used: medium (few techniques appropriate). Photo-interprétation with coastal orthophotographs associated with Lidar altimetric data was used for mapping rocky bottoms, but not for determine vegetal cover. This technique is less addapted for mapping sedimentary substrata, it can be used to map habitats like seagrasses or maërl beds.
- Coverage: high (excellent couverage)
This area is less heterogeneous than littoral area. Coastal orthophotographs covers 100% of the area and LIDAR altimetric data covers more than 50% of the area.
- Positional accuracy: high. Coastal orthophotographs are made by National Geographical Institute, they are the spatial reference in France for coastal area. Topographic Lidar positional accuracy is better than 5 meters.
Interpretation
- Method: medium (Evidence of expert interpretation but not accompanied by accuracy/error matrices).
- Techniques combo: low (photo-interpretation was used primarily, digital elevation model from Lidar data was less used.
- Level of classification: low (Classification in EUNIS level 4 by equivalence with EUR15 classification for soft bottoms).
Cartographic product
- Scale: high (Maximal scale for restitution: 1:10000)
- Resolution: low (Map resolution is better than resolution of data collected). Orthophotographs resolution is 0,5 meters, LIDAR digital elevation model resolution is 2 meters, but ground truthing density is insufficient.
Références
Admiralty coastal surveys, 2005. Survey report, description of operations, les Abers and îles de Glénan, France. Rapport pour l’Ifremer, Altimétrie Lidar pour le secteur des Glénan, 23 p.
Alloncle N., 2005. Evolution récente des herbiers de Zostera marina en Bretagne – approche géomatique. Convention UBO – Université de Perpignan, 39p.
Bensettiti F. (Coordination générale), Connaissance et gestion des habitats et des espèces d'intérêt communautaire. Tome 2, Habitats côtiers . - Paris : La documentation française, 2004.- 399 p. : ill. ; 30 cm. (Cahiers d'habitats Natura 2000) ISBN 2-11-005192-2
CEVA, 2004, Cartographie détaillée des ceintures de fucales : secteur de Glénan, zone intertidale, rapport CEVA - IFREMER/DYNECO/VIGIES/06-18/REBENT, 22p. + annexes.
CEVA, 2005, Cartographie des zones de laminaires à partir de prospections en plongée : secteur de Glénan, zone subtidale, rapport CEVA - IFREMER/DYNECO/VIGIES/06-11/REBENT, 5p. + annexes.
Connor, D. W., D. P. Brazier, T. O. Hill and K. O. Northen, 1997. Marine Nature Conservation Review:
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Derrien-Courtel S., Derrien R., Beaupoil C., 2004. FT12 - Suivi des substrats durs subtidaux : Limites d’extension en profondeur des ceintures algales, suivi faunistique et floristique, 18p. Fiche technique disponible sur le site du Rebent :
http://www.rebent.org//medias/documents/www/contenu/documents/FT12-2004-01.pdf
Ehrhold, A., Blanchet, A., Hamon, D., 2006. Réseau de surveillance benthique (REBENT) – Région Bretagne. Approche sectorielle subtidale : Identification et caractérisation des habitats benthiques du secteur Glénan. RST/IFREMER/DYNECO/écologie benthique/06-03/REBENT, 62p. + 8 annexes.
Ehrhold, A., 2003. FT09 - Cartographie des peuplements macrobenthiques par les méthodes acoustiques en domaine subtidal, 19 p. Fiche technique disponible sur le site du Rebent : http://www.rebent.org//medias/documents/www/contenu/pdf/document/Fiches_techniques/FT09-2003-01.pdf
European Nature Information System, European Environment Agency, 2004. Version 9 http://eunis.eea.eu.int/habitats.jsp p
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Le Hir M., Chauvaud S., Robert G., 2005, Site Natura 2000 - Archipel des Glenan, Cartographie des habitats d'intérêt communautaire - rapport habitats marins, rapport Télédétection et Biologie Marine (TBM)-Mairie de Fouesnant-DIREN Bretagne-Natura 2000, 31 p. + annexes.
Le Hir M., 2005, Site Natura 2000 - Archipel des Glenan, Cartographie des habitats d'intérêt communautaire - notice Habitats marins, rapport Télédétection et Biologie Marine (TBM)-Mairie de Fouesnant-DIREN Bretagne-Natura 2000, 53 p.
Orthophotographie littorale pour le secteur des Glénan et Trévignon (format .ecw), 2000, ORTHOLITTORALE 2000.
Rollet C., 2003. FT13-FO01 - Les Orthophotographies littorales, 5p. (Fiche outil disponible sur le site du Rebent : http://www.rebent.org//medias/documents/www/contenu/documents/FT13-FO01-2005-01.pdf