This service will focus on the identification of open water bodies and wetlands and their associated dynamics. Open water bodies include natural or man-made reservoirs such as ponds or lakes as well as wide rivers. Part of this service will include monitoring of the seasonal and long-term changes in surface water body extent, as well as changes in water levels. This product will be available from watershed to cross-border basin level, depending on the level of detailed requested by the user.
The required information for mapping surface water and wetland extent will be derived from dense time series of optical (e.g. Sentinel 2 & 3, Landsat, MERIS, MODIS) and radar satellite imagery (e.g. Sentinel 1). This high temporal approach helps dealing with the exceptionally variable hydrological conditions associated with many surface water bodies, thereby allowing long-term and seasonal dynamics to be sufficiently captured. Water level estimation with rely on radar Altimetry capabilities (e.g. Sentinel 3, Cryosat-2, Jason-1).
Use Case Examples
The assessment and monitoring of water bodies and wetlands throughout the entire river basin is crucial for water resource management. EO-derived information on surface water extent, both seasonal and long-term, can support regional to national water authorities and relevant basin commissions by: 1) providing vital data on the basin hydrology over poorly gauged watersheds; 2) supporting infrastructural development projects (e.g. planning dam construction or irrigation schemes); 3) providing crucial knowledge for livestock watering and crop irrigation, and 4) helping to monitor the impacts on vulnerable water-related ecosystems. Measuring surface water levels can provide estimates of total water volume in key reservoirs as well as providing estimates of river discharge.
Monitoring historical trends and changing patterns of surface water is complicated by the lack of medium to high resolution data prior to 2000, especially in the radar domain. Generally, radar time series are patchy and temporally intermittent prior to the Sentinel era. Historical optical data is available from Landsat and Spot missions, however, persistent cloud cover renders much of this data unusable. Distinguishing between permanent and temporary surface water and wetlands is therefore difficult considering the available historical data. Many wetland areas are also difficult to access, contributing to a lack of in-situ data for model calibration and validation.
Since the temporal attributes are important in surface water and wetland characterization, denser time series will be the primary enhancement required for reliable estimates of extent and monitoring seasonal change. Sentinel 1 A/B are currently building an impressive archive of radar data that can fulfil these temporal requirements, while Sentinel 2A/B, in combination with Landsat 7 and 8, should provide a sufficient temporal coverage in the optical domain. The Altimetry capabilities of Sentinel 3 will bolster the ability to monitor water levels, especially so when both A and B sensors are in orbit (S 3B scheduled for 2017).