Influence of Alfvénic characteristics on calibration of satellite magnetometer

2020 ◽  
Author(s):  
Zonghao Pan ◽  
Guoqiang Wang ◽  
LiFei Meng ◽  
Tielong Zhang
Keyword(s):  
Interplanetary Space ◽  
Satellite Orbit ◽  
Compressional Wave ◽  
Fluxgate Magnetometer ◽  
Compressional Waves ◽  
Data Window ◽  
True Value ◽  
Smith Method ◽  
Zero Offset ◽  
N Wave

<p>The zero offset of the fluxgate magnetometer in satellite orbit will be changed due to several factors. For this reason, the Davis-Smith method is proposed to calculate the zero compensation of the magnetometer based on the feature that the shear Alfvén waves do not change the total magnetic field strength. In fact, there is no pure Alfvén waves in the interplanetary space. In this paper, numerical simulation is used to analyze the influence of the amplitude, period and phase of the Alfvén waves and the time length of the data window on the zero offset of the magnetometer calculated by the Davis-Smith method in the presence of weak compressional waves. We find that Alfvén waves can produce a non-negligible error in the calculation of zero compensation only when its period is the same as the period of the compressional wave. The greater the amplitude of Alfvén waves, the smaller the error of the zero offset. The error of the zero offset is also affected by the initial phase of the Alfvén wave. In addition, the error of the zero offset tends to decrease to its true value for the longer the data window length.</p>

scholarly journals Automatic calculation of the magnetometer zero offset using the interplanetary magnetic field based on the Wang-Pan method

2021 ◽  
Author(s):  
Xiaowen Hu ◽  
Guoqiang Wang ◽  
Zonghao Pan ◽  
Tielong Zhang
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Alfven Waves ◽  
Alfven Wave ◽  
Alfvén Waves ◽  
Fluxgate Magnetometer ◽  
Smith Method ◽  
Proper Modification ◽  
Zero Offset ◽  
Selection Of

Abstract. The space-borne fluxgate magnetometer (FGM) needs regular in-flight calibration to obtain its zero offset. Recently, a new method based on the properties of Alfvén waves for the zero offset calibration was developed by Wang and Pan (2021). They found that there exists an optimal offset line (OOL) in the offset cube for a pure Alfvén wave, and the zero offset can be determined by the intersection of at least two non-parallel OOLs. Since no pure Alfvén waves exist in the interplanetary magnetic field, the calculation of the zero offset relies on the selection of the highly Alfvénic fluctuation event. Here, we propose an automatic procedure to find highly Alfvénic fluctuations in the solar wind and calculate the zero offset. This procedure includes three parts: (1) selection of highly Alfvénic fluctuation events, (2) evaluation of the OOL of the selected fluctuation events, and (3) determination of the zero offset. We test our automatic procedure by applying it to the magnetic field data measured by the FGM onboard Venus Express. The tests reveal that our automatic procedure is able to achieve as good results as the Davis-Smith method. One advantage of our procedure is that the selection criteria and process for the highly Alfvénic fluctuation event are simpler. Our automatic procedure might also be applied to find fluctuation events for the Davis-Smith method after proper modification.

Delineating a cased borehole in unconsolidated formations using dipole acoustic data from a nearby well

Geophysics ◽  
2021 ◽  
pp. 1-39
Author(s):  
Gu Xihao ◽  
Xiao-Ming Tang ◽  
Yuan-Da Su
Keyword(s):  
Shear Waves ◽  
Low Frequency ◽  
Well Being ◽  
Compressional Wave ◽  
Acoustic Imaging ◽  
Wave Radiation ◽  
Dipole Source ◽  
Compressional Waves ◽  
Single Well ◽  
Cased Borehole

A potential application for single-well acoustic imaging is the detection of an existing cased borehole in the vicinity of the well being drilled, which is important for drilling toward (when drilling a relief well), or away from (collision prevention), the existing borehole. To fulfill this application in the unconsolidated formation of shallow sediments, we propose a detection method using the low-frequency compressional waves from dipole acoustic logging. For this application, we perform theoretical analyses on elastic wave scattering from the cased borehole and derive the analytical expressions for the scattered wavefield for the incidence of compressional and shear waves from a borehole dipole source. The analytical solution, in conjunction with the elastic reciprocity theorem, provides a fast algorithm for modeling the whole process of wave radiation, scattering, and reception for the borehole acoustic detection problem. The analytical results agree well with those from 3D finite-difference simulations. The results show that compressional waves, instead of shear waves as commonly used for dipole acoustic imaging, are particularly advantageous for the borehole detection in the unconsolidated formation. Field data examples are used to demonstrate the application in a shallow marine environment, where dipole-compressional wave data in the measurement well successfully delineate a nearby cased borehole, validating our analysis results and application.

Seismic refraction shooting in an area of the Eastern Atlantic

1952 ◽  
Vol 244 (890) ◽  
pp. 561-594 ◽  
Keyword(s):  
Wave Velocity ◽  
Deep Sea ◽  
Sea Water ◽  
Seismic Refraction ◽  
Compressional Wave ◽  
Crystalline Rock ◽  
Compressional Wave Velocity ◽  
Compressional Waves ◽  
A Value ◽  
Sedimentary Layer

For the experiments described in this paper a new method of seismic refraction shooting was developed. With this method hydrophones suspended at a depth of about 100 ft. below the surface of the sea acted as receivers for the compressional waves developed by depth charges exploding at a depth of approximately 900 ft. The hydrophones were connected with sono-radio buoys which radio-transmitted the electrical signals to a recording system in the ship from which the charges were dropped. Four buoys were in use simultaneously, distributed at differing ranges from the ship. The experiments were carried out at three positions in an area of the eastern Atlantic around the point 53° 50' N, 18° 40' W, where the water depth is approximately 1300 fm. (2400 m). The results showed that the uncrystalline sedimentary layer in this area varied in thickness from 6200 ft. to 9700 ft. (1900 to 3000 m), and that the velocity of compressional waves in it increased from the value for sea water, 4900 ft./s (1.5 km/s), at the surface with an approximately constant gradient of 2.5/s to a limiting value of 8200 ft./s (2.5 km/s). Below the sedimentary layer there was a crystalline rock with compressional wave velocity of approximately 16500 ft./s (5.0 km/s) and of thickness varying between 8800 ft. (2700 m) and 11100 ft. (3400 m). The base of this layer was in both determinations at approximately 25500 ft. (7800 m) below sea-level. The lowest layer concerning which information was obtained gave a value for the compressional wave velocity of about 20500 ft./s (6.3 km/s), but was of undetermined thickness. The characteristics of the sedimentary layer were such as might be expected for a continuous succession of deep-sea sediments, the thickness on this basis being such as to indicate the long existence of the ocean in this area. On the other hand, it is possible that it represents a downwarped continental shelf. The layer below the sedimentary layer has a compressional wave velocity which is low for an igneous rock at this depth, and it is probable that it represents a crystalline sedimentary rock. From the evidence it is not possible to determine whether this rock is of continental or deep-sea origin. The lowest layer of these experiments is unlikely to have a constitution similar to that of the European granitic layer, since the compressional wave velocity in it would, on this hypothesis, be exceptionally high. The value is, however, close to that calculated by Jeffreys for the intermediate layer.

SEISMIC STUDIES ON THE EASTERN SEABOARD OF CANADA: THE ATLANTIC COAST OF NOVA SCOTIA

1964 ◽  
Vol 1 (1) ◽  
pp. 10-22 ◽  
Author(s):  
D. L. Barrett ◽  
M. Berry ◽  
J. E. Blanchard ◽  
M. J. Keen ◽  
R. E. McAllister
Keyword(s):  
Nova Scotia ◽  
Upper Mantle ◽  
Atlantic Coast ◽  
Seismic Refraction ◽  
Compressional Wave ◽  
Crust And Upper Mantle ◽  
Compressional Waves ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Eastern Seaboard

The results of seismic refraction profiles on the Atlantic coast of Nova Scotia and on the continental shelf off Nova Scotia are presented. Compressional and shear waves have been observed in the crust and mantle and suggest that the thickness of the crust is about 34 km. The compressional wave velocities recorded in the main crust and upper mantle are 6.10 and 8.11 km s−1 respectively. No compressional waves with values of velocity between these values can be identified, and this suggests that any "intermediate" layer is thin or absent. The corresponding shear wave velocities are 3.68 and 4.53 km s−1. Values of Poisson's ratio in the crust and mantle are 0.22 and 0.28. Alternative models of the crust which, on the evidence of travel times, might fit the observed results are discussed.

Evaluation of direct hydrocarbon indicators through comparison of compressional‐ and shear‐wave seismic data: a case study of the Myrnam gas field, Alberta

Geophysics ◽  
1985 ◽  
Vol 50 (1) ◽  
pp. 37-48 ◽  
Author(s):  
Ross Alan Ensley
Keyword(s):  
Shear Wave ◽  
Seismic Data ◽  
Compressional Wave ◽  
Bright Spot ◽  
Low Velocity ◽  
Gas Reservoir ◽  
Gas Field ◽  
Compressional Waves ◽  
The Relationship

Shear waves differ from compressional waves in that their velocity is not significantly affected by changes in the fluid content of a rock. Because of this relationship, a gas‐related compressional‐wave “bright spot” or direct hydrocarbon indicator will have no comparable shear‐wave anomaly. In contrast, a lithology‐related compressional‐wave anomaly will have a corresponding shear‐wave anomaly. Thus, it is possible to use shear‐wave seismic data to evaluate compressional‐wave direct hydrocarbon indicators. This case study presents data from Myrnam, Alberta which exhibit the relationship between compressional‐ and shear‐wave seismic data over a gas reservoir and a low‐velocity coal.

A theory of compressional wave attenuation in noncohesive sediments

Geophysics ◽  
1985 ◽  
Vol 50 (8) ◽  
pp. 1311-1317 ◽  
Author(s):  
C. McCann ◽  
D. M. McCann
Keyword(s):  
Wave Attenuation ◽  
Compressional Wave ◽  
Solid Particles ◽  
Biot’S Theory ◽  
Attenuation Coefficients ◽  
Low Frequencies ◽  
Biot's Theory ◽  
Compressional Waves ◽  
High Frequencies ◽  
Water Saturated

Published reviews indicate that attenuation coefficients of compressional waves in noncohesive, water‐saturated sediments vary linearly with frequency. Biot’s theory, which accounts for attenuation in terms of the viscous interaction between the solid particles and pore fluid, predicts in its presently published form variation proportional to [Formula: see text] at low frequencies and [Formula: see text] at high frequencies. A modification of Biot’s theory which incorporates a distribution of pore sizes is presented and shown to give excellent agreement with new and published attenuation data in the frequency range 10 kHz to 2.25 MHz. In particular, a linear variation of attenuation with frequency is predicted in that range.

VELOCITY OF COMPRESSIONAL WAVES IN POROUS MEDIA AT PERMAFROST TEMPERATURES

Geophysics ◽  
1968 ◽  
Vol 33 (4) ◽  
pp. 584-595 ◽  
Author(s):  
A. Timur
Keyword(s):  
Porous Media ◽  
Wave Velocity ◽  
Compressional Wave ◽  
Freezing Process ◽  
Rock Matrix ◽  
Compressional Wave Velocity ◽  
Compressional Waves ◽  
Average Equation ◽  
Wave Velocities ◽  
Time Average

Measurements of velocity of compressional waves in consolidated porous media, conducted within a temperature range of 26 °C to −36 °C, indicate that: (1) compressional wave velocity in water‐saturated rocks increases with decreasing temperature whereas it is nearly independent of temperature in dry rocks; (2) the shapes of the velocity versus temperature curves are functions of lithology, pore structure, and the nature of the interstitial fluids. As a saturated rock sample is cooled below 0 °C, the liquid in pore spaces with smaller surface‐to‐volume ratios (larger pores) begins to freeze and the liquid salinity controls the freezing process. As the temperature is decreased further, a point is reached where the surface‐to‐volume ratio in the remaining pore spaces is large enough to affect the freezing process, which is completed at the cryohydric temperature of the salts‐water system. In the ice‐liquid‐rock matrix system, present during freezing, a three‐phase, time‐average equation may be used to estimate the compressional wave velocities. Below the cryohydric temperature, elastic wave propagation takes place in a solid‐solid system consisting of ice and rock matrix. In this frozen state, the compressional wave velocity remains constant, has its maximum value, and may be estimated through use of the two‐phase time average equation. Limited field data for compressional wave velocities in permafrost indicate that pore spaces in permafrost contain not only liquid and ice, but also gas. Therefore, before attempting to make velocity estimates through the time‐average equations, the natures and percentages of pore saturants should be investigated.

Sonic to ultrasonic Q of sandstones and limestones: Laboratory measurements at in situ pressures

Geophysics ◽  
2009 ◽  
Vol 74 (2) ◽  
pp. WA93-WA101 ◽  
Author(s):  
Clive McCann ◽  
Jeremy Sothcott
Keyword(s):  
Wave Attenuation ◽  
Shear Waves ◽  
Compressional Wave ◽  
Ultrasonic Frequency ◽  
Laboratory Measurements ◽  
Compressional Waves ◽  
Wave Velocities ◽  
Poisson's Ratios ◽  
Poisson’S Ratios

Laboratory measurements of the attenuation and velocity dispersion of compressional and shear waves at appropriate frequencies, pressures, and temperatures can aid interpretation of seismic and well-log surveys as well as indicate absorption mechanisms in rocks. Construction and calibration of resonant-bar equipment was used to measure velocities and attenuations of standing shear and extensional waves in copper-jacketed right cylinders of rocks ([Formula: see text] in length, [Formula: see text] in diameter) in the sonic frequency range and at differential pressures up to [Formula: see text]. We also measured ultrasonic velocities and attenuations of compressional and shear waves in [Formula: see text]-diameter samples of the rocks at identical pressures. Extensional-mode velocities determined from the resonant bar are systematically too low, yielding unreliable Poisson’s ratios. Poisson’s ratios determined from the ultrasonic data are frequency corrected and used to calculate thesonic-frequency compressional-wave velocities and attenuations from the shear- and extensional-mode data. We calculate the bulk-modulus loss. The accuracies of attenuation data (expressed as [Formula: see text], where [Formula: see text] is the quality factor) are [Formula: see text] for compressional and shear waves at ultrasonic frequency, [Formula: see text] for shear waves, and [Formula: see text] for compressional waves at sonic frequency. Example sonic-frequency data show that the energy absorption in a limestone is small ([Formula: see text] greater than 200 and stress independent) and is primarily due to poroelasticity, whereas that in the two sandstones is variable in magnitude ([Formula: see text] ranges from less than 50 to greater than 300, at reservoir pressures) and arises from a combination of poroelasticity and viscoelasticity. A graph of compressional-wave attenuation versus compressional-wave velocity at reservoir pressures differentiates high-permeability ([Formula: see text], [Formula: see text]) brine-saturated sandstones from low-permeability ([Formula: see text], [Formula: see text]) sandstones and shales.

Direct estimation of shear‐wave interval velocities from seismic data

Geophysics ◽  
1985 ◽  
Vol 50 (4) ◽  
pp. 530-538 ◽  
Author(s):  
P. M. Carrion ◽  
S. Hassanzadeh
Keyword(s):  
Shear Wave ◽  
Small Angle ◽  
Seismic Data ◽  
Mode Conversion ◽  
Real Data ◽  
Compressional Wave ◽  
Compressional Waves ◽  
Common Depth Point ◽  
Interval Velocities ◽  
Wave Decomposition

Conventional velocity analysis of seismic data is based on normal moveout of common‐depth‐point (CDP) traveltime curves. Analysis is done in a hyperbolic framework and, therefore, is limited to using the small‐angle reflections only (muted data). Hence, it can estimate the interval velocities of compressional waves only, since mode conversion is negligible when small‐angle arrivals are concerned. We propose a new method which can estimate the interval velocities of compressional and mode‐converted waves separately. The method is based on slant stacking or plane‐wave decomposition (PWD) of the observed data (seismogram), which transforms the data from the conventional T-X domain into the intercept time‐ray parameter domain. Since PWD places most of the compressional energy into the precritical region of the slant‐stacked seismogram, the compressional‐wave interval velocities can be estimated using the “best ellipse” approximation on the assumption that the elliptic array velocity (stacking velocity) is approximately equal to the root‐mean‐square (rms) velocity. Similarly, shear‐wave interval velocities can be estimated by inverting the traveltime curves in the region of the PWD seismogram, where compressional waves decay exponentially (postcritical region). The method is illustrated by examples using synthetic and real data.

Observations of the transition from linear polarization to complex polarization in short-period compressional waves

1991 ◽  
Vol 81 (2) ◽  
pp. 611-621
Author(s):  
William Menke ◽  
Arthur Lerner-Lam
Keyword(s):  
New York ◽  
New England ◽  
Linear Polarization ◽  
Compressional Wave ◽  
P Wave ◽  
Adirondack Mountains ◽  
Compressional Waves ◽  
Short Period ◽  
Shallow Crust ◽  
Complex Polarization

Abstract We measure the polarization of compressional waves from seismograms of chemical explosion of the Ontario-New York-New England refraction experiment recorded by the seven element ECO array in the New York Adirondack mountains. After careful instrument calibration, a precision of about 5° is achieved in measuring the azimuth of the compressional wave polarization direction. The azimuth of the polarization of the onset of the P wave differs from the geometrical source-receiver azimuth by as much as 20°, possible due to deflection of the first-arriving ray by lateral variation in crustal structure. Shortly after the onset of P, the polarization changes from the linear polarization expected of a compressional wave to become very complex. The time of this transition increases with source-receiver distance, from about 0.4 to 0.5 sec at 50 km distance and 0.7 to 0.8 sec at 150 km distance. The complex polarization may be due to the arrival of strongly scattered waves that have propagated mainly in the shallow crust, which would imply that the upper 1 to 2 km of the crust is particularly heterogeneous.

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