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991.
992.
Milan Burša Steve Kenyon Jan Kouba Zdislav Šíma Viliam Vatrt Vojtěch Vítek Marie Vojtíšková 《Journal of Geodesy》2007,81(2):103-110
The TOPEX/Poseidon (T/P) satellite alti- meter mission marked a new era in determining the geopotential constant W
0. On the basis of T/P data during 1993–2003 (cycles 11–414), long-term variations in W
0 have been investigated. The rounded value W
0 = 62636856.0 ± 0.5) m
2
s
−2 has already been adopted by the International Astronomical Union for the definition of the constant L
G
= W
0/c
2 = 6.969290134 × 10−10 (where c is the speed of light), which is required for the realization of the relativistic atomic time scale. The constant L
G
, based on the above value of W
0, is also included in the 2003 International Earth Rotation and Reference Frames Service conventions. It has also been suggested
that W
0 is used to specify a global vertical reference system (GVRS). W
0 ensures the consistency with the International Terrestrial Reference System, i.e. after adopting W
0, along with the geocentric gravitational constant (GM), the Earth’s rotational velocity (ω) and the second zonal geopotential
coefficient (J
2) as primary constants (parameters), then the ellipsoidal parameters (a,α) can be computed and adopted as derived parameters. The scale of the International Terrestrial Reference Frame 2000 (ITRF2000)
has also been specified with the use of W
0 to be consistent with the geocentric coordinate time. As an example of using W
0 for a GVRS realization, the geopotential difference between the adopted W
0 and the geopotential at the Rimouski tide-gauge point, specifying the North American Vertical Datum 1988 (NAVD88), has been
estimated. 相似文献
993.
Mapping the spatial variation of soil water content at the field scale with different ground penetrating radar techniques 总被引:2,自引:0,他引:2
L. Weihermüller J.A. Huisman S. Lambot M. Herbst H. Vereecken 《Journal of Hydrology》2007,340(3-4):205-216
Two ground penetrating radar (GPR) techniques were used to estimate the shallow soil water content at the field scale. The first technique is based on the ground wave velocity measured with a bistatic impulse radar connected to 450 MHz ground-coupled antennas. The second technique is based on inverse modeling of an off-ground monostatic TEM horn antenna in the 0.8–1.6 GHz frequency range. Data were collected on a 8 by 9 m partially irrigated intensive research plot and along four 148.5 m transects. Time domain reflectometry, capacitance sensors, and volumetric soil samples were used as reference measurements. The aim of the study was to test the applicability of the ground wave method and the off-ground inverse modeling approach at the field scale for a soil with a silt loam texture. The results for the ground wave technique were difficult to interpret due to the strong attenuation of the GPR signal, which is related to the silt loam texture at the test site. The root mean square error of the ground wave technique was 0.076 m3 m−3 when compared to the TDR measurements and 0.102 m3 m−3 when compared with the volumetric soil samples. The off-ground monostatic GPR measured less within-field soil water content variability than the reference measurements, resulting in a root mean square error of 0.053 m3 m−3 when compared with the TDR measurements and an error of 0.051 m3 m−3 when compared with the volumetric soil samples. The variability between the two GPR measurements was even larger with a RSME of 0.115 m3 m−3. In summary, both GPR methods did not provide adequate spatial information on soil water content variation at the field scale. The main reason for the deviating results of the ground wave method was the poor data quality due to high silt and clay content at the test site. Additional reasons were shallow reflections and the dry upper soil layer that cannot be detected by the ground wave method. In the case of off-ground GPR, the high sensitivity to the dry surface layer is the most likely reason for the observed deviations. The off-ground GPR results might be improved by using a different antenna that allows data acquisition in a lower frequency range. 相似文献
994.
Suitable scale of Weigan River plain oasis 总被引:2,自引:0,他引:2
HU ShunJun SONG YuDong TIAN ChangYan LI YueTan LI XiuCang CHEN XiaoBing 《中国科学D辑(英文版)》2007,50(Z1):56-64
Desert coexists with oasis in long time, and the existence and development of oasis system demand better oasis vegetation ecological system. Oasis scale of arid zone plain encircling water should be determined in case of desertification caused by land over-reclamation under the circumstance of water resources shortage. Steady oasis with virtuous circle must have appropriate land use structure for agriculture, forestry and graziery. The study on the suitable scale and developmental space of oasis will provide theoretical and applicable foundation for effective construction of oases. By analyzing the hydrothermal, water and soil balance, an optimal mathematical model has been established. Based on hydrometeorology data collected for years in Weigan River plain, and by the principle of water balance, a calculation has been made of the water resources for evapotranspiration and the optimal acreage of oasis and cultivated land, which shows that the water resources for evapotranspiration in the Weigan River plain oasis is 22.32×108 m3 and the optimal oasis acreage under the condition of conventional irrigation mode is 3716.06 km2, in which the suitable cultivated land acreage is 1564.79 km2. Under the condition of water-saving irrigation, the suitable oasis acreage is 5515.49 km2, in which the suitable cultivated land acreage is 2322.31 km2. The oasis area had reached 4123 km2, and the cultivated land acreage had reached 1507 km2 after the Agriculture Irrigation Drainage Water Project of World Bank Loan in Weigan River basin was finished in 1997. The oasis and cultivated land acreage will be more suitable, and the oasis scale can be enlarged moderately by means of water saving irrigation. 相似文献
995.
996.
Taichiro Okazaki Masayoshi Nakashima Keiichiro Suita Tomohiro Matusmiya 《地震工程与结构动力学》2007,36(1):35-53
Interaction between the external wall cladding and the seismic load resisting frame was examined in a full‐scale cyclic loading test of a three‐storey steel building structure. The building specimen had Autoclaved Lightweight Concrete (ALC, also designated as Autoclaved Aerated Concrete) panels installed and anchored to the structural frame as external wall cladding, using a standard Japanese method developed following the 1995 Kobe earthquake. ALC panelling is among the most widely used material for claddings in Japan. In the test, the ALC panel cladding contributed little to the stiffness and strength of the overall structure, even under a very large storey drift of 0.04 rad. No visible damage was noted in the ALC panels other than minor cracks and spalling of the bottom of the panels in the first storey. Consequently, in a Japanese steel building with properly installed ALC panel cladding, the structural frame is likely to be little affected by its cladding, and the ALC panels are capable of accommodating the maximum storey drift generally considered in structural design without sustaining discernible damage. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
997.
998.
The Himalayan region of north India is composed of complex mountain ranges with different altitudes and orientations, causing
prevailing weather conditions to be complex. Wintertime eastward moving synoptic weather systems `Western Disturbances' (WDs)
yield large amounts of precipitation over this region. Numerous micro/mesoscale circulations become generated along with prevailing
weather due to surface heterogeneity and land-use variability of the Himalayan region. WDs along with these circulations may
give rise to very adverse weather conditions over the region. Intraseasonal variability of surface climate over the Himalayas
is studied using regional climate model (RegCM3) with 60 km resolution. A 6-month (Oct. 1999–Mar. 2000) period, as this period
has received an enormous amount of precipitation in the form of snow, is considered to study surface climate variability in
terms of temperature, precipitation and snow amount. Model simulations show cold bias over the Himalayan region and warm bias
over the northwest India. Average monthly distribution of temperature indicates that a controlled experiment could capture
the areas of lowest temperature regime. Precipitation fields could be simulated only up to a certain degree of satisfaction
and the influence of topographic elevation and valleys needs to be seen. RegCM3 provides a representation of resolvable atmospheric
circulations that results in explaining mean variability during winter. 相似文献
999.
The ANELFA scale for hailfall intensity is proposed on the model of the 6-class Fujita scale for tornadoes. It is based on more than three thousand point hailfalls measured by hailpads over a 16-year period in France. The class number of a hailfall is determined by the integer value of the largest measured hailstone diameter in cm, or by equivalence with current objects: A0 to A5 for pea, grape, pigeon's egg, walnut, hen's egg, orange. The class number is followed by a plus or minus sign if the ground is significantly more or less than half-covered by hailstones respectively. When the scale is applied to the ANELFA data, a log-normal distribution is found for the class distribution, allowing the frequency determination of the upper class ever observed until now at the hailpad stations. 相似文献
1000.