Model Calibration

Some modellers routinely calibrate their models using an objective function that that consists solely of some measure of error minimisation at the daily or monthly time step. Such a function might be based on maximising the Nash-Sutcliffe efficiency or the correlation coefficient or by minimising the root mean square error. Other modellers routinely incorporate a bias constraint into their objective function. There are a number of ways of incorporating a bias constraint. One way is to accept a calibration only if the difference in total streamflow between observation and prediction is less than some prescribed limit. Typically, this limit might be expressed as a percentage of the total observed streamflow. In this paper we examine whether the choice of calibration method-using a bias constraint or not-has an effect on the subsequent use of the calibrated parameter sets to regionalise predictions to ungauged catchments. We calibrate five lumped rainfall-runoff models-AWBM, IHACRES, Sacramento, Simhyd and SMAR-G-to 89 gauged catchments in Tasmania ranging in size from 10 to 3500 km 2 . Three separate calibration runs are done for each model. In one, the objective function is based on the daily Nash-Sutcliffe efficiency alone; in the second, we augment the Nash-Sutcliffe efficiency with a severe bias constraint that attempts to ensure that the total predicted streamflow is within 5 % of the total observed streamflow (the bucket constraint); and in the third, we combine a smooth, less severe bias constraint (the log-bias constraint) along with efficiency into the objective function. As expected, overall efficiencies tend to be larger for the unconstrained calibrations, while overall absolute biases tend to be smaller for the constrained calibrations.

A comprehensive apatite fission-track (AFT) study of the passive margin of western peninsular India between 12 ‡ and 16 ‡N is used to reconstruct the denudation chronology of the continental hinterland. In common with other rifted margins, the morphology is characterised by a low-lying coastal plateau separated from an elevated inland plateau by an erosionally controlled escarpment (Western Ghats). We modelled the fission track data using the commonly adopted annealing algorithm of Laslett et al. [Chem. Geol. 65 (1987) 1^13]. Using the default parametrisation (i.e. an initial track length of 16.3 Wm), it was found that during the Mesozoic denudation rates remained extremely low, increasing sporadically when erosion peaked at 130 Ma (rifting with Antarctica) and 80 Ma (rifting with Madagascar). Denudation rates rose considerably during the Cenozoic, reaching maxima of ca 120 m/Myr. Such values are, however, considered as major overestimates and the effects of the Seychelles rifting at 65 Ma remain suspiciously unrecorded. We explored the consequences of changing the initial track length in this model to a value of 14.5 Wm. In practice, this reduces the rapid Cenozoic denudation artefact, model peak rates during the Mesozoic are much more variable, and during the Cenozoic reach values an order of magnitude lower than with the original initial track length. The response to the Seychelles rifting event is almost immediate. Just as previous model calibrations in AFT analysis have been relatively empirical, this revised approach does not provide insights into the physical mechanisms of low-temperature annealing. However, it is shown to agree much better with independently established geomorphic, cosmogenic, stratigraphic and tectono-magmatic evidence in this and other stable shield regions in terms 0012-821X / 03 / $^see front matter ß (K. Gallagher), a.carter@ucl.ac.uk (A. Carter), m.widdowson@open.ac.uk (M. Widdowson), t.hurford@ucl.ac.uk (A.J. Hurford). § Supplementary data associated with this article can be found at 10.1016/S0012-821X 000380-7 Earth and Planetary Science Letters 215 (2003) 187^201 R Available online at www.sciencedirect.com www.elsevier.com/locate/epsl

A methodology for calibration of the activated sludge plant models is proposed on the basis of consolidated engineering experience and a scientific approach. According to the method, the definition of the target(s) plays a crucial role in the selection of the steps incorporated in this so-called 'Biomath-Calibration' protocol. For the activated sludge modelers this protocol tries to combine and link the state of the art methodologies for calibration of different processes in a wastewater treatment plant (hydraulics, biological reactions, sedimentation processes, etc.), and it can thus be used as a complete guideline for extensive model calibration tasks. Finally, an application of the methodology is presented in a case study for a nutrient removing oxidation ditch system.

In a national effort, since 1972, the Swiss Government started the ''National Long-term Monitoring of Swiss Rivers'' (NADUF) program aimed at evaluating the chemical and physical states of major rivers leaving Swiss political boundaries. The established monitoring network of 19 sampling stations included locations on all major rivers of Switzerland. This study complements the monitoring program and aims to model one of the program's catchments -Thur River basin (area 1700 km 2 ), which is located in the north-east of Switzerland and is a direct tributary to the Rhine. The program SWAT (Soil and Water Assessment Tool) was used to simulate all related processes affecting water quantity, sediment, and nutrient loads in the catchment. The main objectives were to test the performance of SWAT and the feasibility of using this model as a simulator of flow and transport processes at a watershed scale. Model calibration and uncertainty analysis were performed with SUFI-2 (Sequential Uncertainty FItting Ver. 2), which was interfaced with SWAT using the generic iSWAT program. Two measures were used to assess the goodness of calibration: (1) the percentage of data bracketed by the 95% prediction uncertainty calculated at the 2.5 and 97.5 percentiles of the cumulative distribution of the simulated variables, and (2) the d-factor, which is the ratio of the average distance between the above percentiles and the standard deviation of the corresponding measured variable. These statistics showed excellent results for discharge and nitrate and quite good results for sediment and total phosphorous. We concluded that: in watersheds similar to Thurwith good data quality and availability and relatively small model uncertainty -it is 0022-1694/$ -see front matter ª a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j h y d r o l feasible to use SWAT as a flow and transport simulator. This is a precursor for watershed management studies. ª

A FRAX model for Canada was constructed for prediction of osteoporotic and hip fracture risk using national hip fracture data with and without the use of femoral neck bone mineral density (BMD). Performance of this system was assessed independently in a large clinical cohort of 36,730 women and 2873 men from the Manitoba Bone Density Program database that tracks all clinical dual-energy X-ray absorptiometry (DXA) test results for the Province of Manitoba, Canada. Linkage with other provincial health databases allowed for the direct comparison of fracture risk estimates from the Canadian FRAX model with observed fracture rates to 10 years (549 individuals with incident hip fractures and 2543 with incident osteoporotic fractures). The 10-year Kaplan-Meier estimate for hip fractures in women was 2.7% [95% confidence interval (CI) 2.1-3.4%] with a predicted value of 2.8% for FRAX with BMD, and in men the observed risk was 3.5% (95% CI 0.8-6.2%) with predicted value of 2.9%. The 10-year estimate of osteoporotic fracture risk for all women was 12.0% (95% CI 10.8-13.4%) with a predicted value of 11.1% for FRAX with BMD, and in men, the observed risk was 10.7% (95% CI 6.6-14.9%) with a predicted value of 8.4%. Discrepancies were observed within some subgroups but generally were small. Fracture discrimination based on receiver operating characteristic curve analysis was comparable with published meta-analyses with area under the curve for osteoporotic fracture prediction of 0.694 (95% CI 0.684-0.705) for FRAX with BMD and for hip fractures 0.830 (95% CI 0.815-0.846), both of which were better than FRAX without BMD or BMD alone. Individual risk factors considered by FRAX made significant independent contributions to fracture prediction in one or more of the models. In conclusion, a Canadian FRAX tool calibrated on national hip fracture data generates fracture risk predictions that generally are consistent with observed fracture rates across a wide range of risk categories. ß O steoporosis is a common condition affecting up to 16% of women and 7% of men over age 50 years in Canada. (1) The consequences of fracture include increased mortality, morbidity, institutionalization, and economic costs. (2,3) An individual with a hip fracture has a one in four risk of death in the year following fracture, and this excess risk continues into subsequent years independent of age and comorbidity. (4) Those with vertebral fractures are also at substantially increased risk of death. Moreover, all osteoporosis-related fractures can lead to significant long-term disability and decreased quality of life. The ability to accurately gauge fracture risk is critical in identifying cost-effective thresholds for intervention. (9,10) The WHO Collaborating Centre for Metabolic Bone Diseases at Sheffield recently has identified a set of seven clinical risk factors [ie, prior fragility fracture, a parental history of hip fracture, smoking, use of systemic corticosteroids, excess alcohol intake, body mass index (BMI), and rheumatoid arthritis] that, in addition to age and sex, contribute to fracture risk independent of bone ORIGINAL ARTICLE J JBMR

Omnidirectional cameras have a wide field of view and are thus used in many robotic vision tasks. An omnidirectional view may be acquired by a fisheye camera which provides a full image compared to catadioptric visual sensors and do not increase the size and the weakness of the imaging system with respect to perspective cameras. We prove that the unified model for catadioptric systems can model fisheye cameras with distortions directly included in its parameters. This unified projection model consists on a projection onto a virtual unitary sphere, followed by a perspective projection onto an image plane. The validity of this assumption is discussed and compared with other existing models. Calibration and partial Euclidean reconstruction results help to confirm the validity of our approach. Finally, an application to the visual servoing of a mobile robot is presented and experimented.

The IWA Anaerobic Digestion Model No. 1 (ADM1) was used to simulate the full-scale anaerobic sludge digester of Ankara Central Wastewater Treatment Plant. The digester is a completely mixed, once through continuous flow type which is being fed with a primary and secondary sludge mixture. The variability and unpredicted nature of the primary sludge composition was expected to challenge the model. A one-year dynamic data set from the digester was used for model calibration and validation in the study. The standard ADM1 model was corrected in the study with regard to nitrogen and carbon mass balances. A good correlation between the measured and simulated data was obtained for biogas yield, total volatile fatty acids and pH after heuristically calibrating stoichiometric and kinetic parameters of the ADM1 model. The simulation is sensitive to influent composition.