Date ( Publication )

2021-03-11

Identifier

https://portail.indigeo.fr/geonetwork/srv/metadata/58ca9626-a0d3-410a-b775-51b29400f854

Credit

UMR 6538 LGO - UMR 6554 LETG

Status

Completed

Keywords ( Theme )

• SNO DYNALIT , Beach profile , Digital Elevation Model , Coastal monitoring , Nearshore waves , Astronomical tides , Bathymetry , Orthoimage

Keywords ( Place )

• Brittany , Finistere , Porsmilin

GEMET - INSPIRE themes, version 1.0 GEMET - INSPIRE themes, version 1.0 ( Theme )

• Orthoimagery , Elevation

Access constraints

Other restrictions

Other constraints

Pas de restriction d'accès public Pas de restriction d'accès public No limitations to public access

Use limitation

Free use subject to mentioning the source (at least the name of the producer) and the date of its last update

Use constraints

Other restrictions

Other constraints

Supplier partner is not able to guarantee the accuracy, update, integrity, completeness of data and in particular that they are free of errors or inaccuracies, including location, identification or qualification. No warranty as to the fitness of the data for a particular purpose is made by the supplier partner. Users use the data under their full responsibility, without recourse against the supplier partner whose liability can be incurred due to damage resulting directly or indirectly from the use of this data. In particular, it is up to users to decide, on their own responsibility: the opportunity to use the data; File compatibility of their computer systems; adequacy of the data to their needs; that they have sufficient competence to use the data. The partner supplier is in no way responsible for external elements including data analysis tools, hardware, software, networks ... used to view and / or process data. The user ensures verify the timeliness of the information provided is compatible with the use of it.

Spatial representation type

Grid

Spatial representation type

Text, table

Distance

0.5  m

Metadata language

Français French

Character set

UTF8

Topic category

• Geoscientific information

Unique resource identifier

RGF93 / Lambert-93 + NGF-IGN69 height (EPSG:5698) RGF93 / Lambert-93 + NGF-IGN69 height (EPSG:5698) RGF93 / Lambert-93 + NGF-IGN69 height (EPSG:5698)

Distribution format

• ASC (1.0 )

  Specification

• GeoTIFF (1.0 )

  Specification

• MATLAB (2018b )

  Specification

OnLine resource

Porsmilin_DEMs_bathy.zip  

Porsmilin bathymetric DEM (2000-2019)

OnLine resource

MNT-Bathy_Porsmilin_2003-2019  

Bathymetric DEMs - Porsmilin beach - 2003-2019 (WMS-T)

OnLine resource

SNO DYNALIT  

SNO DYNALIT

Hierarchy level

Dataset

Statement

24 bathymetric DEMs have been obtained over the period 2008-2019 from hydrographic surveys using a boat-mounted multi-beam echo-sounder (survey method MES). Bathymetric surveys are generally undertaken during spring high tides to increase surface coverage. A topographic survey is often planned the same day at low tide, providing independent data for quality verification and data fusion. The hydrographic equipment aboard the ship consists in a multi-beam echo sounder (RESON SeaBat 8160 until end 2011, KONGSBERG EM 3002 thereafter) connected to RTK-GNSS and inertial measurement unit sensors. Using the EM 3002 (similar specifications prevail for the SeaBat), data were recorded by 254 equidistant beams emitting sound pulses at 300 kHz. Angular resolution was set to 120°, resulting in a maximum lateral coverage of approximately 50 m per track and inter-beam distances of 0.2 m at 15 m water depth (the maximum depth at the study site). In addition, for each survey, probe soundings recorded sound celerity profiles throughout the water column. Planning, collection and processing of bathymetric data were performed using QPS Qinsy software suite (https://qps.nl/qinsy/), which after guided correction of inertial movements of the boat, sound celerity gradients and tidal effects, allowed producing bathymetric DEMs with sub-metre spatial resolutions. Using stable regions of the study site (bedrock reef), bathymetric DEM quality was estimated to be represented by accuracy (mean error) and precision (standard deviation of error) of 0.04 m and 0.07 m, respectively.

Description

To facilitate reuse of the DEMs and to allow direct comparisons, consistent grids and a standard sampling resolution of 0.5 m were chosen to fit the entire dataset. Where necessary, DEM resampling was performed using linear interpolation (function griddata in MATLAB). To reduce operators’ influence on decisions such as filtering outliers and filling gaps in initial data, also contributing to homogenising survey precision across the dataset, all DEMs were applied the same post-processing routine that consists in (i) using the mean elevation difference parameter to filter DEM elevations outside the range μ ± 5σ, with  and σ calculated for each surface grid cell using a three-by-three moving window, and (ii) reasonably filling missing data by averaging at least three known elevations. For the latter, search is done within circles centred on the missing DEM cell with radii increasing incrementally (increment = grid spacing) until at least three known values are found or until a size limit is attained (1 and 10 m over reef and sand, respectively). Reef/sand classification was performed using a combination of orthoimage and roughness analyses. As a final step, DEMs were assessed for systematic and random errors using multi-temporal ground truths, obtained by averaging available surveys over stable terrain, with eventual corrections applied through horizontal and vertical registrations. DEMs are provided in separate folders in geotiff (.tif), Arcgrid ASCII (.asc) and MATLAB (.mat) formats. They are accompanied by detailed metadata text files and figure plots summarising the results of post-processing and error evaluation. The following naming convention is used: yyyymmdd_Porsmilin_MES_L93_IGN69_0.5, where yyyymmdd is the survey date.

Rationale

DEM harmonization

Metadata

File identifier

58ca9626-a0d3-410a-b775-51b29400f854   XML

Metadata language

Français French

Character set

UTF8

Parent identifier

74ecce0a-e650-4c41-9970-97e4602f1cd8

Hierarchy level

Dataset

Hierarchy level name

Parent

Date stamp

2021-09-30T14:15:10

Metadata standard name

ISO 19115

Metadata standard version

1.0