Influence Of Azimuth Research Articles

Modeling and analysis of an ionospheric mapping function considering azimuth angle: A preliminary result

Generally, dual- and multi-frequency global navigation satellite system (GNSS) users can use dual- or multi-frequency combinations to eliminate the ionospheric delay. However, different vertical ionospheric models are applied for single-frequency GNSS users, which need an ionospheric mapping function for conversion. Although many mapping functions can be employed, the influence of latitude, azimuth, solar flux, and other factors are not taken into account. Thus, we proposed a mapping function, named SGG-MF, considering the influence of azimuth. The conversional results of single-layer model mapping function (SLM-MF), Klobuchar mapping function (Klobuchar-MF), modified single layer model mapping function (MSLM-MF) and SGG-MF are evaluated by using coinciding pierce point (CPP) technique as well as single-frequency precise point positioning (SF-PPP) in static mode. For the CPP technique, it is found that the mean absolute errors (MAE) of SLM-MF, Klobuchar-MF, and, MSLM-MF range from 1.5 to 2.1 TECU (total electron content unit), while SGG-MF ranges from 1.5 to 1.7 TECU. The standard deviation (STD) of SGG-MF improved by about 13.6%, 14.9%, and 13.6% compared with that of SLM-MF, Klobuchar-MF, and MSLM-MF, respectively. For the SF-PPP test, the positioning error of SGG-MF was reduced by about 6.0%, 22.9%, and 11.9% compared with that of SLM-MF, Klobuchar-MF, and MSLM-MF, respectively.

Grid transformation and dynamic scattering for tail rotor radar cross section analysis

With the promotion and enhancement of stealth technology of helicopter rotor components, the research on the dynamic radar cross section (RCS) of helicopter rotor is becoming more and more important and imminent. In order to facilitate the calculation and analysis of the electromagnetic scattering characteristics during rotor rotation, a dynamic scattering calculation (DSC) method based on quasi-static principle (QSP) and grid coordinate transformation is presented. After analyzing the advantages and disadvantages of QSP, the dynamic principle is used to describe the rotation process of the rotor. Combined with the grid coordinate transformation method, the RCS of the rotor is accurately calculated by physical optics (PO) and physical theory of diffraction (PTD). Then the influence of azimuth, elevator angle and observation distance on rotor dynamic RCS is analyzed. The results show RCS of the tail rotor is indeed dynamic and periodic and its main influencing factors include azimuth and elevation angle. The proposed DSC method is efficient and effective for studying the dynamic RCS of tail rotor.

Weak scattering of a random electromagnetic source of circular frames upon a deterministic medium

By application of the theory of first-order Born approximation, analytical expressions of the cross spectral density matrix of a newly proposed electromagnetic random source of circular frames scattered upon a deterministic medium in the far zone are derived. In terms of the analytical formulas obtained, the scattered spectral properties of both single circular frame and superposed circular frames are numerically investigated. Results show that the scattered spectral properties of the targeted optical source in the far zone would be significantly influenced by the effective radius σR of the scattering medium and the observation azimuth ϕ, in addition to the parameters of the incident source, such as the index M, the polarization states, and the correlation widths. It is pointed out here that this is the first time, to the best of our knowledge, that the influence of azimuth ϕ on scattered spectral properties has been analyzed, and some meaningful and interesting results have been obtained in this paper.

Prediction of PPFD variance at forest floor in a thinned Japanese cypress plantation

A model for predicting the spatial variance of photon flux density (PPFD) was developed in a thinned Japanese cypress ( Chamaecyparis obtusa) plantation, to quantify the effect of thinning on light availability. Hemispherical diagrams were simulated from the foliage densities of cubes 0.2 × 0.2 × 0.2 m which were estimated from the coordinates of tree apexes. Predicted PPFD values and gap distributions were compared with the actual values, which were measured by quantum sensors and hemispherical photographs through a fish eye lens. After validation, the model predicted gap distribution and daily total PPFD well. The model also produced a frequency pattern of PPFD with sufficient accuracy for evaluating the thinning effects on light availability. This model has the following four merits. (1) The frequency pattern of PPFD can be simulated with this model. The frequency pattern seems to be a more adequate index for eco-physiological discussion than the integral of PPFD, since the photosynthetic rate does not change linearly with PPFD. (2) The compound effect of multiple gaps can be evaluated in this model. (3) The process of decreasing PPFD by canopy closure can be predicted, since the canopy closure process was predicted by the canopy dynamic model, upon which this model is based. (4) The influence of azimuth and inclination of slope on PPFD can be predicted.

Directional AudiometryA Review of F.-M. Tonning's Doctoral Thesis

Tonning's doctoral thesis on directional audiometry is based on eight separate papers, published in Acta Oto-laryngologica (Stockholm). The present report summarizes the results of the research. This was focused mainly on the influence of azimuth of speech and white noise in normal and hard-of-hearing subjects. The latter group was studied without and with hearing aids. The reviewer acted as official opponent when the thesis was defended at the University of Bergen on October 5th, 1974.

Directional audiometry. VII. The influence of azimuth on the perception of speech in aided and unaided patients with binaural hearing loss.

Twenty patients with binaural hearing loss varying from a Pure Tone Average (PTA) of 28 dB hearing level to 45 dB hearing level were examined: The Directional Threshold of Intelligibility (Dn) was measured both without and with background noise, without and with hearing aids. Without background noise, the DTI with binaural hearing aids was found to be significantly better than the DTI with monaural hearing aid in 3 of the 4 positions of the signal loudspeaker. With background noise, the DTI with binaural hearing aids was found to be significantly better than with monaural hesaring aid in 6 of the 16 combinations of signal and noise loudspeakers. For all the 20 experimental listening conditions we found that the DTI was significantly better with binaural hearing aids than with monaural in 11 of the 20 patients. For the 16 experimental listening conditions with background noise we found a significantly better DTI with binaural hearing aids than with monaural in 13 of the 20 patients. The results indicate th...

Directional audiometry. IV. The influence of azimuth on the perception of speech in aided and unaided patients with monaural hearing loss.

In a group of 20 patients with monaural hearing loss varying from a Pure Tone Average (PTA) of 20 dB hearing level to residual hearing, the Directional Threshold of Intelligibility (DTI) was measured both with and without background noise, and with and without hearing aid.Without background noise, the DTI with hearing aid was found to be better than the DTI without hearing aid in 2 of the 4 positions of the signal loudspeaker. the difference was statistically significant. with background noise, the DTI with hearing aid was found to be significantly better than without hearing aid in 6 of the 16 combinations of signal and noise loudspeakers. for all of the 20 experimental listening conditions we found that the DTI was better with hearing aid than without in 11 of the 20 patients. for the 16 experimental listening conditions with background noise we found a significantly better DTI in 9 of the 20 patients, in 2 patients we found a poorer DTI with hearing aid than without.It seems important to evaluate the effect of hearing aid treatment of monaurally hard-of-hearing patients after a sufficiently long trial period.

Directional audiometry. V. The influence of azimuth on the perception of speech in patients with monaural hearing loss treated with hearing aids (CROS).

Severe monaural hearing loss up to unilateral deafness cannot be treated with an ordinary hearing aid on the ear concerned. A microphone, however, can be placed in the vicinity of the bad ear and the sound transmitted to the external auditory canal of the good ear. This form of hearing aid treatment is called, in the literature, “Contralateral Routing of Signals”, CROS. The present investigation shows that such treatment may be advantageous. Nevertheless, under certain conditions, the treatment may lead to the comprehension of speech being worse than without an apparatus. Individual evaluation of the hearing problems of such patients is essential when considering whether treatment with CROS is to be recommended.

Directional audiometry. 3. The influence of azimuth on the perception of speech in patients with monaural hearing loss.

The Directional Threshold of Intelligibility (DTI) both with and without background noise has been determined in 37 patients with one-sided hearing defects ranging from a 30 dB loss to total deafness. Free field speech audiometry was done with an apparatus permitting independent radial positioning of a speech loudspeaker and a noise loudspeaker on the circumference of a horizontal circle centred on the head of the seated person examined. The DTI measured without noise not only depended upon the amount of the hearing loss in the defective ear, but also upon slight variations in the hearing ability of the good ear. A relationship between the DTI without noise and the normal ear's Pure Tone Average (PTA) in the range 500, 1 000, and 2 000 Hz was found. In the persons examined it was also found that when speech was reproduced against background noise under certain conditions the bad ear contributed to the perception oE speech if the person tested had one-sided PTA of 53 dB hearing level or less.

Directional audiometry. II. The influence of azimuth on the perception of speech.

In 30 persons with normal hearing, a previously described apparatus (Tonning, 1970) was used for free field determinations of the intelligibility of speech in relation to the azimuth of the source: Directional Threshold of Intelligibility (DTI) was recorded both with and without background noise. Two loudspeakers, the one producing speech and the other producing white noise, could be rotated independently in the horizontal plane around the test person, permitting an analysis of the dependency of the DTI upon the positions of the speech and the noise source. The assumption is made that DTI is dependant on age. With the help of electronic computer analysis the material collected during the examinations was used to construct a standard diagram showing the DTI values in persons with normal hearing, with and without background noise.

THE INFLUENCE OF AZIMUTH ON SPEECH SIGNALS.

The aim of the investigation was to study how speech signals are influenced by the angle of incidence of the sound towards the head, i.e. azimuth. The study was made by means of an artificial head with condenser microphones at the site of the eardrums. Speech signals were recorded via these microphones and were then subjected to spectrographic analysis. PB lists of Swedish monosyllables were also recorded via the head and their intelligibility was investigated. It was shown that azimuth has a substantial influence on speech signals. The intelligibility for binaural listening is significantly better than for monaural listening at all azimuths tested. The information reaching the ear turned towards the sound source is markedly better than at the ear turned away from the sound source.