Near-surface Channel Research Articles

Assimilation of AMSU-A Surface-Sensitive Channels in CMA_GFS 4D-Var System over Land

Abstract The assimilation of two surface-sensitive channels of the AMSU-A instruments on board the NOAA-15/NOAA-18/NOAA-19 and MetOp-A/MetOp-B satellites over land was achieved in the China Meteorological Administration Global Forecast System (CMA_GFS). The land surface emissivity was calculated by 1) the window channel retrieval method and 2) the Tool to Estimate Land Surface Emissivities at Microwave frequencies (TELSEM2). Quality controls for these satellite microwave observations over land were conducted. The predictors and regression coefficients used for oceanic satellite data were retained during the bias correction over land and found to perform well. Three batch experiments were implemented in CMA_GFS with 4D-Var: 1) assimilating only the default data, and adding the above data over land with land surface emissivity obtained from 2) TELSEM2 and 3) the window channel retrieval method. The results indicated that the window channel retrieval method can better reduce the departure between the observed and simulated brightness temperature. Over most land types, the positive impacts of this method exceed those of TELSEM2. Both TELSEM2 and the window channel retrieval method improve the humidity analysis near the ground, as well as the forecast capability globally, particularly in those regions where the land coverage is greater, such as in the Northern Hemisphere. The data utilization of the two surface-sensitive channels increase by 6% and 12%, respectively, and the additional data every 6 h can cover most land, where there was no surface-sensitive data assimilated before. This study marks the beginning of near-surface channel assimilation over land in CMA_GFS and represents a breakthrough in the assimilation of other surface-sensitive channels in other satellite instruments. Significance Statement Surface-sensitive microwave channels are difficult to assimilate in NWP due to the lack of both direct measurement and appropriate modeling for instantaneous land surface emissivity. This paper discusses a method that improves the surface emissivity estimates, which has allowed the utilization of surface-sensitive microwave channels in CMA_GFS. Those capabilities have resulted in better data utilization, improved forecasts of temperature, geopotential height, and winds in the Northern Hemisphere at 3–7 days, and represent an incremental and important improvement to CMA_GFS.

From new geological paradigm to the problems of regional geological-geophysical survey

Analysis of the latest scientific achievements in different areas of geological and geophysical research showed that investigation of deep Earth degassing from its core up to the surface and atmosphere acquires status of the mainstream in the Earth sciences. Of great fundamental and applied significance is identification of the most energetically active and powerful sub-vertical upward degassing processes, which generate trans-geosphere and cross-formational systems and are localized in the form of a hierarchy of different-sized degassing pipes — from the base plume to the elementary near-surface channel. Existence of this system is ensured by a series of successive exothermic transformations of elementary recovered gases into oxide substances. As a result of given chemical reactions these substances consistently receive new portions of energy sufficient for the gradual upward breakthrough of the mantle and crust internal substance. Interpretation of mantle plumes as the basic degassing mega-tubes allows us to unite the main aspects of endogenous ore formation, naphtidogenesis in the lithosphere and ecological processes in the earth’s crust and atmosphere. The cross-formational systems serve as the structural-geological basis of degassing pipes. Given systems are the basic concentrates of the naphtides upward migration and accumulation in the multi-layered deposits. The relationship between diapirism and mega-plumes derivatives — degassing pipes becomes increasingly clear. The degassing energy is the main factor of diapirism. The locations of possible anomalous degassing in Ukraine were identified based on the analysis of geophysical and other signs of modern activation. An assumption is made of possible commercial production of natural hydrogen in some of these locations. Ecological risks of deep Earth degassing, in particular, catastrophic degassing through super volcanoes are considered. Possible directions of counteraction against these risks with the help of purposeful efforts of the progressive humanity are also discussed. There is a need to revise the strategy and methodology of further development of geological and geophysical researches in general and, in particular, the major applied research areas, such as complex geological survey, mapping, prospecting of mineral resources and geo-ecology.

Features of the Invariant of the Spatial–Frequency Interference Structure of Acoustic Fields in Oceanic Waveguides

The paper considers the regular patterns that can be manifested in the behavior of the invariant of the spatial–frequency interference structure of an acoustic field in oceanic waveguides that are homogeneous and inhomogeneous along a track. Using the WKB and adiabatic approximations, an analytic expression is obtained for the invariant that, when certain conditions are fulfilled, reduces to the well-known classical expression independent of the mode numbers, their parity, or the emission frequency. It has been established that the approximate classical expression for the invariant correctly describes the slope of interference lines only in ranges of variation in the grazing angles of modes where the dependence of the cycle length of their corresponding Brillouin waves on the ray parameter is quite smooth and monotonic. The paper studies the formation of the spatial–frequency interference structure of an acoustic field propagating from a shallowwater isovelocity waveguide to a relatively deep-water waveguide with a near-surface sound channel.

Features of the propagation of pseudorandom pulse signals from the shelf to deep water in the presence of gyre formation on the acoustic track

The paper discusses the results of an experiment conducted in the Sea of Japan in March 2016 on an acoustic track 194 km long in winter hydrological conditions. The most complex case of propagation of pseudorandom pulse signals from the shelf to deep water in the presence of gyre formation on the acoustic track. An analysis of the experimentally obtained pulse characteristics show that at all points, a maximum, in terms of amplitude, first arrival of acoustic energy is recorded. This is evidence that at a given depth horizon, pulses that have passed the shortest distance through a near-surface sound channel at small angles close to zero are received first. The calculation method of mean sound velocity on the track, based on the satellite data of surface temperature monitoring, is proposed. We expect that the results obtained with this method can be successfully used for the purposes of acoustic range finding and navigation.

Formation of caustic beams in a refractive oceanic waveguide

We consider the patterns in the formation of the spatial interference structure of an acoustic field excited in the near-surface channel of a vertical array consisting of point sources emitting a tonal signal inphase. It is established that when the array aperture is increased to a certain optimal size, only one caustic beam forms in the channel. As the array aperture further increases, the sequential formation of a certain number of beams after the first is observed.

Peculiarities of prereverberation formation during long-range propagation of explosion signals

In experiments carried out in different regions of the World Ocean on long range propagation of explosion signals, researchers repeatedly observed bistatic surface reverberation that not only accompanied the probing (specularly reflected from the sea surface) signal but also preceded it. The part of the reverberation that preceded the probing signal was called the prereverberation. A theoretical explanation for this phenomenon in the context of an idealized model of the sea surface for the conditions of a near-surface sound channel was presented in 1978, and a technique for calculating the prereverberation time structure with allowance for the real conditions of the sound propagation in the ocean was developed only in the beginning of the 2000s. A series of calculations carried out according to this technique for the conditions of performing two experiments (for a near-surface sound channel and an underwater sound channel with the speed of sound near the bottom exceeding its value near the surface) resulted in the refinement of our knowledge about the mechanism forming the structure of a prereverberation signal. This paper, in addition to a brief description of other authors’ publications on this topic, presents a description of a technique for calculating the time structure of a prereverberation signal, a brief description of the conditions of two experiments in which prereverberation was observed, and results of analyzing the main prereverberation characteristics.

Stable surface solitons in truncated complex potentials

We show that surface solitons in the one-dimensional nonlinear Schrödinger equation with truncated complex periodic potential can be stabilized by linear homogeneous losses, which are necessary to balance gain in the near-surface channel arising from the imaginary part of potential. Such solitons become stable attractors when the strength of homogeneous losses acquires values from a limited interval and they exist in focusing and defocusing media. The domains of stability of the surface solitons shrink with an increase in the amplitude of the imaginary part of complex potential.

Sedimentary facies of the central part of radial tidal sand ridge system of the eastern China coast

A unique radial tidal sand ridge system (RTSRS) has developed under a complex tidal current field on the eastern China coast between the Yangtze River delta to the south and the abandoned Yellow River (Huanghe) delta to the north. The present study examines the sedimentary evolution of a ridge-channel pair in the central RTSRS. Three cores, with two on the ridges and one in the channel, were drilled to reveal the late Pleistocene-Holocene deposits of the system. Five sedimentary facies were distinguished, i.e. ridgeshallow subtidal facies, ridge-deep subtidal facies, nearsurface channel bottom facies, middle tidal flat facies and low tidal flat facies. The ridge-shallow subtidal facies consists of sandy strata with ripple cross beddings, horizontal lamina, and massive beddings. Bioturbation seldom occurs. The ridge-deep subtidal facies is primarily characterized by sandy and muddy interlayers with common flaser and lenticular bedding structures. Bioturbation appears abundantly. Massive and graded sediment sequences of storm origin are present as characterized by rich shell fragments. The nearsurface channel bottom facies consists of loose, soft, clayey silt deposits with deformed sedimentary layers. This facies occurs in the deeper part of the active channels. The middle tidal flat and lower tidal flat facies composed of silt-clay couplets prevailed primarily in the tidal flats. Incomplete sedimentary successions show that coastal plain deposits dominate in the study area during 12–13 ka B.P. The sandy ridge and channel facies became dominant during 4–6 ka B.P. when the sea level receded temporarily. Tidal ridge and channel in the study area became active during the last four decades. Sediment reworking due to typhoon and sandy ridge migration plays a key role in shaping the present radial ridge system.

Interfacial Energetics of Silicon in Contact with 11 M NH4F(aq), Buffered HF(aq), 27 M HF(aq), and 18 M H2SO4

Open-circuit impedance spectra, channel impedance spectroscopy on solution-gated field-effect devices, and differential capacitance vs potential (Mott−Schottky) measurements were used to determine the energetics of n-Si(111), n-Si(100), and p-Si(111) electrodes in contact with aqueous 11 M (40% by weight) NH4F, buffered HF (BHF), 27 M (48%) HF(aq), and concentrated (18 M) H2SO4. A Mott−Schottky analysis of As2Csc-2-vs-E (where As is the interfacial area, and Csc is the differential capacitance as a function of the electrode potential, E) data yielded reliable barrier heights for some silicon/liquid contacts in this work. Performing a Mott−Schottky analysis, however, requires measurement of the differential capacitance under reverse bias, where oxidation or etching can occur for n-Si and where electroplating of metal contaminants can occur for p-Si. Hence, open-circuit methods would offer desirable, complementary approaches to probing the energetics of such contacts. Accordingly, open-circuit, near-surface channel conductance measurements have been performed using solution-gated n+-p-Si(111)-n+ and p+-n-Si(100)-p+ devices. Additionally, open-circuit impedance spectra were obtained for silicon electrodes in contact with these solutions. The combination of the three techniques indicated that the surfaces of n-Si(111) and n-Si(100) were under accumulation when in contact with either 11 M NH4F(aq) or BHF(aq). The barrier heights for n-Si(111) and n-Si(100) in 11 M NH4F(aq) were −0.065 ± 0.084 V and −0.20 ± 0.21 V, respectively, and were −0.03 ± 0.19 V and −0.07 ± 0.24 V, respectively, for these surfaces in contact with buffered HF(aq). Consistently, p-Si(111) surfaces were determined to be in inversion in contact with these electrolytes, exhibiting barrier heights of 0.984 ± 0.078 V in contact with 11 M NH4F(aq) and 0.97 ± 0.22 V in contact with buffered HF(aq). In contact with 27 M HF(aq), n-Si(111) and n-Si(100) were in depletion, with barrier heights of 0.577 ± 0.038 V and 0.400 ± 0.057 V, respectively, and p-Si(111) was under inversion with a barrier height of 0.856 ± 0.076 V. Measurements performed in 18 M H2SO4 revealed barrier heights of 0.75 ± 0.11 V, 0.696 ± 0.043 V, and 0.889 ± 0.018 V for n-Si(111), n-Si(100), and p-Si(111), respectively, demonstrating that in 18 M H2SO4, the band edge positions of Si were different for different doping types. The barrier height data demonstrate that the observed low recombination rates of silicon in contact with 11 M NH4F, BHF, or 18 M H2SO4 cannot necessarily be attributed to a reduction in the number of surface trap states. In part, low surface recombination rates are expected for such systems because the very large or very small barrier height for silicon in contact with these liquids provides a potential barrier that prevents one type of photogenerated carrier (either electrons or holes) from reaching the surface, thereby producing a low steady-state surface recombination rate.

Near-Surface Channel Impedance Measurements, Open-Circuit Impedance Spectra, and Differential Capacitance vs Potential Measurements of the Fermi Level Position at Si/CH3CN Contacts

Near-surface channel impedance measurements, open-circuit impedance spectra, and differential capacitance vs potential measurements have been used to determine the barrier height of liquid contacts formed with n-type and p-type Si electrodes. Barrier heights were measured as the redox potential, E(A/A-), of a metallocene-based, one-electron, outer-sphere, acceptor/donor (A/A-) pair was varied in CH3CN solvent. The barrier heights of p-Si(111) electrodes in contact with CH3CN−Me10Fc+/0 (where Me10Fc is decamethylferrocene) or CH3CN-CoCp2+/0 (where CoCp2 is cobaltocene) were 0.69 ± 0.1 and 1.1 ± 0.1 V respectively. In contrast, barrier heights for n-Si(111)/CH3CN−Me10Fc+/0 and n-Si(111)/CH3CN-CoCp2+/0 contacts were 0.66 ± 0.1 and 0.09 ± 0.01 V, respectively. These measurements indicate that the barrier heights closely track changes in the electrochemical potential of the contact, instead of being relatively invariant to changes in the Fermi level of the contacting phase, as is observed for Si/metal Schottky barriers. These measurements also demonstrate that the low effective surface recombination velocity, S, for silicon in contact with CoCp2+/0 is primarily the result of an accumulation layer rather than solely being due to a low density of surface electrical defects.

Use of near-surface channel conductance and differential capacitance versus potential measurements to correlate inversion layer formation with low effective surface recombination velocities at n-Si/liquid contacts

Near-surface channel conductance measurements, differential capacitance versus potential measurements, and surface recombination velocity measurements have been performed on (111)- and (100)-oriented n-type Si samples in contact with nitrogen and/or liquid electrolyte solutions containing I2, I2/I−, ferrocene+/0, or decamethylferrocene+/0 in either methanol or tetrahydrofuran. Si/liquid contacts that displayed a low effective surface recombination velocity S corresponded to those that formed an inversion layer at the solid/liquid contact as indicated by channel conductance measurements or by differential capacitance versus potential measurements. Contacts that did not produce an inversion layer at the Si surface did not produce low effective S values. The observed behavior is consistent with the known energetics of Si/liquid contacts and provides an explanation for the low effective S values observed in these systems.

ABSTRACT: Bonga Field, Deepwater Nigeria: Comparison of Near-Surface, Well-Calibrated Submarine Channels with Reservoir Channel Sands

Comparison of near-surface channels with channel reservoirs at Bonga, offshore Nigeria (OML118, 1000 m water depth), demonstrates some important lessons in using shallow analogs for reservoir prediction. Studies of shallow hazards and pipeline routing, integrating 3D and high-resolution 2D seismic with well logs, illustrate seafloor and nearsurface features including a large mud-draped canyon, mud volcanoes, and numerous pockmarks, which indicate fluid expulsion. Both the shallow overburden (Plio-Pleistocene) and the main reservoir intervals (Miocene) are characterized by deepwater channel geometries visible in seismic profiles, on map views, and within 3D volume views. Most near-surface channel features inhabit broad, relatively straight scours 1-3 km wide and 30-300 m deep, filled by composite packages of smaller, often sinuous channels 100500 m wide and 5-50 m deep. Although many of these near-surface channels display a chaotic to low-continuity, high-amplitude seismic facies character often associated with sandy fill, well logs through the near-surface section indicate these are mainly filled with mud. Channel geometries at reservoir level show different characteristics. The smaller-scale map-view geometries are consistent in size with the near-surface channels but the larger host scours are not as prevalent or obvious, and some thin, sheet-like sands are also present. A transition from lower slope to upper slope at the end of the Miocene probably accounts for this variation. A fundamental understanding of geologic setting and rock/fluid variation is critical before extrapolating seismic facies information from shallow analogues to deeper reservoirs.

A study of the NOAA 16 AMSU-A brightness temperatures observed over Libyan Desert

[1] The brightness temperatures over the southeastern Libyan Desert (21°-23°N; 28°-29°E) from the NOAA-16 Advanced Microwave Sounding Unit-A (AMSU-A) were investigated for the months of January and March 2001. Angular distributions of the data from each month show remarkably stable patterns. The stable pattern of angular distributions can be potentially useful for postlaunch calibration and validation of the AMSU-A instrument, if a long-term trend of the angular distributions can be established. Angular distributions from the three window channels (channels 1, 2, and 15 with frequencies centered at 23.8, 31.4, and 89 GHz, respectively) and one near-surface sounding channel (channel 3 at 50.3 GHz) were simulated with a parametric model using the radiative transfer equation and a soil dielectric-emissivity model that generates the required soil emissivity as a function of zenith angle. The simulated results agree well with the data over the Libyan Desert area. The best-fit results indicate that radiation sensed by each channel comes from different thermal sampling depth and that these window channels could be used for temperature sounding in soils. The effect of spacecraft roll error on the angular distribution was also investigated. It was found that 1 ° roll error would produce a left-right asymmetry of 2.6 K in the angular distribution.

The effects of annealing on the distributions of deep and shallow states in CdTe single crystals

Schottky barrier capacitance and DLTS techniques have been employed to study the shallow- and deep-state distributions in bulk-grown CdTe crystals following an annealing treatment designed to convert the samples from semi-insulating to n-type conductivity. Although the annealing conditions (saturated Cd vapour at ) were chosen to ensure that homogeneity was achieved at the annealing temperature, substantial non-uniformities were observed in the test samples at room temperature. Although n-type conductivity was successfully achieved, this was restricted to a near-surface channel with a width of for undoped samples and for In-doped samples. These results can be attributed to diffusion and self-compensation processes occurring during cool-down following the anneal, but the DLTS measurements yield no evidence for the generation of new levels arising from these processes. The existing states (with energy levels in the detectable range from to below the conduction band) are found to be non-uniformly distributed as a function of depth below the surface, the form of the actual depth profiles being very similar to the corresponding free carrier concentration profile.

Numerical Solution of the Second Moment Equation for Waves in an Inhomogeneous Waveguide

An accurate numerical method for the solution of the second moment equation is presented. This may be applied to scalar wavefields in a wide variety of scattering regimes and inhomogeneous waveguides, for many of which explicit analytical solutions cannot be obtained. The method is applied here to the solution of a waveguide similar to the acoustic near-surface ocean channel. For the case of a Gaussian beam in a parabolic channel the method yields the asymptotic behaviour of focusing with increasing scattering, expressed as functional laws.

Acoustic properties of surface water masses in the tropical Atlantic and their seasonal variability

The peculiarities of the vertical hydroacoustic structure of surface water masses in the tropical Atlantic are reported. The near-surface acoustic channel in areas of strong freshening of oceanic waters by continental discharge and rainfall is studied. Quantitative characteristics of the seasonal variability of the channel's parameters are given. The mechanism responsible for the long-range acoustic conductivity in the upper layer of waters is analysed. The areas of maximum horizontal refraction in the near-surface layer are identified and the refraction angles of acoustic rays determined.

Determining contemporary stress directions from neotectonic joint systems

A neotectonic joint is a crack which propagated in a tectonic stress field that has persisted with little or no change of orientation until the present day. Investigating neotectonic joints is of value because the approximate orientation of the contemporary stress field can be inferred from them. Although exposed neotectonic joints in the flat-lying sedimentary rocks of some cratons are related to regional stress fields, their initiation and propagation occurred close to the Earth’s surface. For example, neotectonic joints in the centre of the Ebro basin (N. Spain) preferentially developed in a thin, near-surface channel sited within a sequence of weak Miocene limestones underlying the upper levels of plateaux. The Ebro basin joints strike uniformly NNW-SSE throughout an area of at least 10 000 km 2 and they are parallel or subparallel to the direction of greatest horizontal stress extrapolated from in situ stress measurements and fault-plane solutions of earthquakes.