HYDROWEB experiment: RIVER PRODUCTEntry ID: CNES_http__cnes.fr_ark_68059_0b7a761c3e62fd4332cd4f66eff0c845_IDN
Abstract: The products offered by the Hydroweb project consist of continuous, long-duration time-series of the levels of large lakes with surface areas over 100 km2, reservoirs and the 20 biggest rivers in the world.The operational measurement series are updated no later than 1.5 days after a new altimetry measurement becomes available. They cover about 80 large lakes and 300 measurement points along about ... 20 major rivers.The research measurement series are updated at regular intervals according to the progress made with processing by the LEGOS laboratory. They cover about 150 large lakes and 1,000 measurement points along about 20 major rivers.Continental waters account for only 0.65% of the total amount of water on Earth, 97% being stored in the oceans and 2.15% in the cryosphere. However, these waters have a significant impact on life on Earth and household needs. They also play a major role in climate variability. Water on Earth is continually recycled through precipitation, evaporation and run-off towards the sea. The increasingly accurate characterisation of the water cycle on land surfaces enables more accurate forecasting of the climate and more careful control of global water resources (human consumption and activities such as agriculture, urbanisation and the production of hydroelectric power, for example).
Radar echoes over land surfaces are hampered by interfering reflections due to water, vegetation and topography. As a consequence, waveforms (e.g., the power distribution of the radar echo within the range window) may not have the simple broad peaked shape seen over ocean surfaces, but can be complex, multi-peaked, preventing from precise determination of the altimetric height. If the surface is flat, problems may arise from interference between the vegetation canopy and water from wetlands, floodplains, tributaries and main river. In other cases, elevated topography sometimes prevents the altimeter to lock on the water surface, leading to less valid data than over flat areas. The time series available in Hydroweb are constructed using Jason-2 and Saral GDRs. The basic data used for rivers are the 20 or 40Hz data(?high rate? data).To construct river water level time series, we need to define virtual stations corresponding to the intersection of the satellite track with the river. For that purpose, we select for each cycle a rectangular ?window? taking into account all available along track high rate altimetry data over the river area. The coordinate of the virtual station is defined as the barycenter of the selected data within the ?window?. After rigourous data editing, all available high rate data of a given cycle are geographically averaged. At least two high rate data are needed for averaging otherwise no mean height is provided. Scattering of high rate data with respect to the mean height defines the uncertainty associated with the mean height.The water level and volume time series is operationally updated less than 1.5 working days after the availability of the input altimetry data, for some virtual stations on rivers. Other virtual stations are monitored on a research mode basis.
Data Set Citation
Dataset Originator/Creator: CNES
Dataset Title: HYDROWEB experiment: RIVER PRODUCT
Dataset Release Date: 1992-01-01
Dataset Release Place: CNES
Start Date: 1992-01-01
Use Constraints Access is public.
Role: DIF AUTHOR
Email: serad at cnes.fr
Centre National d'Etudes Spatiales
City: Toulouse Cedex 9
Postal Code: 31401
Extended Metadata Properties
(Click to view more)
Creation and Review Dates
DIF Creation Date: 2016-08-15
Last DIF Revision Date: 2017-08-23