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The use of light within the visible spectrum allows the sensor to most accurately simulate human perception of visibility.Find out more about how we record and monitor observations.Sunshine is measured using either Campbell-Stokes sunshine recorders or modern sunshine sensors. Anybody can answer -RA means light rain, which if just using vis concerns is defined as, "From scattered drops that, regardless of duration, do not completely wet an exposed surface up to a condition where individual drops are easily seen." Source(s): https://shrinkurl.im/a0thM. Visibility sensors measure the meteorological optical range which is defined as the length of atmosphere over which a beam of light travels before its luminous flux is reduced to 5% of its original value.For a great many years meteorological visibility was estimated by the human observer judging the appearance of distant objects against a contrasting background, usually the sky.
Moderate rain is 2-6mm an hour, heavy rain is more than 6mm an hour. Bright conditions will also cause the system to over-report visibility.The perspective of surface observers will also be different from the view pilots have higher up.Thanks for contributing an answer to Aviation Stack Exchange! [Edit Post comment about RA]: Sorry, used a few more abbreviations. During these hours of 10 mi visibility, there are multiple conditions of cloud cover, ranging from Light Clouds, to Overcast, to Light Rain.What is "visibility" when added to a weather report broadcast from an airport? Learn more about hiring developers or posting ads with us No CB or TCU and no cloud below 5000 feet or Minimum Sector Altitude (MSA) (whichever is the greater). It applies the forward scattering characteristics of light to measure the extinction coefficient of a beam generated by a high intensity xenon strobe transmitter directed at a volume of air close to the sensor. It seems that if I am in the middle of Light Rains, well then my visibility cannot be "10 miles".Visibility is defined as "Visibility is a measure of the horizontal opacity of the atmosphere at the point of observation and is expressed in terms of the horizontal distance at which a person should be able to see and identify specific objects. Start here for a quick overview of the site This is done by measuring the amount of light scattered from a light source, such as a Xenon flash lamp, across a distance of 0.75 feet. SM = Statute Miles, which is like a regular mile that most people use in their daily lives. site design / logo © 2020 Stack Exchange Inc; user contributions licensed under All my quotes for this post comes from FAA Order 7900.5C, the Surface Weather Observing Guide.. Visibility is defined as "Visibility is a measure of the horizontal opacity of the atmosphere at the point of observation and is expressed in terms of the horizontal distance at which a person should be able to see and identify specific objects." This is measured every 30 seconds, and each minute is averaged over the past 10 minutes to produce the reported value. By using our site, you acknowledge that you have read and understand our Aviation Stack Exchange is a question and answer site for aircraft pilots, mechanics, and enthusiasts. Although this is adjusted to allow for changing conditions, there will be some lag before the average reflects new conditions.This system can differ from human vision for various reasons, and reflected light from precipitation is one possibility. "All METARs report Prevailing Visibility, which is: "Prevailing visibility is the greatest visibility equaled or exceeded throughout at least half the horizon circle, which does not necessarily have to be continuous. Anybody can ask a question The Visibility, Cloud, and Weather groups are replaced by the term CAVOK (cloud and visibility OK) when the following conditions exist simultaneously: Visibility is 10km or more. It means a rainfall rate of less than 2mm an hour. Anonymous. 0 0. The best answers are voted up and rise to the top 4 years ago. KBJC(when I worked there it was a completely manual station), we'd report anywhere up to 70SM or higher visibility, due to our visibility markers.-RA can often be easily seen through, RA or RA+ do become harder to see through, and as always, it can be dependant on where the -RA is, if it's only in a tiny quadrant of the horizon circle, it can often be a greater visibility. Detailed answers to any questions you might have Reasonably accurate measurements are possible over a range of visibility extending from a few tens of metres to a few tens of kilometres. An inch of rain is 25.4mm which, if it fell in an hour, would be very heavy rain. in the daytime, a prominent dark object against the sky at the horizon, and 2.) This is the visibility that is considered representative of visibility conditions at the station. A pyranom…Atmospheric pressure is measured by a barometer that employs a silicon capacitive pressure sensor having e…Everything you need to know about the forecast, and making the most of the weather.The latest breakthroughs, research and news from the Met Office.Support your business with world-leading science and technology. Meaning, pronunciation, picture, example sentences, grammar, usage notes, synonyms and more. Visibility In Weather. 0 0.