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a ) up to 0.5° , b) 0.5°- 1.5° , c) 1.5°- 3.0° , d) 3.0°- 5.0° , e) 5.0° - 10.0° , e) 10.0°- 15.0° The attraction effect using 2D data from the innermost zone has an amplitude of 18 µGal and a RMS value of 3.0 µGal. The attraction effect from the zone of 0.5° - 1.5° is 10 times smaller than that of the innermost zone. Moreover the impact of the zone of 1.5° - 3° is 100 times smaller than the innermost zone and this variation is 3 times smaller than the variation calculated using 3D data. The variations from the remaining zones have similar features as the effect based on 3D data. The differences between the gravity reductions using 3D data and 2D data are given for one year in Fig. 6.
Figure 6 Differences between the attraction effects derived from 3D data and 2D with temperature data for zones of a) up to 0.5° , b) 0.5° - 1.5°, c) 1.5°-3°, d) 3°-5°, e) 5°-10°, f) 10°-15° from 2007/01/01 to 2007/12/31 (different scaling) It shows also the gravity effect of the surface pressure independent (SPI) part caused by the mass redistribution within the atmosphere from each zone. For the zone up to 0.5° (Fig.6a), the differences are in the range of 4.5 µGal with a maximum in summer and have a RMS value of 0.88 µGal. The differences for the zones 0.5° - 1.5° and 1.5° - 3° have a peak-to-peak amplitude of 3 µGal and 0.8 µGal (Fig.6b, c) and a minimum in summer. RMS values are 0.58 µGal and 0.16 µGal. As mentioned before, in these areas, the amplitude of the attraction effect using 3D data is 2-3 times larger than the effect obtained from 2D data. Thus, the differences show variations similar to the attraction effect using 3D data. The differences for the zone of 3° - 5° , 5° - 10° and 10°- 15° (Fig.6d,e,f) reach a peak-to-peak amplitude of 0.26 µGal, 0.14 µGal, and 0.18 µGal and RMS values are 0.05 µGal, 0.02 µGal and 0.03 µGal. The differences for the zone larger than 5° are below 0.2 µGal. This is two orders of magnitude smaller values than the total atmospheric effect. Therefore it is concluded that it is sufficient to use 3D data up to 5° and to compute the attraction effect for the remaining earth’s surface from 2D data and atmospheric Green’s functions. Up to the zone of 5°, there is a peak-to-peak difference of 0.5 µGal including seasonal variations with an amplitude of 0.15 µGal. The RMS value is 0.1 µGal considering a time span of 4 years (Fig.8a). The difference between the 3D and 2D data sets becomes smaller if we sum up the atmospheric attraction effect from each zone. 3-2 Comparison with 3 different atmospheric reductions In order to gain insight on where the various pressure reductions differ, the three reductions are compared again for the example of Moxa station. Reductions comprise a) 3D data for an area up to 5° to calculate the atmospheric attraction effect, 2D data (pressure and temperature) for the rest of the Earth to calculate the atmospheric attraction effect and 2D data for the whole Earth to calculate the atmospheric loading effect (physical approach), b) 2D data (pressure and temperature) for the whole Earth for the calculation of the atmospheric attraction and loading effect (physical approach), c) an admittance factor (-0.3649 µGal/hPa) which is estimated from the regression analysis between observed barometric pressure data and SG data (standard method). Fig.7 shows these reductions for a time span of 4 years.
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MAREES TERRESTRES BULLETIN D'INFORM
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BIM 146 December 15, 2010 New Chall
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1994), and TPXO.6 (Egbert et al., 1
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4. An attempt to improve the region
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From Fig. 2, we also see that, the
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GPS network called GEONET (GPS Eart
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References Bos, M. S., Baker, T. F.
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Planets Space, 59, 307-311. Sato, T
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Fig. 1. Locations of the observatio
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the dense seismic observation netwo
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difference of loading effects of oc
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is done with an optical lever using
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6. Application of laser interferome
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Figure 11. Strain seismograms of th
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Higashi, T., 1996, A study on chara
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2. Fundamentals and techniques At t
Page 40 and 41: 100 low frequencies earth tide freq
Page 42 and 43: Tab. 4: Averages of noise levels at
Page 44 and 45: References Asch, G., Elstner, C., J
Page 46 and 47: The 1 / s part is also worth mentio
Page 48 and 49: As it was mentioned before the resu
Page 50 and 51: Fig. 9. Morlet Wavelet Spectrum, su
Page 52 and 53: 9. CONCLUSIONS This investigation w
Page 54 and 55: 2. Objectives of Aswan Tidal Gravit
Page 56 and 57: 5. Recording of Data The data logge
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Page 64 and 65: time. In addition, models for gravi
Page 66 and 67: Fig. 3 (Zahran, 2005) shows gravity
Page 68 and 69: during the years 2003 and 2004. It
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Page 76 and 77: The instrumentation of the tidal st
Page 78 and 79: 4. Tidal analysis The tidal analysi
Page 80 and 81: References Banka, D., Crossley, D.
Page 82 and 83: 1. Introduction The estimation of a
Page 84 and 85: Figure 1 Air density distributions
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Page 88 and 89: Figure 4 Attraction effect from the
Page 92 and 93: Figure 7 Atmospheric reductions for
Page 94 and 95: Figure 9 Amplitude spectra of diffe
Page 96 and 97: Figure 10 SG observation and gravit
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