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Methods are presented for counting areas in an image in a parallel manner using noncoherent optical techniques. The techniques presented include the Levialdi algorithm for counting, optical techniques for binary operations, and cross-correlation.
Spectroheliograms obtained in extreme ultraviolet (EUV) lines and the Lyman continuum are used to determine the rotation rate of the solar chromosphere, transition region, and corona. A cross-correlation analysis of the observations indicates the presence of differential rotation through the chromosphere and transition region. The rotation rate does not vary with height. The average sidereal rotation rate is given by omega (deg/day) = 13.46-2.99 sin squared B where B is the solar latitude. This rate agrees with spectroscopic determinations of the photospheric rotation rate, but is slower by about 1 deg/day than rates determined from the apparent motion of photospheric magnetic fields and from the brightest points of active regions observed in the EUV. The corona does not clearly show differential rotation as do the chromosphere and transition region.
An experimental investigation has been conducted to compare the results obtained with six different instruments that sense fluctuating quantities in free jets. These sensors are typical of those that have recently been used by various investigators who are engaged in experimental studies of jet noise. Intensity distributions and two-point correlations with space separation and time delay were obtained. The static pressure, density, and velocity fluctuations are well correlated over the entire cross section of the jet and the cross-correlations persist for several jet diameters along the flow direction. The eddies appear to be flattened in the flow direction by a ratio of 0.4.
Simultaneous observations by identical ionization chambers aboard the satellites OGO-1 and OGO-3 are utilized to investigate spatial variations in particle intensity near and inside the magnetosphere during the solar cosmic ray events of September 1966. Cross-correlation of the absolute proton flux computed from the chamber rate during three solar particle events shows good agreement with the measurements by the IMP-F Solar Proton Monitor during the same events. The chamber has a dynamic range of over six orders of magnitude. Before launch it was calibrated in the laboratory with radiation dosages in the range 1 R/hr-6000 R/hr. The OGO-1 and OGO-3 chambers, which were normalized in the laboratory prior to the launch, are found to maintain their normalization within approximately equal to 1 per cent during their flight. The high sensitivity and absolute inter-comparability of the instruments allow small intensity differences to be detected and it is established that the observed differences can be explained by a magnetospheric screening effect when an anisotropic beam of particles is present in space. Evidence is presented to show that the screening is at times complete for a duration of as much as 110 min in the tail of the magnetosphere so that during this period the solar cosmic rays (E approximately equal to 15 MeV) have virtually no access to that region of the magnetosphere. Small intensity fluctuations of a temporal nature observed and found to be subjected to a damping effect inside the magnetosphere.
An extension is presented of Rice's classic solution for the exceedances of a constant level by a single random process to its counterpart for an n-dimensional vector process. An interaction boundary, analogous to the constant level considered by Rice for the one-dimensional case, is assumed in the form of a hypersurface. The theory for the numbers of boundary exceedances is developed by using a joint statistical approach which fully accounts for all cross-correlation effects. An exact expression is derived for the n-dimensional exceedance density function, which is valid for an arbitrary interaction boundary. For application to biaxial states of combined random stress, the general theory is reduced to the two-dimensional case. An elliptical stress interaction boundary is assumed and the exact expression for the density function is presented. The equations are expressed in a format which facilitates calculating the exceedances by numerically evaluating a line integral. The behavior of the density function for the two-dimensional case is briefly discussed.
Ultrasonic signature analysis shows promise of being a singularly well-suited method for detecting fatigue in structures as complex as aircraft. The method employs instrumentation centered about a Fourier analyzer system, which features analog-to-digital conversion, digital data processing, and digital display of cross-correlation functions and cross-spectra. These features are essential to the analysis of ultrasonic signatures according to the procedure described here. In order to establish the feasibility of the method, the initial experiments were confined to simple plates with simulated and fatigue-induced defects respectively. In the first test the signature proved sensitive to the size of a small hole drilled into the plate. In the second test, performed on a series of fatigue-loaded plates, the signature proved capable of indicating both the initial appearance and subsequent growth of a fatigue crack. In view of these encouraging results it is concluded that the method has reached a sufficiently advanced stage of development to warrant application to small-scale structures or even actual aircraft.
Properties of density fluctuations were measured in the turbulent regions of a 2.54 cm air jet, at M = 0.7, 1.0 and 1.94. After calibration tests, it was found that the absorption of infrared radiation at 4.3 microns by the naturally present quantities of carbon-dioxide in air was directly proportional to the air density if a sufficiently wide bandpass (0.08 microns) was used. Moreover, regions of the band could be selected that adequately discriminated against temperature variations. The cross-correlation of two such beams intersecting in the jet gave a measure of the local properties at the intersection point. A derivation is presented relating the local density correlation function to the self and shear generated noise in the far field of the jet. The measured correlations are used to predict the axial distribution of source strengths and the spectrum of noise due to a unit volume of turbulence.
The results of a series of experimental and analytical cavitation studies are presented. Cross-correlation is performed of the developed cavity data for a venturi, a hydrofoil and three scaled ogives. The new correlating parameter, MTWO, improves data correlation for these stationary bodies and for pumping equipment. Existing techniques for predicting the cavitating performance of pumping machinery were extended to include variations in flow coefficient, cavitation parameter, and equipment geometry. The new predictive formulations hold promise as a design tool and universal method for correlating pumping machinery performance. Application of these predictive formulas requires prescribed cavitation test data or an independent method of estimating the cavitation parameter for each pump. The latter would permit prediction of performance without testing; potential methods for evaluating the cavitation parameter prior to testing are suggested.
Preliminary evaluations of limited cross beam data taken with the rebuilt optical cross beam units at the Gun Barrel Hill Test Site of ESSA are presented. The evaluations were made using the analogue Princeton Time Correlator. A study of these evaluations indicates that the rebuilt units are performing satisfactorily. However, there are indications that, in order to obtain useful information from the cross-correlations, it is essential to make judicious choices of computation time and frequency band pass filtering for the analysis of the data.
A series of cross beam experiments was conducted at the ESSA field site at Haswell, Colorado. Both the optical visual and infrared units were operated on a comparison basis. A data report of the initial auto- and cross-correlation evaluation of these tests is presented. The original test data from the Haswell tests were recorded on F M magnetic tape. A copy of the original tapes was made and employed for the present analysis. The tapes were played back at 60 inches per second for analysis. Some of the infrared units runs (Run Nos. 8,25,40,41,42,43,44,45) were played back at 30 inches per second in order to gain sufficient averaging time. The averaging time was nominally 3200 seconds real time at 60 inches per second and 1600 seconds real time at 30 inches per second. These averaging times correspond to 100 seconds of averaging time of the correlator.
Recent experimental and theoretical studies on the sources of far field noise generated by subsonic circular jets have given convincing indications that a coherent wave motion does exist in the potential core of subsonic jets. Cross-covariance measurements using single and cross hot-wire probes in the potential core as well as the turbulent mixing region and microphone measurements in the far field have resulted in cross-correlation coefficients of sufficiently high magnitudes to indicate that significant, if not dominant, noise sources may be located in the potential core. The paper presents the analytical and experimental results of this research.
Normalized autocorrelation and cross-correlation coefficients have been calculated for the X-ray emission of Cygnus X-1 in two energy bins, 2.1-5.1 keV and 5.1-12 keV. The analysis shows a strong correlation between the pulsations in the two energy bins, with the low-energy pulsations lagging behind the high-energy ones, or alternatively a shorter duration of the pulse trains in the high-energy bin. The power spectral density derived from the autocorrelation functions indicates a larger contribution of the high-frequency components for the higher-energy X-rays.
A new method based on cross-correlation techniques is presented for studying the near- and far-field noise characteristics of a jet impinging on a surface. Analyses show that, in near and far fields, the noise characteristics due to the contribution of fluctuating pressure on the surface and due to the combined contribution of turbulence in the impinging jet and fluctuating pressure on the surface can be determined. Both far-field noise intensities and near-field acoustic energy fluxes can be expressed in terms of appropriate cross correlations. These correlations are obtained by making microphone measurements in three different regions: on the surface, in the near field, and in the far field. The method is currently being applied to study a cold, circular, subsonic jet impinging on a large rigid surface. Some preliminary experimental data are presented on fluctuating surface pressures and narrow-band far-field noise characteristics.
Existing microwave radiometer technology now provides a suitable method for remote determination of the ocean surface's absolute brightness temperature. To extract the brightness temperature of the water from the antenna temperature equation, an unstable Fredholm integral equation of the first kind was solved. Fast Fourier Transform techniques were used to invert the integral after it is placed into a cross-correlation form. Application and verification of the methods to a two-dimensional modeling of a laboratory wave tank system were included. The instability of the Fredholm equation was then demonstrated and a restoration procedure was included which smooths the resulting oscillations. With the recent availability and advances of Fast Fourier Transform techniques, the method presented becomes very attractive in the evaluation of large quantities of data. Actual radiometric measurements of sea water are inverted using the restoration method, incorporating the advantages of the Fast Fourier Transform algorithm for computations.
A technique is described for theoretical, statistical evaluation of the thrust imbalance of pairs of solid-propellant rocket motors (SRMs) firing in parallel. Sets of the significant variables, determined as a part of the research, are selected using a random sampling technique and the imbalance calculated for a large number of motor pairs. The performance model is upgraded to include the effects of statistical variations in the ovality and alignment of the motor case and mandrel. Effects of cross-correlations of variables are minimized by selecting for the most part completely independent input variables, over forty in number. The imbalance is evaluated in terms of six time - varying parameters as well as eleven single valued ones which themselves are subject to statistical analysis. A sample study of the thrust imbalance of 50 pairs of 146 in. dia. SRMs of the type to be used on the space shuttle is presented. The FORTRAN IV computer program of the analysis and complete instructions for its use are included. Performance computation time for one pair of SRMs is approximately 35 seconds on the IBM 370/155 using the FORTRAN H compiler.
Study of the cross-correlation between cosmic-ray intensity fluctuations and the interplanetary magnetic field, using the low-frequency limit of the theory of the interplanetary scintillations of cosmic rays. Cross-spectral analysis of the flux of the Alert neutron monitor and simultaneous values of the interplanetary magnetic field components are presented which support the theory. A model of cosmic-ray fluctuations is described, with effects of gradients and interplanetary sector structure dominating for very low frequencies (less than or about equal to .000005 Hz) and magnetic-field induced interplanetary scintillations of cosmic rays dominating for higher frequencies.
A microwave technique for determining the roughness (rms wave height) of a randomly varying air-water interface has been developed theoretically, verified with laboratory wavetank studies and is currently being implemented for ocean surface measurements in a series of applications flight experiments. These aircraft observations will be near the Chesapeake Light Tower and will include a range of altitudes and sea conditions. The measurement concept involves cross-correlating the envelope fluctuations on two received carriers that are monochromatic when transmitted in a normal direction to the interface and are observed in a backscatter direction after reflection by the large number of randomly distributed specular points on the surface. The measured correlation coefficient (normalized covariance) as a function of carrier frequency separation will depend on the surface roughness, specifically the probability density function of the specular point height. Details of the flight system are discussed, and preliminary flight results are presented.
Aircraft structures located in the near noise field of a jet engine are subjected to extremely high fluctuating pressures that may cause structural fatigue. Studies of such structures have been limited by lack of knowledge of the loadings involved. The acoustic near field produced by the exhaust of a stationary turbojet engine having a high pressure ratio was measured for a single operating condition without burning. The maximum overall sound pressure without afterburning was found to be about 42 pounds per square foot along the jet boundary in the region immediately downstream of the jet-nozzle exit. With afterburning maximum sound pressure was increased by 50 percent. The sound pressures without afterburning were obtained on a constant percentage band width basis in the frequency range from 350 to 700 cps. Cross-correlation measurements with microphones were made for a range of jet velocities at locations along the jet and at a distance from the jet. In general, little change in the correlation curves was found as a function of jet velocity or frequency-band width.