The accuracy of the high resolution infrared radiometer on Nimbus 2
Data processing and error analysis of noise and systematic errors in high resolution infrared radiometer cloud cover data from Nimbus 2
Williamson, E. J.↗
SEARCH · Engineering Papers
Results for “Process noise”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Pyrometer for measurement of surface temperature distribution on a rotating turbine blade
A conceptual optical method and some test results are presented for measuring the surface temperature distribution on one of the rotating turbine blades with a surface resolution of 0.05 cm spot diameter at a tip speed of 400 m/sec. The blade is scanned line-by-line by a fixed optical system. During each line-scan, the detector analog output signal is converted to two hundred consecutive digital values that are temporarily stored in a high speed buffer memory, and then transferred at a slower rate to a computer for processing. The signal-to-noise ratio of the silicon avalanche detector is large enough to obtain an accuracy of one percent at 1050 K blade temperature. By averaging 25 scans of the same line the same accuracy can be obtained at 900 K.
Buchele, D. R.↗
Pyrometer for measurement of surface temperature distribution on a rotating turbine blade.
A conceptual optical method and some test results are presented for measuring the surface temperature distribution on one of the rotating turbine blades with a surface resolution of 0.05 cm spot diameter at a tip speed of 400 m/sec. The blade is scanned line-by-line by a fixed optical system. During each line-scan, the detector analog output signal is converted to 200 consecutive digital values that are temporarily stored in a high-speed buffer memory and then transferred at a slower rate to a computer for processing. The signal-to-noise ratio of the silicon avalanche detector is large enough to obtain an accuracy of 1% at 1050 K blade temperature. By averaging 25 scans of the same line the same accuracy can be obtained at 900 K.
Buchele, D. R.↗
Solution of the stochastic control problem in unbounded domains.
Bellman's dynamic programming equation for the optimal index and control law for stochastic control problems is a parabolic or elliptic partial differential equation frequently defined in an unbounded domain. Existing methods of solution require bounded domain approximations, the application of singular perturbation techniques or Monte Carlo simulation procedures. In this paper, using the fact that Poisson impulse noise tends to a Gaussian process under certain limiting conditions, a method which achieves an arbitrarily good approximate solution to the stochastic control problem is given. The method uses the two iterative techniques of successive approximation and quasi-linearization and is inherently more efficient than existing methods of solution.
Robinson, P.↗
Combustion contribution to noise in jet engines
The relative importance of combustion as a source of noise in a flow regime representative of a subsonic jet engine exhaust was investigated. The combustion noise source characteristics were obtained from pressure and temperature fluctuation measurements in the combustor and exhaust nozzle. The similarity between the fluctuations in this source region and the far field noise were compared. In the jet exhaust velocity range between 450 and 660 ft/sec investigated in detail, the frequencies of dominant pressure and temperature fluctuations in the combustor were also the frequencies of the dominant far field noise. The overall noise levels were 14 to 20 dB higher than from a corresponding clean jet in the same velocity range. Thus it seemed clear that the unsteadiness associated with the combustion process was responsible for the dominant noise in the far field. A simple analysis to predict the far field noise due to the internal pressure fluctuations causing exit plane velocity fluctuations produced trends closely resembling the measured results, but under predicted the far field noise over the spectral range examined. The possible reason for the higher far field noise is direct transmission of acoustic waves through the nozzle, which was not accounted for in the prediction scheme.
Plett, E. G.↗
Initial development of a method of significant waveheight estimation for GEOS-III
The numerical method by which ocean surface significant waveheight estimates are produced from the GEOS-3 radar altimeter data is described. Four parameters characterizing the expected radar mean return waveform are determined from the altimeter's sixteen sample-and-hold waveform samplers through use of an iterative, least squares approach. One of the four parameters is a risetime term which has contributions from both the transmitted radar pulse width and the rms ocean surface height; the estimated significant waveheight is extracted from this risetime. The noise character of the estimation process leads to occasional negative significant waveheight estimates, and the origin of these nonphysical negative results is discussed. Possible modifications and areas for additional investigation are indicated.
Hayne, G. S.↗
A unique method to study acoustic transmission through ducts using signal synthesis and averaging of acoustic pulses
An acoustic impulse technique using a loudspeaker driver is developed to measure the acoustic properties of a duct/nozzle system. A signal synthesis method is used to generate a desired single pulse with a flat spectrum. The convolution of the desired signal and the inverse Fourier transform of the reciprocal of the driver's response are then fed to the driver. A signal averaging process eliminates the jet mixing noise from the mixture of jet noise and the internal noise, thereby allowing very low intensity signals to be measured accurately, even for high velocity jets. A theoretical analysis is carried out to predict the incident sound field; this is used to help determine the number and locations of the induct measurement points to account for the contributions due to higher order modes present in the incident tube method. The impulse technique is validated by comparing experimentally determined acoustic characteristics of a duct-nozzle system with similar results obtained by the impedance tube method. Absolute agreement in the comparisons was poor, but the overall shapes of the time histories and spectral distributions were much alike.
Salikuddin, M.↗
ROLM computers in the flight testing of the Fokker F29 aircraft
The design, development, installation, and operation of the test equipment (MRVS) is discussed. The main feature of the MRVS is continuous recording on an instrumentation recorder data of up to 1500 parameters with a total sample rate of up to 10,000 samples per second. In order to compress the evaluation and calibration time period, the following additional requirements were set for two test systems: (1) recording of selected parameters, time tagged on computer compatible tape (CCT); (2) recording of selected high bandwidth signals and ad hoc parameters on analog tape; (3) onboard presentation of calibrated parameter data, in engineering units, in numerical as well as graphical form for: system checkout during pre-, in- and post-flight, and quick look analysis during in-flight; (4) real time presentation on the ground by telemetry for: flight monitoring, takeoff and landing measurements, and noise measurements; and (5) data processing on the ground on the Fokker-NLR computer network.
Manders, P. J.↗
Simulation and studies of spaceborne synthetic aperture radar image quality with reduced bit rate
A computer simulation program that is used to study the effects of digitization in spaceborne synthetic aperture radar systems is described. An analytical study of the distortion noise introduced by the digitization process at various gain settings, sampling rates and bit error rates is presented and the results agree well with those obtained from the simulation program. The simulation program is also used to study the spatial frequency response of hard-limiting (quantizing to 1-bit) synthetic aperture radar systems. The implications of these results on synthetic aperture radar system design are discussed.
Li, F.↗
Effects of photon noise on speckle image reconstruction with the Knox-Thompson algorithm
An analysis of the effects of photon noise on astronomical speckle image reconstruction using the Knox-Thompson algorithm is presented. It is shown that the quantities resulting from the speckle average arre biased, but that the biases are easily estimated and compensated. Calculations are also made of the convergence rate for the speckle average as a function of the source brightness. An illustration of the effects of photon noise on the image recovery process is included.
Nisenson, P.↗
The information content of synthetic aperture radar images of terrain
A statistical model is developed that portrays an imaging radar as a noisy communication channel with multiplicative noise, and the model is used to evaluate the average amount of information that can be extracted about a target from its radar image. The average information content is also used to define a measure of radiometric resolution for radar images. It is shown that the information content and the resolution capabilities of an imaging radar reach a limit beyond which an increase in scene dynamic range does not improve the information content or the resolution. This limitation results from the multiplicative nature of the noise introduced in the imaging process.
Frost, V. S.↗
Numerical simulations of magnetospheric plasmas - Review and quadrennial report to the IUGG
This article provides a broad survey of U.S. progress during the quadrennium 1983-1986 in the category 'numerical simulations of magnetospheric plasmas'. There has been a substantial increase of activity in this area during this period. Simulations have been instrumental in providing valuable insights into large scale dynamic phenomena, nonlinear effects, and complex kinetic phenomena in a wide variety of subject areas, including shocks and double layers, ionosphere-magnetosphere coupling phenomena, and important microphysical processes such as broadband electrostatic noise. The methodology of computer simulation has also been advanced during this quadrennium. Vlasov algorithms have been improved; hybrid codes in 2 and 3D have been developed and applied to magnetospheric problems; and complex problems have been subjected with increasing frequency to a multipronged attack in which several types of simulation models, each designed to accurately model phenomena within a particular range of temporal or spatial scales, are employed synergistically.
Palmadesso, Peter J.↗
A digital beacon receiver
A digital satellite beacon receiver is described which provides measurement information down to a carrier/noise density ratio approximately 15 dB below that required by a conventional (phase locked loop) design. When the beacon signal fades, accuracy degrades gracefully, and is restored immediately (without hysteresis) on signal recovery, even if the signal has faded into the noise. Benefits of the digital processing approach used include the minimization of operator adjustments, stability of the phase measuring circuits with time, repeatability between units, and compatibility with equipment not specifically designed for propagation measuring. The receiver has been developed for the European Olympus satellite which has continuous wave (CW) beacons at 12.5 and 29.7 GHz, and a switched polarization beacon at 19.8 GHz approximately, but the system can be reconfigured for CW and polarization-switched beacons at other frequencies.
Ransome, Peter D.↗
Formulation and verification of frequency response system identification techniques for large space structures
The advantages of designing control systems for large space structures (LSS) using frequency-domain models extracted from empirical time data are discussed. Techniques for performing MIMO system identification from test data are presented as well as techniques for improving the performance of the system identification process in the presence of noise. The utility of the proposed system identification scheme is demonstrated on the basis of experimental data obtained at the LSS Ground Test Facility at Marshall Space Flight Center.
Mitchell, Jerrel R.↗
Inhomogeneous diffusion-limited aggregation
It is demonstrated here that inhomogeneous diffusion-limited aggregation (DLA) model can be used to simulate viscous fingering in a medium with inhomogeneous permeability and homogeneous porosity. The medium consists of a pipe-pore square-lattice network in which all pores have equal volume and the pipes have negligible volume. It is shown that fluctuations in a DLA-based growth process may be tuned by noise reduction, and that fluctuations in the velocity of the moving interface are multiplicative in form.
Selinger, Robin Blumberg↗
Dynamics of a class of vortex rings
The contour dynamics method is extended to vortex rings with vorticity varying linearly from the symmetry axis. An elliptic core model is also developed to explain some of the basic physics. Passage and collisions of two identical rings are studied focusing on core deformation, sound generation and stirring of fluid elements. With respect to core deformation, not only the strain rate but how rapidly it varies is important and accounts for greater susceptibility to vortex tearing than in two dimensions. For slow strain, as a passage interaction is completed and the strain relaxes, the cores return to their original shape while permanent deformations remain for rapidly varying strain. For collisions, if the strain changes slowly the core shapes migrate through a known family of two-dimensional steady vortex pairs up to the limiting member of the family. Thereafter energy conservation does not allow the cores to maintain a constant shape. For rapidly varying strain, core deformation is severe and a head-tail structure in good agreement with experiments is formed. With respect to sound generation, good agreement with the measured acoustic signal for colliding rings is obtained and a feature previously thought to be due to viscous effects is shown to be an effect of inviscid core deformation alone. For passage interactions, a component of high frequency is present. Evidence for the importance of this noise source in jet noise spectra is provided. Finally, processes of fluid engulfment and rejection for an unsteady vortex ring are studied using the stable and unstable manifolds. The unstable manifold shows excellent agreement with flow visualization experiments for leapfrogging rings suggesting that it may be a good tool for numerical flow visualization in other time periodic flows.
Shariff, Karim↗
Short wavelength HgCdTe staring focal plane for low background astronomy applications
The design of a 128x128 staring short wave infrared (SWIR) HgCdTe focal plane incorporating charge integrating transimpedance input preamplifiers is presented. The preamplifiers improve device linearity and uniformity, and provide signal gain ahead of the miltiplexer and readout circuitry. Detector's with cutoff wavelength of 2.5 microns and operated at 80 K have demonstrated impedances in excess of 10(exp 16) ohms with 60 percent quantum efficiency. Focal plane performance using a smaller format device is presented which demonstrates the potential of this approach. Although the design is capable of achieving less than 30 rms electrons with todays technology, initial small format devices demonstrated a read noise of 100 rms electrons and were limited by the atypical high noise performance of the silicon process run. Luminescence from the active silicon circuitry in the multiplexer limits the minimum detector current to a few hundred electrons per second. Approaches to eliminate this excessive source of current is presented which should allow the focal plane to achieve detector background limited performance.
Hall, D.↗
Algorithm For Solution Of Subset-Regression Problems
Reliable and flexible algorithm for solution of subset-regression problem performs QR decomposition with new column-pivoting strategy, enables selection of subset directly from originally defined regression parameters. This feature, in combination with number of extensions, makes algorithm very flexible for use in analysis of subset-regression problems in which parameters have physical meanings. Also extended to enable joint processing of columns contaminated by noise with those free of noise, without using scaling techniques.
Verhaegen, Michel↗