Diapositiva 1

1
Runway Visual Range  (RVR) is a term used
in aviation meteorology to define the distance
over which a pilot of an aircraft on the
centreline of the runway can see the runway
surface markings delineating the runway or
identifying its centre line. RVR is normally
expressed in feet or metres. RVR is used as one
of the main criteria for minima on instrument
approaches, as in most cases a pilot must obtain
visual reference of the runway to land an
aircraft. The maximum RVR reading is 2,000 metres
or 6,000 feet, above which it is not significant
and thus does not need to be reported. RVRs are
provided in METARs and are transmitted by air
traffic controllers to aircraft making approaches
to allow pilots to assess whether it is prudent
and legal to make an approach.
2
RVR is also the main criteria used to determine
the category of visual aids that are installed at
an airport. The International Civil Aviation
Organisation ICAO stipulates that for RVR values
above 550 m, CAT I lighting shall be installed,
if RVR is between 300 m and 549 m then CAT II
lighting is required. CAT IIIa is installed for
RVR values between 175 m and 300 m. CAT IIIb is
required for RVR values between 50 m and 175 m
while there is no RVR limitation for CAT IIIc
visual aids.citation needed Originally RVR was
measured by a person, either by viewing the
runway lights from the top of a vehicle parked on
the runway threshold, or by viewing special
angled runway lights from a tower at one side of
the runway. The number of lights visible could
then be converted to a distance to give the RVR.
This is known as the human observer method and
can still be used as a fall-back.
3
Today most airports use Instrumented Runway
Visual Range or IRVR, which is measured by
devices called (forward scatter meters) which
provide simplified installation as they are
integrated units and can be installed as single
unit(s) at a critical location along the runway
or transmissometers which are installed at one
side of a runway relatively close to its edge.
Normally three transmissometers are provided, one
at each end of the runway and one at the
mid-point. In the US, Forward Scatter RVRs are
replacing transmissometers at most airports.
According to the US Federal Aviation
Administration "There are approximately 279 RVR
systems in the NAS, of which 242 are forward
scatter NG RVR Systems and 34 are older
Transmissometer Systems."
4
A transmissometer is an instrument for measuring
the extinction coefficient of the atmosphere, and
for the determination of visual range. It
operates by sending a narrow, collimated beam of
energy (usually a laser) through
the propagation medium. A narrow field of
view receiver at the designated measurement
distance determines how much energy is arriving
at the detector, and determines the
path transmission and/or extinction coefficient.
Atmospheric extenction is wavelength dependent
phenomenon, but the most common wavelength in use
for transmissometers is 550 nm, which is right in
the middle of the visible waveband, and allows a
good approximation of visual range. Transmissomete
rs are sometimes referred to as telephotometers,
transmittance meters, orhazemeters. The term
transmissometer is also used by oceanographers and
 limnologists to refer to a device for measuring
the optical properties of natural water. In this
context, a transmissometer measures
thetransmittance or attenuation of incident
radiation from a light source with a select
wavelength, often 660 nm, through a defined cell
volume.
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EMOR - Extended MOR Technology Latest generation
transmissometer technology makes use of a
co-located forward scatter visibility sensor on
the transmitter unit to allow for higher
accuracies over an Extended Meteorological
Optical Range or EMOR. After 10,000 meters the
accuracy of transmissometer technology drops off
and it is at higher visibilities that forward
scatter visibility sensor technology is more
accurate. The co-location of the two sensors
allows for the most accurate technology to be
used when reporting on current visibility. The
forward scatter sensor also enables
auto-alignment and auto-calibration of the
transmissometer device.
6
Unidades Una candela se define como la intensidad
luminosa de una fuente de luz monocromatica de
540 THz que tiene una intesidad radiante de
1/683 vatios por estereorradián, o
aproximadamente 1.464 mW/sr. La frecuencia de
540 THz corresponde a una longitud de onda de
555 nm, que se corresponde con la luz verde
pálida cerca del límite de visión del ojo. Ya que
hay aproximadamente 12.6 estereorradianes en una
esfera, el flujo radiante total sería de
aproximadamente 18.40 mW, si la fuente emitiese
de forma uniforme en todas las direcciones. Una
vela corriente produce con poca precisión una
candela de intensidad luminosa.