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71.
Multibeam echosounders (MBES) have become a widely used acoustic remote sensing tool to map and study the seafloor, providing co-located bathymetry and seafloor backscatter. Although the uncertainty associated with MBES-derived bathymetric data has been studied extensively, the question of backscatter uncertainty has been addressed only minimally and hinders the quantitative use of MBES seafloor backscatter. This paper explores approaches to identifying uncertainty sources associated with MBES-derived backscatter measurements. The major sources of uncertainty are catalogued and the magnitudes of their relative contributions to the backscatter uncertainty budget are evaluated. These major uncertainty sources include seafloor insonified area (1–3 dB), absorption coefficient (up to >?6 dB), random fluctuations in echo level (5.5 dB for a Rayleigh distribution), and sonar calibration (device dependent). The magnitudes of these uncertainty sources vary based on how these effects are compensated for during data acquisition and processing. Various cases (no compensation, partial compensation and full compensation) for seafloor insonified area, transmission losses and random fluctuations were modeled to estimate their uncertainties in different scenarios. Uncertainty related to the seafloor insonified area can be reduced significantly by accounting for seafloor slope during backscatter processing while transmission losses can be constrained by collecting full water column absorption coefficient profiles (temperature and salinity profiles). To reduce random fluctuations to below 1 dB, at least 20 samples are recommended to be used while computing mean values. The estimation of uncertainty in backscatter measurements is constrained by the fact that not all instrumental components are characterized and documented sufficiently for commercially available MBES. Further involvement from manufacturers in providing this essential information is critically required. 相似文献
72.
V band photometry of three RS CVn stars, II Peg, IM Peg and UX Ari, is carried out to study the physical properties of these variables. We verified the significant and regular optical photometric variability to be present in all three stars. The strong photometric variability and emission of Hα and Ca II H K using high resolution optical spectroscopy with the Hanle Echelle Spectrograph(HESP),which operates in conjunction with the Himalayan Chandra Telescope, verify the strong chromospheric activity which is present in RS CVn stars. The photometric studies of II Peg, UX Ari and IM Peg were subjected to light curve analysis for spot parameters using a two-starspot model. 相似文献
73.
The production of carbon in the ocean, the so-called primary production, depends on various physicobiological parameters:
the biomass and nutrient amounts in oceans, the salinity and temperature of the water and the light available in the water
column. We focus on the visible spectrum of the solar radiation defined as the Photosynthetically Active Radiation (PAR).
We developed a model (Chamiet al. 1997) to simulate the behavior of the solar beam in the atmosphere and the ocean. We first describe the theoretical basis
of the code and the method we used to solve the radiative transfer equation (RTE): the successive orders of scattering (SO).
The second part deals with a sensitivity study of the PAR just above and below the sea surface for various atmospheric conditions.
In a cloudy sky, we computed a ratio between vector fluxes just above the sea surface and spherical fluxes just beneath the
sea surface. When the optical thickness of the cloud increases this ratio remains constant and around 1.29. This parameter
is convenient to convert vector flux at the sea surface as retrieved from satellite to PAR. Subsequently, we show how solar
radiation as vector flux rather than P A R leads to an underestimate of the primary production up to 40% for extreme cases. 相似文献
74.
N. A. Malik 《Journal of Volcanology and Seismology》2011,5(4):268-277
An explosive eruption occurred on Bezymyannyi Volcano December 24, 2006. The distribution of ashfall deposits over the peninsula
was studied. The tephra was investigated for its chemical, mineral, and grain-size composition, its water-soluble complex
was studied. About 30 000 tons of water-soluble substances along with 7 million tons of ash entered the environment over an
area of over 8000 km2. Information is supplied for this eruption from various sources and its geological impact has been estimated. The total volume
of erupted pyroclastics was 0.01–0.014 km3, of which 0.004 km3 consisted of ash and 0.006–0.01 km3 were pyroclastic flow deposits. 相似文献
75.
Muhammad Nauman Malik Mehdi Murtuza Iqbal Asif Bakar Muhammad Saifullah Abu Brahim Aissa Dk Nur Afiqah Jalwati Puteri Amer Farhan Rafique 《地下水科学与工程》2014,7(4):373-382
In many circumstances involving heat and mass transfer issues, it is considered impractical to measure the input flux and the resulting state distribution in the domain. Therefore, the need to develop techniques to provide solutions for such problems and estimate the inverse mass flux becomes imperative. Adaptive state estimator (ASE) is increasingly becoming a popular inverse estimation technique which resolves inverse problems by incorporating the semi-Markovian concept into a Bayesian estimation technique, thereby developing an inverse input and state estimator consisting of a bank of parallel adaptively weighted Kalman filters. The ASE is particularly designed for a system that encompasses independent unknowns and /or random switching of input and measurement biases. The present study describes the scheme to estimate the groundwater input contaminant flux and its transient distribution in a conjectural two-dimensional aquifer by means of ASE, which in particular is because of its unique ability to efficiently handle the process noise giving an estimation of keeping the relative error range within 10% in 2-dimensional problems. Numerical simulation results show that the proposed estimator presents decent estimation performance for both smoothly and abruptly varying input flux scenarios. Results also show that ASE enjoys a better estimation performance than its competitor, Recursive Least Square Estimator (RLSE) due to its larger error tolerance in greater process noise regimes. ASE’s inherent deficiency of being slower than the RLSE, resulting from the complexity of algorithm, was also noticed. The chosen input scenarios are tested to calculate the effect of input area and both estimators show improved results with an increase in input flux area especially as sensors are moved closer to the assumed input location. 相似文献
76.
77.
Huang Rui Malik Arunima Lenzen Manfred Jin Yutong Wang Yafei Faturay Futu Zhu Zhiyi 《Natural Hazards》2022,110(3):2227-2248
Natural Hazards - With the development of interregional trade, a potential disaster that happens in one place could cause enormous economic losses in distant areas. Timely and comprehensive... 相似文献
78.
We discuss the range of validity of solutions of the Schrödinger equation with a temperaturemodified Coulomb potential. Such a potential, as was recently pointed out, may be relevant to the resolution of the long-standing problem of unidentified solar emission lines. We also consider in detail a predictive test of our approach, and draw attention to some related conceptual issues. 相似文献
79.
Theoretical and Applied Climatology - This study investigates the spatial and temporal patterns of trends and magnitude of rainfall on monthly, seasonal and annual time scales of 13 districts of... 相似文献
80.
The evolution of two dimensional wave packets on the surface of a self-gravitating fluid layer is investigated and shown to be governed by a nonlinear Schrödinger equation. The wave train of finite amplitude is modulationally unstable. Obtained also are the dynamical equations for the second harmonic resonance. The analysis reveals that the general motion consists of both amplitude and phase modulated waves of which the pure phase and amplitude modulated waves, solitary waves, and phase jump are just the special cases. 相似文献