Pléiades Days, 2014 CONTRIBUTION OF SATELLITE IMAGERY TO SEARCH CLUES OF SURFACE DRAINAGE WITHIN 1. Methods, remote sensing 2. Applications of achieved results 3. Contact : Sébastien RUCQUOI & Christelle BOSC CEREMA \ Dter Sud-Ouest \ DALETT \SCGSI 1
- Context - Kind of index Need initiated by the DGALN (MEDDE) in 2010 then project by DREAL MP, continuing methodological work of BRGM & Agence de l Eau Adour-Garonne State of the art of the use of remote sensing applied to the study catchment areas supply ( : Aires d Alimentation de Captage) Local users interested in developing a method for high performance : DREAL Midi-Pyrénées Context Agence Régionale de Santé (ARS) Midi-Pyrénées = Surface area where water seeps or streams involved in the supply of water resources in which is the water extraction (surface water or groundwater extraction) 2
Speed of movement of water Contribution of - Context - Kind of indices Indicators tracked Main elements drainage : Valleys and thalwegs forming the of natural waterways Water infiltration points (mainly on karstic environment) : dolines, depressions / sinkholes, chasm,, promoting the flow of water to underground s Surface soil horizons, permeable, welcoming flows called "subsurface", usually temporary Large discontinuities in rock masses (faults, contact between geological formations,...), playing a lead role Artificial s (agricultural or road drains and ditches mainly), ensuring the collection and disposal of stormwater 3
: Structured and hierarchical thalwegs Water drain (active / real ) Dry drain (potential ) Définition Extraction method : Radiometric approach based on image processing Morphological approach, based on the processing of DEM 4
1. Radiometric approach Extraction methods Search linear, tree structures, discontinuities or radiometric alignments by PHOTO- INTERPRETATION Spot 5 image Spatial resolution : 2,5 m Spot Image 2006 5
1. Radiometric approach Extraction methods Search linear, tree structures, discontinuities or radiometric alignments by PHOTO- INTERPRETATION Spot 5 image Spatial resolution : 2,5 m Spot Image 2006 photo-interpreted 6
Extraction methods 2. Morphological approach based on the processing of DEM AUTOMATIC EXTRACTION from morphological algorithms, hydrological or hydrogeomorphological (tested for several years, configurable methods) DEM Spot 5 Spatial resolution : 20 m Spot Image 2006 7
Extraction methods 2. Morphological approach based on the processing of DEM AUTOMATIC EXTRACTION from morphological algorithms, hydrological or hydrogeomorphological (tested for several years, configurable methods) DEM Spot 5 Spatial resolution : 20 m Spot Image 2006 calculated (logiciel SAGA) 8
Methods validation Comparison between the two approaches (radiometric and morphological) : Radiometric : Realistic detection but not exhaustive Morphological : exhaustive détection but flows modeling angular and local inaccuracies photointerpretation calculated 9
: Définition Water circulation in permeable upper soil horizons, often temporary Identification : Groundwater micro-table Drainage channels located Subflows Diffuse indices (slightly marked), punctual, varying climate Hardly visible directly on the ground (need some distance) Possible confusion with other indices (wetland, artificially drained subsoil, traces of moisture at the bottom of the valley,...) 10
Extraction Method : Extraction Method PHOTO-INTERPRETATION (which can be facilitated by the use of different spectral bands of sensors, including infra-red) PLEIADES image Cnes 2012 Axis and direction of sub-surface flow 11
- Identification / sinkholes : / Sinkholes (water infiltration points) Définition Closed topographic depressions of generally sub-circular or elliptical shape, usually multi-metric or multidecametric scale (micro-features), sometimes coalescing (ouvalas) Formation : Karstic environment Usually related to the presence of geological accidents or underground cavities continuous (= preferential flow axes) Dissolution sinkholes (depressions flared shallow) Collapse sinkholes (depressions small areas marked by the sides restated) 12
Morphology (topographic depressions ) / Sinkholes (water inflitration points) Identification criteria Radiometry (characteristics depending on the nature of soils occupying funds sinkhole) Spatial distribution (alignment, grouping, isolated sinkhole) - Identification Overview of the spectral diversity of sinkholes in two different contexts 1. Landscape of bare land (Causse Méjean, Lozère) 2. Agricultural landscape (Bouriane, Lot) 13
- Identification No «standard» automated methods / Sinkholes (water infiltration points) Extraction Methods Detection possibilities soil fills karst from processing of optical or radar image without distinction of depression areas Detection possibilities topographic depressions of a DEM / DTM from correction algorithms 1 2 Operation of filling depressions in 3 steps (method «Fill Sinks») 3 A B B - A 14
/ Sinkholes (water infiltration points) Method validation Comparative analysis with other data sources on a test area - Identification Reference map 15
Contribution of / Sinkholes (water inflitration points) Method validation Comparative analysis with other data sources on a test area - Identification IGN & BRGM maps 16
Contribution of / Sinkholes (water inflitration points) Method validation Comparative analysis with other data sources on a test area - Identification Mapping based on IGN DEM processing 17
Contribution of / Sinkholes (water inflitration points) Method validation Comparative analysis with other data sources on a test area - Identification 18
Other drainage elements Geological discontinuities and artificial s Draining faults Agricultural drainage Aeronautic drainage Small fracturation on limestone plateau PLEIADES Image Cnes 2012 Ditches and drains buried in «cross» SPOT 5 Image Spot Image 2006 Network of drains and ditches in «ears» PLEIADES Image Cnes 2012 19
Other drainage elements Geological discontinuities and artificial s Draining faults Agricultural drainage Aeronautic drainage Small fracturation on limestone plateau PLEIADES Image Cnes 2012 Ditches and drains buried in «cross» SPOT 5 Image Spot Image 2006 Network of drains and ditches in «ears» PLEIADES Image Cnes 2012 20
Interest, applications, prospects Contribution of imagey compared to traditional methods (field surveys,...) : Automatic detection and topographic depressions (some not listed by IGN & BRGM) Stepping back, wide fields of view, spectral richness, revisiste, facilitating analysis by photo-interpretation (for flows sub-surface) Applications : Characterization of catchments and their environment (predimensioning basins search with precision tracking water,...) Risk assessment Prospect : THRS imagery Pleiades : detection of small landform (depressions, ditches,...) 21
THANK YOU FOR YOUR ATTENTION 22