H23E-1168 1340h
Air-to-Soil Transition Model
Within the last three years, a 1.4 GHz radiometer has been applied for bare soil experiments. The radiometer observations were compared with simultaneously measured soil water content and temperature. The remotely sensed and in-situ measured data were synchronous and therefore suitable to test radiative transfer models by comparing predicted and measured data. The soil reflectivities derived from the radiometer and from the ground truth data were inconsistent when using the Fresnel formula. To examine possible reasons for the observed discrepancy, other physically based surface reflectivity models were tested, but none of them was able to explain the observations. Hence, we propose a new roughness model denoted as air-to-soil transition model. It describes the influence of the topsoil structure on the L-band radiation as an impedance matching between the dielectric constants of the topsoil and air using an effective dielectric profile to describe the transition from air to soil. The new model is capable to explain the observations.
H23E-1169 1340h
Towards operational monitoring of wetland water levels using InSAR: Applications for the Everglades Restoration Project.
In a recent study [Wdowinski et al., 2004], we demonstrated that L-band InSAR can measure water levels in the Everglades with a vertical precision of 5-10 cm and horizontal resolution of a few hundred meters. The observations reveal spatially detailed, quantitative images of water levels in the Everglades, capturing dynamic water level topography and providing the first detailed picture of wetland sheet flow. We observed localized radial sheet flow in addition to well-known southward unidirectional sheet flow. The observation were used to constrain a linear diffusive flow model, which allowed us to obtain quantitative estimates of flow diffusivity (23-91 m2/s), the first space-based estimates of such hydrologic parameter for the Everglades. Although conventional wisdom suggests that C-band interferometry does not work in vegetated areas, we recently found, to our great surprise, that C-band interferograms with short acquisition intervals (1-105 days) can maintain excellent coherence over the Everglades wetlands. Our experimental study was part of an ESA CAT-1 proposal, where we used archived ERS-1/2 acquired over south Florida during the years1995-1998. Initial data processing shows superb interferometric coherence with the tandem mission (1-day interval between acquisitions) and variable coherence levels with the 1-3 repeated orbit cycles (35 days), depending on the acquisition time interval, baseline, and atmospheric conditions. The immediate advantage in using C-band SAR data for detecting wetland water level changes is the availability of current data, due to two active C-band satellites - RADARSAT-1 and ENVISAT. We are currently ordering SAR data from both satellites in order to evaluate optimal acquisition parameters (view angel, polarization, and resolution) and access near-real time operation of InSAR based monitoring of water level changes. * Wdowinski, S., F. Amelung, F. Miralles-Wilhelm, T. Dixon, and R. Carande, Space-based measurements of sheet-flow characteristics in the Everglades wetland, Florida, Geophys. Res. Lett., 31, L15503, 10.1029/2004GL020383, 2004.
H23E-1170 1340h
An Assessment Of Meso-Scale Hydraulic And Vegetation Characteristics Of The Middle Rio Grande River Using High Resolution Multispectral Airborne Imagery
Middle Rio Grande River (MRGR) is the main source of fresh water for the population of New Mexico as well as for irrigated agriculture. Extensive water diversion over the last few decades has affected the composition of the native Riparian vegetation such as Cottonwood population and enhanced the spread of introduced species harmful to the river system like Tamarisk and Russian Olives. High resolution airborne remote sensing is a powerful technique for riparian vegetation mapping and monitoring. Airborne multispectral digital images were acquired over the riparian corridor of the MRGR, New Mexico in June 1999 and July 2001, using the Utah State University (USU) airborne digital imaging system. The imagery were corrected for vignetting effects, geometric lens distortions, rectified to a map base, mosaicked, verified in the field, classified and checked for accuracy. Areas of the vegetation classes and in-stream features were extracted and presented per reach of the river. In this paper a relationship was developed between the total surface water area mapped and both the river water flow rate and water table readings. The consequence of this relationship on riparian vegetation distribution along the river was studied and graphically demonstrated. Strong relationship was found between the total surface water area and water flow rate. In addition the reduction in surface water area resulted in reduction of native trees downstream.
H23E-1171 1340h
Evaluation of MODIS snow-cover products with constraints from streamflow and SNOTEL data
Evaluation of the Moderate Resolution Imaging Spectroradiometer (MODIS) daily and 8-day snow-cover products is carried out by utilizing the streamflow and the Snowpack Telemetry (SNOTEL) measurements as constraints. Time series of the snow areal extent (SAE) of the Upper Rio Grande Basin are retrieved from MODIS during the period 2000 to 2004 using an automatic Geographic Information System (GIS) based algorithm developed for this study. Statistical analysis between the streamflow at Otowi (NM) station and the SAE retrieved from the two MODIS snow-cover products shows that there is a statistically significant correlation between the streamflow and SAE for both products. This relationship can be disturbed by heavy rainstorms in the later springtime, especially in May. Correlation analyses show that the MODIS 8-day product has a better correlation (r = -0.404) with streamflow and has less percentage of spurious snowmelt events in wintertime than the MODIS daily product (r = -0.300). Intercomparison of these two products, with the SNOTEL datasets as the ground truth, shows that the MODIS 8-day product has higher classification accuracy for both snow and land. The major cause that reduces the overall accuracy of the MODIS daily product is due to the cloud. Improvement in suppressing cloud in the 8-day product is obvious from this comparison study. The sacrifice is the temporal resolution which is reduced from one day to 8 days. The significance of the results is that the 8-day product may be more useful in evaluating the streamflow response to the snow-cover extent changes, especially from the long-term point of view considering its lower temporal resolution than the daily product. For clear days, the MODIS daily algorithm works quite well or even better than the MODIS 8-day algorithm.
H23E-1172 1340h
Potential and feasibility of operating satellite sensor systems dedicated to monitoring inland water bodies
The lack of adequate hydrological monitoring and the steady decline of hydrologic monitoring facilites are among the most important obstacles in the advancement of hydrological sciences and water resource management. Remote sensing (satelliteborne in particular) might be the only technology to provide the much needed data in a systematic global manner. Since none of the major existing sensor system are optimized for inland water monitoring a significant improvement is expected by designing and launching a dedicated satellite system. To assess how much improvement would be afforded by such a strategy and the feasibility of operating a such a system will require a ``hydrological testbed'' organized as an Observing System Simulation Environment (OSSE) that can be sampled virtually according to alternate satellite orbit configurations and sensor characteristics. We will discuss the potential of operating a satellite system dedicated to inland surface waters and the criteria designing such a system. We will demonstrate the use of a simple prototype OSSE to carry out virtual missions that could be used to assess the monitoring capabilities of different satellite orbit and sensor configurations and describe the current components of the virtual mission testbed plus its missing features that are essential for comprehensive analysis. We will present the first results applying the virtual mission testbed in its present form for altimeter sensors. We will demonstrate how to assess the achievable accuracies given various sensor characteristics, and orbital repeat frequencies.
H23E-1173 1340h
Stream Discharge Measurement Using A Large-Scale Particle Image Velocimetry Prototype
Good water management is founded on accurate open-channel flow measurements. New technology for measuring discharge in streams and rivers has been pursued due to concerns about safety, accuracy, and costs of traditional methods. Large-Scale Particle Image Velocimetry (LSPIV) is an emerging technology for measuring discharge in streams and rivers. LSPIV is a system capable of measuring velocity fields by collecting and analyzing recorded images of the flow field. The LSPIV system tracks the movement of `tracers' through successive images using statistical correspondence. Cross-correlation algorithms divide the image into small interrogation areas; each producing one displacement vector. The surface velocity field can be used to estimate discharge based on the channel bathymetry. Use of LSPIV for flow measurements in low-order streams has several advantages. LSPIV is not as labor intensive and does not present the safety concerns of the conventional methods during high flow events. Another promise for LSPIV is remote monitoring applications, which could also reduce labor and data management costs. The scheme used in this study for the development of LSPIV follows a logical progression: assimilate current knowledge, develop methods and acquire equipment, conduct laboratory and field experiments for `proof-of-concept', and refine the methods to decrease costs and increase usability. A laboratory prototype was developed and tested in a flume, with good results. The experiment evaluated the LSPIV prototype and a Marsh-McBirney flow meter against the flume manometer. Several conclusions were made from the statistical analysis. The Froude number affects the accuracy of the Marsh-McBirney flow meter and the LSPIV prototype. Therefore, future applications may wish to use an adaptive method to determine input parameters based on flow conditions. The LSPIV prototype produced poor flow measurements at camera angles above a 30 degree oblique angle. Therefore, field applications should use camera positions that reduce the oblique angle below 30 degrees. However, a zero degree camera angle may cause out-of-plane losses, which will reduce velocity measurements. The LSPIV discharge measurements were found to be equivalent to the flow meter in the laboratory application. Additionally, the prototype was adapted to field conditions and an operating procedure was developed. An experiment testing the proof-of-concept in the field will be completed during the fall of 2004.
H23E-1174 1340h
Spatial and temporal patterns in river ice breakup observed with MODIS and AVHRR time series
The timing of spring river ice breakup, a major annual event for physical, biological, and human systems on Arctic rivers, has been used to infer regional climate variations over the past century or more. Most observations of ice breakup are recorded as point data taken from selected ground-based stations. It is unknown whether these point observations are fully representative of breakup patterns elsewhere along the course of a river. Here, daily time series of MODIS and AVHRR satellite images are used to remotely sense spatial and temporal patterns in ice breakup along 1600-3300 km lengths of the Lena, Ob', Yenisey, and Mackenzie Rivers. The first day of predominantly ice-free water is visually identified and mapped for the years 1992-1993, 1995-1998, and 2000-2003, with a mean precision of ± 1.75 days. The derived breakup dates show high correlation with ground-based observations, though a slight trend towards earlier satellite-derived dates can be traced to differences in the way ice breakup date is defined. Large ice jams are often observed, particularly at confluences, though smaller ice jams may not be visible due to the limited spatial resolution of the imagery used. At the watershed scale, spatial patterns in breakup seem to be primarily governed by latitude, timing of the spring flood wave, and location of confluences with major tributaries. Interestingly, channel-scale factors such as slope, width, and radius of curvature, which are known to influence ice breakup at the reach scale, do not appear to be major factors at the scale observed here. The degree of similarity between interannual trends in breakup date at distant points along a river is generally high, which supports the use of point-scale data to infer regional climate variations. This similarity does not hold true for the Mackenzie River, where substantial spatial differences in breakup trends are observed. A new variable, spatially integrated breakup date (di), uses weighted spatial averaging to provide a more encompassing measure of breakup timing. The Ob' and Yenisey Rivers show similar trends in spatially integrated breakup date from year to year. In contrast, the Mackenzie and Lena show a remarkably consistent negative correlation, here attributed to sea surface temperature anomalies associated with the Pacific Decadal Oscillation Index.
H23E-1175 1340h
Near-Real Time Monitoring of Global Lakes and Reservoirs
Satellite radar altimetry has the ability to monitor variations in surface water height (stage) for large lakes and reservoirs. A clear advantage is the provision of data where traditional gauges are lacking or where there is restricted access to ground-based measurements. As part of a new USDA-funded program, near-real time altimetric monitoring of the largest lakes and reservoirs in the world is taking place. Data ingestion and manipulation, to some degree, follows the concepts of the NASA Ocean Altimeter Pathfinder although extra provisions have to be made regarding these smaller targets. Archived data from the TOPEX/POSEIDON (T/P) mission are utilized to provide a historical time series of height variations from 1992-2002. Near-real time stage measurements with respect to the T/P historical mean reference are derived from incoming data from the Jason-1 mission. The project utilizes the IGDR Jason-1 data with its $<$5 cm orbit accuracy and delivery time of $<$4 days after satellite overpass. A USDA maintained web site (http://www.pecad.fas.usda.gov/cropexplorer/global_reservoir) provides free access to new measurements to the public about a week to ten days after the satellite passes over. Currently there are stage levels from 70 lakes/reservoirs worldwide being made available. As the project progresses, other data from the ERS and ENVISAT missions will also be included. The Foreign Agricultural Service's, Precipitation Estimation and Crop Assessment Division utilize these observations to note potential flood/drought conditions, and to estimate reservoir volume and irrigation potential. In this presentation we demonstrate the current capabilities and limitations of ocean radar altimetry for inland water level monitoring.
http://www.pecad.fas.usda.gov/cropexplorer/global_reservoir
H23E-1176 1340h
Floods and Droughts in Africa: Relation to Short-term Climate Variability
The overall goal of this project is to utilize predicted sea surface temperature (SST) together with near-real time remote sensing tools, to aid in the forecast of regional drought and flood. The focus of the study is centered on the African continent for the time period ~1900-2002. There are several objectives, i) To utilize the surface status of water as a proxy indicator of precipitation and as a direct measure of hydrological drought and flood, ii) To derive this surface water status, using historical records and recent remote sensing data, for a selection of geographically distributed target sites, and to seek correlations between the data and known drought/flood episodes, iii) To examine the relationships between drought/flood episodes and short-term climate events, and iv) To deduce the vulnerability of these regions to short-term climatic events and to determine the future role of combined satellite data and predictive SST forecasts. Surface water is that defined by the level or areal status of lakes, rivers and wetlands. Here, we present results from a remote sensing survey of the continent, revealing time series of water-level variations over the 1990's decade. This has been undertaken by the application of satellite radar altimetry using the TOPEX/POSEIDON and ERS mission data. This survey contains validation results for ERS-derived elevations and a study of ERS instrument performance. Inter-comparison of these ERS and T/P results with preliminary elevation data from the ENVISAT mission is also shown. In addition, a survey of the decade's outbreaks of floods and droughts is reported and correlations between these conditions and the remote sensing observations are presented as the second stage of this multi-year project.
H23E-1177 1340h
Virtual mission stage I: Implications of a spaceborne surface water mission
The interannual and interseasonal variability of the land surface water cycle depend on the distribution of surface water in lakes, wetlands, reservoirs, and river systems; however, measurements of hydrologic variables are sparsely distributed, even in industrialized nations. Moreover, the spatial extent and storage variations of lakes, reservoirs, and wetlands are poorly known. We are developing a virtual mission to demonstrate the feasibility of observing surface water extent and variations from a spaceborne platform. In the first stage of the virtual mission, on which we report here, surface water area and fluxes are emulated using simulation modeling over three continental scale river basins, including the Ohio River, the Amazon River and an Arctic river. The Variable Infiltration Capacity (VIC) macroscale hydrologic model is used to simulate evapotranspiration, soil moisture, snow accumulation and ablation, and runoff and streamflow over each basin at one-eighth degree resolution. The runoff from this model is routed using a linear transfer model to provide input to a much more detailed flow hydraulics model. The flow hydraulics model then routes runoff through various channel and floodplain morphologies at a 250 m spatial and 20 second temporal resolution over a 100 km by 500 km domain. This information is used to evaluate trade-offs between spatial and temporal resolutions of a hypothetical high resolution spaceborne altimeter by synthetically sampling the resultant model-predicted water surface elevations.
H23E-1178 1340h
Channel Slopes on Amazon Basin Rivers From the SRTM DEM
Changes in surface water storage (S) and discharge (Q) are poorly known globally but are critical for constraining the terrestrial branch of the water cycle. To date, only the SRTM mission provides global measurements of both surface water area and elevation. However, little is known about the instrument performance for collecting delta-S and Q. The Amazon Basin is a particularly appealing target given its sparse gauge density, lack of continuous and reliable slope data that can be used in the estimation of discharge, and complexity of flow hydraulics. We have used SRTM elevation data in conjunction with flow distance to estimate water surface slope for the area 0S-8S, 72W-54W. Using a 3rd order polynomial fit to the distance-elevation data, slope values of the mainstem Amazon range from less than 0.5 cm km-1 downstream of Obidos to 4.10 cm km-1 3000 km upstream of this location. The central Amazon slope ranges from 1.86 cm km-1 to 3.10 cm km-1 from Manaus to the Rio Japura (about 800 km upstream). Local slopes for specific gauge locations were achieved using both a linear fit to the data and the polynomial fit. The slope value at Itapeua, about 430 km upstream of Manaus, was found to be 3.22 cm km-1 using a linear fit, and 2.65 - 2.79 cm km-1 using a 3rd order polynomial fit, for a reach of 24 km. The slope value for Manacapuru, about 90 km upstream of Manaus, was determined to be 3.56 cm km-1 using a linear fit and 1.97 - 2.12 cm km-1 for a reach of 70 km centered on the local gauge. This slope is used in the Manning equation (n = 0.03) with depth values from navigation charts and river width measured from JERS-1 SAR imagery to yield discharge values for Manacapuru of 93,500 m3 sec-1and for Itapeua of 81,900 m3 sec-1. The observed discharge value at the Manacapuru gauge is 96,300 m3 sec-1 over an 11-day average in February for the years 1973-1991. The average observed discharge value for Itapeua is 83,100 m3 sec-1 for the same time period.
H23E-1179 1340h
A New View of Amazon Floodplain Inundation Hydraulics
Community based efforts are underway to propose a satellite mission for measuring surface water hydraulics. Such a mission is essential for advancing our hydrologic view from 1D point-based gauge measurements of discharge to 2D measurements of surface water that capture the complex spatial dynamics of flow (e.g., measurements of elevations, h, and their change, dh/dt and dh/dx). Examples are essential for demonstrating the utility of such measurements for improving our understanding of the mass-balances in the global water cycle and of the dynamics of complex floodplain hydraulics. Interferometric SAR yields high-spatial resolution images of dh/dt, albeit with a dt greater than desired and the method only permits measurements from inundated vegetation (it fails for open-water). Nevertheless, new observations from interferometric JERS-1 data during inundation over the central Amazon floodplain show dh/dt changes marking flow corridors of several kilometers width that are particularly apparent for the Cabaliana region. Many floodplain channels are conspicuous because dh/dt changes are not equivalent on both sides suggesting that flow delivery and decantation to surrounding floodplain areas is uneven. In fact, for some floodplain channels, dh/dt is greatest on the upstream side of the adjacent main channel (e.g., the Solimoes, Purus Rivers) during inundation but at peak stage, water delivery from the Amazon dominates resulting in a greater dh/dt on the downstream side of these floodplain channels. During early rising water, inundation appears first as a patchwork bordered by small floodplain channels, whereas at mainstem peak stage, floodplain flow appears to sub-parallel the mainstem. Essentially, the hydraulics of Amazon floodplain inundation are a complex interaction of local geomorphology and water stage. These views are only apparent from a spaceborne platform, yet are key for improving our understanding of floods and their transported biogeochemical and sediment constituents.
H23E-1180 1340h
Evaluation of Digital Elevation Model Uncertainty in Flood Inundation Modeling
Flood is one of the most life threatening natural hazard on the earth and it is very important to estimate flood magnitudes and to map areas under inundation. Flood inundation modeling is the final stage of a flood study in which inundation area for a certain flood magnitude is determined. In the last decade integration of Geographic Information Systems (GIS) with flood studies increased the efficiency and visualization of basin and river modeling. Since all GIS datasets suffer from error, when they are used as input to a GIS operation, then the errors in the input propagate to the output of the operation. In GIS integrated flood inundation modeling, where topographic conditions of the river network are obtained from a Digital Elevation Model (DEM), error inherent in the DEM will propagate through the analysis till its outputs. In this study propagation of DEM uncertainty in flood inundation modeling is investigated. Monte Carlo Simulations method is utilized for uncertainty propagation modeling, and flood inundation modeling is performed by integrating HEC-RAS and ArcView softwares. The methodology is applied to a small area selected within Ulus Basin which is located in the West Black Sea region of Turkey. At the end of the study, results of uncertainty propagation modeling are compared with the results of GIS integrated flood inundation modeling of the same study site.