lennunduses mõistetakse nähtavuse all suurimat kaugust, kust on nähtav ja äratuntav maapinna lähedal heledal taustal asetsev sobivas suuruses must objekt või suurimat kaugust, kust vaateväljas asuvat valgusallikat tugevusega umbes 1000 kandelat on võimalik valgustamata taustal näha ja identifitseerida, olenevalt sellest kumb kaugus on suurem
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Neil kahel kaugusel on erinev õhus hajumiskoefitsient ja viimatinimetatud kaugus sõltub tausta valgustusest. Esimesena nimetatud kaugus on väljendatud meteoroloogilise optilise kaugusena (Meteorological Optical Range – MOR).
Definitsioon kehtib nähtavuse määratlemisel kohalikes tava- ja spetsiaalteadetes, METAR (Aviation Routine Weather Report) ja SPECI (Aviation Selected Special Weather Report) teadetes toodud üld- ja miinimumnähtavuse määratlemisel ja nähtavuse määramisel maapinnal.
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;
b) the greatest distance at which lights in the vicinity of 1 000 candelas can be seen and identified against an unlit background.
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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).
The definition applies to the observations of visibility in local routine and special reports, to the observations of prevailing and minimum visibility reported in METAR and SPECI and to the observations of ground visibility.
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Valdkond ICAO lisade põhjal loodud klassifikaatori järgi: Lennureeglid
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