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Becker, F.

Publications and source records attributed to Becker, F..

12 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Atmospheric effects on SMMR and SSM/I 37 GHz polarization difference over the Sahel

The atmospheric effects on the difference of vertically and horizontally polarized brightness temperatures, Delta(T) observed at 37 GHz frequency of the SMMR on board the Nimbus-7 satellite and SSM/I on board the DMSP-F8 satellite are studied over two 2.5 by 2.5 deg regions within the Sahel and Sudan zones of Africa from January 1985 to December 1986 through radiative transfer analysis using surface temperature, atmospheric water vapor, and cloud optical thickness. It is found that atmospheric effects alone cannot explain the observed temporal variation of Delta(T), although the atmosphere introduces important modulations on the observed seasonal variations of Delta(T) due to rather significant seasonal variation of precipitable water vapor. These Delta(T) data should be corrected for atmospheric effects before any quantitative analysis of land surface change over the Sahel and Sudan zones.

Choudhury, B. J.↗
NASA NTRS1987

The impact of spectral emissivity on the measurement of land surface temperature from a satellite

The effect of emissivity on the measurement of land surface (LS) temperature from satellite radiances using the split-window method is investigated. Formulas are derived to relate the LS temperatures to two brightness temperatures measured from space in the AVHRR 4 and AVHRR 5 channels, and their accuracies are discussed. Results indicate that to determine LS temperatures from a satellite, the spectral emissivity must be known to an accuracy on the order of 0.005 for the average and 0.0007 for the difference in order to obtain an error of the order of 0.5 K.

Becker, F.↗
NASA NTRS1987

Measurement from satellites of land surface parameters and fluxes in the thermal infrared bands: Problems and methods

The main problems arising in the elaboration of accurate and reliable algorithms for extracting land surface parameters and flux from their measured radiances are discussed. Methods of solution in the thermal infrared spectral domain are described. Particular interest is given to the inversion of thermal models and to the problems resulting from the heterogeneity of the observed surfaces.

Becker, F.↗
NASA NTRS1987

The Fringe Reading Facility at the Max-Planck-Institut fuer Stroemungsforschung

A Mach-Zehnder interferometer is used for optical flow measurements in a transonic wind tunnel. Holographic interferograms are reconstructed by illumination with a He-Ne-laser and viewed by a video camera through wide angle optics. This setup was used for investigating industrial double exposure holograms of truck tires in order to develop methods of automatic recognition of certain manufacturing faults. Automatic input is achieved by a transient recorder digitizing the output of a TV camera and transferring the digitized data to a PDP11-34. Interest centered around sequences of interferograms showing the interaction of vortices with a profile and subsequent emission of sound generated by this process. The objective is the extraction of quantitative data which relates to the emission of noise.

Becker, F.↗
NASA NTRS1987

Problems related to the determination of land surface parameters and fluxes over heterogeneous media from satellite data

Problems encountered in the definition of relevant parameters which can describe heterogeneous media as a whole are discussed. A procedure to extend the definition of parameters from local to regional scales via inversion of appropriate models is tentatively proposed. The adequacy of these models for describing physical processes at the earth/atmosphere interface as observed with satellite systems is addressed.

Becker, F.↗
NASA NTRS1985

Three-dimensional, transonic rotor flow field reconstructed from holographic interferogram data

Holographic interferometry and computer-assisted tomography (CAT) are used to determine the transonic flow field of a model rotor blade in hover. A pulsed ruby laser records 40 interferograms with a 61 cm-diam view field near the model rotor-blade tip operating at a tip Mach number of 0.90. After digitizing the interferograms and extracting fringe-order functions, the data are transferred to a CAT code. The CAT code then calculates pressure coefficients in several planes above the blade surface. The values from the holography-CAT method compare favorably with previously obtained numerical computations and laser velocimeter measurements at most locations near the blade tip. The results demonstrate the technique's potential for three-dimensional transonic rotor flow studies.

Kittleson, J. K.↗
NASA NTRS1985

Digital fringe reduction techniques applied to the measurement of three-dimensional transonic flow fields

A system for digital inteferogram evaluation based on an image-processing system connected to a host computer has been implemented. The system supports one- and two-dimensional interferogram evaluations. Interferograms are digitized, enhanced, and segmented. The fringe coordinates are extracted, and the fringes are represented as polygon data structures. Fringe numbering and fringe interpolation modules are implemented. The system supports editing and interactive features as well as graphic visualization. An application of the system to the evaluation of double exposure interferograms from the transonic flow field around a helicopter blade and the reconstruction of the 3-D flow field are given.

Becker, F.↗
NASA NTRS1985

Reconstruction of a 3-dimensional transonic rotor flow field from holographic interferogram data

Holographic interferometry and computer-assisted tomography (CAT) are used to determine the transonic velocity field of a model rotor blade in hover. A pulsed ruby laser recorded 40 interferograms with a 2-ft-diam view field near the model rotor-blade tip operating at a tip Mach number of 0.90. After digitizing the interferograms and extracting fringe-order functions, the data are transferred to a CAT code. The CAT code then calculates the perturbation velocity in seeral planes above the blade surface. The values from the holography-CAT method compare favorably with previously obtained numerical computations in most locations near the blade tip. The results demonstrate the technique's potential for three-dimensional transonic rotor flow studies.

Yu, Y. H.↗
NASA NTRS1985

Reconstruction of a three-dimensional, transonic rotor flow field from holographic interferogram data

Holographic interferometry and computer-assisted tomography (CAT) are used to determine the transonic velocity field of a model rotor blade in hover. A pulsed ruby laser recorded 40 interferograms with a 2-ft-diam view field near the model rotor-blade tip operating at a tip Mach number of 0.90. After digitizing the interferograms and extracting fringe-order functions, the data are transferred to a CAT code. The CAT code then calculates the perturbation velocity in several planes above the blade surface. The value from the holography-CAT method compare favorably with previously obtained numerical computations in most locations near the blade tip. The results demonstrate the technique's potential for three-dimensional transonic rotor flow studies.

Yu, Y. H.↗
NASA NTRS1982

Automatic evaluation of interferograms

A system for the evaluation of interference patterns was developed. For digitizing and processing of the interferograms from classical and holographic interferometers a picture analysis system based upon a computer with a television digitizer was installed. Depending on the quality of the interferograms, four different picture enhancement operations may be used: Signal averaging; spatial smoothing, subtraction of the overlayed intensity function and the removal of distortion-patterns using a spatial filtering technique in the frequency spectrum of the interferograms. The extraction of fringe loci from the digitized interferograms is performed by a foating-threshold method. The fringes are numbered using a special scheme after the removal of any fringe disconnections which appeared if there was insufficient contrast in the holograms. The reconstruction of the object function from the fringe field uses least squares approximation with spline fit. Applications are given.

Becker, F.↗