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1.
The Bayesian detection of discontinuities in a polynomial regression and its application to the cycle-slip problem 总被引：4，自引：1，他引：3
Maria Clara de Lacy Mirko Reguzzoni Fernando Sansò Giovanna Venuti 《Journal of Geodesy》2008,82(9):527-542
This paper deals with the problem of detecting and correcting cycle-slips in Global Navigation Satellite System (GNSS) phase
data by exploiting the Bayesian theory. The method is here applied to undifferenced observations, because repairing cycle-slips
already at this stage could be a useful pre-processing tool, especially for a network of permanent GNSS stations. If a dual
frequency receiver is available, the cycle-slips can be easily detected by combining two phase observations or phase and range
observations from a single satellite to a single receiver. These combinations, expressed in a distance unit form, are completely
free from the geometry and depend only on the ionospheric effect, on the electronic biases and on the initial integer ambiguities;
since these terms are expected to be smooth in time, at least in a short period, a cycle-slip in one or both the two carriers
can be modelled as a discontinuity in a polynomial regression. The proposed method consists in applying the Bayesian theory
to compute the marginal posterior distribution of the discontinuity epoch and to detect it as a maximum a posteriori (MAP)
in a very accurate way. Concerning the cycle-slip correction, a couple of simultaneous integer slips in the two carriers is
chosen by maximazing the conditional posterior distribution of the discontinuity amplitude given the detected epoch. Numerical
experiments on simulated and real data show that the discontinuities with an amplitude 2 or 3 times larger than the noise
standard deviation are successfully identified. This means that the Bayesian approach is able to detect and correct cycle-slips
using undifferenced GNSS observations even if the slip occurs by one cycle. A comparison with the scientific software BERNESE
5.0 confirms the good performance of the proposed method, especially when data sampled at high frequency (e.g. every 1 s or
every 5 s) are available. 相似文献
2.
When inverting large matrices, iterative techniques are necessary because of their speed and low memory requirements, as opposed to singular value decomposition (SVD). Recently, there have been attempts to obtain information on the quality of the solutions calculated using conjugate gradient (CG) methods such as LSQR. The purpose of this note is to comment on the paper titled "Estimation of resolution and covariance for large matrix inversions' by Zhang & McMechan (1995), who extend Paige and Saunders' LSQR algorithm to obtain an orthonormal basis used to approximate resolution and covariance. We show that for larger problems, where the number of orthogonal vectors is several orders of magnitude smaller than the number of model parameters, the vectors obtained do not adequately span the range of the model space. We use a synthetic borehole experiment to illustrate the differences between the singular value spectrum obtained through the more complete method of SVD and the Ritz value spectrum that results from a simple extension of LSQR, We also present a trivial numerical example to illustrate the differences between Zhang & McMechan's approximate resolution matrix and the true resolution. 相似文献
3.
Nullspace shuttles 总被引：1，自引：0，他引：1
4.
Using geodetic GPS receivers to measure vegetation water content 总被引：1，自引：0，他引：1
Wei Wan Kristine M. Larson Eric E. Small Clara C. Chew John J. Braun 《GPS Solutions》2015,19(2):237-248
5.
6.
Real-time cycle slip detection in triple-frequency GNSS 总被引：7，自引：2，他引：5
The modernization of the global positioning system and the advent of the European project Galileo will lead to a multifrequency global navigation satellite system (GNSS). The presence of new frequencies introduces more degrees of freedom in the GNSS data combination. We define linear combinations of GNSS observations with the aim to detect and correct cycle slips in real time. In particular, the detection is based on five geometry-free linear combinations used in three cascading steps. Most of the jumps are detected in the first step using three minimum-noise combinations of phase and code observations. The remaining jumps with very small amplitude are detected in the other two steps by means of two-tailored linear combinations of phase observations. Once the epoch of the slip has been detected, its amplitude is estimated using other linear combinations of phase observations. These combinations are defined with the aim of discriminating between the possible combinations of jump amplitudes in the three carriers. The method has been tested on simulated data and 1-second triple-frequency undifferenced GPS data coming from a friendly multipath environment. Results show that the proposed method is able to detect and repair all combinations of cycle slips in the three carriers. 相似文献
7.
The influence of elevation on soil properties and forest litter in the Siliceous Moncayo Massif,SW Europe 总被引：1，自引：0，他引：1
David Badía Alberto Ruiz Antonio Girona Clara Martí José Casanova Paloma Ibarra Raquel Zufiaurre 《山地科学学报》2016,13(12):2155-2169
Understanding the effects of elevation and related factors (climate, vegetation) on the physical and chemical soil properties can help to predict changes in response to future climate or afforestation forcings. This work aims to contribute to the knowledge of soil evolution and the classification of forest soils in relation to elevation in the montane stage, with special attention to podzolization and humus forms. The northern flank of the Moncayo Massif (Iberian Range, SW Europe) provides a unique opportunity to study a forest soils catena within a consistent quartzitic parent material over a relatively steep elevation gradient. With increasing elevation, pH, base saturation, exchangeable potassium, and fine silt-sized particles decrease significantly, while organic matter, the C/N ratio, soil aggregate stability, water repellency and coarse sand-sized particles increase significantly. The soil profiles shared a set of properties in all horizons: loamy-skeletal particle-size, extreme acidity (pH-H2O<5.6) and low base saturation (<50%). The most prevalent soil forming processes in the catena include topsoil organic matter accumulation and even podzolization, which increases with elevation. From the upper to lower landscape positions of wooded montane stage of the Moncayo Massif, mull-moder-mor humus and an Umbrisol-Cambisol-Podzol soil unit sequences were found. 相似文献
8.
Clara Lemos France Floc’h Marissa Yates Nicolas Le Dantec Vincent Marieu Klervi Hamon Véronique Cuq Serge Suanez Christophe Delacourt 《Ocean Dynamics》2018,68(9):1207-1220
Eleven-year long time series of monthly beach profile surveys and hourly incident wave conditions are analyzed for a macrotidal Low Tide Terrace beach. The lower intertidal zone of the beach has a pluriannual cycle, whereas the upper beach profile has a predominantly seasonal cycle. An equilibrium model is applied to study the variation of the contour elevation positions in the intertidal zone as a function of the wave energy, wave power, and water level. When forcing the model with wave energy, the predictive ability of the equilibrium model is around 60% in the upper intertidal zone but decreases to 40% in the lower intertidal zone. Using wave power increases the predictive ability up to 70% in both the upper and lower intertidal zones. However, changes around the inflection point are not well predicted. The equilibrium model is then extended to take into account the effects of the tide level. The initial results do not show an increase in the predictive capacity of the model, but do allow the model free parameters to represent more accurately the values expected in a macrotidal environment. This allows comparing the empirical model calibration in different tidal environment. The interpretation of the model free parameter variation across the intertidal zone highlights the behavior of the different zones along the intertidal beach profile. This contributes to a global interpretation of the four model parameters for beaches with different tidal ranges, and therefore to a global model applicable at a wide variety sites. 相似文献
9.
Using the classic thermoluminescence (TL) dating technique for fired ceramic materials, we have obtained the first direct ages for five ceramic artifacts recovered from BfDa-1, a prehistoric archaeological site located in St. Croix, southcentral Nova Scotia. BfDa-1 is the only archaeological site in Nova Scotia to produce the full range of ceramic styles associated with the Woodland or Ceramic Period (c. 1050 B.C. to A.D. 1500); thus our new chronology can be used to revise the current local and regional ceramic chronologies. The five sherds from the St. Croix site yielded absolute gas of 1.15 ± 0.15 ka to 2.62 ± 0.29 ka (1 ka = 1000 years). The oldest of these TL ages was obtained on a sherd decorated with a pseudoscallop shell design and is in excellent agreement with a 14C date of 2500 ± 120 B.P. associated with Early Ceramic artifacts at this site. The other TL ages are in agreement with the relative ceramic chronology deduced from their decorative attributes. All five TL dates are in the correct depth-age order. This demonstrates that the recent excavations explored a part of the site which remained undisturbed in spite of extensive agricultural and horticultural activities in the vicinity in recent centuries. The dates also indicate a high degree of compression for the cultural remains at the site. They suggest a sediment deposition rate of 1.3 cm/100 yr during the early stages of the occupation period (2000–2600 yr B.P.), and a decrease in the deposition rate to 0.5 cm/100 yr during the last 2000 years. These dates provide the first successful application of TL dating to ceramics of the Minas Basin area. They confirm an initial hypothesis based on the stylistic attributes of ceramics recovered from BfDa-1, that human occupation at the site must have been of long duration. The excellent quality of the analytical data indicates that the TL dating technique should be well suited to the study of ceramic technology in other parts of the province, and that local mineralogy is suitable for optical dating of sediments at the site and elsewhere in Nova Scotia. © 1997 John Wiley & Sons, Inc. 相似文献
10.
Connecting Satellite Observations with Water Cycle Variables Through Land Data Assimilation: Examples Using the NASA GEOS-5 LDAS 总被引：1，自引：1，他引：0
Rolf H. Reichle Gabriëlle J. M. De Lannoy Barton A. Forman Clara S. Draper Qing Liu 《Surveys in Geophysics》2014,35(3):577-606
A land data assimilation system (LDAS) can merge satellite observations (or retrievals) of land surface hydrological conditions, including soil moisture, snow, and terrestrial water storage (TWS), into a numerical model of land surface processes. In theory, the output from such a system is superior to estimates based on the observations or the model alone, thereby enhancing our ability to understand, monitor, and predict key elements of the terrestrial water cycle. In practice, however, satellite observations do not correspond directly to the water cycle variables of interest. The present paper addresses various aspects of this seeming mismatch using examples drawn from recent research with the ensemble-based NASA GEOS-5 LDAS. These aspects include (1) the assimilation of coarse-scale observations into higher-resolution land surface models, (2) the partitioning of satellite observations (such as TWS retrievals) into their constituent water cycle components, (3) the forward modeling of microwave brightness temperatures over land for radiance-based soil moisture and snow assimilation, and (4) the selection of the most relevant types of observations for the analysis of a specific water cycle variable that is not observed (such as root zone soil moisture). The solution to these challenges involves the careful construction of an observation operator that maps from the land surface model variables of interest to the space of the assimilated observations. 相似文献