Water Body Extent
Image credit: Hatfield Consultants
Water Quantity & Quality
Mapping of permanent and ephemeral water bodies is needed to manage environmental impacts for exploration and development and reduce development impacts on aquatic habitats. Typically, safe setbacks will be applied to water bodies for seismic survey and to avoid impacts to water bodies from development. Monitoring impacts on water levels and re-charge rate of water bodies following water use is a regulatory requirement in some countries.
Mapping the extent of lakes from EO is operational, whereas determining and monitoring lake water level (a related product) is more challenging. Different types of satellite data may be used for the water body extent mapping:
Depending on the desired coverage and accuracy, optical sensors can be used from very high resolution (1 m or better) to high resolution (30 m or better). Freely available sensors such as Landsat 8 may be used to automatically identify reservoirs down to a size of one hectare. The Sentinel-2 satellite will provide frequent acquisitions that may be of great value for operational water extent mapping.
Radar data provides waterbody extent products with a high accuracy due to the contrast in radar backscatter from open water surfaces and the land. Radar may be especially useful for the monitoring of water bodies in cloudy regions to ensure increased (seasonal) coverage.
Water body products include maps showing the extent of water bodies (e.g., lakes, rivers, and reservoirs) and changes in their boundaries.
Known restrictions / limitations
The effective mapping resolution of radar data and products may be less than the stated sensor resolution due to effects of image speckle and the need to filter image and output products. The capability to map narrow linear features (e.g., small rivers, ditches) may also be reduced by vegetation cover.
A limitation for optical mapping is capturing cloud-free imagery during the wet season or after spring snow melt to capture maximum water body extent. A potential limitation with radar is mapping the extent of water bodies with emergent vegetation.
Lifecycle stage and demand
Pre-License: Knowledge of water body extent for situational awareness and planning.
Exploration: Water body extent maps are useful to ensure environmental impacts of seismic surveys are reduced and appropriate setbacks are applied. In exploration that requires water use, the maps can help to select lakes as potential sources of water. Lake extent provides a valuable baseline before water use.
Development: Water body extent maps are of value for logistics planning, monitoring of use of resources, and estimation of environmental impacts.
Production: Monitoring of water usage and potential indirect effects on water bodies during the production phase. Monitoring the variability in water body extent over time to monitor potential impacts from development or climate change.
Decommissioning: Environmental monitoring and remediation.
Geographic coverage and demand
Demand and coverage is global.
OTM:036 Geohazard exposure analysis
OTM:068 Water quality monitoring
Input data sources
Optical: VHR1,VHR2, HR1, HR2
Radar: VHR1, VHR2, HR1, HR2 (resolution dependent on the desired coverage and minimum mapping unit)
Spatial resolution and coverage
Spatial resolution: 0.5–30 m
Varies depending on input imagery used but mapping scales from 1:5,000 to 1:50,000 are possible.
In the case of radar images, speckle effects may reduce the final spatial resolution of images, which needs to be factored into acquisition plans.
Minimum Mapping Unit (MMU)
Variable, depending on source data resolution, and assumed scale of the final product. MMU as low as 0.01 hectares is possible from VHR1 data.
Accuracy / constraints
Thematic accuracy: above 90% in areas of low canopy cover. Uncertainties related to water body boundary with emergent and floating vegetation.
Spatial accuracy: dependent on source data, but typically 1 pixel.
Accuracy assessment approach & quality control measures
The accuracy of water extent mapping should be checked by field data using standard methods.
Frequency / timeliness
Observation frequency: observation may be required for a specific time or period within a year (e.g., before and after spring freshet). Frequency of acquisition of optical imagery can be high but is limited by cloud cover.
The frequency of new acquisitions of radar imagery can be as low as 3-5 days from the same satellite depending on the beam mode (resolution/extent) selected. The frequency of historical maps is highly variable depending on the archive.
Timeliness of delivery: both optical and radar processing can be completed quickly – water body products can be easily completed within one week for large areas.
On-demand availability from commercial suppliers.
New acquisitions can be requested globally.
Archived products available for public search. Availability may be limited for specific dates or locations.
Delivery / output format
Dean, Aleksandrowicz, Pierce
Water Body Extent
# of Pages:
Internal – Project consortium and science partners
External – ESA
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