Meteorological Equipment




The Biral ALS-2 is a sensor designed to provide an accurate and reliable determination of the amount of background light during all weather conditions. Such a sensor is usually referred to either as an Ambient Light Sensor (ALS) or Background Luminance Sensor. Such sensors are typically used as part of a system to determine the Runway Visual Range at an aerodrome. The ambient light received by the sensor’s 6° field of view is focussed onto a photodiode of similar spectral response to the human eye. The output from the photodiode is used to determine the ambient light level using the standard (SI) units of candela per square metre (cd m-2), averaged over one minute.

The Biral ALS-2 sensor is a significantly upgraded version of Biral’s original ALS and is designed to meet the world’s most stringent ambient light sensor requirements as stated by the US Federal Aviation Authority (FAA) and ICAO recommendations. This sensor offers significant versatility including the option of serial or analogue outputs and the ability to be used standalone or integrated with a Biral visibility/present weather sensor. Calibration can be checked in the field using the custom-designed portable calibration unit. Extensive self-checking is also featured to ensure optimal performance.
To ensure the sensor’s viewing window remains unobstructed by precipitation, a hood is fitted around the window that has the option of being automatically heated to prevent the build-up of snow if the temperature falls below 2°C. The amount of contamination on the window is checked automatically and compensated for. The window heater is continuously active to remove any water or ice. For operation in extremely cold (below -40°C) conditions, the Biral ALS-2 has the option of additional internal heaters activated along with that on the hood, permitting full functionality down to a temperature of -55°C.

ALS-2 Features:

  • Designed to Federal Aviation Authority (FAA) requirements
  • Built to existing Biral HSS and SWS design standards.
  • Optical response to mimic a human observer
  • Standalone or integrated to Biral HSS or SWS sensors
  • Digital and/or Analogue outputs
  • Extensive self-checkingield calibration can be carried out using




18 February 2017


Biral Products

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