Visibility Sensor FS11

Measuring visibility at ports and harbors

Model: FS11
Manufacturer: Vaisala – Finland

  • Unique window contamination correction
  • Accurate and traceable forward scattering measurement
  • Technical design and high-power heating according to FAA guideline
  • Frangible composite fiber mast
  • Can be upgraded for sensing present weather

Designed according to ICAO, FAA, and WMO guidelines, the FS11 is an ideal instrument for runway visual range (RVR) assessment and airport visibility measurement, as well as other demanding applications. It provides the optimal combination of the best accuracy, the highest reliability, broad measurement range, and low maintenance needs.


The main applications of FS11 are runway visual range (RVR) and synoptical and aeronautical visibility measurements. FS11 is also well suited for other demanding applications, such as visibility measurement at ports and harbors.

Scientifically Valid Chain of Calibration

FS11 is calibrated through a scientifically valid chain of reference. The scattering response of the calibration device can be clearly traced to a reference FS11 visibility sensor, which is in continuous operation at Vaisala outdoor test field along with reference transmissometers and other

instrumentation. The visibility measurement of FS11 is also traceable to FAA reference sensors.

Low Maintenance Need

FS11 incorporates a technique that measures and compensates for window contamination. It ensures unparalleled measurement accuracy between window cleanings. It also enables much longer window cleaning intervals than compared to conventional visibility sensors. The unique system works by monitoring the total reflectance of the window surface. It automatically compensates for visibility measurement errors caused by window contamination. The sophisticated self-diagnostics and modular design allow for very short service times. The measurement fork and optional background luminance sensor LM21 are independent instruments that can be replaced quickly as pre-calibrated spare parts.

Reliable Operation in the Harshest Weather

Four main design features are combined in FS11 to ensure reliable operation in the harshest weather. The first is the window contamination compensation technique. The second is the “head-down” design of the optical heads, which protects them against virtually all windblown particles (even those flying horizontally). High-power heaters are the third feature. Each heater has its own temperature monitoring and control mechanism to prevent snow accumulation during the heaviest snowstorm. As a final measure, there is an optical path clearance monitoring circuitry to verify that measurement is not affected by obstructions.

Measurement Performance
Measurement range of MOR 5 … 75 000 m (16 ft … 46.6 mi) with 1, 3, and 10 min averaging
Accuracy ±10 % range 5 … 10 000 m (16 ft … 6.2 mi) ±20 % range 10 000 … 75 000 m (6.2 … 46.6 mi)
Scatter measurement accuracy ±3 % 


Optical Specifications
Operating principle Forward scatter measurement
Scattering angle 42°
Light source  Near-infrared LED


Operating Environment
Operating temperature −40 … +65 °C (−40 … +149 °F),

 −55 … +65 °C (−67 … +149 °F) (optional)

Operating humidity 0 … 100 %
Wind speed Up to 60 m/s (134 mph)


Inputs and Outputs
AC (mains) power supply 100/115/230 VAC ±10 %, 50 … 60 Hz
Power consumption Max. 300 VA (60 VA + 240 VA defrosting heaters)
Battery backup option Battery 2 Ah, typical backup time 30 min at 25 °C (77 °F) and 5 min at −40 °C (−40 °F)
Outputs Serial data line RS-232 or optoisolated RS-485 (2-wire) or optional data modem Separate maintenance line RS-232 +12 VDC max. 0.8 A output for option powering


Mechanical Specifications
Dimensions (H × W × D) 2.8 × 0.9 × 1.0 m (9.19 × 2.95 × 3.28 ft)
Weight without mast  37 kg (81.57 lb)
Weight, including Frangible Mast FSFM250 52 kg (115 lb)
IP rating IP66
Mast Frangible and hinged glass fiber mast


Spare Parts and Accessories
Calibration set FSA11
Background luminance sensor LM21
Battery backup FSB101
Modem for long distance communication (> 1 km / 0.6 mi) DMX501
Obstruction light FS11OBS


EMC Compliance
Radiated emissions EN55022
Radiated susceptibility IEC 61000-4-3, 10 V/m
Conducted emissions EN55022
Conducted susceptibility IEC 61000-4-6
EFT immunity IEC 61000-4-4
ESD immunity IEC 61000-4-2
Surge IEC 61000-4-5
Harmonics to the AC (mains) grid IEC 61000-3-2

Visibility Sensor FS11


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