Aviation Weather Instruments Dictionary

孤蓝et

Note.- These explanations are generally based on established scientific definitions, some of which have been simplified to assist non-specialist readers. Approved ICAO definitions are marked with an asterisk (*) and published WMO definitions1 with a double asterisk (**). The units, where appropriate, are indicated in brackets.

Air temperature. The temperature indicated by a thermometer exposed to the air in a place sheltered from direct solar radiation (degree Celsius, ° C).

Allard's law. An equation relating luminance (E) produced by a point source of light of intensity (I) on a plane normal to the line of sight, at distance (x) from the source, in an atmosphere having a transmissivity (T).

Note.- Applicable to the visual range of lights.

Atmospheric pressure. Pressure (force per unit area) exerted by the atmosphere on any surface by virtue of its weight; it is equivalent to the weight of a vertical column of air extending above a surface of unit area to the outer limit of the atmosphere. (hectopascal, hPa)

Ceilometer. Instrument for measuring the height of the base of a cloud layer, with or without a recording device. Measurement done by calculating the return time of laser light pulses reflected by the cloud base.

Cloud amount. The fraction of the sky covered by the clouds of a certain genus, species, variety, layer, or combination of clouds.

Cloud base. The lowest level of a cloud or cloud layer. (meter, m (or foot, ft)).

Convective cloud. Cumuliform cloud which form in an atmospheric layer made unstable by heating at the base or cooling at the top.

Dedicated display. A display connected to a sensor, designed to provide a direct visualization of the operational variables.

Dew-point temperature. Temperature to which a volume of air must be cooled at constant pressure and constant moisture in order to reach saturation; any further cooling causes condensation. (degree Celsius, °C)

Disdrometer. A device used for catching the drops of liquid hydrometeors and for measuring the distribution of their diameters.

Extinction coefficient** (s). The proportion of luminous flux lost by a collimated beam, emitted by a incandescent source at a color temperature of 2,700 K, while traveling the length of a unit distance in the atmosphere. (per meter, m-1)

Note.- The coefficient is a measure of the attenuation due to both absorption and scattering.

Luminance** (E). The luminous flux per unit area (lux, lx).

Koschmieder's law. A relationship between the apparent luminance contrast (Cx) of an object, seen against the horizon sky by a distant observer, and its inherent luminance contrast (C0), i.e. the luminance contrast that the object would have against the horizon when seen from very short range.

Note. - Applicable to the visual range of objects by day

Lightning detection network. Network of lightning detectors transmitting in real time to a central computer, locating lightning flashes by combining information received from each detector.

Luminance (photometric brightness) (L). The luminous intensity of any surface in a given direction per unit of projected area (candela per square meter, cd/m2)

Luminance contrast (C). The ratio of the difference between the luminance of an object and its background to the luminance of the background (dimensionless).

Luminance intensity (I)**. The luminous flux per unit solid angle (candela, cd).

Magnetic wind direction. The direction, with respect to magnetic north, from which the wind is blowing. The magnetic wind directions are used in aircraft operations, necessitated by the magnetic frame of reference applied to air navigation facilities. (degree)

Meteorological optical range (MOR)**. The length of the path in the atmosphere required to reduce the luminous flux in a collimated beam from an incandescent lamp, at a color temperature of 2 700 K, to 0.05 of its original value, the luminous flux being evaluated by means of the photometric luminosity function of the International Commission on Illumination (CIE) (meter, m or kilometer, km).

Note. - The relationship between meteorological optical range and extinction coefficient (at the contrast threshold of e = 0.05) using Koschmieder's law is : MOR = In(0.05)/s " 3/s. MOR = visibility under certain conditions. (see visibility)

Precipitation intensity. An indication of the amount of precipitation collected per unit time interval. It is expressed as light, moderate or heavy. Each intensity is defined with respect to the type of precipitation occurring, based on rate of fall.

Present weather. Weather existing at a station at the time of observation.

Present weather sensor. Sensor measuring physical parameters of the atmosphere and calculating a limited set of present weather, always including present weather related to precipitation.

Prevailing visibility*. The visibility value, observed in accordance with the definition of "visibility", which is reached or exceeded within at least half the horizon circle or within at least half of the surface of the aerodrome. These areas could comprise contiguous or non-contiguous sectors. (meter, m or kilometer, km)

Note: - This value may be assessed by human observation and/or instrumented systems. When instruments are installed, they are used to obtain the best estimate of the prevailing visibility.

QFE. Atmospheric pressure at aerodrome elevation (or at runway threshold) (hectopascal, hPa) .

QNH. Altimeter sub-scale setting to obtain elevation when on the ground (hectopascal, hPa).

Runway visual range (RVR)*. The range over which the pilot of an aircraft on the center line on a runway can see the runway surface markings or the lights delineating the runway or identifying its center line (meter, m).

Scatter meter. An instrument for estimating extinction coefficient by measuring the flux scattered from a light beam by particles present in the atmosphere.

Transmissivity (or transmission coefficient) (T). The fraction of luminous flux which remains in a beam after traversing an optical path of a unit distance in the atmosphere (dimensionless).

Transmissometer. An instrument that takes a direct measurement of the transmittance between two points in space, i.e. over a specified path length or base line.

Transmittance (tb). Transmissivity within an optical path of a given length b in the atmosphere (dimensionless).

True Wind Direction. Direction from which the wind blows, measured clockwise from true north.

Visibility*. Visibility for aeronautical purposes is the greater of:

    a) the greatest distance at which a black object of suitable dimensions, situated near the ground, can be seen and recognized when observed against a bright background; and

    b) the greatest distance at which lights in the vicinity of 1,000 candelas can be seen and identified against an unlit background.

Note: -The two distances have different values in air of a given extinction coefficient, and the latter b) varies with the background illumination. The former a) is represented by the meteorological optical range (MOR).

Visual threshold of illumination (ET). The smallest luminance required by the eye to make a small light source visible (lux, lx).

Weather radar. An adaptation of radar for meteorological purposes. The scattering of electromagnetic waves, at wavelengths of a few millimeters to several centimeters, by raindrops and cloud drops is used to determine the distance, size, shape, location, motion, phase (liquid and solid), as well as the intensity of the precipitation. Another application is in the detection of clear-air phenomena through scattering by insects, birds, etc. and fluctuation of the refractive index.

1 Guide to Meteorological Instruments and Methods of Observation

http://www.allweatherinc.com/reference/definitions.html

mofangbao

木有看明白啊 有简单介绍木有？

探空一哥

不太明白 有中文的么

Akbar

中英文一起好

航空气象

航空气象上最主要的观测系统：跑道自动观测系统、机场天气雷达。

叶弘翔

不是很懂，有翻译么

shanyimumu

高人啊。。。

孤飞流云

感觉航空气象里面的东西好少啊，还需要大家一起继续的充实！

非地球男

看来航空气象距离地方气象还有很大差距呀

winnyye

一看英文就头晕！