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101.
General sufficiency conditions are developed for the stability of a discrete-time cascaded-filter architecture. An application of the result is in the filtering of prefiltered Global Positioning System (GPS) data during times in which the GPS receiver is tracking less than four satellites. Simulation results are presented for the case where the master filter processes the GPS filter estimate after the GPS filter attains uniform complete observability and controllability following its third filter cycle as well as the case where the observability condition is not met 相似文献
102.
The problems of attitude control of a Skylark rocket are considered on the specific occasion of a night flight during which, of course, the sun was not available as a pointing vector. Pointing was achieved using magnetometers, while roll control was obtained using a suitably placed moon sensor. The logical sequence, as well as the electronic solution, that insured the acquisition of the correct payload orientation is presented. 相似文献
103.
104.
Two-dimensional cross-correlation techniques are applied to the problem of image registration under the assumption of small geometric distortion. Optimum filter functions for use with arbitrary window functions are derived for two performance measures of interest: peak-to-sidelobe ratio, and mean- square registration error; the latter is examined in terms of the contribution due to distortion and the contribution due to noise. A generalized Lagrange multiplier approach is used to derive at least approximate ate solutions to the case where the images are modeled as random processes and to the case where the images are assumed to be deterministic. 相似文献
105.
106.
We present data on the solar irradiance as derived from a number of sources. An attempt was made to bring these data onto a uniform scale. The results are presented in Table IV and Figure 6. Summation of fluxes at all wavelengths yields a figure of 1357.826 W m-2 for the solar constant. Estimates are made of the solar flux variations due to flares, active regions (slowly varying component), solar rotation and the 11-year cycle.Solar activity does not produce a significant variation in the value of the solar constant. Nevertheless, variations in the X-ray and extreme ultraviolet portions of the solar flux may be several orders of magnitude during solar activity, especially at times of major flares. It is well established that these short wavelength flux enhancements cause significant changes in the terrestrial ionosphere. 相似文献
107.
M. van der Klis A. Peacock A. Smith N. White K. Mason G. Manzo 《Space Science Reviews》1985,40(1-2):297-304
Cygnus X-3 was observed with the GSPC on board EXOSAT on several occasions, one observation lasting for 7 orbital cycles. The width W and centroid energy E of the iron emission feature near 6.7 keV show a smooth, correlated, sinusoidal-type modulation, the iron line being widest and E being lowest just before X-ray maximum. The line profile may show a low-energy wing, but apart from this does not deviate strongly from a symmetric, Gaussian-type shape. The continuum at higher energies than the line is not completely smooth, but shows bumps which remain stable in time. Two possible explanations are discussed for the correlated variation of E and W as a function of orbital phase. 相似文献
108.
M.J. Smith 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1983,3(1):25-28
In the 95km height region of the atmosphere, ground-based techniques made an important contribution to the CIRA 72 [1] wind model. Recent wind measurements from a partial reflection experiment at 44S covering one and a half years are presented and compared with CIRA 72. The zonal wind component compares favourably, although the measured values are more easterly above 80km in autumn and winter; a feature of the autumn winds is a temporary easterly reversal above 90km. Winter mesospheric winds can be very disturbed. The summer mesosphere easterly maximum appears earlier in the season and at a higher altitude than the model. A much poorer comparison is shown between the measured meridional wind component and the 1969 model of Groves [2]. 相似文献
109.
M. Friedrich K.D. Baker A. Brekke P.H.G. Dickinson A. Dumbs B. Grandal E.V. Thrane L.G. Smith K.M. Torkar 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(10):81-84
Electron density profiles from ground based and rocket borne measurements are presented which were derived at three sites in northern Scandinavia under various degrees of geophysical disturbance. These data are checked against the instantaneous picture of the ionospheric absorption as observed with the dense riometer network. 相似文献
110.
The effect of geometric distortion on the local accuracy of the image registration algorithms using cross correlation is presented. Using a probabilistic model describing images as homogeneous random patterns, expressions for the mean and covariance of the local error vector in terms of image and noise autocorrelation functions, geometric distortion, and reference image area are derived. The geometric distortions considered are those represented by an affine transformation of image coordinates. It is shown that for a fixed geometric distortion there is an image size (integration area) that minimizes the local error. The optimum area decreases with increasing geometric distortion. 相似文献