Total water content thresholds for shallow landslides,Outer Western Carpathians     

Michal Bíl  Richard Andrášik  Pavel Zahradníček  Jan Kubeček  Jiří Sedoník  Petr Štěpánek 《Landslides》2016,13(2):337-347

Shallow landslides are fairly frequent natural processes which emerge as a result of both rainfall and rapid snowmelt in the Flysch Belt of the Outer Western Carpathians. We estimated the total water content thresholds for the previously defined seven phases of increased landsliding which took place between 1939 and 2010 around the Napajedla meteorological station. The time series were reconstructed on the basis of data from surrounding stations. Rainfalls with the highest intensities (>1 mm/min) were removed from the set. Rainfall of such an intensity primarily causes overland flow and soil erosion and does not contribute to landslide threshold. The snow water equivalent was computed on the basis of the snow height, and possible errors were evaluated as interval estimations. An interval of 10 days before a landslide phase was selected for the total water content threshold. The resulting lower boundary (67.0 mm/10 days) and upper boundary (163.3 mm/10 days) thresholds of water infiltrated into soil during an event shall be part of the prepared online warning system in this area.  相似文献   

Spotless flares and type II radio bursts     

Michal Šeršeň  Boris Valníček 《Solar physics》1993,145(2):339-345

Flares accompanied by type II meter radio bursts that occurred in plages with no visible spots are examined in this paper. There have been found 12 such spotless flares observed in the period of January 1981–August, 1990. Six out of all the flares may be said to have not been associated with any filament activation or disruption. A few of these flares have shown features of major events. The study suggests that a filament activation seems not to be the crucial factor for the occurrence of major flares in regions with no visible spots.  相似文献   

A search for acoustic amplitude deficit at the antipodes of sunspots     

Michal L. Peri  Ken G. Libbrecht 《Solar physics》1991,132(2):223-231

We present a search for the acoustic oscillation deficit which may exist at the antipodes of sunspots. Dopplergrams from Big Bear Solar Observatory 1988 helioseismology data were selected for five days on which large sunspots were known to be on the unseen hemisphere of the Sun. Acoustic oscillation amplitudes in the antipodal regions of these sunspots were compared with amplitudes in surrounding quiet-Sun regions. We did not detect a statistically significant acoustic amplitude deficit in our data. Our results indicate that the amplitude deficit at the sunspot antipodal points is limited to no more than 3% of the acoustic amplitude in the region, for solar oscillation modes of spherical harmonic degree l 200. We conclude that no strong acoustic deficit exists at the antipodes of sunspots. A more sensitive search, requiring more elaborate observations than we have performed, would be desirable in order to determine if a weak acoustic amplitude deficit exists at some level at the antipodes of sunspots, perhaps at higher spatial frequencies of oscillation. The noise level in any signals detected by such observations would probably limit their usefulness as seismic probes. However, information on the lifetimes of solar oscillation modes can be deduced even if no acoustic amplitude deficit is detected.  相似文献   

Using external tropospheric corrections to improve GNSS positioning of hot-air balloon     

Pavel Vaclavovic  Jan Dousa  Michal Elias  Jakub Kostelecky 《GPS Solutions》2017,21(4):1479-1489

High accurate global navigation satellite systems (GNSS) require to correct a signal delay caused by the troposphere. The delay can be estimated along with other unknowns or introduced from external models. We assess the impact of the recently developed augmentation tropospheric model on real-time kinematic precise point positioning (PPP). The model is based on numerical weather forecast and thus reflects the actual state of weather conditions. Using the G-Nut/Geb software, we processed GNSS and meteorological data collected during the experiment using a hot-air balloon flying up to an altitude of 2000 m. We studied the impacts of random walk noise setting of zenith total delay (ZTD) on estimated parameters and the mutual correlations, the use of external tropospheric corrections, the use of data from a single or dual GNSS constellation and the use of Kalman filter and backward smoothing processing methods. We observed a significant negative correlation of the estimated rover height and ZTD which depends on constraining ZTD estimates. Such correlation caused a degraded performance of both parameters when estimated simultaneously, in particular for a single GNSS constellation. The impact of ZTD constraining reached up to 50-cm differences in the rover height. Introducing external tropospheric corrections improved the PPP solution regarding: (1) shortened convergence, (2) better overall robustness, particularly, in case of degraded satellite geometry, (3) less adjusted parameters with lower correlations. The numerical weather model-driven PPP resulted in 9–12- and 5–6-cm uncertainties in the rover altitude using the Kalman filter and the backward smoothing, respectively. Compared to standard PPP, it indicates better performance by a factor of 1–2 depending on the availability of GNSS constellations, the troposphere constraining and the processing strategy.  相似文献   

Spatial modelling of summer climate indices based on local climate zones: expected changes in the future climate of Brno,Czech Republic     

Geletič  Jan  Lehnert  Michal  Dobrovolný  Petr  Žuvela-Aloise  Maja 《Climatic change》2019,152(3-4):487-502

Climatic Change - With global climate change ongoing, there is growing concern about future living conditions in urban areas. This contribution presents the modelled spatial distribution of two...  相似文献   

Automated calibration of advanced soil constitutive models. Part II: hypoplastic clay and modified Cam-Clay     

Kadlíček  Tomáš  Janda  Tomáš  Šejnoha  Michal  Mašín  David  Najser  Jan  Beneš  Štěpán 《Acta Geotechnica》2022,17(8):3439-3462

This paper introduces an automated deterministic method for the calibration of the Modified Cam-Clay and hypoplastic clay model. The calibration is structured in a hierarchical order established based on the apriori sensitivity study performed. The proposed method favours the clear physical meaning of the model parameters to a complete optimization of the objective error function. The method requires only basic laboratory experiments and it is currently implemented in the free-to-use online application called ExCalibre.

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On the integral inversion of satellite-to-satellite velocity differences for local gravity field recovery: a theoretical study     

Mehdi?EshaghEmail author  Michal??prlák 《Celestial Mechanics and Dynamical Astronomy》2016,124(2):127-144

The gravity field can be recovered locally from the satellite-to-satellite velocity differences (VDs) between twin-satellites moving in the same orbit. To do so, three different integral formulae are derived in this paper to recover geoid height, radial component of gravity anomaly and gravity disturbance at sea level. Their kernel functions contain the product of two Legendre polynomials with different arguments. Such kernels are relatively complicated and it may be impossible to find their closed-forms. However, we could find the one related to recovering the geoid height from the VD data. The use of spectral forms of the kernels is possible and one does not have to generate them to very high degrees. The kernel functions are well-behaving meaning that they reduce the contribution of far-zone data and for example a cap margin of \(7^{\circ }\) is enough for recovering gravity anomalies. This means that the inversion area should be larger by \(7^{\circ }\) from all directions than the desired area to reduce the effect of spatial truncation error of the integral formula. Numerical studies using simulated data over Fennoscandia showed that when the distance between the twin-satellites is small, higher frequencies of the anomalies can be recovered from the VD data. In the ideal case of having short distance between the satellites flying at 250 km level, recovering radial component of gravity anomaly with an accuracy of 7 mGal is possible over Fennoscandia, if the VD data is contaminated only with the spatial truncation error, which is an ideal assumption. However, the problem is that the power of VD signal is very low when the satellites are close and it is very difficult to recognise the signal amongst the noise of the VD data. We also show that for a successful determination of gravity anomalies at sea level from an altitude of 250 km mean VDs with better accuracy than 0.01 mm/s are required. When coloured noise at this level is used for the VDs at 250 km with separation of 300 km, the accuracy of recovery will be about 11 mGal over Fennoscandia. In the case of using the real velocities of the satellites, the main problems are downward/upward continuation of the VDs on the mean orbital sphere and taking the azimuthal integration of them.  相似文献   

Environment and Age of the Upper Devonian‒Carboniferous Zhulumute and Hongguleleng Formations, Junggar Basin, NW China: Ichnological and Palynological Aspects     

Michal STACHACZ  Marcelina KONDAS  MA Xueping  Pawel FILIPIAK 《《地质学报》英文版》2021,95(3):724-739

Two Upper Devonian to Lower Carboniferous sections, namely the Bulongguoer and Haer(Gennaren area) in the Junggar Basin, Central Asian Orogenic Belt, in northwestern China were examined with regard to ichnology and palynology. The deposits of the Hongguleleng Formation and Namu Member of the Heishantou Formation, respectively, are mostly unbioturbated or poorly bioturbated, with poorly diversified trace fossils, which indicate unfavourable conditions for the burrowing benthic community during the Late Devonian and Early Carboniferous. The main factor governing the growth of the bioturbating population was the rapid sedimentation of fine-grained, volcanic material documented as tempestites, which buried the benthic fauna. In the Bulongguoer section, the presence of miospores Teichertospora torquata and Grandispora gracilis enabled identification of the broad Teichertospora torquata–Grandispora gracilis Miospore Zone from the transitional Frasnian/Famennian interval. More accurate identification of palynostratigraphical levels(DE and CZ Miospore zones) is only tentative. On the basis of palynofacies analysis, samples from the lower Bulongguoer section indicate deposition in more proximal conditions, whereas samples from the top of the section indicate deposition in a more distal environment. In the Haer section, only a general biostratigraphic indication for the Tournaisian was possible, owing to poor preservation of organic matter.  相似文献   

Earthquake readiness in volatile regions: the case of Israel     

Shmueli  Deborah F.  Segal  Ehud  Ben Gal  Michal  Feitelson  Eran  Reichman  Amnon 《Natural Hazards》2019,98(2):405-423

Natural Hazards - The Jordan Rift Valley is a high-risk low-occurrence zone for earthquakes, with documented incidences within the last millennium causing widespread destruction. This research...  相似文献   

Field Investigation of Vapor‐Phase‐Based Groundwater Monitoring     

David T. Adamson  Thomas E. McHugh  Michal W. Rysz  Roberto Landazuri  Charles J. Newell 《Ground Water Monitoring & Remediation》2012,32(1):59-72

The use of in‐field analysis of vapor‐phase samples to provide real‐time volatile organic compound (VOC) concentrations in groundwater has the potential to streamline monitoring by simplifying the sample collection and analysis process. A field validation program was completed to (1) evaluate methods for collection of vapor samples from monitoring wells and (2) evaluate the accuracy and precision of field‐portable instruments for the analysis of vapor‐phase samples. The field program evaluated three vapor‐phase sample collection methods: (1) headspace samples from two locations within the well, (2) passive vapor diffusion (PVD) samplers placed at the screened interval of the well, and (3) field vapor headspace analysis of groundwater samples. Two types of instruments were tested: a field‐portable gas chromatograph (GC) and a photoionization detector (PID). Field GC analysis of PVD samples showed no bias and good correlation to laboratory analysis of groundwater collected by low‐flow sampling (slope = 0.96, R² = 0.85) and laboratory analysis of passive water diffusion bag samples from the well screen (slope = 1.03; R² = 0.96). Field GC analysis of well headspace samples, either from the upper portion of the well or at the water‐vapor interface, resulted in higher variability and much poorer correlation (consistently biased low) relative to laboratory analysis of groundwater samples collected by low‐flow sample or passive diffusion bags (PDBs) (slope = 0.69 to 0.76; R² = 0.60 to 0.64). These results indicate that field analysis of vapor‐phase samples can be used to obtain accurate measurements of VOC concentrations in groundwater. However, vapor samples collected from the well headspace were not in equilibrium with water collected from the well screen. Instead, PVD samplers placed in the screened interval represent the most promising approach for field‐based measurement of groundwater concentrations using vapor monitoring techniques and will be the focus of further field testing.  相似文献