"Visibility sensors"
Range

TR 30 DB
The TR30DB transmissometer is a visibility sensor designed for aeronautical purposes
TR 30

	The transmissometer TR30 is a visibility sensor designed for aeronautical purposes.

DF 20+

	The forward scatter sensor DF 20+ is a sensor designed for visibility measurements. It has been specially built for synoptic meteorological use, but can also be used for aeronautical purposes.

DF 320

	The forward scatter sensor DF 320 is a sensor designed for visibility measurements. It has a 4 meter mast. It gives a large scale of accurate and traceable data (up to 70 kms), even in very difficult climatic conditions.

Visibility measurement

The main principles
Aeronautical visibility is the greatest of the two following values :

• The greatest distance at which a black object with the appropriate dimensions located near the ground when being observed with a luminous background can be seen and recognized,
• The greatest distance at which lights bordering on 1,000 candelas when being observed on an unlit background can be seen and identified.

(According to Annex 3 of the Convention relating to the International Civil Aviation of the ICAO)

There are 2 ways to measure visibility. The first, thanks to forward scatter sensors which measure the capacity of a portion of the atmosphere to diffuse radiation. The second is a transmissometer which allows a more direct approach as it measures the capacity of a portion of the atmosphere to transmit radiation.

The transmissometer is made up of a light source and a receiver placed facing each other. The intersection of the source’s and receiver’s visual fields defines the analysis volume, which is ideally cylindric.
The suspended particles in this volume absorb or scatter the light in all directions and thus reduces the amount of light received by the receiver. The flux measurement means we can measure the transmission ability of the atmosphere (TAA, record of the flux received and the flux emitted) and calculates the optical range in contrast (MOR, coming from Koeschmider’s laws).

The forward scatter sensor is made up of a white light source and a receiver placed off axis from this source. The intersection of the source’s and receiver’s visual fields defines the analysis volume. The suspended particles in this volume scatter the light in all directions and notably in that of the receiver. The measurement of the flux calculates the optical range.

This data, along with the luminance measurement (luminancemeter LU 30, which can be bought as an option) means we can have the Runvway Visual Range (RVR).

Our advantages
DEGREANE HORIZON’s visibility sensors have been recognized by national meteorological services, worldwide.

Some advice
The forward scatter sensor should be set up on a cleared area of about 15 meters. It should be fixed on a concrete block with the receiver pointing northward.