Including geophysical data in ground water model inverse calibration   总被引：1，自引：0，他引：1  

Dam D  Christensen S 《Ground water》2003,41(2):178-189

A nonlinear regression method is developed that can be used to estimate parameters of a ground waterflow model from a combination of observations of hydrological variables and observations of geophysical properties that are functionally related with the hydraulic conductivity. The procedure estimates: parameters characterizing the hydraulic conductivity field (e.g., zonal or pilot point values); geophysical properties that have been observed and that are functionally related with the hydraulic conductivity parameters; and a few parameters of the function that relates the hydraulic conductivity parameters with the geophysical properties (the type of function is assumed known). A fidelity factor, sigma(r)2, of a term of the minimized objective function reflects the faith one has in the validity of this functional relationship. The estimation methodology has been tested by means of synthetic models. The experimental results demonstrate that the number of estimated hydraulic conductivity parameters can be increased by adding geophysical observations to the set of hydrological observations that are traditionally used for model calibration. The improvement of the estimated hydraulic conductivity field and the simulated hydraulic head field can be significant but is dependent on the number, the locations, and the uncertainty of geophysical observations. The sensitivity of the estimation results to the value of sigma(r) is small for the studied problems except when the uncertainty of geophysical observations is high. In the latter case, a large sigma(r) value was found to be optimal to avoid that hydraulic conductivity estimates are closely tied to corresponding but highly uncertain geophysical observations.  相似文献   

Regulation of eelgrass (Zostera marina) cover along depth gradients in Danish coastal waters     

Dorte Krause-Jensen  Morten Foldager Pedersen  Claus Jensen 《Estuaries and Coasts》2003,26(4):866-877

A large data set, collected under the national Danish monitoring program, was used to evaluate the importance of photon flux density (PFD), relative wave exposure (REI), littoral slope, and salinity in regulating eelgrass cover at different depth intervals in Danish coastal waters. Average eelgrass cover exhibited a bell-shaped pattern with depth, reflecting that different factors regulate eelgrass cover at shallow- and deep-water sites. The multiple logistic regression analysis was used to identify regulating factors and determine their role in relation to eelgrass cover at different depth intervals. PFD, REI, and salinity were main factors affecting eelgrass cover while littoral slope had no significant effect. Eelgrass cover increased with increasing PFD at water depths of more than 2 m, while cover was in versely related to REI in shallow water. This pattern favored eelgrass cover at intermediate depths where levels of PFD and REI were moderate. Salinity had a minor, but significant, effect on eelgrass cover that is most likely related to the varying costs of osmoregulation with changing salinity. The analysis provided a useful conceptual framework for understanding the factors that regulate eelgrass abundance with depth. Although the regression model was statistically significant and included the factors generally considered most important in regulating eelgrass cover, its explanatory power was low, especially in shallow water. The largest discrepancies between predicted and observed values of cover appeared in cases where no eelgrass occurred despite sufficient light and moderate levels of exposure (almost 50% of all observations). These discrepancies suggest that population losses due to stochastic phenomena, such as extreme wind events, played an important regulating role that is not adequately described by average exposure levels. A more thorough knowledge of the importance of such loss processes and the time scales involved in recovery of seagrass populations after a severe disturbance are necessary if we are to understand the regulation of seagrass distribution in shallow coastal areas more fully.  相似文献   

Genetic impact of gadoid culture on wild fish populations: predictions, lessons from salmonids, and possibilities for minimizing adverse effects   总被引：2，自引：3，他引：2  

Bekkevold  Dorte; Hansen  Michael M.; Nielsen  Einar E. 《ICES Journal of Marine Science》2006,63(2):198-208

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On the radiation characteristics of Antarctic Sea Ice     

Gerd Wendler  Blake Moore  Dorte Dissing  John Kelley 《大气与海洋》2013,51(2):349-366

Abstract

Radiative measurements were carried out continuously during a cruise from Australia to Antarctica during austral summer 1995/96. Both shortwave and longwave radiative fluxes were measured. Some of the results are:

• The incoming solar radiation had a mean value of 217 W m^–2; this was a relatively weak value due to the large amount of fractional cloud cover observed. The sun was, for a large part of the trip, above the horizon for 24 hours a day.

• The reflectivity varied widely, not only as a function of sea‐ice concentration, but also as a function of ice type.

• Snow covered pack ice gave the highest albedo values (<70%), while flooded sea ice and thin ice reflected much less (<30%).

• For each sea‐ice type, short term observations showed a good relationship between albedo and ice concentration.

• The albedo increased with decreasing solar elevation.

• The net longwave radiation was negative (mean –27 W m–2); this small absolute value is due to a high amount of fractional cloud cover. There was a weak diurnal variation with a maximum loss (–33 W m^–2) in the early afternoon.

• On the average, the net radiation was positive for 17 hours, and negative for 7 hours a day. However, the duration of a positive balance depended strongly on the surface albedo.

• For the observed albedo values, modelling results showed that the net radiation was always positive when averaged over a day. The magnitude, however, depended strongly on the surface albedo, varying by more than the factor of three.

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