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21.
Methodology for comparing two carrier phase tracking techniques 总被引：1，自引：0，他引：1
The carrier phase tracking loop is the primary focus of the current work. In particular, two carrier phase tracking techniques
are compared, the standard phase tracking loop, i.e., the phase lock loop (PLL), and the extended Kalman filter (EKF) tracking
loop. In order to compare these two different techniques and taking into consideration the different models adopted in each,
it is important to bring them to one common ground. In order to accomplish this, the equivalent PLL for a given EKF has to
be determined in terms of steady-state response to both thermal noise and signal dynamics. A novel method for experimentally
calculating the equivalent bandwidth of the EKF is presented and used to evaluate the performance of the equivalent PLL. Results
are shown for both the L1 and L5 signals. Even though the two loops are designed to track equivalent dynamics and to have
equivalent carrier phase standard deviations, the EKF outperforms the equivalent PLL in terms of both the transient response
and sensitivity. 相似文献
22.
Summary From a data set of sea-breeze observations corresponding to cases of no synoptic-scale flow in Barcelona during the period 1970–89, some features of this wind have been deduced. Maximum velocities of between 6–14 m/s generally occur during 12–16 SLT. Diurnal evolution gives a clockwise rotation of sea breeze so that this wind blows roughly parallel to the shoreline in late afternoon. The rate of the change of direction is in agreement with numerical results from a simple nonlinear sea breeze model.With 7 FiguresThis work has been supported by the DGICYT, Project No. PB87-0718. 相似文献
23.
M. C. Casas B. Codina A. Redaño J. Lorente 《Theoretical and Applied Climatology》2004,77(3-4):139-150
Summary From a large data set (1927–1992) of rainfall rate in Barcelona, the relationship between maximum rainfall rates for time intervals between 5 minutes and 24 hours has been investigated. Intensity-Duration-Frequency (IDF) curves and their master equation for every return period in Barcelona have been obtained. A cluster analysis has yielded four main classes of extreme rainfall events in this area, corresponding to durations shorter than 35 minutes, 1 hour, 2–6 hours and those longer than 6 hours respectively. An index to classify extreme rainfall events has been proposed. This index gives some information about the severity of storms taking into account the contribution of different scales implied in rainfall processes. 相似文献
24.
BVRI CCD photometry of the poorly studied open cluster NGC 6724 has been carried out down to a limiting magnitude of V ～20 mag. The stars of the cluster have been observed using the Newtonian focus(f/4.84) of the 74-inch telescope at Kottamia Astronomical Observatory in Egypt.Also, the 2 MASS-JHK system is used to confirm the results we obtained. The main photometric parameters have been estimated for the present object; the diameter is found to be 6 arcmin, the distance is 1530±60 pc from the Sun and the age is 900±50 Myr. The optical reddening E(B-V) = 0.65 mag,while the infrared reddening is E(J-H) = 0.20 mag. The slope of the mass function distribution and the relaxation time estimations indicate that cluster NGC 6724 is dynamically relaxed. 相似文献
25.
We have studied solar activity by analyzing naked-eye sunspot observations and aurorae borealis observed at latitudes below \(45^{\circ}\). We focused on the medieval epoch by considering the non-telescopic observations of sunspots from AD 974 to 1278 and aurorae borealis from AD 965 to 1273 that are reported in several Far East historical sources, primarily in China and Korea. After setting selection rules, we analyzed the distribution of these individual events following the months of the Gregorian calendar. In December, an unusual peak is observed with data recorded in both China and Japan, but not within Korean data.In extreme conditions, where the collection of events is reduced and discontinuous in some temporal intervals, we used the non-parametric kernel method. We opted for the plug-in approach of Sheather and Jones instead of cross-validation techniques to estimate the probability density functions (pdf) of the events. We obtained optimized bandwidths of 13.29 years for sunspots and 9.06 years for auroras, and 95% confidence intervals. The pdf curves exhibit multiple peaks occurring at quasi-periodic times with a very high positive correlation, \(r_{\mathrm{tt}} = 0.9958\), between the dates of occurrence of the nine extrema of sunspots and auroras. Furthermore, these extrema enabled us to evaluate mean periods at two standard deviations, \(66.77 \pm 7.25~\mbox{years}\) for sunspots and \(65.06 \pm 9.36~\mbox{years}\) for auroras. The accuracy of the average periods, 62.00 years for sunspots and 61.80 years for auroras, was improved by the use of the power spectrum method. The percentage of the total number of non-observed sunspots, using redundant data, from AD 1151 to 1275 was estimated to be greater than or equal to 78%. 相似文献
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G. Delgado A. Redaño J. Lorente R. Nieto L. Gimeno P. Ribera D. Barriopedro R. García-Herrera A. Serrano 《Meteorology and Atmospheric Physics》2007,96(1-2):141-157
Summary This paper reports a cloud cover analysis of cut-off low pressure systems (COL) using a pattern recognition method applied
to IR and VIS bispectral histograms. 35 COL occurrences were studied over five years (1994–1998). Five cloud types were identified
in COLs, of which high clouds (HCC) and deep convective clouds (DCC) were found to be the most relevant to characterize COL
systems, though not the most numerous.
Cloud cover in a COL is highly dependent on its stage of development, but a higher percentage of cloud cover is always present
in the frontal zone, attributable due to higher amounts of high and deep convective clouds. These general characteristics
are most marked during the first stage (when the amplitude of the geopotencial wave increases) and second stage (characterized
by the development of a cold upper level low), closed cyclonic circulation minimizing differences between rearward and frontal
zones during the third stage. The probability of heavy rains during this stage decreases considerably. The centres of mass
of high and deep convective clouds move towards the COL-axis centre during COL evolution. 相似文献
28.
R. Nieto L. Gimeno L. De la Torre P. Ribera D. Barriopedro R. García-Herrera A. Serrano A. Gordillo A. Redaño J. Lorente 《Meteorology and Atmospheric Physics》2007,96(1-2):85-101
Summary An earlier developed multidecadal database of Northern Hemisphere cut-off low systems (COLs), covering a 41 years period (from
1958 to 1998) is used to study COLs interannual variability in the European sector (25°–47.5° N, 50° W–40° E) and the major
factors controlling it. The study focus on the influence on COLs interannual variability, of larger scale phenomena such as
blocking events and other main circulation modes defined over the Euro-Atlantic region. It is shown that there is a very large
interannual variability in the COLs occurrence at the annual and seasonal scales, although without significant trends. The
influence of larger scale phenomena is seasonal dependent, with the positive phase of the NAO favoring autumn COL development,
while winter COL occurrence is mostly related to blocking events. During summer, the season when more COLs occur, no significant
influences were found. 相似文献
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Summary In order to derive some statistical rainfall characteristics applicable to hydrology, data of continuous rainfall rate recordings of a Jardí gauge installed in Barcelona (Spain) have been converted to an hourly precipitation series. From these data, four useful distributions have been obtained and further compared with some theoretical models. It has been found that the duration of events is distributed exponentially. The duration of rainless intervals follow a generalized Pareto distribution, and the cumulative rainfall in the cumulative rain duration is beta distributed. Concerning the distribution of rain amounts, two models can be accepted, depending on the duration of the events. Comparison with a similar study carried out in Farnborough (United Kingdom) indicates that the events are shorter and that the amounts of rain collected in short events are larger in Barcelona.This work was supported by the DGICYT (Project NAT91-0596) and the CCE (Project PL 910104 Environment).With 7 Figures 相似文献