Present Weather Detector PWD12


Thousands of Vaisala present weather and visibility sensors are installed around the world, working reliably and accurately in diverse applications and climates. In the Vaisala PWD-series of present weather detectors and visibility sensors, you will find the mix you require of visibility measurement range (MOR), characterization of reduced visibility, precipitation type identification, precipitation accumulation/intensity measurement, and report formats (WMO, NWS code tables)


​Accurate measurement of visibility

Robust and versatile

Indicates the cause of reduced visibility

Identifies precipitation type

Measures the intensity and accumulation of precipitation

Estimates snow accumulation

Present Weather Detectors PWD22 and PWD52


Dependability is the critical requirement for many of Vaisala's customers. Automated observation networks need to operate with maximum reliability. Maritime and aviation observing systems need to perform in extremely harsh conditions and many meteorological institutes face challenging productivity and performance requirements.

The Vaisala's systems answer these needs with a mixture of robustness, dependability, versatility, and reliability. They deliver a wide visibility measurement range and dependable present weather reporting.


Accurate, traceable measurement of prevailing visibility

Detects precipitation type

Measures the intensity and accumulation of precipitation

Estimates snow accumulation

Indicates the cause of reduced visibility

Robust and dependable

Weather-proof design reduces need for maintenance

Easy to install, easy to integrate

Present Weather Sensor FS11P


The Vaisala Present Weather Sensor FS11P is intended for demanding weather applications such as runway visual range (RVR), aeronautical and synoptical visibility and present weather observation. The FS11P is a combined RVR, visibility and present weather sensor. It delivers valuable multi-parameter measurement, all in one. It transmits data on visibility up to 75km, present weather covering obscuration, precipitation type and intensity, and optionally background luminance.


Detects precipitation type and intensity

Well suited for synoptic​ and aeronautical applications

The most widely proven forward scatter RVR sensor, selected and used by FAA

Meets FAA and ICAO specifications for RVR and visibility measurement

The most widely proven present weather sensing technology

Meets ICAO frangibility standards

Visibility Sensors PWD10, PWD20 and PWD20W


While often required for safety, flashing lights can disturb those nearby so it is smart to dim them to the optimal level. Vaisala's PWD series sensors allow you to create a comfortable living environment for the surrounding community, while offering best-in-class measurement performance and proven reliability. With built-in hood heaters, these sensors prevent ice accumulation on the device and also have a special firmware that ensures flashing lights near the visibility sensor are not mixed with light pulses from the sensor.

Thousands of PWD sensors have been installed worldwide in demanding applications and in all kinds of climates where visibility is a critical factor. For example, the FAA and other leading aviation authorities rely on Vaisala's visibility measurements and have placed their confidence in us. This is due to our low failure rate statistics which indicate a mean time between failures (MTBF) in excess of 20 years. We also offer fast delivery times to quickly meet our customers needs.


Robust and versatile

Accurate measurement of visibility

Visibility Sensor PWD50


Dependable operation of automated observation networks is a must today. Maritime observing systems need to work in inhospitable environments and also meteorological institutes face tough productivity and performance prerequisites.

The Vaisala Visibility Sensor PWD50 answers these needs with a mixture of robustness, dependability, versatility and reliability. The PWD50 measures visibility from 10 m up to 50 km.


Accurate, traceable measurement of prevailing visibility

Robust and dependable

Visibility Sensor FS11


Visibility Sensor FS11 is the choice for demanding applications where an optimal combination of the best accuracy, the highest reliability, broad measurement range and a low maintenance need is required. The main applications are Runway Visual Range, synoptical and Aeronautical Visibility. FS11 is also well suited for other demanding applications, such as visibility measurement at ports and harbors.


Specially built for Runway Visual Range (RVR) applications

Meets FAA and ICAO specifications

Mechanical design and high-power heating

Can also be used for aeronautical and SYNOP visibility measurements

Forward Scatter FD70 Series


Vaisala Forward Scatter FD70 Series combines forward scatter and optical disdrometer technologies. The novel utilization of a single thin light sheet instead of the conventional light cone results in a high detection sensitivity. This enables a scatter‑properties analysis of each single particle and allows the detection of even the smallest drizzle droplets. The particle size and fall speed distributions provide additional information, enhancing precipitation type identification. The receiver measures the forward scattered light at an angle of 42° with a very high sampling rate and powerful signal processing.


Reports visibility up to 100 km (62 mi)

Reports precipitation type, intensity, and accumulation

Exceptional precipitation detection sensitivity

Precise type identification even for low-intensity precipitation

Superior liquid/frozen differentiation

Optimal forward scatter angle 42°

Look-down geometry to minimize measurement disturbances

Transmissometer LT31


Accurate and reliable, WMO and ICAO compliant determination of the Runway Visual Range (RVR) reduces airport downtime and improves safety of operations. The Vaisala Transmissometer LT31 is the qualified observer of RVR providing correct visibility data without interruptions and with minimal maintenance.


Single baseline for the measurement range 10...10 000 m MOR

State-of-the-art white light source

Window contamination compensation

Sophisticated self-diagnostics

Internal back-up battery

Meets the ICAO ad WMO requirements for RVR and visibility

Based on decades of field experience

Compatible with Vaisala Transmissometer MITRAS and SKOPOGRAPH II Flamingo

Background Luminance Sensor LM21


The Vaisala Background Luminance Sensor LM21 is a state of the art luminance sensor for Runway Visual Range (RVR) assessment. The background luminance has an effect on the distance from which the pilot can see the runway lights. Resembles Human Eye The LM21 is a precision photometer with a verified photopic spectral response. The LM21 measures the total amount of light coming in from an angle of 6 degrees, and converts the measured data to cd/m2. The LM21 sends the measurement data to the interface unit of a Vaisala transmissometer or forward scatter visibility sensor. The interface unit combines both the visibility and background luminance data into the same message and sends it to the main RVR computer. The LM21 can be connected to the Vaisala Transmitter LT31, and Forward Scatter Sensor FS11. The LT31 and FS11 are connected using a RS-485 serial line.


Intelligent, stand-alone sensor

Verified accuracy and photopic response

Extensive self-diagnostics

Window contamination measurement and compensation

Optical path blockage detection

High power heaters to prevent snow accumulation

Calibration traceable to measurement standards

Field calibration device available

Easy to calibrate


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