Hydrology From Space: Applications of Space Geodesy to Problems in Surface and Subsurface Water Flow and Storage I
Presiding: S Wdowinski, University of Miami; S Buckley, University of Texas
G14A-01 INVITED 15:30h
Surface Water Monitoring: Brief History, Current State and Future Needs
Surface water bodies represent the most important water resources to human society, and their accurate monitoring is essential for proper water management and resource allocation. Furthermore, river discharge is one of the most accurately measured components of the hydrological cycle, yet it is not fully utilized in Earth Systems sciences. The value of surface monitoring was recognized by ancient civilizations. Human expansion in the last two centuries were often followed by the establishment of discharge monitoring networks. The currently operating discharge gauges monitor over 50% of the continental land mass, capturing more than 70% of the freshwater discharge to the oceans. Approximately 30% of the continental land mass is arheic (i.e. do not contribute any freshwater to the oceans) and the remaining 20% non-monitored areas are primarily in small coastal basins that would be hard to fully instrument. Despite the reasonably good spatial coverage, the current monitoring network is inadequate in terms of spatial density and the availability of the monitored records. Information about the state of standing water bodies (lakes, reservoirs, wetlands and floodplains) is almost non-existent for global analysis. However, traditional surface water monitoring techniques are well established and highly accurate, but their operation is labor intensive (in particular, the calibrations that require intensive field surveys). Major improvement in surface water monitoring would require either substantial investment or a technological breakthrough. Remote sensing techniques (especially satellite borne sensors) have the potential to offer the much needed data about inland surface waters that would complement the existing monitoring network. The planned presentation will give a brief overview of the evolution of global discharge monitoring. It will demonstrate the temporal and spatial distribution of discharge records by geographic regions. The requirement of the adequate monitoring network for large scale applications will be discussed both in terms of network density and observation frequency. The potential of remote sensing will be assessed by evaluating various satellite sensors and platforms in the context of a virtual mission that allows the assessment of retrieved information as a function of orbital configurations and sensor characteristics.
G14A-02 INVITED 15:45h
Characterization of elastic and inelastic aquifer motion from satellite geodetic measurements
The production of ground water in confined aquifer systems often results in a land- surface motion that is in a gradient between two end-member models--elastic deformation and inelastic deformation--that is directly measurable by satellite-based geodetic techniques. Elastic deformation is manifested by seasonal motion associated with the pumping, but with no permanent deformation; inelastic deformation results from permanent compaction of the fine-grained units and unrecoverable subsidence of the land surface. The combination of InSAR imagery, GPS measurements, and water-levels for Salt Lake City, UT, Chino Basin, CA and the metropolitan Los Angeles-Santa Ana region, CA, are used to characterize the end-member models and a hybrid model to show how aquifers respond to ground-water pumping stresses. In Salt Lake City, ground-water pumping results in a strong seasonal motion of as much as 85 mm that is not associated with any measurable long-term subsidence signal. Conversely the Chino Basin is subsiding at a rate of 34 mm/yr from ground-water pumping, with little seasonal motion. In the Los Angeles-Santa Ana region there is both elastic and inelastic motion, with greater than 60 mm of seasonal motion associated with 20 mm/year of subsidence. The inelastic subsidence began in 1995 and has been associated with a change in ground-water pumping policy. Improved characterization of these aquifer systems, and associated subsidence, may result in more effective approaches to ground-water resource management.
G14A-03 16:00h
InSAR Reveals Aquifer System Response in Heavily Pumped Basins in Nevada: A Tool for Groundwater Resource Management
Owing to the arid climate and a rapidly growing population, many pumped groundwater basins in Nevada are experiencing declining water levels. We have been conducting InSAR studies in selected groundwater basins of Nevada in order to better understand the physical character and response of these heavily pumped aquifer systems. Our results for three basins in southern Nevada illustrate how InSAR can provide a powerful tool for characterizing aquifer system response that can be used for groundwater resource management and subsidence hazard mitigation. In Las Vegas Valley, conventional InSAR using ERS-1 and -2 data has allowed us to define the spatial dimensions of the compacting aquifer system and demonstrate that faults within the basin fill strongly control the location and amount of aquifer system response. InSAR also shows that the principal zones of aquifer system response in Las Vegas are spatially offset from the sites of heaviest pumping. In the Virgin Valley, InSAR reveals that the aquifer system response has migrated as new production wells have come on-line, and the results are being utilized to manage pumping and to locate new well sites outside of the zone of aquifer compaction. In Pahrump Valley where subsidence has resulted in extensive structural damage, InSAR has revealed a relation between aquifer compaction and earth fissuring that will provide a hazard identification and mitigation tool. In addition to the application of conventional InSAR, we have conducted preliminary studies in the use of the permanent scatterer (PS) methodology to examine time-series and range-change trends. Using 50 ERS-1 and -2 scenes and all currently available Envisat scenes, we have identified more than 15 million PS targets in Las Vegas. Using the PS method, we are able to resolve surface motion at a resolution of about 0.5 mm/yr on individual targets. We believe this methodology has great potential for extracting detailed aquifer response measurements that can be used for directly determining hydraulic properties such as aquifer system storage coefficients. (Supported by NASA Grant NAG13-02017.)
G14A-04 16:15h
Hydrological applications of ICESat/GLAS
A new spaceborne geodetic tool was placed into a 600 km, near polar Earth orbit in January 2003. Although the laser altimeter carried on ICESat, known as the Geoscience Laser Altimeter System (GLAS), was designed to generate high accuracy profiles of the polar ice sheets to enable detection of surface change, many other applications of the instrument have been demonstrated, such as land topography, atmospheric characteristics, vegetation canopy height, and hydrology. With a laser pulse repetition rate of 40 Hz and a 70-meter laser footprint on the surface, successive illuminated laser spots (footprints) are separated on the surface by 170 meters. The GLAS instrument has been shown to produce an altitude measurement of 2-3 cm precision, depending on the surface characteristics within the illuminated laser footprint. ICESat instrumentation enables determination of the direction of the laser pulse, which in turn supports the determination of the geodetic location of the laser footprint centroid (geodetic latitude, longitude and ellipsoidal height). A variety of tests have been applied to validate the accuracy of the resulting laser altimeter surface profiles. Current accuracy estimates of the laser footprint location are decimeter level in geodetic height and 15 meters in horizontal position (latitude/longitude). The agile satellite allows pointing the laser at targets of opportunity as well. The global surface water level observations made by GLAS have broad application due to a very high spatial resolution compared to traditional radar altimetry and especially in remote regions. Using a variety of examples from rivers, lakes, wetlands, and coastal applications, the performance of the GLAS instrument will be illustrated. With the current demonstrated accuracy, it is evident that the laser profiles can serve as geodetic control points for other instrumentation and as constraints for modeling. With ongoing calibration/validation efforts, the performance is expected to improve, allowing GLAS to accurately monitor seasonal and long-term elevation and spatial changes of surface waters.
G14A-05 INVITED 16:30h
ICESat Observations of Mississippi River Stage and Slope Changes
River discharge and changes in lake, reservoir and wetland water storage are critical terms in the global surface water balance, yet they are poorly observed globally and the prospects for adequate observations from in-situ networks are poor (Alsdorf et al., 2003). The NASA-sponsored Surface Water Working Group has established a framework for advancing satellite observations of river discharge and water storage changes which focuses on obtaining measurements of water surface height (stage), slope, and extent. Satellite laser altimetry provides a method to obtain these inland water parameters and contribute to global water balance monitoring. Since its launch in January, 2003, the Ice, Cloud, and land Elevation Satellite (ICESat), a NASA Earth Observing System mission, has achieved over 650 million laser pulse observations of ice sheet, ocean surface, land topography, and inland water elevations and cloud and aerosol height distributions. ICESat carries the Geoscience Laser Altimeter System (GLAS) that obtains elevation measurements from 80 m diameter footprints spaced 175 m apart along profiles. For surfaces of low slope, single-footprint absolute elevation and horizontal accuracies of 10 cm and 6 m (1 sigma), respectively, referenced to the ITRF 2002 TOPEX/Poseidon ellipsoid are being obtained. Precisely repeated profiles of the Mississippi River from Vicksburg, MS to the confluence with the Arkansas River have been acquired to evaluate ICESat's recovery of river stage and slope. Cloud-free profiles collected on three dates in 2003 and 2004 document river stage and slope measurement precision of 10 cm and 1 cm per km, respectively, at and between crossings of channel meanders. Changes in ICESat-derived stage, average slope of the reach, and local slopes between meander crossings are observed between the three profiles, and the stage changes correlate with in-situ gage measurements. Implications for satellite laser altimeter estimation of river discharge will be discussed.
G14A-06 INVITED 16:45h
Seasonal Fluctuations of Water Storage in the Mekong River Basin from Satellite Altimetry, GRACE and other Remote Sensing data
We investigate the seasonal water storage over the Mekong basin using GRACE data over 2002-2004 which provides the total water storage (soil and underground waters plus surface waters). In parallel, we determine the seasonal variations of the surface water volume using 6 years (1998-2004) of SPOT/Vegetation imagery and Topex/Poseidon, ERS-2 and ENVISAT altimeter data. Surface water heights over seasonally inundated areas are measured using combined altimetry data from Topex/Poseidon, ERS-2 and ENVISAT. The seasonally varying extent of the inundated areas are derived from SPOT/Vegetation NDVI data. Over the common period of data (2002-2004), the surface water storage is subtracted to the total GRACE water storage to estimate the soil and underground water contributions. These results are compared with global/regional hydrological predictions. We also investigate the spatio-temporal response of each reservoir (surface, upper soil and underground water reservoirs) to seasonal precipitation forcing.