Below is a practical, end-to-end guide for integrating remote sensing and field studies to monitor coastal erosion patterns. It covers objectives, recommended sensors and field methods, data processing and analysis workflows, validation and uncertainty estimation, sampling design and frequency, tools, and key pitfalls & best practices.
1) Define objectives and scale
- Clarify management/scientific questions: shoreline change rates, volumetric sediment budget, post-storm response, erosion drivers, habitat impacts, hazard mapping.
- Define spatial and temporal scale: local beach (100s m), regional coast (10s km), decadal vs. event-based monitoring. This determines sensor choice and sampling frequency.
2) Sensors and data sources — remote and in situ
Remote sensing
- Optical multispectral satellites: Sentinel-2 (10–20 m, free, 5-day revisit), Landsat 8/9 (30 m, 16-day), PlanetScope/Skysat (3–5 m, commercial, daily) — good for shoreline mapping, vegetation change.
- SAR: Sentinel-1 (10 m, all-weather) — useful through clouds, detect intertidal changes and shoreline in some conditions.
- Very-high-resolution commercial: WorldView/GeoEye (0.3–1 m) — for detailed shoreline extraction, urban coasts.
- Airborne lidar (topographic/bathymetric): high-accuracy DEMs for volumetric change, pre/post-storm surveys.
- UAVs (drones) with RGB or multispectral sensors: SfM photogrammetry to produce orthoimages and dense point clouds (sub-decimeter horizontal, centimeter vertical in good conditions).
- Satellite/airborne altimetry and stereo imagery when relevant.
In situ / field measurements
- Beach/profile surveys: RTK-GNSS or total station transects across shore at fixed benchmarks; Emery rod or EDM for simpler surveys.
- Erosion pins/marker stakes for short-term changes.
- Continuous sensors: tide gauges, pressure sensors, wave buoys or ADCPs (nearshore currents and wave statistics).
- Sediment sampling: grain-size, composition, tracer studies (e.g., painted tracer, RFID) for transport paths.
- Vegetation mapping and biophysical surveys (dune plants, marsh elevation).
- Bathymetry: single/multi-beam echosounder for subtidal morphology.
3) Sampling design and frequency
- Baseline mapping: full-coverage lidar or UAV orthophoto + ground-truth within first campaign.
- Routine monitoring:
- Satellite: monthly to weekly (Sentinel-2/Planet).
- UAV: quarterly or after major storms for high-res assessment.
- Field profiles: monthly to seasonally, and immediately pre/post significant storms.
- Continuous sensors: ongoing with telemetry if possible.
- Establish fixed transects every 100–500 m for beaches; higher density near infrastructure or hotspots.
4) Data processing & analysis workflows
A. Preprocessing
- Georeference and project all data to a common datum (e.g., WGS84 + local vertical datum). Use vertical datum transforms carefully for volumetric work.
- Correct optical imagery for atmospheric effects (e.g., Sen2Cor for Sentinel-2) and for tidal stage where necessary.
- For UAV and SfM: use ground control points (GCPs) tied to RTK-GNSS benchmarks.
B. Shoreline extraction
- Choose a shoreline proxy: wet/dry boundary (high-water line), vegetation edge, cliff edge — be consistent.
- Methods: NIR thresholding, NDWI, band ratio, object-based classification, manual digitization for high-res imagery.
- Automate with reproducible scripts where possible; use quality checks (manual validation of subsets).
C. Change detection
- Shoreline change rates: use DSAS (Digital Shoreline Analysis System) or comparable tools to compute rates (e.g., linear regression rate, end-point rate).
- DEM differencing (DoD): for volumetric change, subtract co-registered DEMs; apply error thresholding to avoid spurious change.
- Time series analysis: temporal smoothing, trend detection, seasonality decomposition.
- Combine subaerial and bathymetric change to build sediment budgets.
D. Integration of remote and field data
- Validate shoreline positions from imagery with field-profile intersection points and photographs.
- Use field profiles to convert shoreline movement into volumetric change (cross-sectional area × shoreline change).
- Upscale point measurements (e.g., grain size, profile change) using spatial interpolation constrained by remote sensing-derived features.
- Use wave/tide data to attribute drivers (storm surge, runup, seasonal wave climate).
5) Uncertainty quantification and validation
- Propagate uncertainties from sensor resolution, georeferencing, tidal stage, and DEM vertical error into shoreline position and volume estimates.
- Apply a change detection threshold based on combined error (e.g., minimum level of detection for DEM differencing).
- Use independent field measurements (RTK transects, GCP residuals, erosion pins) for validation and error estimation.
- Report errors and confidence intervals with all change metrics (m/yr for shoreline, m3/m for volumetric).
6) Analysis outputs and metrics
- Maps: multi-temporal shoreline overlays, erosion/accretion hotspots, DEM change maps.
- Tables/time-series: shoreline change rates (m/yr), volume change per unit length (m3/m), sediment budget components.
- Profiles: cross-shore change plots for key transects.
- Drivers: correlation/causal analysis linking change to wave/tide/storm events, human activities, coastal defenses.
- Risk products: erosion hazard maps, asset exposure, long-term projections under sea-level rise scenarios.
7) Tools and software recommendations
- GIS: QGIS, ArcGIS.
- Shoreline analysis: DSAS (ArcGIS/standalone), custom Python (rasterio, shapely, geopandas).
- DEM and point cloud: CloudCompare, LAStools, PDAL.
- SfM photogrammetry: Agisoft Metashape, OpenDroneMap.
- SAR processing: SNAP (ESA), GAMMA, ISCE.
- Python/R libraries: rasterio, xarray, numpy, scipy, scikit-learn, pyproj, R packages like bcsd?; statistical time-series packages.
- Visualization: matplotlib, R ggplot, QGIS.
8) Practical workflow example (typical project)
- Month 0: baseline high-resolution survey: airborne lidar (or dense UAV SfM) + field transects and GCP network.
- Ongoing: Sentinel-2 monitoring weekly/monthly; automated shoreline extraction and early-warning for significant change.
- Quarterly/seasonal UAV surveys: targeted at hotspots and post-storm.
- Monthly/seasonal field profile surveys at fixed transects; continuous wave/tide logging.
- Annual DEM differencing and sediment budget update; present to stakeholders.
9) Common challenges and mitigation
- Tidal uncertainty: record concurrent tidal stage or use modeled tide to correct imagery dates.
- Vegetation and turbidity: NIR and multispectral indices can confuse shoreline detection in marsh/delta systems; use field rules and object-based classification.
- Co-registration errors: use robust GCP deployment and iterative control point checks.
- Cloud cover: use SAR or high-temporal-resolution commercial imagery to fill gaps.
- Scale mismatch between point field data and coarse satellite pixels: use stratified sampling and upscaling methods; prioritize targeted UAV/airborne data where high resolution is needed.
10) Permissions, logistics, and stakeholder engagement
- Obtain UAV permits, marine survey permits, land access permissions.
- Engage local managers and communities early—local knowledge improves site selection and interpretation.
- Plan for data management and long-term archiving (consistent metadata, standardized file naming, open formats).
11) Deliverables and communication
- Produce reproducible workflows (scripts, notebooks) and metadata.
- Provide maps, time-series dashboards, and clear summaries of uncertainties and management implications.
- Create a decision-support product: erosion hotspot list, prioritized interventions, monitoring schedule.
12) References and resources (short list)
- USGS DSAS: https://www.usgs.gov/centers/erosion-and-shoreline-change
- ESA Sentinel Hub/SNAP documentation
- Agisoft Metashape / OpenDroneMap documentation
- CloudCompare and PDAL tutorials
- Relevant literature: coastal geomorphology textbooks and recent review papers on remote sensing for coastal monitoring.
If you’d like, I can:
- Draft a site-specific monitoring plan (sampling locations, frequency, estimated costs) if you provide the coastline length, environment (sandy beach, cliffed, marsh), and budget.
- Produce example code snippets for automated shoreline extraction (Sentinel-2) and DSAS-style rate calculation.
- Recommend a minimal instrument list for a constrained budget.
