2,863 research outputs found
River monitoring from satellite radar altimetry in the Zambezi River basin
Satellite radar altimetry can be used to monitor surface water levels from space. While current and past altimetry missions were designed to study oceans, retracking the waveforms returned over land allows data to be retrieved for smaller water bodies or narrow rivers. The objective of this study is the assessment of the potential for river monitoring from radar altimetry in terms of water level and discharge in the Zambezi River basin. Retracked Envisat altimetry data were extracted over the Zambezi River basin using a detailed river mask based on Landsat imagery. This allowed for stage measurements to be obtained for rivers down to 80m wide with an RMSE relative to in situ levels of 0.32 to 0.72m at different locations. The altimetric levels were then converted to discharge using three different methods adapted to different data-availability scenarios: first with an in situ rating curve available, secondly with one simultaneous field measurement of cross-section and discharge, and finally with only historical discharge data available. For the two locations at which all three methods could be applied, the accuracies of the different methods were found to be comparable, with RMSE values ranging from 4.1 to 6.5% of the mean annual in situ gauged amplitude for the first method and from 6.9 to 13.8% for the second and third methods. The precision obtained with the different methods was analyzed by running Monte Carlo simulations and also showed comparable values for the three approaches with standard deviations found between 5.7 and 7.2% of the mean annual in situ gauged amplitude for the first method and from 8.7 to 13.0% for the second and third methods
Radar altimetry systems cost analysis
This report discusses the application and cost of two types of altimeter systems (spaceborne (satellite and shuttle) and airborne) to twelve user requirements. The overall design of the systems defined to meet these requirements is predicated on an unconstrained altimetry technology; that is, any level of altimeter or supporting equipment performance is possible
Operational reservoir inflow forecasting with radar altimetry: The Zambezi case study
River basin management can greatly benefit from short-term river discharge
predictions. In order to improve model produced discharge forecasts, data
assimilation allows for the integration of current observations of the
hydrological system to produce improved forecasts and reduce prediction
uncertainty. Data assimilation is widely used in operational applications to
update hydrological models with in situ discharge or level measurements. In
areas where timely access to in situ data is not possible, remote sensing
data products can be used in assimilation schemes.
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While river discharge itself cannot be measured from space, radar altimetry
can track surface water level variations at crossing locations between the
satellite ground track and the river system called virtual stations (VS).
Use of radar altimetry versus traditional monitoring in operational settings
is complicated by the low temporal resolution of the data (between 10 and 35
days revisit time at a VS depending on the satellite) as well as the fact
that the location of the measurements is not necessarily at the point of
interest. However, combining radar altimetry from multiple VS with
hydrological models can help overcome these limitations.
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In this study, a rainfall runoff model of the Zambezi River basin is built
using remote sensing data sets and used to drive a routing scheme coupled to
a simple floodplain model. The extended Kalman filter is used to update the
states in the routing model with data from 9 Envisat VS. Model fit was
improved through assimilation with the Nash–Sutcliffe model efficiencies
increasing from 0.19 to 0.62 and from 0.82 to 0.88 at the outlets of two
distinct watersheds, the initial NSE (Nash–Sutcliffe efficiency) being low at one outlet due to large
errors in the precipitation data set. However, model reliability was poor in
one watershed with only 58 and 44% of observations falling in the
90% confidence bounds, for the open loop and assimilation runs
respectively, pointing to problems with the simple approach used to
represent model error
Gravity, geoid and the oceanic lithosphere
Plate tectonics and its contribution to progress in studies of the Earth's gravitational field is discussed. In acquisition, the development of forced feedback accelerometers, satellite navigation, and satellite radar altimetry significantly improved the accuracy and coverage of gravity data over the oceans. In interpretation, gravity and geoid anomalies are used to determine information on the thermal and mechanical properties of the oceanic lithosphere and the forces that drive plate motions
Field-calibrated model of melt, refreezing, and runoff for polar ice caps : Application to Devon Ice Cap
Acknowledgments R.M.M. was supported by the Scottish Alliance for Geoscience, Environment and Society (SAGES). The field data collection contributed to the validation of the European Space Agency Cryosat mission and was supported by the Natural Sciences and Engineering Research Council, Canada, the Meteorological Service of Canada (CRYSYS program), the Polar Continental Shelf Project (an agency of Natural Resources Canada), and by UK Natural Environment Research Council consortium grant NER/O/S/2003/00620. Support for D.O.B. was provided by the Canadian Circumpolar Institute and the Climate Change Geoscience Program, Earth Sciences Sector, Natural Resources Canada (ESS contribution 20130371). Thanks are also due to the Nunavut Research Institute and the communities of Resolute Bay and Grise Fjord for permission to conduct fieldwork on Devon Ice Cap. M.J. Sharp, A. Gardner, F. Cawkwell, R. Bingham, S. Williamson, L. Colgan, J. Davis, B. Danielson, J. Sekerka, L. Gray, and J. Zheng are thanked for logistical support and field assistance during the data collection. We thank Ruzica Dadic, two other anonymous reviewers, and the Editor, Bryn Hubbard, for their helpful comments on an earlier version of this paper and which resulted in significant improvements.Peer reviewedPublisher PD
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