Vaisala MITRAS BROCHURE

MITRAS Transmissometer

Reliable RVR with
MITRAS Transmissometer

Accurate RVR measurement reduces airport down­time and improves safety and reliability of
operations.
The MITRAS Transmissometer system provides You
with correct visibility data without breaks.

Vaisala’s MITRAS is a well­proven solution to Runway
Visual Range assessment. The
system has been in operational
use since 1986 and has demons­trated excellent performance in
international intercomparisons.
MITRAS provides many operat­ional and reliability benefits:

• Conformance to all ICAO and
WMO requirements for RVR and
Meteorological Optical Range
(MOR)

• Fully automatic operation with
excellent accuracy and stability

• Unique contamination detect­ion and compensation

• Double baseline for CAT IIIB
by means of two different beams
from one transmitter

• Extensive built-in monitoring
to verify performance and to
generate warnings before
failures actually occur

• Verified operation in all
weather conditions

SYSTEM STRUCTURE

The standard MITRAS Trans­missometer consists of a light
transmitter and a light receiver
installed at a suitable distance
from each other. MITRAS meas­ures transmission of white light
over the baseline path and con­verts the measurement value to
the corresponding MOR value.
The transmittance measurement
resolution of MITRAS is better
than 0.1 % and the measurement
accuracy is better than 1 %.

A single baseline MITRAS can be
easily and economically up­graded to a double baseline
system when extended measure­ment range is needed for CAT
IIIB applications. The two base­lines are realized by adding an
individual lens system in the
transmitter unit and a second
receiver unit. Excellent accuracy
is guaranteed because the two
separate light beams from the
single transmitter unit do not
interfere with each other.

Vaisala’s LM11 Background
Luminance Meter can be con­nected to a MITRAS transmitter
unit. The luminance sensor is
interfaced to the MITRAS pro­cessor unit and it shares the
same communication line with
the transmissometer.

MITRAS communicates the
measurement results to a host
system via a modem line. RVR
calculations are carried out by a
dedicated RVR computer or an
integrated airport weather
observation system and the
results are sent to various
displays.

COST SAVINGS THROUGH
EASY MAINTENANCE

Contamination of the optical
windows with time is inevitable
and it can have a significant
impact on RVR accuracy. MIT­RAS measures the window con­tamination and automatically
compensates for the loss in
measured transmittance. When

The visibility measurement ranges achieved
by single and double baseline MITRAS
systems are shown below. The baseline of
MITRAS can be freely selected between
10 ... 200 m.

Baseline MOR range RVR range*)

35 m 25 ... 1500 m 100 ... 1500 m
50 m 40 ... 2000 m 150 ... 2000 m
75 m 50 ... 3000 m 200 ... 3000 m
100 m 70 ... 5000 m 300 ... 5000 m
200 m 150 ... 10 000 m 500 ... 10 000 m

*) The actual RVR range is dependent on runway lighting.
The values shown are based on usual lighting arrangements.

Baseline MOR range RVR range*)

10 and 75 m 7 ... 3000 m 40 ... 3000 m
10 and 200 m 7 ... 10 000 m 40 ... 10 000 m

(Double baseline is required in CAT IIIB operating category.)

One background luminance meter, mounted

on top of the light transmitter, is sufficient per

runway to measure the background luminance

window contamination exceeds
an acceptable level, a warning is
sent out and the window can be
cleaned. This unique function
extends the cleaning intervals
significantly, while the user is
assured of consistently high data
quality.

Each MITRAS unit continuously
monitors several technical para­meters and generates warning
and alarm messages in cases of
fault. The MITRAS status can be
monitored remotely over the
modem line. Automatic monit­oring in the transmitter and re­ceiver covers supply voltages,
internal temperatures, optical
performance including correct
calibration/alignment and detect­ed failures. This information can
be interrogated by the service
technician before leaving for the
site. Warnings of lamp ageing
and window contamination are
generated as needed.

The xenon flash lamp’s nominal
lifetime is 8 years at one flash
per second. MITRAS extends the
lifetime by adjusting the flash
rate depending on visibility. An

value needed in visibility calculation.

interval of one second between
flashes is used in low visibility.
The flash interval increases step­wise to 10 seconds when visibili­ty improves to a measured value
above 10 km.

SUPERIOR ACCURACY

In the WMO intercomparison of
visibility measurements, MITRAS
achieved the best results con­cerning measurement accuracy.

MITRAS measures both the trans­mitted and the received light
pulse amplitudes. Instead of re-

lying on estimates of projected
light power, every transmitted
pulse is measured. Atmospheric
transmittance is then calculated
as the ratio of received and
transmitted light power on a
single pulse basis. Receiver el­ectronics are gated to receive
only light pulses from the trans­mitter, and will not accept any
interference light during the
interval.

The wide-bandwidth white light
of the transmitter’s xenon flash
lamp and the photopically
corrected receiver sensitivity
provide an ideal match of the
human eye’s spectral range.

MITRAS beams are optimized.
Interference from other light
sources, such as the sun or the
aircraft lights is minimized by
accurate beam forming. Light
distribution across the beam is
even. Multiple forward scattering
and dispersion in fog is minim­ized. Simplicity of optical design
and good temperature stability
are key factors of the system’s
exceptional stability.

Temperature of the optics is
maintained constant and above
the ambient to prevent con­densed moisture on the optical
surfaces. Control is proportional
to avoid temperature cycling.

Technical Information

GENERAL

Measuring range 0 ... 100 % transmittance
Resolution 0.02 % of transmittance
Accuracy (verified by calibrated optical filters) 1 % of FSR
Meets ICAO (Annex 3) recommendations in specific ranges.
Time constant 60 s
Sample interval 1 s
Baseline allocations 10 ... 200 m altered by neutral density filters
Height with standard pedestal (others on request) 2500 mm
Calibration and checks With optical filters &

maintenance terminal command checks
Operating temperature –40 ... +55 °C
Operating humidity 0 ... 10 % RH
Wind speed Construction withstands up to 60 m/s
Power supply 115/130/230/240 VAC

+10 % -15 % of nominal value 45.65 Hz,

Weight 35 kg
Dimensions
Optical head with hood 390(h) × 225(w) × 980(l) mm
Electron. box without rad. shield 310(h) × 400(w) × 190(l) mm
Colour White
Housing Aluminum, weatherproof
Mounting On concrete foundation

LP11 LIGHT TRANSMITTER

Light source Xenon flash bulb
Peak radiated power (adjustable by commands) 40 ... 160 kW
Lamp life 55 000 hours

Spectral output range 300 .... 1100 nm

Microprocessor 8031 with application program

to control all functions, calculations,

communications and built-in test facilities
Power consumption 250 W/300 W with LM11
MTBF (MIL-STD-217E) > 13 700 hours
RVR computer interface Modem CCITT V.21

Dedicated line to RVR computer

Without modem: RS-232C interface
Maintenance terminal interface RS-232C, 300 baud
Output message Visibility, transmittance values,

luminance data (if connected),

Options Double baseline optics (LPO11)

LM11 Background Luminance Meter

single phase

status data in ASCII

LR11 LIGHT RECEIVER

Reception angle 9 mrad
Immunity to external light 75 000 W halogen lamp

30 m far (cont. light) has no influence
Spectral response range 300 ... 700 nm
Peak wavelength 550 nm
Microprocessor 8031 with application program

to control all functions, calculations,

communications and built-in test facilities
Power consumption 250 W
Maintenance terminal interface RS-232C, 300 baud
MTBF (MIL-STD-217E) 22 100 hours

LM11 BACKGROUND LUMINANCE METER

Measuring range 4 ... 30 000 cd/m
Accuracy 10 %
Spectral response range 300 ... 700 nm
Peak wavelength 550 nm
Field of view 5 degrees
MTBF (MIL-STD-217E) 183 000 hours
Connection To any LP11 Light Transmitter
Mounting On top of LP11 by a screw

2

Head Office:

VAISALA Oy

PL 26, FIN-00421 Helsinki
FINLAND
Phone (int.): ([phone]
Telefax: ([phone]
Telex: 122832 vsala fi

VAISALA GmbH

Postfach 540267
D-22502 Hamburg
DEUTSCHLAND
Phone (nat.): [phone]
Telefax: [phone]

VAISALA (UK) Ltd

Cambridge Science Park
Milton Road
Cambridge CB4 4GH
UNITED KINGDOM
Phone (nat.): [phone]
Telefax: [phone]

VAISALA TMI Ltd

Vaisala House
349 Bristol Road
Birmingham B5 7SW
UNITED KINGDOM
Phone (nat.): [phone]
Telefax: [phone]

VAISALA SA

3, Parc Ariane
Saint-Quentin-En-Yvelines
F-78284 Guyancourt Cedex
FRANCE
Phone (nat.): (1) 3057 2728
Telefax: (1) 3096 0858

VAISALA Inc.

100 Commerce Way
Woburn, MA 01801 - 1068
USA
Phone (nat.): [phone]
Telefax: [phone]

VAISALA KK

42 Kagurazaka 6-Chome
Shinjuku-Ku,
Tokyo 162
JAPAN
Phone (nat.): [phone]
Telefax: [phone]

VAISALA Pty. Ltd.

A.C.N. 006 500 616
80 Dodds Street
South Melbourne, VIC 3205
AUSTRALIA
Phone (nat.): (3) 9696 5699
Telefax: (3) 9696 5776

VAISALA Beijing
Representative Office

Room 518, 520
Wangfujing Grand Hotel
No. 57 Wangfujing Street
Beijing 100006
PEOPLE'S REPUBLIC OF CHINA
Phone (nat.): (10) 522 4050
Telefax: (10) 522 4051

Ref. A591en 1995-11