Apparatus for estimating slant visibility in fog
First Claim
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1. An apparatus for estimating slant visual range in fog comprising:
- a transmissometer array, having at least three transmissometer elements at respectively greater differing heights h1, h2 and h3 above the ground and disposed for operation between the differing heights and ground level, for generating transmissometer signals indicative of a fog strength; and
a slant visual range (SVR) computer coupled to said transmissometer array so as to receive the transmissometer signals therefrom, said SVR computer having;
means for converting the transmissometer signals into signals σ
h1, σ
h2, σ
h3 representing the mean integral of extinction coefficient between said respectively greater heights h1, h2, h3, above ground and ground level;
means for storing a predetermined set of extinction coefficient σ
h function models, each model characterising a different type of fog pattern, each model having predetermined criteria for its selection and use, and containing at least one empirical constant;
means for selecting one of the models in accordance with values of σ
h1, σ
h2, σ
h3 determined by said converting means;
means for determining the values of the empirical constant in the selected model thus obtaining a definitive extinction coefficient profile,means for storing values representing airfield lighting and accepting values representing flight path and background brightness, andmeans for estimating slant visual range from the definitive profile and the airfield lighting, background brightness and flight path values.
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Abstract
Apparatus for estimating the slant visibility in obscured atmospheres such as fog, whereby an indication is derived as to when, during an aircraft landing approach in such conditions, the aircrew are likely to be able to see the runway lights. The apparatus comprises a transmissometer array arranged to take visibility readings over a slanted distance from different heights not far from a runway threshold, and a computer arranged to compare the readings with a plurality of fog profile models, to determine the definitive model and hence to derive and indicate a visual acquisition estimate.
22 Citations
17 Claims
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1. An apparatus for estimating slant visual range in fog comprising:
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a transmissometer array, having at least three transmissometer elements at respectively greater differing heights h1, h2 and h3 above the ground and disposed for operation between the differing heights and ground level, for generating transmissometer signals indicative of a fog strength; and a slant visual range (SVR) computer coupled to said transmissometer array so as to receive the transmissometer signals therefrom, said SVR computer having; means for converting the transmissometer signals into signals σ
h1, σ
h2, σ
h3 representing the mean integral of extinction coefficient between said respectively greater heights h1, h2, h3, above ground and ground level;means for storing a predetermined set of extinction coefficient σ
h function models, each model characterising a different type of fog pattern, each model having predetermined criteria for its selection and use, and containing at least one empirical constant;means for selecting one of the models in accordance with values of σ
h1, σ
h2, σ
h3 determined by said converting means;means for determining the values of the empirical constant in the selected model thus obtaining a definitive extinction coefficient profile, means for storing values representing airfield lighting and accepting values representing flight path and background brightness, and means for estimating slant visual range from the definitive profile and the airfield lighting, background brightness and flight path values. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. An apparatus for estimating slant visual range in fog, comprising:
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a transmissometer array disposed for slant operation and having reflector elements disposed at respectively greater different heights h1, h2 and h3 above ground and a source/detector unit transmissometer unit mounted substantially at ground level, said array being arranged for generating signals indicative of a fog structure; a background brightness detector, and signal processing means, arranged for receiving said signals derived from said transmissometer array and signals representing background brightness from said brightness detector and for estimating slant visual range, said signal processing means comprising; converter means for converting the transmissometer signals into signals σ
h1, σ
h2, σ
h3 representing the mean integral of extinction coefficient between the respectively greater heights h1, h2, h3, (and the ground, said converter means for converting) in accordance with the function ##EQU13## where R is the distance over which the measurement is taken,Ih is the fog structure indicative signal from the transmissometer in respect of a height h1, h2, h3, and Io is a clear day datum transmissometer signal, comparison means for comparing the σ
h signals and selecting one model from the following groups of three (3) models in accordance with the predetermined criteria associated with each model ##EQU14## where a, b, c, j, k, p, q, r are empirical constants and σ
hU and σ
hL are mean integrals of extinction coefficient between the ground and a height above and below the fog top respectively,determining means, coupled to said comparison means, for determining the values of the empirical constants in the selected model to establish a definitive model, store means for storing values representing airfield lighting and accepting values representing flight path, Log10 (ET) deriving means operative to determine the value of Log10 (ET) from the function
space="preserve" listing-type="equation">Log.sub.10 (E.sub.T)=u log.sub.10 β
-vwhere ET represents the eye illuminance threshold, measured in lux, β
represents background brightness in nits and u and v are empirical constants;
(and)Visual contact height determining means coupled to said Log10 (ET) determining means, for determining the intersection of the function ##EQU15## with the definitive model, where γ and
α
are empirical constants respectively related to flight path about the lighting pattern of an airport, and iterative visual sequence determination means coupled to said comparison means and to said store means for providing a visual sequence.
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Specification