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1.
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
2.
The GRACE mission will map the Earth's gravity fields and its variations with unprecedented accuracy during its 5-year lifetime.
Unless ocean tide signals and their load upon the solid earth are removed from the GRACE data, their long period aliases obscure
more subtle climate signals which GRACE aims at. In this analysis the results of Knudsen and Andersen (2002) have been verified
using actual post-launch orbit parameter of the GRACE mission. The current ocean tide models are not accurate enough to correct
GRACE data at harmonic degrees lower than 47. The accumulated tidal errors may affect the GRACE data up to harmonic degree
60. A study of the revised alias frequencies confirm that the ocean tide errors will not cancel in the GRACE monthly averaged
temporal gravity fields. The S2 and the K2 terms have alias frequencies much longer than 30 days, so they remain almost unreduced in the monthly averages. Those results
have been verified using a simulated 30 days GRACE orbit. The results show that the magnitudes of the monthly averaged values
are slightly higher than the previous values. This may be caused by insufficient sampling to fully resolve and reduce the
tidal signals at short wavelengths and close to the poles.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
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
4.
This paper presents a review of geoid error characteristics of three satellite gravity missions in view of the general problem
of separating scientifically interesting signals from various noise sources. The problem is reviewed from the point of view
of two proposed applications of gravity missions, one is the observation of the mean oceanic circulation whereby an improved
geoid model is used as a reference surface against the long term mean sea level observed by altimetry. In this case we consider
the presence of mesoscale variability during assimilation of derived surface currents in inverse models. The other experiment
deals with temporal changes in the gravity field observed by GRACE in which case a proposed experiment is to monitor changes
in the geoid in order to detect geophysical interesting signals such as variations in the continental hydrology and non-steric
ocean processes. For this experiment we will address the problem of geophysical signal contamination and the way it potentially
affects monthly geoid solutions of GRACE.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
The NASA/DLR satellite gravity mission GRACE, launched in March, 2002, will map the Earth's gravity field at scales of a few
hundred km and greater, every 30 days for five years. These data can be used to solve for time-variations in the gravity field
with unprecedented accuracy and resolution. One of the many scientific problems that can be addressed with these time-variable
gravity estimates, is post glacial rebound (PGR): the viscous adjustment of the solid Earth in response to the deglaciation
of the Earth's surface following the last ice age.
In this paper we examine the expected sensitivity of the GRACE measurements to the PGR signal, and explore the accuracy with
which the PGR signal can be separated from other secular gravity signals. We do this by constructing synthetic GRACE data
that include contributions from a PGR model as well as from a number of other geophysical processes, and then looking to see
how well the PGR model can be recovered from those synthetic data. We conclude that the availability of GRACE data should
result in improved estimates of the Earth's viscosity profile.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
7.
Tidal Models in a New Era of Satellite Gravimetry 总被引:3,自引:0,他引:3
The high precision gravity measurements to be made by recently launched (and recently approved) satellites place new demands
on models of Earth, atmospheric, and oceanic tides. The latter is the most problematic. The ocean tides induce variations
in the Earth's geoid by amounts that far exceed the new satellite sensitivities, and tidal models must be used to correct
for this. Two methods are used here to determine the standard errors in current ocean tide models. At long wavelengths these
errors exceed the sensitivity of the GRACE mission. Tidal errors will not prevent the new satellite missions from improving
our knowledge of the geopotential by orders of magnitude, but the errors may well contaminate GRACE estimates of temporal
variations in gravity. Solar tides are especially problematic because of their long alias periods. The satellite data may
be used to improve tidal models once a sufficiently long time series is obtained. Improvements in the long-wavelength components
of lunar tides are especially promising.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
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
9.
One long-standing difficulty in estimating the large-scale ocean circulation is the inability to observe absolute current
velocities. Both conventional hydrographic measurements and altimetric measurements provide observations of currents relative
to an unknown velocity at a reference depth in the case of hydrographic data, and relative to mean currents calculated over
some averaging period in the case of altimetric data. Space gravity missions together with altimetric observations have the
potential to overcome this difficulty by providing absolute estimates of the velocity of surface oceanic currents. The absolute
surface velocity estimates will in turn provide the reference level velocities that are necessary to compute absolute velocities
at any depth level from hydrographic data.
Several studies have been carried out to quantify the improvements expected from ongoing and future space gravity missions.
The results of these studies in terms of volume flux estimates (transport of water masses) and heat flux estimates (transport
of heat by the ocean) are reviewed in this paper. The studies are based on ocean inverse modeling techniques that derive impact
estimates solely from the geoid error budgets of forthcoming space gravity missions. Despite some differences in the assumptions
made, the inverse modeling calculations all point to significant improvements in estimates of oceanic fluxes. These improvements,
measured in terms of reductions of uncertainties, are expected to be as large as a factor of 2.
New developments in autonomous ocean observing systems will complement the developments expected from space gravity missions.
The synergies of in situ and satellite observing systems are considered in the conclusion of this paper.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
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
11.
Monitoring Changes in Continental Water Storage with GRACE 总被引:1,自引:0,他引:1
The Gravity Recovery and Climate Experiment, GRACE , will enable the recovery of monthly estimates of changes in water storage,
on land and in the ocean, averaged over arbitrary regions having length scales of a few hundred km and larger. These data
will allow the examination of changes in the distribution of water in the ocean, in snow and ice on polar ice sheets, and
in continental water and snow storage. Extracting changes in water storage from the GRACE dataset requires the use of averaging
kernels which can isolate a particular region. To estimate the accuracy to which continental water storage changes in a few
representative regions may be recovered, we construct a synthetic GRACE dataset from global, gridded models of surface-mass
variability. We find that regional changes in water storage can be recovered with rms error less than 1 cm of equivalent water
thickness, for regions having areas of 4 × 105 km2 and larger. Signals in smaller regions may also be recovered; however, interpretations of such results require a careful
consideration of model resolution, as well as the nature of the averaging kernel.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
12.
Possible Future Use of Laser Gravity Gradiometers 总被引:1,自引:0,他引:1
With the GRACE mission under way and the GOCE mission well along in the design process, detailed questions concerning the
type of future mission that may follow them have arisen. It is generally agreed that determining the time variations in the
Earth's gravity field with as high spatial and temporal resolution as is feasible will be the main driver for such a mission.
The possible use of laser heterodyne measurements between separate satellites in such a mission has been discussed by a number
of people. The first suggestion of emphasizing time variation measurements in a laser mission was the TIDES concept presented
in 1992 by Colombo and Chao. Then, in 2000, a GRACE Follow-On mission using laser measurements between two drag-free satellites
was discussed by Watkins el al. (2000).
More recently, the possibility of utilizing laser measurements between more than two satellites in order to determine two
or more components of the gravity gradient tensor simultaneously has been proposed by Balmino. This approach may be desirable
in order to reduce the aliasing of time variations between geopotential terms of different degree and order, as well as to
improve the resolution in longitude, despite the cost of the additional satellites. In this paper, we discuss specific possible
mission geometries for measuring the two diagonal in-plane components of the gravity gradient tensor simultaneously. This
could be done, for example, by laser heterodyne measurements between two pairs of satellites in coplanar and nearly polar
orbits.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
13.
Geodetic Methods for Calibration of GRACE and GOCE 总被引:2,自引:0,他引:2
It is beyond doubt that calibration and validation are essential tools in the process of reaching the goals of gravity missions
like GRACE and GOCE and to obtain results of the highest possible quality. Both tools, although general and obvious instruments
for any mission, have specific features for gravity missions. Therefore, it is necessary to define exactly what is expected
(and what cannot be expected) from calibration and what from validation and how these tools should work in our case. The general
calibration and validation schemes for GRACE and GOCE are outlined. Calibration will be linked directly to the instrument
and the measurements whereas validation will be linked to data derived from the original measurements. Calibration includes
on-ground, internal, and external calibration as well as error assessment. The calibration phase results in corrected measurements
along with an a posteriori error model. Validation of e.g. calibrated measurements or geoid heights means checking against
independent data to assess whether there are no systematic errors left and/or whether the error model describes the true error
reasonably well. Geodetic methods for calibration typically refer to external calibration and error assessment, and will be
illustrated with an example.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
14.
Spaceborne GPS receiver antenna phase center offset and variation estimation for the Shiyan 3 satellite 总被引:3,自引:2,他引:1
《中国航空学报》2016,(5):1335-1344
In determining the orbits of low Earth orbit (LEO) satellites using spaceborne GPS, the errors caused by receiver antenna phase center offset (PCO) and phase center variations (PCVs) are gradually becoming a major limiting factor for continued improvements to accuracy. Shiyan 3, a small satellite mission for space technology experimentation and climate exploration, was developed by China and launched on November 5, 2008. The dual-frequency GPS receiver payload delivers 1 Hz data and provides the basis for precise orbit determination within the range of a few centime-ters. The antenna PCO and PCV error characteristics and the principles influencing orbit determi-nation are analyzed. The feasibility of PCO and PCV estimation and compensation in different directions is demonstrated through simulation and in-flight tests. The values of receiver antenna PCO and PCVs for Gravity Recovery and Climate Experiment (GRACE) and Shiyan 3 satellites are estimated from one month of data. A large and stable antenna PCO error, reaching up to 10.34 cm in the z-direction, is found with the Shiyan 3 satellite. The PCVs on the Shiyan 3 satellite are estimated and reach up to 3.0 cm, which is slightly larger than that of GRACE satellites. Orbit validation clearly improved with independent k-band ranging (KBR) and satellite laser ranging (SLR) measurements. For GRACE satellites, the average root mean square (RMS) of KBR resid-uals improved from 1.01 cm to 0.88 cm. For the Shiyan 3 satellite, the average RMS of SLR resid-uals improved from 4.95 cm to 4.06 cm. 相似文献
15.
Long-range surveillance radars use MTI techniques to detect moving targets in a clutter background. The transmitter PRF is usually staggered to eliminate the blind speeds due to aliasing of the target and clutter spectra. A spectral analysis of the target and clutter signals is performed for the case of nonuniform sampling, and it is shown that the clutter spectral density continues to fold over at the basic PRF, but the signal spectrum becomes dispersed in frequency, which means that an MTI rader will never be completely blind to moving targets. 相似文献
16.
在基于数字卫星电视信号的无源探测系统中,分析其波形特点,探讨其用于雷达照射源信号的性能,对于整个系统研究来说,具有重要的意义。文中以“鑫诺一号”卫星为例,给出了基于“鑫诺一号”卫星参数为数字卫星电视信号的模型,并对该模型进行了仿真。仿真结果表明,数字卫星直播电视信号作为无源探测雷达的照射源信号具有较强的适应性,是一种优良的照射源信号。 相似文献
17.
星载GPS测量数据预处理方法研究 总被引:1,自引:1,他引:0
针对低地球轨道(LEO)卫星星载全球定位系统(GPS)接收机应用的特点,对星载GPS测量数据误差及其对周跳探测的影响进行了分析,提出TurboEdit数据预处理方法中周跳探测算法的改进算法。在原周跳判断算法的基础上,通过引入与测量数据观测高度角相关的加权系数,将周跳探测与测量误差紧密联系起来。根据观测高度角的变化对测量数据误差进行估计,并根据估计情况对加权系数取值,从而实现对周跳探测算法进行调节,达到降低周跳探测失误率的目的。增加参与定轨计算的观测数据量,提高了低轨卫星连续定轨的能力。通过GRACE编队卫星实测数据对改进算法进行了仿真验证。 相似文献
18.
This paper describes the application of a simulation software and the comparison of its results with actual data recorded from operating ATC radars in S and L bands. Results obtained in an application on actual signals (relative to commercial aircraft echoes) collected from observations on the echo received at an ATC radar system are presented. These signals were recorded along many field experiments carried out by the authors on a recording system specifically developed for this purpose. Due to the constitutive and operative characteristics of the systems, the results are affected by a low spectral resolution and a strong aliasing which give rise to problems in a correct analysis. The observed results have been related to the physical phenomena generated by the structure of the complex target we suppose to be made of a rigid body and rotating parts which originate such a modulation on the echo signal that it is known in related literature as Jet Engine Modulation (JEM). These phenomena may be regarded as a signature of the particular couple “engine-aircraft body” and in some flight conditions may offer significant help to a correct characterization of the aircrafts 相似文献
19.
卫星导航接收机矢量跟踪环路的核心就是用一个Kalman滤波器将标量接收机的信号跟踪和导航解算一起完成,优点是能够形成通道之间的相互辅助,缺点是也会相互影响。尤其在部分卫星信号被遮挡或者部分通道信号质量较差的环境下,问题通道会影响其他通道,甚至导致矢量跟踪环路滤波器发散,常规的方法是检测故障通道然后将故障通道剔除,这样需要对导航滤波器进行变维操作。针对此问题,提出了一种新的消除问题通道对其他通道影响的方法,同时不需要对导航滤波器进行变维。首先给出了一种标度因子,用来判断通道是否存在故障通道,然后给出一种利用模糊控制的导航滤波器自适应调整方法。仿真表明,在通道卫星信号被频繁遮挡的极端情况,矢量接收机依旧能保持正常的导航精度,并没有明显受到误差通道的影响,同时避免了对导航滤波器进行变维操作。 相似文献
20.
Application of successive interference cancellation to the GPS pseudolite near-far problem 总被引:4,自引:0,他引:4
Madhani P.H. Axelrad P. Krumvieda K. Thomas J. 《IEEE transactions on aerospace and electronic systems》2003,39(2):481-488
Ground-based transmitters called pseudolites have been proposed to augment the basic Global Positioning System (GPS) in environments where satellite visibility is limited. One difficulty in their use is the so-called near-far problem, where in close proximity to the ground transmitter, the pseudolite signal can be orders of magnitude stronger than the satellite signals. This large range of signal levels prevents a conventional receiver from simultaneously detecting both types of signals. This paper describes the application of a signal processing technique, known as successive interference cancellation (SIC), to the acquisition and tracking of weak satellite signals in the presence of a nearby pseudolite and possible multipath reflections of this pseudolite signal. The SIC architecture is implemented on simulated and experimental near-far data sets. The results are compared with a conventional detector and improvements in acquisition and tracking performance are illustrated. 相似文献