Vignette d'image

Brunner, Philip

Nom
Brunner, Philip
Affiliation principale
Fonction
Professeur ordinaire
Email
philip.brunner@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/165
_
0000-0001-6304-6274

Résultat de la recherche

Filtres

2
2
2
Réinitialiser les filtres

Paramètres

Voici les éléments 1 - 2 sur 2
  • Publication
    Accès libre
    Calibration of a groundwater model using pattern information from remote sensing data
    (2009-5-26)
    Li, H. T.
    ;
    Brunner, Philip 
    ;
    Kinzelbach, Wolfgang
    ;
    Li, W. P.
    ;
    Dong, X. G.
    Due to the chronic lack of verification data, hydrologic models are notoriously over-parameterized. If a large number of parameters are estimated, while few verification data are available, the calibrated model may have little predictive value. However, recent development in remote sensing (RS) techniques allows generation of spatially distributed data that can be used to construct and verify hydrological models. These additional data reduce the ambiguity of the calibration process and thus increase the predictive value of the model. An example for such remotely sensed data is the spatial distribution of phreatic evaporation. In this modeling approach, we use the spatial distribution of phreatic evaporation obtained by remote sensing images as verification data Compared to the usual limited amount of head data, the spatial distribution of evaporation data provides a complete areal coverage. However, the absolute values of the evaporation data are uncertain and therefore three ways of using the spatial distribution pattern of evaporation were tested and compared. The first way is to directly use the evaporation pattern defined in a relative manner by dividing the evaporation rate in a pixel by the total evaporation of a selected rectangular area of interest. Alternatively, the discrete fourier transform (DFT) or the discrete wavelet transform (DWT) are applied to the relative evaporation pattern in the space domain defined before. Seven different combinations of using hydraulic head data and/or evaporation pattern data as conditioning information have been tested. The code PEST, based on the least-squares method, was used as an automatic calibration tool. From the calibration results, we can conclude that the evaporation pattern can replace the head data in the model calibration process, independently of the way the evaporation pattern is introduced into the calibration procedure. (C) 2009 Elsevier B.V All rights reserved.
  • Publication
    Accès libre
    Topography representation methods for improving evaporation simulation in groundwater modeling
    (2008-5-26)
    Li, H. T.
    ;
    Kinzelbach, Wolfgang
    ;
    Brunner, Philip 
    ;
    Li, W. P.
    ;
    Dong, X. G.
    In a groundwater model, surface elevations which are used in simulating the phreatic evaporation process are usually incorporated as spatially constant over discretized cells. Traditionally, a modeler obtains the data for surface elevations from point data or a digital elevation model (DEM) by means of extrapolation or interpolation. In this way, a smoothing error of surface elevations is introduced, which via the depth to groundwater propagates into evaporation simulation. As a consequence, the evaporation simulation results can be biased. In order to explore the influence of surface elevations on evaporation simulation, three alternative methods of representation of topography in calculating evaporation were studied. The first one is a traditional method which uses cell-wise constant elevations obtained by averaging surface elevations from the DEM with higher resolution for the corresponding model cells. The second one retains some information on the sub-pixet statistics of surface elevations from the DEM by a perturbation approach, calculating the second order first moment of evaporation with a Taylor expansion. In the third method, a finer discretization is used to represent the topography in calculating evaporation than is used to compute global groundwater flow. This allows to take into account the smaller scale variations of the surface elevation as given in the high resolution DEM data. For all the three methods, two different evaporation functions, a linear segment function and an exponential function have been used individually. In this paper, a groundwater model with a discretization of 500 x 500 m has been established white DEM data with a resolution of 90 x 90 m are available and resampled to 100 x 100 m cells for convenience of model input. The evaporation rates from a groundwater model with a discretization of 100 x 100 m, which has the same spatial distribution pattern of hydraulic parameters as the 500 x 500 m model, is taken as validation data. The comparisons of evaporation rates were carried out on different averaging scales ranging from 500 m to 2 km. The compared evaporation rates for each scale are obtained by summing up the corresponding evaporation rates from the 500 x 500 m model and the 100 x 100 m model. It is shown that the third method, which uses a finer resolution of topography in the evaporation calculation, yields the best results no matter which evaporation function is used. It is also seen that the correlation between the evaporation rates from the 500 x 500 m model and the 100 x 100 m model increases and values converge when comparing the evaporation results on an increasingly coarser scale, independently of the selected method and evaporation function. (C) 2008 Elsevier B.V. All rights reserved.