Willem A. Schreüder

Estimating temporal changes in hydraulic head using InSAR data in the San Luis Valley, Colorado

The sustainability of the confined aquifer system in the San Luis Valley, Colorado is of utmost importance to the valleys agricultural economy. There is a dearth of hydraulic head measurements in the confined aquifer to which the current groundwater flow model can be calibrated. Here we investigate the extent to which spatially and temporally dense measurements of deformation from Interferometric Synthetic Aperture Radar (InSAR) data can be used to fill in spatial and temporal gaps in the head data set by calibrating the InSAR data with head at the monitoring well locations. We conduct this calibration at 11 wells where we expect sufficient deformation for reliable InSAR measurement, given the accepted level of uncertainty (∼1 cm). In the San Luis Valley, crop growth degrades the quality of the InSAR signal, which means that the high-quality deformation data may not be collocated with the wells. We use kriging to estimate the deformation directly at the well locations. We find that the calibration is valid at three well locations where the seasonal magnitude of the deformation is much larger than the uncertainty of the InSAR measurement. At these well locations, we predict head prior to and within the temporal sampling window of the head measurements. We find that 59% of the InSAR-predicted hydraulic head values agree with the measured values, within the uncertainty of the data. Given our success in extending the hydraulic head data temporally, the next step in our research is to use InSAR data to interpolate spatially between head measurements.

High quality InSAR data linked to seasonal change in hydraulic head for an agricultural area in the San Luis Valley, Colorado

In the San Luis Valley (SLV), Colorado legislation passed in 2004 requires that hydraulic head levels in the confined aquifer system stay within the range experienced in the years 1978–2000. While some measurements of hydraulic head exist, greater spatial and temporal sampling would be very valuable in understanding the behavior of the system. Interferometric synthetic aperture radar (InSAR) data provide fine spatial resolution measurements of Earth surface deformation, which can be related to hydraulic head change in the confined aquifer system. However, change in cm-scale crop structure with time leads to signal decorrelation, resulting in low quality data. Here we apply small baseline subset (SBAS) analysis to InSAR data collected from 1992 to 2001. We are able to show high levels of correlation, denoting high quality data, in areas between the center pivot irrigation circles, where the lack of water results in little surface vegetation. At three well locations we see a seasonal variation in the InSAR data that mimics the hydraulic head data. We use measured values of the elastic skeletal storage coefficient to estimate hydraulic head from the InSAR data. In general the magnitude of estimated and measured head agree to within the calculated error. However, the errors are unacceptably large due to both errors in the InSAR data and uncertainty in the measured value of the elastic skeletal storage coefficient. We conclude that InSAR is capturing the seasonal head variation, but that further research is required to obtain accurate hydraulic head estimates from the InSAR deformation measurements.

Confined aquifer head measurements and storage properties in the San Luis Valley, Colorado, from spaceborne InSAR observations

Interferometric Synthetic Aperture Radar (InSAR), a remote sensing technique for measuring centimeter-level surface deformation, is used to estimate hydraulic head in the confined aquifer of the San Luis Valley (SLV), Colorado. Reconstructing head measurements from InSAR in agricultural regions can be difficult, as InSAR phase data are often decorrelated due to vegetation growth. Analysis of 17 L-band ALOS PALSAR scenes, acquired between January 2007 and March 2011, demonstrates that comprehensive InSAR deformation measurements can be recovered over the vegetated groundwater basin with an improved processing strategy. Local skeletal storage coefficients and time delays between the head change and deformation are estimated through a joint InSAR-well data analysis. InSAR subsidence estimates are transformed to head changes with finer temporal and spatial resolution than is possible using existing well records alone. Both InSAR and well data suggest that little long-term water-storage loss occurred in the SLV over the study period and that inelastic compaction was negligible. The seasonal head variations derived from InSAR are consistent with the existing well data at most locations where confined aquifer pumping activity dominates. Our results demonstrate the advantages of InSAR measurements for basin-wide characterization of aquifer storage properties and groundwater levels over agricultural regions.

Approaches in highly parameterized inversion - GENIE, a general model-independent TCP/IP run manager

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NUMERICAL MODELING OF INTERIOR BOUNDARIES

The numerical modeling of interior boundaries of finite and infinitesimal volume (area) is described for finite volume numerical methods. The treatment of passive structures such as solid obstacles and infinitesimally thin porous and nonporous walls, as well as hydro-dynamically active structures such as pumps and fans, are discussed. Properties peculiar to the pressure-velocity coupling are stressed, while more generally applicable techniques for other dependencies are shown. Heal transfer and turbulence effects complementary to the hydrodynamics are discussed. An example is presented showing application of the techniques to the flow of air about a very large directly air-cooled heat exchanger.

NUMERICAL MODELING OF ATMOSPHERIC BOUNDARIES

The half cell method, a practical method of computing the flow pattern on an atmospheric boundary where both inflow and outflow conditions can occur, is described. The method is useful when most of the boundary conditions, even the velocity and pressure, are given in terms of gradients. The treatment of the velocity and pressure boundaries for the discrete momentum and continuity equations is described for the SIMPLE family of methods. As an example, the flow of air about a directly air-cooled heat exchanger is discussed. The method makes it possible to restrict the computational domain for this problem to manageable limits.