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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Characterizing x-ray transmission through filters used in high energy density physics diagnostics

We report on the design and implementation of a new system used to characterize the energy-dependent x-ray transmission curve, Θ(E), through filters used in high-energy density physics diagnostics. Using an Amptek X-123-CdTe x-ray spectrometer together with a partially depleted silicon surface barrier detector, both the energy spectrum and total emission of an x-ray source have been accurately measured. By coupling these detectors with a custom PROTO-XRD x-ray source with interchangeable cathodes, accurate characterizations of Θ(E) for filters of varying materials and thicknesses have been obtained. The validity of the technique has been confirmed by accurately reproducing areal densities for high-purity filters with known x-ray transmission properties. In this paper, the experimental setup is described and the results of absorption calibrations performed on a variety of different filters are presented.

Pearcy, J.↗
NASA NTRS1964

Spectral measurements by the filter method on Lewis' carbon arc solar simulators

There exists a problem in the measuring of the spectral irradiance of solar simulators. This difficulty has manifested intself in both monochromator and filter measurements. This report is the discussion of the measurements by Eppley Laboratory on the Lewis carbon arc solar Simulators, the further analysis of the method of filter radiometry made by Lewis personnel, and the comparison with the monochromator measurements. Previously when the filter technique was used it was assumed that the a priori knowledge of the source's spectral characteristics must be known. In this report it will be shown that for a carb0n arc source a knowledge of the source is not required after the filters have been properly chosen.

RADIOMETRY↗
NASA NTRS1972

DDP-116 general digital filtering

The methods are described for calibrating, selecting filter weights, filtering, and computing filter response functions. These methods are computed on a statistical analyzer (STAN) system with a Honeywell DDP-116 central processor. The following filter types are computed: all pass, low pass, high pass, band pass, band rejection, and derivative.

Jones, J. A.↗
NASA NTRS1972

Investigation of the epoch state filter

A navigation filtering technique has been formulated using as state variables the initial or epoch position and velocity of the spacecraft. The estimate of this initial state is then improved by filtering new measurements. The current state may be obtained by a conic extrapolation of the epoch state. Results of a digital computer simulation of the epoch state filter show that this formulation of the navigational problem results in less computer run time and less computer storage space than conventional techniques. The errors produced by this technique have been demonstrated to be comparable to those obtained by conventional maximum-likelihood filtering.

Edwards, J. A.↗
NASA NTRS1971

A class of orthogonal nonrecursive binomial filters.

The time- and frequency-domain properties of the orthogonal binomial sequences are presented. It is shown that these sequences, or digital filters based on them, can be generated using adders and delay elements only. The frequency-domain behavior of these nonrecursive binomial filters suggests a number of applications as low-pass Gaussian filters or as inexpensive bandpass filters.

Haddad, R. A.↗
NASA NTRS1972

Optimum filters for narrow-band frequency modulation.

The results of a computer search for the optimum type of bandpass filter for low-index angle-modulated signals are reported. The bandpass filters are discussed in terms of their low-pass prototypes. Only filter functions with constant numerators are considered. The pole locations for the optimum filters of several cases are shown in a table. The results are fairly independent of modulation index and bandwidth.

Shelton, R. D.↗
NASA NTRS1972

Minimax design of Kalman-like filters in the presence of large parameter uncertainties.

An attempt is made to guide the designer by means of a systematic procedure which will yield a filter that performs in an acceptable fashion when there is some uncertainty in the various system parameters. Very general restrictions are placed upon these uncertainties, and it is shown that they are applicable in most practical situations. The minimax approach results in a unique fixed filter design which places a least upper bound on a given sensitivity measure over the assumed range of uncertain parameters. The resulting filters are identical in form to the Kalman filter, provide nearly optimal performance over the entire range of uncertain statistics, and are independent of the actual noise statistics. Examples are given.

Hutchinson, C. E.↗
NASA NTRS1972

Application of advanced filtering methods to the determination of the interplanetary orbit of Mariner '71.

This paper presents the results of the applications of advanced filtering methods to the determination of the interplanetary orbit of the Mariner '71 spacecraft. The advanced techniques are specific extensions of the Kalman filter. The special problems associated with applying these techniques are discussed and the particular algorithmic implementations are outlined. The advanced methods are compared against the weighted least squares filters of conventional application. The results reveal that relatively simple advanced filter configurations yield solutions superior to those of the conventional methods when applied to the Mariner '71 radio measurements.

Rourke, K. H.↗
NASA NTRS1973

Combined diplexer and harmonic filter

By using two directional filters having circular waveguide filter cavities, diplexing and harmonic filtering functions can be combined into a more compact integrated waveguide assembly. Device is filter which passes power within its pass band limits, but also has a directional characteristic so power transmitted into two-port output waveguide will travel in only one direction.

Allen, C. C.↗
NASA NTRS1972

Survey of digital filtering

A three part survey is made of the state-of-the-art in digital filtering. Part one presents background material including sampled data transformations and the discrete Fourier transform. Part two, digital filter theory, gives an in-depth coverage of filter categories, transfer function synthesis, quantization and other nonlinear errors, filter structures and computer aided design. Part three presents hardware mechanization techniques. Implementations by general purpose, mini-, and special-purpose computers are presented.

Nagle, H. T., Jr.↗
NASA NTRS1973

Contrast elements in birefringent filters.

Calculations were made to determine the effects which contrast elements of various thicknesses have in Lyot filters. A filter which is significantly narrower than the line at which it is looking produces the best results. Therefore, if the filter is broad the addition of as thick an element as possible is desired. However, if the filter is already narrow, a contrast element whose thickness equals that of the second Lyot element will produce the best performance.

Schoolman, S. A.↗
NASA NTRS1973

Filtering theory applied to orbit determination

Modifications to the extended Kalman filter and the Jazwinski filter are made and compared with the classical extended Kalman filter in applications to orbit determination using real data. The results show that with the kind of data available today, the application of filtering theories in this field presents many problems.

Torroglosa, V.↗
NASA NTRS1973

Increase in transmittance of unbacked aluminum filters exposed to RF or dc discharges in oxygen

Results of an experimental study of the effect of discharges in oxygen on the oxide thickness and transmittance of aluminum filters. The studies were performed by exposing the filters to RF discharges and dc glow discharges in oxygen. In all experiments except one in which an aluminum ring was used as the cathode an increase in the transmittance of the filters is noted. It is thus demonstrated that the transmittance of aluminum filters increases on exposure to electrical discharges in oxygen, although it is not certain whether this phenomenon is caused by atomic oxygen.

Hunter, W. R.↗
NASA NTRS1974

Implementation of digital filters for minimum quantization errors

In this paper a technique is developed for choosing programing forms and bit configurations for digital filters that minimize the quantization errors. The technique applies to digital filters operating in fixed-point arithmetic in either open-loop or closed-loop systems, and is implemented by a digital computer program that is based on a digital simulation of the system. As an output the program gives the programing form required for minimum quantization errors, the total bit configuration required in the filter, and the location of the binary decimal point at each quantizer within the filter.

Phillips, C. L.↗
NASA NTRS1974

A balloon-borne cryogenically cooled filter radiometer

The development of a cryogenically cooled filter radiometer for use with high altitude balloons is discussed. The radiometer has features which include the options for remote operation of two filter wheels each containing six filters at helium temperature and a cryogenic rotary chopper which may be run at 200 cycles per second or positioned open or closed, and a remotely operable chopped blackbody calibration source. The radiometer contains a ten inch diameter liquid nitrogen cooled Cassegrain telescope with nine individually filtered field stops in the focal plane. The telescope is mounted on a two-axis servo operated gimbal which is used to make sky scans under the control of an onboard programmer.

Debell, A. G.↗
NASA NTRS1975

A complementary filtering technique for deriving aircraft velocity and position information

An onboard navigation system which employed complementary filtering was developed to provide velocity and position information. The inputs to the mix filter included both acceleration inputs, which provided high-frequency position and velocity information, and radar position inputs, which provided the low-frequency position and velocity information. Onboard aircraft instrumentation, including attitude reference gyros and body-mounted accelerometers, was used to provide the acceleration information. An in-flight comparison of signal quality and accuracy showed good agreement between the complementary filtering system and an aided inertial navigation system. Furthermore, the complementary filtering system was proven to be satisfactory in control and display system applications for both automatic and pilot-in-the-loop instrument approaches and landings.

Niessen, F. R.↗
NASA NTRS1976

Multi-star processing and gyro filtering for the video inertial pointing system

The video inertial pointing (VIP) system is being developed to satisfy the acquisition and pointing requirements of astronomical telescopes. The VIP system uses a single video sensor to provide star position information that can be used to generate three-axis pointing error signals (multi-star processing) and for input to a cathode ray tube (CRT) display of the star field. The pointing error signals are used to update the telescope's gyro stabilization system (gyro filtering). The CRT display facilitates target acquisition and positioning of the telescope by a remote operator. Linearized small angle equations are used for the multistar processing and a consideration of error performance and singularities lead to star pair location restrictions and equation selection criteria. A discrete steady-state Kalman filter which uses the integration of the gyros is developed and analyzed. The filter includes unit time delays representing asynchronous operations of the VIP microprocessor and video sensor. A digital simulation of a typical gyro stabilized gimbal is developed and used to validate the approach to the gyro filtering.

Murphy, J. P.↗
NASA NTRS1976

A numerical comparison of discrete Kalman filtering algorithms: An orbit determination case study

The numerical stability and accuracy of various Kalman filter algorithms are thoroughly studied. Numerical results and conclusions are based on a realistic planetary approach orbit determination study. The case study results of this report highlight the numerical instability of the conventional and stabilized Kalman algorithms. Numerical errors associated with these algorithms can be so large as to obscure important mismodeling effects and thus give misleading estimates of filter accuracy. The positive result of this study is that the Bierman-Thornton U-D covariance factorization algorithm is computationally efficient, with CPU costs that differ negligibly from the conventional Kalman costs. In addition, accuracy of the U-D filter using single-precision arithmetic consistently matches the double-precision reference results. Numerical stability of the U-D filter is further demonstrated by its insensitivity of variations in the a priori statistics.

Thornton, C. L.↗