scholarly journals Computing height anomalies using spherical harmonic coefficients at certain degrees and orders in long-wavelength components

2016 ◽  
Vol 19 (2) ◽  
pp. 11-18
Author(s):  
Bao-Binh Luong
Keyword(s):  
Spherical Harmonic ◽  
Geoid Undulation ◽  
Height Anomaly ◽  
Reliability Of Results ◽  
Long Wavelength ◽  
Basic Quantity ◽  
Near Future

Height anomaly / geoid undulation) is a basic quantity in geodesy. It can be directly measured from GPS and leveling or computed from gravitational models. This paper introduces program GeoH to compute height anomalies using spherical harmonic coefficients at certain degrees and orders in longwavelength components. By reasonably comparing with official values of EGM96, the reliability of results from GeoH is proved for the long-wavelength components, and then can be applied in the “remove-restore” technique for determining Vietnamese quasi-geoid in near future.

scholarly journals Centimeter Precision Geoid Model for Jeddah Region (Saudi Arabia)

2020 ◽  
Vol 12 (12) ◽  
pp. 2066
Author(s):  
Alessandra Borghi ◽  
Riccardo Barzaghi ◽  
Omar Al-Bayari ◽  
Suhail Al Madani
Keyword(s):  
Gravity Field ◽  
Ocean Circulation ◽  
Gravity Data ◽  
Independent Set ◽  
Geoid Undulation ◽  
Height Anomaly ◽  
Geoid Model ◽  
Satellite Gravity ◽  
Earth’S Gravity Field ◽  
Long Wavelength

In 2014, the Jeddah Municipality made a call for an estimate of a centimetric precision geoid model to be used for engineering and surveying applications, because the regional geoid model available at that time did not reach a sufficient precision. A project was set up to this end and dedicated sets of gravity and Global Positioning System (GPS)/levelling data were acquired in the framework of this project. In this paper, a thorough analysis of these newly acquired data and of the last available Global Gravity Field Models (GGMs) has been done in order to obtain a geoid undulation estimate with the prescribed precision. In the framework of the Remove–Compute–Restore (RCR) approach, the collocation method was used to obtain the height anomaly estimation that was then converted to geoid undulation. The remove and restore steps of the RCR approach were based on GGMs, derived from the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) and Gravity Recovery and Climate Experiment (GRACE) dedicated gravity satellite missions, which were used to improve the long wavelength components of the Earth’s gravity field. Furthermore, two different quasi-geoid collocation estimates were computed, based on gravity data only and on gravity plus GPS/levelling data (the so-called hybrid estimate). The best solutions were obtained with the hybrid geoid estimate. This was tested by comparison with an independent set of GPS/levelling geoid undulations that were not included in the computed solutions. By these tests, the precision of the hybrid geoid is estimated to be 3.7 cm. This precision proved to be better, by a factor of two, than the corresponding one estimated from the pure gravimetric geoid. This project has been also useful to verify the importance and reliability of GGMs developed from the last satellite gravity missions (GOCE and GRACE) that have significantly improved our knowledge of the long wavelength components of the Earth’s gravity field, especially in areas with poor coverage of terrestrial gravity data. In fact, the geoid models based on satellite-only GGMs proved to have a better performance, despite the lower spatial resolution with respect to high-resolution models (i.e., Earth Gravitational Model 2008 (EGM2008)).

scholarly journals An indium tin oxide metasurface filter for terahertz applications: Design, fabrication, and characterization

2017 ◽  
Vol 31 (08) ◽  
pp. 1750074 ◽  
Author(s):  
Mehmet Ali Nebioğlu ◽  
Taylan Takan ◽  
Hakan Altan ◽  
Yasemin Demirhan ◽  
Hakan Alaboz ◽  
...  
Keyword(s):  
Tin Oxide ◽  
Indium Tin Oxide ◽  
Fused Silica ◽  
Thz Radiation ◽  
Terahertz Time Domain Spectroscopy ◽  
Long Wavelength ◽  
Security Applications ◽  
Unit Cell Size ◽  
Transparent Media ◽  
Near Future

In this paper, using a cross-shaped complementary Indium Tin Oxide (ITO)-based metasurface design, the transmission of THz radiation is shown to be filtered within the 3 dB level from maximum in the frequency range of interest ([Formula: see text][Formula: see text]333 GHz). Various metasurface structures primarily composed of cross-shaped openings with a 400 micron unit cell size are patterned on top of 1750 micron thick fused silica substrates. They are patterned using UV lithography methods after the films were grown using DC sputtering. The fabricated structures were characterized using Terahertz Time Domain Spectroscopy (THz-TDS) measurement technique. The measured transmission agrees well with the simulation of the structure for four different samples with different geometries. These results suggest that metasurface and/or metamaterial patterns based on ITO in visibly transparent media can be utilized for filtering of frequencies in the long wavelength spectrum. These types of filters can be very useful in the near future for THz communication and security applications.

Long-wavelength lithospheric magnetic field of China

2020 ◽  
Vol 224 (3) ◽  
pp. 1780-1792
Author(s):  
Yi Jiang ◽  
Richard Holme ◽  
Sheng-Qing Xiong ◽  
Yong Jiang ◽  
Yan Feng ◽  
...  
Keyword(s):  
Spherical Harmonic ◽  
Tibet Plateau ◽  
Changbai Mountains ◽  
Data Sets ◽  
Aeromagnetic Data ◽  
Spherical Harmonic Degree ◽  
Aeromagnetic Survey ◽  
Long Wavelength ◽  
Degree Correlation ◽  
Good Agreement

SUMMARY We present new regional models, denoted CLAS, of the Chinese lithospheric field, combining the long-wavelength information provided by satellite-derived models: CHAOS-6, MF7, LCS-1 and NGDC720, and an extremely high-quality compilation of 97 994 aeromagnetic survey data with 10 km × 10 km resolution for shorter wavelength. The models are estimated using a depleted basis of global spherical harmonic functions centred on China. CLAS models are determined include harmonic degrees up to 400. Although some accuracy of aeromagnetic data is lost in order to balance the consistent of two data sets, the results show that CLAS models have a high correlation with the satellite models at low-degree terms (degree correlation > 0.9) but with more power at high-degree terms, reflecting more features of the lithospheric field in continental China. Examples of improvement include Changbai mountains, Sichuan Basin and Qinghai–Tibet Plateau. CLAS models have good agreement (coherence > 0.9) with Chinese aeromagnetic data at wavelength down to about 100 km (corresponding to spherical harmonic degree n = 400), filling the usual gap between satellite models and aeromagnetic data. Comparison with aeromagnetic data filtered at 100 km gives good agreement (correlation > 0.95). The residuals between CLAS models and aeromagnetic data are still large (rms > 70 nT), but with most of misfits arising from shorter wavelength fields that the model cannot fit at degree up to 400; such misfit could be reduced by increasing the model degree. We provide a geological example of how the inclusion of satellite data can change the geological conclusions that can be drawn from the magnetic information. However, the two data sets are not completely consistent, future models should start from a reanalysis of the aeromagnetic data and its line levelling to ensure consistency with the satellite model.

scholarly journals A NEW APPROACH FOR THE TSUNAMI PREDICTION USING SATELLITE ALTIMETRY: TRIALS FOR ACEH TSUNAMI EVENTS IN 2004 AND 2005

2010 ◽  
Vol 3 (-) ◽  
Author(s):  
Susumu Kanno ◽  
Yasuo Furushima ◽  
I Wayan Nuarsa ◽  
I Gede Hendrawan
Keyword(s):  
Satellite Altimetry ◽  
Bottom Topography ◽  
Sea Surface Height ◽  
Sea Surface ◽  
Height Anomaly ◽  
New Approach ◽  
Disaster Monitoring ◽  
Tsunami Earthquake ◽  
Sea Surface Height Anomaly ◽  
Near Future

Change in the sea surface height anomaly derived from satellite altimeter was examined and applied to evaluate the possibility of tsunami prediction before the occurance. Sea surface height anomaly was composed period during earthquake and tsunami occurance. Daily variability in the sea surface height anomaly was traced about the location of hypocenter, aftershock, and the end of erthquakes from satellite altimetry. Results shows that there are the locations where the sea surface height anomaly suddenly increased or decreased before tsunami event at least. This result can be utilized and applied for the development in not only the stunami monitoting system as the disaster monitoring, but also for the effective tsunami prediction system in the near future. Keywords: tsunami, earthquake, bottom topography, sea surface height, satellite altimetry, altimeter, disaster prevention.

Spectrophotometric reductions with an IBM 1620

1966 ◽  
Vol 24 ◽  
pp. 116-117
Author(s):  
P.-I. Eriksson
Keyword(s):  
Astronomical Data ◽  
Spectrophotometric Data ◽  
Electronic Computers ◽  
The University ◽  
Near Future

Nowadays more and more of the reductions of astronomical data are made with electronic computers. As we in Uppsala have an IBM 1620 at the University, we have taken it to our help with reductions of spectrophotometric data. Here I will briefly explain how we use it now and how we want to use it in the near future.

Activated Prominences; Mechanisms for Activation and Eruption

1979 ◽  
Vol 44 ◽  
pp. 307-313
Author(s):  
D.S. Spicer
Keyword(s):  
Pressure Gradient ◽  
Density Gradient ◽  
Current Density ◽  
Convective Instability ◽  
Tearing Mode ◽  
Magnetic Shear ◽  
Long Wavelength ◽  
Ideal Mhd ◽  
Gradient Change ◽  
Accelerated Particles

A possible relationship between the hot prominence transition sheath, increased internal turbulent and/or helical motion prior to prominence eruption and the prominence eruption (“disparition brusque”) is discussed. The associated darkening of the filament or brightening of the prominence is interpreted as a change in the prominence’s internal pressure gradient which, if of the correct sign, can lead to short wavelength turbulent convection within the prominence. Associated with such a pressure gradient change may be the alteration of the current density gradient within the prominence. Such a change in the current density gradient may also be due to the relative motion of the neighbouring plages thereby increasing the magnetic shear within the prominence, i.e., steepening the current density gradient. Depending on the magnitude of the current density gradient, i.e., magnetic shear, disruption of the prominence can occur by either a long wavelength ideal MHD helical (“kink”) convective instability and/or a long wavelength resistive helical (“kink”) convective instability (tearing mode). The long wavelength ideal MHD helical instability will lead to helical rotation and thus unwinding due to diamagnetic effects and plasma ejections due to convection. The long wavelength resistive helical instability will lead to both unwinding and plasma ejections, but also to accelerated plasma flow, long wavelength magnetic field filamentation, accelerated particles and long wavelength heating internal to the prominence.

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