In This Space
Image credit: DigitalGlobe
Water Quantity & Quality
This product is focused on satellite-derived bathymetry for lakes or shallow coastal areas. Information about bathymetry may be indirectly derived from optical images, derived from a wide variety of sensors (resolutions ranging from HR2 to VHR1 – 30 m to less than 1 m). Water absorbs all light above red wavelengths, but its spectral response in shorter wavelengths (particularly in blue) is significant. Methods for detecting the water depth are most accurate when water is clear, above a light surface (e.g., sand). For that reason satellite-derived bathymetry products have been delivered mostly for shallow coastal environments. The products compete with technologies such as sounding surveys from vessels as well as bathymetric LIDAR. The International Hydrographic Bureau publishes the standard, “Bathymetric Surface Product Specification S 102”, which can be referenced to develop accuracy standards.
Complimentary information on lake levels may be available from EO-based radar altimeters – Water levels in lakes and reservoirs can currently be obtained from four different satellite altimetry databases: (i) Global Reservoir and Lake Monitoring (GRLM); (ii) River Lake Hydrology (RLH); (iii) Hydroweb; and (iv) ICESat-GLAS level 2 Global Land Surface Altimetry data (ICESat-GLAS). Recent studies have demonstrated the potential of combining satellite imagery and radar altimetry to estimate the volume of water stored in lakes, rivers, and ﬂoodplains.
The water body volume product delivers depth values (raster) for water bodies along a regularized grid. Depth contour lines can also be provided.
Known restrictions / limitations
Turbidity of water can limit the utility of satellite derived bathymetry. The morphology of the lakes being measured is also important; the product is suited to relatively shallow lakes and coastal waters. The detectable depth is usually limited to 20 m. The accuracy of the retrieved bathymetry varies with water depth, with the accuracy substantially lower at a depth beyond 12 m. Properties of the bottom materials influence accuracy, and ice cover may prohibit depth retrieval.
Altimetry instruments are primarily designed to operate over uniform surfaces such as oceans and ice-sheets. Highly undulating or complex topography may cause data loss or non-interpretability of data. Derived height accuracy is driven by the satellite orbit, the altimetric range (distance between antenna and target), the geophysical range corrections and the size and type of the target).
Lifecycle stage and demand
Pre License Exploration
Pre-License: Knowledge of significant potential sources for water extraction can factor into project feasibility.
Exploration: Bathymetry and lake volume estimates are useful to plan water use and to select lakes as potential sources of water for operations. Lake extent and depth information provides valuable baseline environmental information before water use.
Development: During development and production, the long term impact on water bodies can be monitored, and satellite-derived lake volume, bathymetry and water levels can supplement in-situ monitoring.
Production: Monitoring of lake water levels in a region is important, especially for unconventional operations such as hydraulic fracturing or steam assisted gravity drainage. Anomalies in lake levels may indicate indirect environmental impacts.
Decommission: Environmental monitoring and remediation.
Geographic coverage and demand
Coverage and demand is global.
HC:2102 Understanding hydrogeology
Input data sources
Optical: VHR2, HR1, HR2
Radar (for altimetry):
Spatial resolution and coverage
Studies show that it is possible to derive bathymetry products of up to 1 m resolution using VHR data.
Minimum Mapping Unit (MMU)
The smallest lake that could be mapped is in the range of 1 ha, based on the resolution of input imagery.
Minimum target size is controlled by the instrument footprint size and the telemetry/data rates, and also by the surrounding topography and the target-tracking method used. Lakes monitored are typically large and over 100 km2 in size.
Accuracy / constraints
The accuracy of satellite-derived measurements depends on the quality of satellite data, atmospheric correction, water column turbidity and the model applied to the data. Mostly non-linear models gives better results comparing to linear models. Contours in the range of 1 m can be produced for depths down to 20 m.
Bathymetry from multispectral satellite data is:
Satellite bathymetry, within its range of recoverable depths, compares with LiDAR (that can reach depths up to 70 m) with similar contour intervals.
Several factors affect the accurate recovery of height data from inland water. The most important limitation is the presence of very bright components within the radar echo resulting from still pools. Further complications include: the presence of islands and sandbars within the water body; surrounding still water (for example, from irrigation and rice paddies); and the effect of surrounding terrain. All of these factors affect the echo shape and complicate retrieval of the range from the satellite to the water surface. Typically, altimetry stage measurements can range in accuracy from a few centimetres to tens of centimetres. For example, in the case of products derived from the ERS and ENVISAT satellites the accuracy is 3 cm over oceans and large lakes and 10 cm over the Amazon. The accuracy may be further reduced over smaller rivers. These are indicative numbers that can vary widely for different targets.
Accuracy assessment approach & quality control measures
Frequency / timeliness
Optical data provide the basis for frequent mapping (typically new scenes are available within one or more days), but baseline information is needed, such as lake extents.
Radar altimetry data:
Timeliness of delivery:
Data processing is semi-automated. Depending on the need for a new acquisition, bathymetry data can be provided within a few weeks.
Commercial optical data may need to be tasked due to limited archived coverage in remote areas.
Altimetry data is available at no charge.
Delivery / output format
# of Pages:
Internal – Project consortium and science partners
External – ESA
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