Wet tropospheric effects on precise relative GPS height determination

Summary Considerable interest has been generated recently in the use of the Global Positioning System (GPS) for precise height determination. A major error source in these measurements is the propagation delay due to atmospheric water vapour. In order to achieve the high precisions required for such applications as absolute sea-level monitoring improvement of wet delay modelling is necessary. Results from a GPS campaign show a significant correlation (0.91) between the variability of the wet delay measured using a water vapour radiometer (WVR) at the Onsala site and the absolute value of the residual error in the height determination of a 134 km baseline from Onsala to Jönköping. This correlation indicates that the atmosphericvariability as inferred from the WVR data includes information on the quality of the GPS height estimate. During periods of high atmospheric activity, e.g., during the passage of a weather front, the use of a six-parameter gradient model reduces the spread for the vertical coordinate from 40 mm to 20 mm (with standard deviations of 17 mm and 9 mm respectively) over the 134 km baseline (less than 1 × 10^–7) using 8 hour data spans on 11 different days over a six month period.     

Forest cover mapping of East district,Sikkim using IRS-1A LISS II satellite data

Remote sensing techniques have been applied to classify tour density classes within each of the forest type along with other major landuse/landcover classes in the East district, Sikkim using IRS-1A LISS II satellite data pertaining to the period of November, 1988. The shadow problem in rugged terrain and difficulty in acquiring cloud free data for different seasons pose problems to achieve considerable mapping accuracy. In the present study, the forests of the district were delineated through supervised classification techniques using maximum likelihood algorithm into five forest types as sal forests, subtropical broad-leaved forests, Himalayan wet temperate forests, Rhododendron forests and alpine forests. The alpine forests were further stratified into two categories as moist alpine scrub and dry alpine scrub. The statistical data obtained from the present study shows that 55.47 percent of the total geographical area of the East district was under forest cover. An overall accuracy of more than 85 percent in correctly delineating forest classes was achieved.     

Compatibility of NMEA GGA with GPS Receivers Implementation

The NMEA GGA standard for global positioning system (GPS) and GLONASS receiver interfaces provides smooth data transfer from receiver to computer for postprocessing. Specifically, the NMEA GGA specifies that the orthometric height and the undulation be listed in addition to other quantities. The Ashtech manual (Ashtech, 1997; p. 104), however, specifies that the respective field in the NMEA GGA message contains the ellipsoidal height when outputting from Ashtech's GG24 receiver. Because such an inconsistency between the official NMEA GGA specifications and the implementation by a manufacturer can potentially confuse the user, we carried out a numerical test to confirm Ashtech's implentation. The result indicates that Ashtech indeed gives the ellipsoidal height in the fielt that should actually contain the orthometric height according to the NMEA GGA specifications. Firmware version after and including GF02 have corrected this situation. ? 2000 John Wiley & Sons, Inc.     

Variation in Coronal Activity from Solar Cycle 24 Minimum to Maximum Using Three-Dimensional Reconstructions of the Coronal Electron Density from STEREO/COR1

Three-dimensional electron density distributions in the solar corona are reconstructed for 100 Carrington rotations (CR 2054?–?2153) during 2007/03?–?2014/08 using the spherically symmetric method from polarized white-light observations with the inner coronagraph (COR1) onboard the twin Solar Terrestrial Relations Observatory (STEREO). These three-dimensional electron density distributions are validated by comparison with similar density models derived using other methods such as tomography and a magnetohydrodynamics (MHD) model as well as using data from the Solar and Heliospheric Observatory (SOHO)/Large Angle and Spectrometric Coronagraph (LASCO)-C2. Uncertainties in the estimated total mass of the global corona are analyzed based on differences between the density distributions for COR1-A and -B. Long-term variations of coronal activity in terms of the global and hemispheric average electron densities (equivalent to the total coronal mass) reveal a hemispheric asymmetry during the rising phase of Solar Cycle 24, with the northern hemisphere leading the southern hemisphere by a phase shift of 7?–?9 months. Using 14 CR (\(\approx13\)-month) running averages, the amplitudes of the variation in average electron density between Cycle 24 maximum and Cycle 23/24 minimum (called the modulation factors) are found to be in the range of 1.6?–?4.3. These modulation factors are latitudinally dependent, being largest in polar regions and smallest in the equatorial region. These modulation factors also show a hemispheric asymmetry: they are somewhat larger in the southern hemisphere. The wavelet analysis shows that the short-term quasi-periodic oscillations during the rising and maximum phases of Cycle 24 have a dominant period of 7?–?8 months. In addition, it is found that the radial distribution of the mean electron density for streamers at Cycle 24 maximum is only slightly larger (by \(\approx30\%\)) than at cycle minimum.     

Cultures monoalgales: courte description et discussion d'une méthode permettant une observation à fort grossissement des cellules avant leur isolement à l'aide d'un emporte-pièce

A method allowing isolation of phytoplancton algae for unialgal cultures is briefly described. Advantages and limits of the method are discussed.     

Precipitation variability during the past 400?years in the Xiaolong Mountain (central China) inferred from tree rings

We developed the first tree-ring chronology, based on 73 cores from 29 Pinus tabulaeformis trees, for the Xiaolong Mountain area of central China, a region at the boundary of the Asian summer monsoon. This chronology exhibits significant (at 0.01 level) positive correlations with precipitation in May and June, and negative correlations with temperature in May, June and July. Highest linear correlation is observed between tree growth and the seasonalized (April–July) precipitation, suggesting that tree rings tend to integrate the monthly precipitation signals. Accordingly, the April–July total precipitation was reconstructed back to 1629 using these tree rings, explaining 44.7?% of the instrumental variance. A severe drought occurred in the area during the 1630s–1640s, which may be related to the weakened Asian summer monsoon caused by a low land-sea thermal gradient. The dry epoch during the 1920s–1930s and since the late 1970s may be explained by the strengthened Hadley circulation in a warmer climate. The dry (wet) epochs of the 1920s–1930s (the 1750s and 1950s) occurred during the warm (cold) phases of the El Ni?o-Southern Oscillation and the Pacific Decadal Oscillation that are often associated with weakened (strengthened) East Asian summer monsoon. These relationships indicate significant teleconnections operating over the past centuries in central China related to large-scale synoptic features.     

柴北缘鱼卡地区中侏罗统石门沟组含煤层段沉积有机相分析

柴达木盆地北缘鱼卡地区中侏罗统石门沟组含煤段中发育有油页岩、煤、碳质泥岩和泥岩等富有机质细粒沉积.为了研究其沉积有机相的类型及煤和油页岩形成的控制因素,本文通过岩心观察、工业分析结合有机地球化学测试分析等方法将含煤段细粒沉积物划分为了类型A(三角洲平原沉积环境)、B(三角洲前缘-浅湖沉积环境)、C1(湖沼非油页岩亚相)及C2(湖沼油页岩亚相)四种类型,其中类型C1沉积物中发育煤,类型C2中发育油页岩,且煤较油页岩具有更高的含油率、水分、挥发分以及发热量值.有机质类型特征方面,沉积有机相类型A、B及C1沉积物有机质类型均为Ⅱ2-Ⅲ型、有机质来源均以陆源和混合来源两种有机质来源为主,而类型C2中主要为Ⅱ2型,以混合有机质来源为主;类型A及C2其沉积物有机质均处于未成熟阶段,而类型B和C1中有机质均处于未成熟-低成熟阶段;有机质保存条件方面,类型A沉积物主要形成于缺氧的淡水环境,类型B主要形成于贫氧-缺氧的淡水-半咸水环境,类型C1形成于贫氧-缺氧的淡水-半咸水环境,而类型C2则主要形成于缺氧的淡水-半咸水环境.其中类型B较类型A,类型C2较类型C1,其沉积物均形成于更为还原且盐度更高的水体环境中.石门沟组含煤段是煤和油页岩的形成层位,稳定的沉积环境、丰富的湖泊有机质来源、良好的保存条件及较少的陆源碎屑的稀释共同促进了类型C2中油页岩的形成,而丰富的陆源植物供给及良好的保存条件则促进了类型C1中煤层的形成.     

Neutron stars in the multidimensional einstein theory of gravitation

The radius, mass, total number of baryons, and other parameters of static, spherically symmetric, superdense stars are calculated. A model with one Ricci-flat inner space of arbitrary dimensionality and the approximation p₁=?0.5ε + ap for additional components of the energy — momentum tensor are used (ε and ρ are the total energy density and the pressure of the stellar matter and a is a fitting parameter). In the case of white dwarfs, the results of the multidimensional theory do not depend on the dimensionality D of space-time for ?10 ? a ? 10 and coincide with the analogous data of the general theory of relativity (GTR). For neutron stars there is a dependence on D and a. For D>4, in particular, the greatest mass M_max of a neutron star as a function of a has a maximum at 3<a(D) ? 4, which exceeds the greatest mass M _max ⁰ =2.14 M_⊙ in the GTR. A comparison of theoretical results with observational data determines the allowable values of a. Data for PSR 1913 + 16 lead to 0.2 ≤ a ≤ 9.2 in the case of D=26, while the results of [P. C. Joss and S. A. Rappaport, Annu. Rev. Astron. Astrophys.,22, 537 (1984)] lead to the stricter limits 1 ≤ a ≤ 7.4.