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1.
An experiment aboard the Scripps Institution of Oceanography's RV Thomas Washington has demonstrated the seafloor mapping advantages to be derived from combining the high-resolution bathymetry of a multibeam echo-sounder with the sidescan acoustic imaging plus wide-swath bathymetry of a shallow-towed bathymetric sidescan sonar. To a void acoustic interference between the ship's 12-kHz Sea Beam multibeam echo-sounder and the 11-12-kHz SeaMARC II bathymetric sidescan sonar system during simultaneous operations, Sea Beam transmit cycles were scheduled around SeaMARC II timing events with a sound source synchronization unit originally developed for concurrent single-channel seismic, Sea Beam, and 3.5-kHz profile operations. The scheduling algorithm implemented for Sea Beam plus SeaMARC II operations is discussed, and the initial results showing their combined seafloor mapping capabilities are presented 相似文献
2.
V. A. Shor Yu. A. Chernetenko O. M. Kochetova N. B. Zheleznov 《Solar System Research》2012,46(2):119-129
In October 2009, a new set of optical observations of Apophis, a potentially hazardous asteroid, was published. These data
have significantly expanded the interval of observations and their total number. In the article we compare the results of
refinement of Apophis’ orbit made at the Jet Propulsion Laboratory (JPL, United States), the University of Pisa (Italy), and
the Institute of Applied Astronomy (IAA) of the Russian Academy of Sciences with consideration for new observations. New orbits
lead to a significant decrease in the probability of Apophis’ collision with the Earth in 2036. As a result of processing
a large number of observations of asteroids approaching the Earth and main belt asteroids less than 40 km in size, with a
large number of optical and, in many cases, radar observations in different oppositions, one of the authors revealed that
additional acceleration affects their motion. This acceleration can be represented by the transversal component A
2 in the orbital coordinate system. The presence of this acceleration can be interpreted as the Yarkovsky effect. The statistical
properties of distribution of A
2 for asteroids, for which it is determined quite reliably, evidence in favor of this interpretation. The value of additional
acceleration for bodies the size of Apophis falls in the range ±10−13 AU/day2. In this paper we have calculated the probability of Apophis colliding with the Earth in 2036 at different values of the
transversal component of additional acceleration A
2. For the resulting points, a plot of the probability of the collision against the A
2 value has been constructed. At A
2 = −8.748 × 10−14 AU/day2 (and zero values of the radial A
1 and normal A
3 components) the nominal solution for Apophis’ orbit on April 13, 2029, is only 90 m from the middle of a “keyhole” 600 m
in width, which leads to a collision of Apophis with the Earth in 2036. Since the scattering ellipse in the target plane in
2029 significantly overlaps the keyhole, the probability of collision at the given additional acceleration value is 0.0022.
This result has been verified by the Monte Carlo method. Tests of 10000 random sets of orbital elements, which were found
taking into account their correlation, have shown that 22 cases have resulted in virtual asteroids colliding with Earth in
2036. A plot of the probability of the collision against the value of A
2 has been constructed. 相似文献
3.
A SeaMARC I side-scan sonar survey on the central Scotian Slope shows a blocky debris flow with high surface roughness between
the 1,000 and 2,000 m isobaths, covering an area of about 1,000 km2. The flow is at least 20 m thick, occuring as lenses within channels and as sheets on intervalley areas. The surface reflectivity
is variable, with blocks and depressions 50 to 200 m wide and relief of 5 to 20 m. The source zone lies within two canyons
on the upper slope and has relatively smooth surface reflectivity, in contrast to the gullied slope to either side. 相似文献
4.
Collisions in the Solar System play an important role in its history. Impact processes depend essentially on the velocity distribution of meteoroids colliding with a chosen planet. According to Carleman's theorem it is sufficient to find the set of M
k
= mathematical expectation of v
k
, v being the collisional velocity. We suppose that M
k
for meteoroids of asteroidal nature differs slightly from that for asteroids themselves. So among all numbered minor planets we select those which may potentially collide with the chosen major planet. Then we calculate v at intersection points and count the average over all such points and all selected asteroids. The gravitation of a body-target may be taken into account or not. Numerical results are collected in four Tables.St.Petersburg University 相似文献
5.
S. A. Naroenkov B. M. Shustov Yu. D. Medvedev V. A. Shor A. V. Devyatkin 《Solar System Research》2014,48(6):439-445
The concept is presented of the Russian information and analytical center for asteroid and comet hazards (IAC ACH) as a part of the national IAC for space threats. An overview is given of the center’s goals and objectives, as well as the requirements for the center, its structure, and the possible cooperation between the institutes of the Russian Academy of Sciences and other organizations in the creation of the center. 相似文献
6.
B. M. Shustov L. V. Rykhlova Yu. P. Kuleshov Yu. N. Dubov K. S. Elkin S. S. Veniaminov G. K. Borovin I. E. Molotov S. A. Naroenkov S. I. Barabanov V. V. Emel’yanenko A. V. Devyatkin Yu. D. Medvedev V. A. Shor K. V. Kholshevnikov 《Solar System Research》2013,47(4):302-314
The basic science of astronomy and, primarily, its branch responsible for studying the Solar System, face the most important practical task posed by nature and the development of human civilization—to study space hazards and to seek methods of counteracting them. In pursuance of the joint Resolution of the Federal Space Agency (Roscosmos) and the RAS (Russian Academy of Sciences) Space Council of June 23, 2010, the RAS Institute of Astronomy in collaboration with other scientific and industrial organizations prepared a draft concept of the federal-level program targeted at creating a system of space hazard detection and counteraction. The main ideas and astronomical content of the concept are considered in this article. 相似文献
7.
The nearest in time close approach of potentially hazardous asteroid (99942) Apophis with the Earth will take place on April 13, 2029, when the minimum distance of the asteroid from the Earth’s center will be as small as 38 000 km. Such a close approach will result in substantial transformation of the asteroid’s orbit. The value of the perturbations depends on the minimum distance between the bodies during the approach. Among possible transformations of the orbit are those which result in new dangerous approaches and even in probable Apophis collisions with the Earth starting from 2036. At present, at least four solutions are known for the Apophis orbit which were obtained using all radar and most of available optical observations. The procedures of assigning weights to conditional equations and the models of the asteroid’s motion have differed to some extent when finding these solutions. Of considerable interest is the comparison of the found orbital parameters with the estimates of their accuracy, since small distinctions in their values result in considerable distinctions in the forecast of Apophis’ motion after 2029 and beyond. It is shown in the paper that the estimates of the probability of an Apophis collision with the Earth in 2036 differ by some orders of magnitude, according to various solutions. The influence of factors which were disregarded in the models of motion even more increases the uncertainty in forecasting the motion after 2029. More accurate forecasting can be achieved as a result of additional optical and, to a greater extent, a series of radar observations in 2013 and then in 2020–2021, and/or as a result of processing radio signals of the transmitter delivered to the Apophis surface or to the orbit of its artificial satellite, as it was proposed in a number of papers. 相似文献
8.
Yu. D. Medvedev Yu. S. Bondarenko D. E. Vavilov V. A. Shor 《Kinematics and Physics of Celestial Bodies》2016,32(5):223-226
The most relevant tasks associated with the problem of asteroid–comet hazard are discussed. A review is given of the respective research at the Institute of Applied Astronomy. The institute is currently implementing a project to create an information center whose tasks include the collection and processing of optical and radar observations of small solar system bodies, determination of their orbits, and assessment of the impact hazard of the newly discovered small bodies with respect to the earth, moon, and the other major planets and their satellites. 相似文献
9.
T. A. Vinogradova O. M. Kochetova Yu. A. Chernetenko V. A. Shor E. I. Yagudina 《Solar System Research》2008,42(4):271-280
The results of improving the orbit accuracy for the asteroid Apophis and the circumstances of its approach to Earth in 2029 are described. Gravitational perturbations from all of the major planets and Pluto, Ceres, Pallas, and Vesta are taken into account in the equations of motion of the asteroid. Relativistic perturbations from the Sun and perturbations due to the oblateness of the Sun and Earth and due to the light pressure are also included in the model. Perturbations from the Earth and Moon are considered separately. The coordinates of the perturbing bodies are calculated using DE405. The phase correction and the gravitational deflection of light are taken into account. The numerical integration of the equations of motion and equations in variations is performed by the 15th-order Everhart method. The error of the numerical integration over the 2005–2029 interval, estimated using forward and backward computations, is not more than 3 × 10?11 AU. Improved coordinates and velocities at epoch JD2454200.5 (April 10, 2007) were obtained applying the weighted leastsquares fit. For the period from March 15, 2004, to August 16, 2006, 989 optical and 7 radar observations were used. The resulting system represents the optical observations with an error of 0.37 (66 conditional equations were rejected). The residuals of the radar observations are an order, or more, smaller than their errors. The system of Apophis’ elements and the estimates of their precision obtained in this study are in perfect agreement with the results published by other authors. The minimum Apophis-Earth distance is about 38 200 km on April 13, 2029. This estimate agrees to within 20 km with those calculated based on other published systems of elements. The effect of some model components on the minimum distance is estimated. 相似文献
10.
俄罗斯西西伯利亚和外贝加尔地区古河道型铀矿床 总被引：4，自引：0，他引：4
本文系统地介绍了俄罗斯 3个具有工业意义的古河道型铀矿化发育区 (外乌拉尔、西西伯利亚和外贝加尔 )的地质背景、铀矿化特征和铀成矿条件 ,指出切割到基底中的古河道型铀矿床 ,既可产于跨地区的造山带周围 ,也可产于活化的年青地台和古老地盾 ;既可形成于干燥的气候条件 ,也可形成于潮湿的气候条件。古河道型铀矿化可以从含矿层的沉积开始一直延续到被泥岩层或玄武岩层完全封盖。古河道的后成氧化分带有两种形式 :氧化带 铀矿化带 原生灰色岩石 ;氧化带 氧化铁再沉积带 漂白带 原生灰色岩石。古河道型铀矿床具宽广的元素谱 ,这主要是与含矿围岩富含有机质和在氧化带尖灭处存在各种地球化学障有关 相似文献