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1.
Parker D. E. Basnett T. A. Brown S. J. Gordon M. Horton E. B. Rayner N. A. 《Space Science Reviews》2000,94(1-2):309-320
A survey is given of the available instrumental data for monitoring and analysis of climatic variations. We focus on temperature measurements, both over land and ocean, at the surface and aloft.Over land, the older observations were subject to exposure changes which may not have been fully compensated. The effects of urbanization have been largely avoided in studies of climatic change over the last 150 years. There are few records for pre-1850 outside Europe and eastern North America, and the global network shows a recent decline. Over the ocean, sea surface temperature (SST) has been measured using buckets, engine intakes, hull sensors, buoys, and satellites. Many of these data have been effectively homogenized, but new challenges arise as observing systems evolve. Available SST and marine air temperature datasets begin in the 1850s. The data are concentrated in shipping lanes especially before 1900, and very sparse during the world wars, but additional historical data are being digitized.The radiosonde record is short (40 years) and has major gaps over the oceans, tropics and Southern Hemisphere. Instrumental heterogeneities are beginning to be assessed and removed using physical and statistical techniques. The MSU record is complete but only began in 1979, and is not highly resolved in the vertical: major biases, mainly affecting the lower-tropospheric retrieval, have been reduced as a result of recent analyses.Advanced interpolation or data-assimilation techniques are being applied to these data, but the results must be interpreted with care. 相似文献
2.
Parts of geodesy and physical oceanography are about to mature into a single modeling problem involving the simultaneous estimation
of the marine geoid and the general circulation. Both fields will benefit. To this end, we present an ocean state estimation
(data assimilation) framework which is designed to obtain a dynamically consistent picture of the changing ocean circulation
by combining global ocean data sets of arbitrary type with a general circulation model (GCM). The impact of geoid measurements
on such estimates of the ocean circulation are numerous. For the mean circulation, a precise geoid describes the reference
frame for dynamical signals in altimetric sea surface height observations. For the time-varying ocean signal, changing geoid
information might be a valuable new information about correcting the changing flow field on time scales from a few month to
a year, but the quantitative utility of such information has not yet been demonstrated. For a consistent estimate, some knowledge
of the prior error covariances of all data fields is required. The final result must be consistent with prior error estimates
for the data. State estimation is thus one of the few quantitative consistency checks for new geoid measurements anticipated
from forthcoming space missions. Practical quantitative methods will yield a best possible estimate of the dynamical sea surface
which, when combined with satellite altimetric surfaces, will produce a best-estimate marine geoid. The anticipated accuracy
and precision of such estimates raises some novel modeling error issues which have not conventionally been of concern (the
Boussinesq approximation, self-attraction and loading). Model skill at very high frequencies is a major concern because of
the need to de-alias the data obtained by the inevitable oceanic temporal undersampling dictated by realistic satellite orbit
configurations.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
The Gravity Recovery and Climate Experiment (GRACE), which was successfully launched March 17, 2002, has the potential to
create a new paradigm in satellite oceanography with an impact perhaps as large as was observed with the arrival of precision
satellite altimetry via TOPEX/Poseidon (T/P) in 1992. The simulations presented here suggest that GRACE will be able to monitor
non-secular changes in ocean mass on a global basis with a spatial resolution of ≈500 km and an accuracy of ≈3 mm water equivalent.
It should be possible to recover global mean ocean mass variations to an accuracy of ≈1 mm, possibly much better if the atmospheric
pressure modeling errors can be reduced. We have not considered the possibly significant errors that may arise due to temporal
aliasing and secular gravity variations. Secular signals from glacial isostatic adjustment and the melting of polar ice mass
are expected to be quite large, and will complicate the recovery of secular ocean mass variations. Nevertheless, GRACE will
provide unprecedented insight into the mass components of sea level change, especially when combined with coincident satellite
altimeter measurements. Progress on these issues would provide new insight into the response of sea level to climate change.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
V: SEA LEVEL: Benefits of GRACE and GOCE to sea level studies 总被引:1,自引:0,他引:1
The recently published Third Assessment Reports of the Intergovernmental Panel on Climate Change have underlined the scientific
interest in, and practical importance of past and potential future sea level changes. Space gravity missions will provide
major benefits to the understanding of the past, and, thereby, in the prediction of future, sea level changes in many ways.
The proposal for the GOCE mission described well the improvements to be expected from improved gravity field and geoid models
in oceanography (for example, in the measurement of the time-averaged, or ‘steady state’, ocean surface circulation and better
estimation of ocean transports), in geophysics (in the improvement of geodynamic models for vertical land movements), in geodesy
(in positioning of tide gauge data into the same reference frame as altimeter data, and in improvement of altimeter satellite
orbits), and possibly in glaciology (in improved knowledge of bedrock topography and ice sheet mass fluxes). GRACE will make
many important steps towards these ‘steady state’ aims. However, its main purpose is the provision of oceanographic (and hydrological
and meteorological) temporally-varying gravity information, and should in effect function as a global ‘bottom pressure recorder’,
providing further insight into the 3-D temporal variation of the ocean circulation, and of the global water budget in general.
This paper summaries several of these issues, pointing the way towards improved accuracy of prediction of future sea level
change.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
《中国航空学报》2021,34(9):1-10
The full constellation of Chinese Global Navigation Satellite System (GNSS) BeiDou-3 has been deployed completely and started fully operational service. In addition to providing global Positioning, Navigation and Timing (PNT) services, the BeiDou-3 satellites transmissions can also be used as the sources of illumination for Earth Observation (EO) with a bistatic radar configuration. This innovative EO concept, known as GNSS reflectometry (GNSS-R), allows to measure the Earth surface characteristics at high resolution via the reflected L-band radar signals collected by a constellation of small, low cost and low Earth orbiting satellites. For the first time in orbit, earth reflected BeiDou-3 signal has been detected from the limited sets of raw data collected by the NASA’s Cyclone GNSS (CYGNSS) constellation. The feasibility of spaceborne BeiDou-3 reflections on two typical applications, including sea surface wind and flooding inundation detection, has been demonstrated. The methodology and results give new strength to the prospect of new spaceborne GNSS-R instruments and missions, which can make multi-GNSS reflectometry observations available to better capture rapidly changing weather systems at better spatio-temporal scales. 相似文献
6.
Francis S. Johnson 《Space Science Reviews》1969,9(3):303-324
The near absence of noble gases on earth, other than those of radioactive origin, indicates that the earth was formed by the accumulation of planetesimals; this process systematically excluded all constituents that did not enter into the solid phase. The atmosphere and the ocean with many of its dissolved salts have arisen from gases emitted from the earth's interior, a process that continues today. The oxygen in the earth's atmosphere plus a greater quantity that has been removed from the atmosphere to oxidize geologic materials, has arisen mainly from a small excess of photosynthesis over decay of organic material. The atmospheres of Mars and Venus have probably arisen in a manner similar to the atmosphere on earth, by emission from the planetary interiors. However, they have not received any oxygen from photosynthesis and so are nearly oxygen free. Mars has very little water in its atmosphere, and this can be explained by its lower than freezing average surface temperature. Venus also has very little water, and this requires an ad hoc explanation; one possibility is that Venus was formed from much drier planetesimals than was the earth. Mercury and the moon are virtually without atmospheres. Although some gases may be emitted from their interiors, they are presumably rapidly lost by escape. Whatever atmosphere they possess is probably due to the neutralized solar wind that impinges upon them. The outer planets retained volatiles, including hydrogen and helium, to a much greater extent than did the terrestrial planets. 相似文献
7.
The impact of variations in solar irradiance on the variability of climate is still a topic of debate. Herein we assess the response of a coupled General Circulation Model (GCM) of intermediate complexity to an estimate of the solar variability since 1700 and to a series of idealized sinusoidal solar forcings. On the continental to global scale and averaged over periods longer than 30 years, the solar-induced variability dominates internal variability in the annual global mean surface air temperature. Locally and on the regional scale, the internal variability dominates. The dominant patterns of natural variability and explained variance are not affected by a variable solar forcing, the spectra however are sensitive. The control run shows a preferred decadal time scale of 18 year in a sea surface temperature mode associated with the North Atlantic Oscillation. The preferred decadal time scale disappears for a variable solar forcing. This is caused by small changes in oceanic circulation resulting in subsurface oceanic modes with modified structure and time scale. 相似文献
8.
Present-Day Sea Level Change: Observations and Causes 总被引:3,自引:0,他引:3
Cazenave A. Cabanes C. Dominh K. Gennero M.C. Le Provost C. 《Space Science Reviews》2003,108(1-2):131-144
We investigate climate-related processes causing variations of the global mean sea level on interannual to decadal time scale.
We focus on thermal expansion of the oceans and continental water mass balance. We show that during the 1990s where global
mean sea level change has been measured by Topex/Poseidon satellite altimetry, thermal expansion is the dominant contribution
to the observed 2.5 mm/yr sea level rise. For the past decades, exchange of water between continental reservoirs and oceans
had a small, but not totally negligible contribution (about 0.2 mm/yr) to sea level rise. For the last four decades, thermal
contribution is estimated to about 0.5 mm/yr, with a possible accelerated rate of thermosteric rise during the 1990s. Topex/Poseidon
shows an increase in mean sea level of 2.5 mm/yr over the last decade, a value about two times larger than reported by historical
tide gauges. This would suggest that there has been significant acceleration of sea level rise in the recent past, possibly
related to ocean warming.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
9.
10.
Theoretical analyses are made to determine expected relative values of average radar cross section for idealized scatterers above the sea. Horizontal, vertical, and circular polarizations are considered along with various sea states and radar depression angles. The results are considered to be useful for providing insight into effects of the sea on the polarization dependence of rain return. Effects of the earth's curvature and atmospheric refraction are neglected. 相似文献
11.
数据链作用距离的试飞结果受试验区电波传播衰减影响很大,需要对其进行精确计算,为分析试飞结果提供支持.Fock级数法是计算电波衰减的一种精确方法,本文详细讨论了应用该方法求解试验区电波传播衰减的工程计算问题. 相似文献
12.
Solar magnetic field is believed to play a central role in solar activities and flares, filament eruptions as well as CMEs
are due to the magnetic field re-organization and the interaction between the plasma and the field. At present the reliable
magnetic field measurements are still confined to a few lower levels like in photosphere and chromosphere. Although IR technique
may be applied to observe the coronal field but the technique is not well-established yet. Radio techniques may be applied
to diagnose the coronal field but assumptions on radiation mechanisms and propagations are needed. Therefore extrapolation
from photospheric data upwards is still the primary method to reconstruction coronal field. Potential field has minimum energy
content and a force-free field can provide the required excess energy for energy release like flares, etc. Linear models have
undesirable properties and it is expected to consider non-constant-alpha force-free field model. As the recent result indicates
that the plasma beta is sandwich-ed distributed above the solar surface (Gary, 2001), care must be taken in modeling the coronal
field correctly. As the reconstruction of solar coronal magnetic fields is an open boundary problem, it is desired to apply
some technique that can incorporate this property. The boundary element method is a well-established numerical techniques
that has been applied to many fields including open-space problems. It has also been applied to solar magnetic field problems
for potential, linear force-free field and non-constant-alpha force-free field problems. It may also be extended to consider
the non-force-free field problem. Here we introduce the procedure of the boundary element method and show its applications
in reconstruction of solar magnetic field problems.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
13.
Otto Schneider 《Space Science Reviews》1967,6(5):655-704
The general characteristics and dimensions of the earth's magnetosphere, turbulent transition region, and shock wave are reviewed and examined with regard to their possible active or passive interaction with the moon. The moon may, in turn, have a wake either detectable by space experiments outside the terrestrial shock wave or capable of interacting with the earth's shock wave, wake, or magnetospheric tail. The length and detectability of such a lunar wake depend, among other factors, on the selenomagnetic field and flow characteristics of the solar wind. Direct experimental information on a lunar wake is scanty, being, in fact, limited to one supposed case recorded by the IMP-1 satellite. Some evidence has been claimed, on the other hand, for statistical relationships between geomagnetic disturbance observed at the surface and the age of the moon. These results, however, are partly conflicting with each other as regards the phase of the supposed monthly variations, and partly are lacking statistical significance or merely grazing the significance level. The proximity of the lunar period with the length of the solar rotation, as well as a yearly and half-yearly modulation of the quasi-persistent 27-day fluctuations of geomagnetic disturbance contribute to encumber the question, rendering it very difficult, with the records presently available, to free the supposed lunar effects from solar interference. It seems, therefore, recommendable to postpone a judgement on the reality of such effects.Contribución del Instituto Antártico Argentino No. 109. 相似文献
14.
The azimuth and elevation angles of an airborne beacon transmitter can be determined using a direction finder comprised of two orthogonal interferometers located near the earth's surface. In this paper we consider the reflection of the incident electromagnetic field by the earth's surface and the resultant effect on the direction-finding system. The analysis yields an upper bound or limit to the interferometer phase error and the corresponding error in bearing angle that can result because of specular reflection and diffuse scattering. 相似文献
15.
Over the last few years, great strides have been made in providing access to data, both archival and near-real-time, for researchers
throughout the field of Space Science. Neutron monitor data, in particular, has for many decades enjoyed a unique history
of world-wide collaborative efforts and the unrestricted sharing of datasets among researchers. This is in large part due
to the nature of the measurements made by neutron monitors; an understanding of the time-varying, anisotropic galactic or
solar cosmic ray spectrum in most cases requires that data from a large array of stations needs to be considered, and often
that array must be global in scope. This paper will attempt to summarize the current availability of neutron monitor data,
by (a) describing the current status of archival data and near-real-time data access to neutron monitor data, and (b) looking
into the future, with an emphasis on the use of the World Wide Web and other electronic means as the source mechanism. Public
outreach efforts using active neutron monitors will also be discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
16.
Resolution Needed for an Adequate Determination of the Mean Ocean Circulation from Altimetry and an Improved Geoid 总被引:4,自引:0,他引:4
The sea surface topography observed by satellite altimetry is a combination of the geoid and of the ocean dynamic topography.
Satellite altimetry has thus the potential to supply quasi-global maps of mean sea surface heights from which the mean geostrophic
surface ocean currents can be derived, provided that the geoid is known with a sufficient absolute accuracy. At present, however,
given the limited accuracy of the best available geoid, altimetric mean sea surface topographies have been derived only up
to degree 15 or so, i.e. for wavelengths of approximately 2000 km and larger. CHAMP, GRACE, and the future GOCE missions are
dedicated to the improvement of the Earth's gravity field from space. Several studies have recently investigated the impact
of these improvements for oceanography, concluding to reductions of uncertainties on the oceanic flux estimates as large as
a factor of 2 in the regions of intense an narrow currents. The aim of this paper is to focus on what are the typical horizontal
scales of the mean dynamic topography of the ocean, and to compare their characteristics to the error estimates expected from
altimetry and these future geoids. It gives also an illustration of the oceanic features that will be resolved by the combination
of altimetry and the GRACE and GOCE geoids. It further reassesses the very demanding requirements in term of accuracy and
resolution agreed in the design of these new gravity missions for ocean science applications. The present study relies on
recent very high-resolution numerical Ocean General Circulation Model simulations.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
17.
Detection of small objects in a radar or satellite image is an important problem with many applications. Due to a recent discovery that sea clutter, the electromagnetic wave backscatter from a sea surface, is chaotic rather than purely random, computational intelligence techniques such as neural networks have been applied to reconstruct the chaotic dynamic of sea clutter. The reconstructed sea clutter dynamical system which usually takes the form of a nonlinear predictor does not only provide a model of the sea scattering phenomenon, but it can also be used to detect the existence of small targets such as fishing boats and small fragments of icebergs by observing abrupt changes in the prediction error. We applied a genetic algorithm (GA) to obtain an optimal reconstruction of sea clutter dynamic based on a radial basis function (RBF) neural network. This GA-RBF uses a hybrid approach that employes a GA to search for the optimum values of the following RBF parameters: centers, variance, and number of hidden nodes, and uses the least square method to determine the weights. It is shown here that if the functional form of an unknown nonlinear dynamical system can be represented exactly using an RBF net (i.e., no approximation error), this GA-RBF approach can reconstruct the exact dynamic from its time series measurements. In addition to the improved accuracy in modeling sea clutter dynamic, the GA-RBF is also shown to enhance the detectability of small objects embedded in the sea. Using real-life radar data that are collected in the east coast of Canada by two different radar systems: a ground-based radar and a satellite equipped with synthetic aperture radar (SAR), we show that the GA-RBF network is a reliable detector for small surface targets in various sea conditions and is practical for real-life search and rescue, navigation, and surveillance applications 相似文献
18.
The Geology of Mercury: The View Prior to the MESSENGER Mission 总被引:1,自引:0,他引:1
James W. Head Clark R. Chapman Deborah L. Domingue S. Edward Hawkins III William E. McClintock Scott L. Murchie Louise M. Prockter Mark S. Robinson Robert G. Strom Thomas R. Watters 《Space Science Reviews》2007,131(1-4):41-84
Mariner 10 and Earth-based observations have revealed Mercury, the innermost of the terrestrial planetary bodies, to be an
exciting laboratory for the study of Solar System geological processes. Mercury is characterized by a lunar-like surface,
a global magnetic field, and an interior dominated by an iron core having a radius at least three-quarters of the radius of
the planet. The 45% of the surface imaged by Mariner 10 reveals some distinctive differences from the Moon, however, with
major contractional fault scarps and huge expanses of moderate-albedo Cayley-like smooth plains of uncertain origin. Our current
image coverage of Mercury is comparable to that of telescopic photographs of the Earth’s Moon prior to the launch of Sputnik
in 1957. We have no photographic images of one-half of the surface, the resolution of the images we do have is generally poor
(∼1 km), and as with many lunar telescopic photographs, much of the available surface of Mercury is distorted by foreshortening
due to viewing geometry, or poorly suited for geological analysis and impact-crater counting for age determinations because
of high-Sun illumination conditions. Currently available topographic information is also very limited. Nonetheless, Mercury
is a geological laboratory that represents (1) a planet where the presence of a huge iron core may be due to impact stripping
of the crust and upper mantle, or alternatively, where formation of a huge core may have resulted in a residual mantle and
crust of potentially unusual composition and structure; (2) a planet with an internal chemical and mechanical structure that
provides new insights into planetary thermal history and the relative roles of conduction and convection in planetary heat
loss; (3) a one-tectonic-plate planet where constraints on major interior processes can be deduced from the geology of the
global tectonic system; (4) a planet where volcanic resurfacing may not have played a significant role in planetary history
and internally generated volcanic resurfacing may have ceased at ∼3.8 Ga; (5) a planet where impact craters can be used to
disentangle the fundamental roles of gravity and mean impactor velocity in determining impact crater morphology and morphometry;
(6) an environment where global impact crater counts can test fundamental concepts of the distribution of impactor populations
in space and time; (7) an extreme environment in which highly radar-reflective polar deposits, much more extensive than those
on the Moon, can be better understood; (8) an extreme environment in which the basic processes of space weathering can be
further deduced; and (9) a potential end-member in terrestrial planetary body geological evolution in which the relationships
of internal and surface evolution can be clearly assessed from both a tectonic and volcanic point of view. In the half-century
since the launch of Sputnik, more than 30 spacecraft have been sent to the Moon, yet only now is a second spacecraft en route
to Mercury. The MESSENGER mission will address key questions about the geologic evolution of Mercury; the depth and breadth
of the MESSENGER data will permit the confident reconstruction of the geological history and thermal evolution of Mercury
using new imaging, topography, chemistry, mineralogy, gravity, magnetic, and environmental data. 相似文献
19.
Sustaining weapons system hardware and software represents a significant and ever-increasing portion of total system cost. Hardware components are becoming obsolete much sooner while weapons system lifetimes are increasing, We must identify more cost-effective solutions to engineering and reengineering these subsystems. Verifying and validating weapons systems are two of the most costly parts of either engineering process. Traditionally, hardware validation and verification is done by simulation and testing, In the past few years, math- and logic-based formal methods tools have begun to scale up to and be applied successfully to real-world problems. Incorporating formal verification methods into engineering and reengineering processes will cost-effectively and significantly improve the level of trust and the quality of our weapons systems. Formal methods are especially well suited for redesigning current weapon systems which have become unsupportable due to component obsolescence because they help minimize the astronomical costs of rigorously reverifying the reengineered components. We believe that formal methods are an important tool for effective engineering of future weapon systems 相似文献
20.
Mars is unique to have undergone all planetary evolutionary steps, without global resets, till its geological death: this is reflected in the variety of its surface features. The determination of Mars surface composition has thus the potential to identify the processes responsible for the entire Mars evolution, from geological timescales to seasonal variations. Due to technical challenges, only few investigations have been performed so far. They are summarized in this paper, and their interpretation is discussed in terms of surface materials (minerals, ices and frosts). 相似文献