Aliasing due to sampling of the Adriatic temperature, salinity and density in space     

Zoran Pasari&#x;  Mirko Orli&#x;  Craig M. Lee 《Estuarine, Coastal and Shelf Science》2006,69(3-4):636

High-resolution underway temperature and conductivity measurements collected by R/V Knorr during winter and spring 2003 are used to characterize errors associated with spatial aliasing in the northern and central Adriatic Sea. During winter, 99th percentile temperature, salinity and density errors were 0.62 °C, 0.25 and 0.12 kg/m³ (0.25 °C, 0.10 and 0.05 kg/m³) for sampling at 10 km (5 km) horizontal resolution, respectively. The corresponding values in spring were 1.31 °C, 0.50 and 0.40 kg/m³ (0.93 °C, 0.25 and 0.22 kg/m³) for the 10 km (5 km) sample spacing, respectively. The largest errors were associated with energetic regions over the shallow, western Adriatic, in front of the Po River mouth and off the tip of the Istrian peninsula. The deeper eastern basin exhibited smaller errors. The variability of errors in time and space reflected the variability of small-scale density features, characterized by wavelengths as small as 2 km in winter and 1 km in spring and being more pronounced in the western and northern parts of the Adriatic. As these results indicate that errors associated with undersampling can be considerable, they should be taken into account while planning future CTD measurements in the region.  相似文献   

The Bayesian detection of discontinuities in a polynomial regression and its application to the cycle-slip problem   总被引：4，自引：1，他引：3  

Maria Clara de Lacy  Mirko Reguzzoni  Fernando Sansò  Giovanna Venuti 《Journal of Geodesy》2008,82(9):527-542

This paper deals with the problem of detecting and correcting cycle-slips in Global Navigation Satellite System (GNSS) phase data by exploiting the Bayesian theory. The method is here applied to undifferenced observations, because repairing cycle-slips already at this stage could be a useful pre-processing tool, especially for a network of permanent GNSS stations. If a dual frequency receiver is available, the cycle-slips can be easily detected by combining two phase observations or phase and range observations from a single satellite to a single receiver. These combinations, expressed in a distance unit form, are completely free from the geometry and depend only on the ionospheric effect, on the electronic biases and on the initial integer ambiguities; since these terms are expected to be smooth in time, at least in a short period, a cycle-slip in one or both the two carriers can be modelled as a discontinuity in a polynomial regression. The proposed method consists in applying the Bayesian theory to compute the marginal posterior distribution of the discontinuity epoch and to detect it as a maximum a posteriori (MAP) in a very accurate way. Concerning the cycle-slip correction, a couple of simultaneous integer slips in the two carriers is chosen by maximazing the conditional posterior distribution of the discontinuity amplitude given the detected epoch. Numerical experiments on simulated and real data show that the discontinuities with an amplitude 2 or 3 times larger than the noise standard deviation are successfully identified. This means that the Bayesian approach is able to detect and correct cycle-slips using undifferenced GNSS observations even if the slip occurs by one cycle. A comparison with the scientific software BERNESE 5.0 confirms the good performance of the proposed method, especially when data sampled at high frequency (e.g. every 1 s or every 5 s) are available.  相似文献   

A new degree-2190 (10 km resolution) gravity field model for Antarctica developed from GRACE,GOCE and Bedmap2 data     

Christian Hirt  Moritz Rexer  Mirko Scheinert  Roland Pail  Sten Claessens  Simon Holmes 《Journal of Geodesy》2016,90(2):105-127

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Stratigraphic filtering and source penetration depth     

Mirko van der Baan  James Wookey  Dirk Smit 《Geophysical Prospecting》2007,55(5):679-684

Seismic exploration underneath highly heterogeneous layers such as basalt flows is possible by lowering the principal source frequency. Unfortunately this also reduces resolution. Wave‐localization theory is a multiple scattering theory that can be used to study stratigraphic filtering in chaotic lithologies. It predicts the apparent attenuation due to scattering of a plane wave traversing a layer with high velocity fluctuations. It can therefore predict the optimum principle source frequency in the trade‐off between loss of resolution and increased penetration depth. We show how this can be done with the help of a few statistical parameters derived from a well‐log analysis; namely, the average background velocity, the expected standard deviation in the velocity fluctuations, the typical scale length of the heterogeneities and the thickness of the basalt layer. In the likely situation that no local well logs exist, a multitude of scenarios can easily be examined at low cost.  相似文献   

High-frequency climatic variability and crop yields     

Daniel S. Wilks  Susan J. Riha 《Climatic change》1996,32(3):231-235

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Assessing possible changes in flood frequency due to climate change in mid‐sized watersheds in New York State,USA     

Stephen B. Shaw  Susan J. Riha 《水文研究》2011,25(16):2542-2550

The frequency of flooding is often presumed to increase with climate change because of projected increases in rainfall intensities. In this paper, using 50‐plus years of historical discharge and meteorological data from three watersheds in different physiographic regions of New York State, USA, we find that annual maximum stream discharges are associated with 20% or less of the annual maximum rainfall events. Instead of rainfall events, approximately 20% of annual maximum stream discharges are associated with annual maximum snowmelt events while 60% of annual maximum discharges are associated with moderate rainfall amounts and very wet soil conditions. To explore the potential for changes in future flood risk, we employed a compound frequency distribution that assumes annual maximum discharges can be modelled by combining the cumulative distribution functions of discharges resulting from annual maximum rainfall, annual maximum snowmelt, and occurrences of moderate rain on wet soils. Basing on a compound frequency distribution comprised of univariate general extreme value (GEV) and gamma distributions, we found that a hypothetical 20% increase in the magnitude of rainfall‐related stream discharge results in little change in 96th percentile annual maximum discharge. For the 99th percentile discharge, two waterbodies in our study had a 10% or less increase in annual maximum discharge when annual maximum rainfall‐related discharges increased 20% while the third waterbody had a 16% increase in annual maximum discharges. Additionally, in some cases, annual maximum discharges could be offset by a reduction in the discharge resulting from annual maximum snowmelt events. While only intended as a heuristic tool to explore the interaction among different flood‐causing mechanisms, use of a compound flood frequency distribution suggests a case can be made that not all waterbodies in humid, cold regions will see extensive changes in flooding due to increased rainfall intensities. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Numerical determination of pressure-dependent effective thermal conductivity in Berea sandstone     

Mirko Siegert  Marcel Gurris  Claudia Finger  Erik H. Saenger 《Geophysical Prospecting》2022,70(1):152-172

In this paper, the methods of digital rock physics are applied to determine pressure-dependent effective thermal conductivity in rock samples. Simulations are performed with an in-house three-dimensional finite volume code. In the first step, four numerical models are derived from a given tomographic scan of Berea sandstone. Consequently, simulations of the thermal conductivity at ambient conditions are performed and validated with experimental data. In a second step, a new workflow for the determination of the pressure-dependent thermal conductivity in rock samples is elaborated, tested and calibrated. Results originating from the derived workflow show very good agreement with experimental data.  相似文献   

Real-time cycle slip detection in triple-frequency GNSS   总被引：7，自引：2，他引：5  

Maria Clara de Lacy  Mirko Reguzzoni  Fernando Sansò 《GPS Solutions》2012,16(3):353-362

The modernization of the global positioning system and the advent of the European project Galileo will lead to a multifrequency global navigation satellite system (GNSS). The presence of new frequencies introduces more degrees of freedom in the GNSS data combination. We define linear combinations of GNSS observations with the aim to detect and correct cycle slips in real time. In particular, the detection is based on five geometry-free linear combinations used in three cascading steps. Most of the jumps are detected in the first step using three minimum-noise combinations of phase and code observations. The remaining jumps with very small amplitude are detected in the other two steps by means of two-tailored linear combinations of phase observations. Once the epoch of the slip has been detected, its amplitude is estimated using other linear combinations of phase observations. These combinations are defined with the aim of discriminating between the possible combinations of jump amplitudes in the three carriers. The method has been tested on simulated data and 1-second triple-frequency undifferenced GPS data coming from a friendly multipath environment. Results show that the proposed method is able to detect and repair all combinations of cycle slips in the three carriers.  相似文献   

Chrystal and Proudman resonances simulated with three numerical models     

Maja Bubalo  Ivica Janeković  Mirko Orlić 《Ocean Dynamics》2018,68(4-5):497-507

The aim of this work was to study Chrystal and Proudman resonances in a simple closed basin and to explore and compare how well the two resonant mechanisms are reproduced with different, nowadays widely used, numerical ocean models. The test case was based on air pressure disturbances of two commonly used shapes (a sinusoidal and a boxcar), having various wave lengths, and propagating at different speeds. Our test domain was a closed rectangular basin, 300 km long with a uniform depth of 50 m, with the theoretical analytical solution available for benchmark. In total, 2250 simulations were performed for each of the three different numerical models: ADCIRC, SCHISM and ROMS. During each of the simulations, we recorded water level anomalies and computed the integral of the energy density spectrum for a number of points distributed along the basin. We have successfully documented the transition from Proudman to Chrystal resonance that occurs for a sinusoidal air pressure disturbance having a wavelength between one and two basin lengths. An inter-model comparison of the results shows that different models represent the two resonant phenomena in a slightly different way. For Chrystal resonance, all the models showed similar behavior; however, ADCIRC model providing slightly higher values of the mean resonant period than the other two models. In the case of Proudman resonance, the most consistent results, closest to the analytical solution, were obtained using ROMS model, which reproduced the mean resonant speed equal to 22.00 m/s— i.e., close to the theoretical value of 22.15 m/s. ADCIRC and SCHISM models showed small deviations from that value, with the mean speed being slightly lower—21.97 m/s (ADCIRC) and 21.93 m/s (SCHISM). The findings may seem small but could play an important role when resonance is a crucial process producing enhancing effects by two orders of magnitude (i.e., meteotsunamis).  相似文献   

A two-layer primitive equation model of an idealized Strait of Gibraltar connected to an eastern basin     

Stefan Riha  Alvaro Peliz 《Ocean Dynamics》2013,63(6):615-631

We describe the solutions of a numerical two-layer primitive equation model of an idealized Strait of Gibraltar and an adjacent eastward basin. The quasi-steady circulation pattern in the basin features an anticyclonic gyre southward of the strait exit and an eastward boundary current attached to the southern boundary of the basin. A variation of the initial upper-layer depth and the target interface height at the eastern boundary causes minor changes of the upper-layer circulation in a basin with rectangular coastline and larger changes when a cape is added to the coastline of the southern boundary.  相似文献