RVR / Transmissometer for Runway Visibility Measurement
Automated visibility measurement, engineered as part of the whole weather system
RVR (Runway Visual Range) / Transmissometer systems provide automated measurement of atmospheric visibility for airport meteorological monitoring and runway visual range assessment. An optical measurement path determines atmospheric extinction or visibility-related parameters and passes processed data to an airport weather observation system, RVR display, ATIS interface or other approved reporting infrastructure. Precision AGL Solutions provides configurations suited to airport weather networks, AWOS installations, ATIS systems and centralized monitoring platforms.
RVR / Transmissometer
For precision approach runways and low-visibility operations, reliable visibility measurement is an important part of the airport's overall meteorological and operational information system.
The final installation arrangement should be selected according to runway classification, operational requirements, sensor location criteria, reporting architecture and applicable aviation authority requirements.
Where RVR / Transmissometers Are Used
How a Transmissometer Works
A transmissometer measures the attenuation of light travelling through a defined atmospheric path. An optical transmitter and receiver are positioned at a known separation. Fog, mist, dust, smoke and other suspended matter reduce the light reaching the detector. The equipment processes this attenuation into an atmospheric visibility parameter. Configured for RVR, the visibility information can be combined with other runway and meteorological inputs to give runway visual range for operational reporting.
Many airports also use forward-scatter visibility sensors as the RVR input, which ICAO Doc 9328 recognises alongside transmissometers. A transmissometer measures over a fixed baseline, while a forward-scatter sensor measures a small sample volume. Select the sensor type from the airport's RVR requirement, the runway category and the aviation authority's approval basis.
A typical installation may include:
- Optical transmitter
- Optical receiver
- Transmissometer mounting structures
- Controller or processing unit
- Communication interface
- Power supply and protection
- Local maintenance interface
- Integration with AWOS/RVR processing equipment
- Remote RVR or visibility display
- Interface to ATIS or airport meteorological systems
From Transmittance to Runway Visual Range
The transmissometer measures transmittance (T) over a fixed baseline (L). From this the system derives the extinction coefficient (σ), and meteorological optical range (MOR) follows from it. RVR is then calculated for the pilot's viewing conditions, not just reported as MOR:
By day
RVR is computed from the extinction coefficient and the background luminance (Koschmieder's law, for the visibility of a dark object against the horizon sky). Runway lights matter less in strong daylight.
By night and at low light
RVR is computed from the extinction coefficient and the intensity of the runway lights in use (Allard's law, for the range at which lights are seen). The processor needs the actual runway light brightness step from the constant current regulator (CCR) or the lighting control system.
AGL link: if the brightness step reaching the RVR processor does not match the step set on the CCR, the reported RVR will be wrong. Commissioning must verify this interface end to end, and it must be re-verified after any change to the lighting control system or CCR replacement. Confirm that the step table in the RVR processor matches the actual intensity of the approach, edge and centreline lights in use on that runway.
RVR Reporting Basics
| Item | Typical ICAO practice (Annex 3 / Doc 9328) |
|---|---|
| When RVR is assessed and reported | Required on CAT II/III runways. Also assessed for CAT I and other runways used in low visibility, whenever visibility or RVR falls below about 1,500 m |
| Reported range | Approximately 50 m to 2,000 m; values outside are reported as below or above the limits |
| Reporting steps | 25 m below 400 m, 50 m from 400 to 800 m, 100 m above 800 m |
| Averaging period | One minute for local reports and ATS displays; ten minutes for METAR/SPECI, with trend where required |
| Sensor positions | Representative of the touchdown zone; midpoint and stop-end as well for CAT II/III runways |
Note: Values are given as general guidance. Confirm ranges, steps, averaging and the number of RVR positions against the current edition of Annex 3, Doc 9328 and your aviation authority's requirements before the page is used as a specification.
Typical Measurement Parameters
Depending on configuration, the installation may provide:
- Atmospheric visibility
- Meteorological optical range / visibility-related data
- Transmittance or extinction-related measurement
- RVR output where configured as an RVR system
- Sensor status and equipment health information
- Communication status
- Diagnostic and maintenance data
- Alarm or fault indications
Exact parameters, calculation methods, reporting resolution and interfaces depend on the selected equipment and airport system architecture.
What the System Provides
Typical Configuration
| Parameter | Typical Configuration |
|---|---|
| Measurement principle | Optical transmissometer / atmospheric light attenuation measurement |
| Measurement parameter | Atmospheric visibility / transmissivity-derived visibility |
| RVR capability | Available when configured as part of a compliant RVR system |
| Measurement range | Model and configuration dependent |
| Measurement accuracy | Model and environmental-condition dependent |
| Optical system | Transmitter and receiver with defined optical measurement path |
| Optical path length | Baseline selected to suit the visibility range to be measured; shorter baselines favour low-visibility resolution, longer baselines extend the upper range |
| Reporting output | Extinction coefficient / MOR to the RVR processor; RVR in reporting steps from the processor |
| Light-intensity input | Runway light brightness step from the CCR or lighting control system |
| Background luminance input | Ambient light sensor for day/night computation |
| Data output | Digital communication interface, according to selected configuration |
| Communication interface | Ethernet, serial or other supported interface |
| Power supply | Airport AC/DC supply according to equipment configuration |
| Environmental performance | Outdoor airport environmental rating, model dependent |
| Mounting | Dedicated poles, structures or equipment supports |
| Enclosure | Weather-resistant outdoor construction |
| Diagnostics | Equipment and measurement-status monitoring |
| Maintenance interface | Local and/or remote service interface |
| System integration | AWOS, RVR processor, ATIS, weather display and airport network |
| Installation | Site-specific optical alignment and location requirements apply |
Note: Exact measurement range, accuracy, optical path length, interface protocol, power consumption, environmental rating and mounting dimensions should be confirmed against the selected manufacturer's current technical documentation before procurement.
Main System Components
A Complete RVR Measurement System
A transmissometer is one component of a complete RVR system. Depending on the airport configuration, RVR determination may require integration with:
- Visibility measurement
- Runway light intensity setting (brightness step from the CCR or lighting control system)
- Background luminance (ambient light) sensor
- Runway configuration
- Sensor location
- Relevant meteorological parameters
- RVR processing algorithms
- Operational reporting interfaces
Engineer the RVR architecture as a complete system, not the transmissometer as an isolated visibility sensor.
Installation Requirements
Correct installation is essential for reliable visibility measurement. The design should consider:
- Transmitter and receiver separation
- Optical alignment and sensor height
- Runway geometry and sensor location relative to the runway
- Obstructions within or near the optical path
- Aircraft and vehicle clearance, including runway strip and obstacle-limitation surfaces
- Frangible mounting of equipment within the operational area (Annex 14, Vol. I, Chapter 9)
- Lateral offset from runway centreline and height above runway, to suit the sensor position
- Effects of jet blast, spray, de-icing fluid and snow clearance on the optical windows
- Maintenance access
- Electrical power availability
- Communication cable routing
- Earthing and surge protection
- Environmental exposure
- Protection against accidental impact
- Airport construction and safety restrictions
Establish exact sensor location from the applicable airport design criteria and operational requirements. Typical ICAO guidance puts sensors close to the runway (of the order of 120 m from the centreline or less) at about 2.5 m height, with the touchdown-zone sensor about 300 m from the threshold. Check these figures against Annex 3 Appendix 3 and Doc 9328 for your edition.
Optical Alignment
Transmissometer performance depends heavily on correct optical alignment. During installation and maintenance:
- Confirm the transmitter and receiver mounting positions.
- Verify mechanical stability of both structures.
- Align the optical axes according to the manufacturer's procedure.
- Check the optical measurement path for obstructions.
- Confirm signal strength and measurement stability.
- Record alignment and commissioning measurements.
- Repeat verification after major structural work or equipment relocation.
Follow the manufacturer's approved maintenance documentation.
Commissioning Procedure
Calibration, Verification and Maintenance
Visibility measurement equipment requires periodic verification to maintain confidence in reported data. Activities may include optical inspection, alignment verification, transmitter output and receiver response verification, window/lens cleaning, diagnostic review, communication testing, comparison against approved reference procedures, and calibration using manufacturer-approved equipment. Intervals follow the manufacturer's recommendations, the airport maintenance program and regulatory requirements.
Troubleshooting
| Symptom | Possible Cause | Recommended Action |
|---|---|---|
| No visibility data | Power or communication failure | Check supply, controller and communication interface |
| Unstable measurement | Optical contamination or alignment issue | Inspect and realign optical units |
| Reduced optical signal | Dirty window/lens or degraded optical component | Clean and inspect optical surfaces |
| Communication alarm | Network or interface fault | Check communication link and configuration |
| Incorrect or unexpected values | Sensor condition, calibration or environmental issue | Review diagnostics and perform approved verification |
| Intermittent operation | Power, connector or environmental problem | Inspect wiring, connectors and enclosure |
| Persistent optical fault | Transmitter/receiver problem | Perform manufacturer diagnostic procedure |
| RVR does not change with lighting brightness setting | Light-intensity interface fault or wrong step mapping | Check CCR/lighting control feedback and the processor step table |
| Day/night changeover wrong | Background luminance sensor dirty, shaded or faulty | Clean, check view of the sky and verify luminance reading |
| RVR output unavailable | RVR processing/integration fault | Check visibility input and RVR processor interface |
Use the manufacturer's approved service procedures and airport maintenance requirements.
Environmental Performance and Electrical Protection
Environmental Exposure
- Rain, fog, mist, dust and sand
- High humidity and condensation
- Temperature variation and solar radiation
- Wind
- Electrical transients
- Bird and wildlife activity
- Operating temperature, humidity, ingress protection and wind loading are model-specific; confirm during technical evaluation
Electrical Protection
- Overcurrent protection
- Surge protection
- Equipment earthing and lightning protection
- Shielding and cable segregation
- Communication-line protection
- Proper termination of field cables
- Coordinate with the airport electrical design and lightning environment
Replacement and Retrofit Applications
Equipment can be supplied for new runway installations, existing RVR upgrades, replacement of obsolete transmissometers, AWOS modernization, migration to digital communications, replacement of legacy visibility sensors, and integration with centralized airport weather networks.
For retrofits, review the existing sensor locations, optical path, mounting structures, power supply, communication architecture and RVR processing equipment before selecting replacements.
Ordering Checklist
Before ordering, confirm:
- Runway and installation location
- Required visibility measurement range
- RVR requirement
- Number of measurement positions
- Optical path arrangement
- Required measurement accuracy
- Required data outputs
- Communication interface
- AWOS and ATIS integration requirements
- Existing RVR processor compatibility
- Power supply
- Environmental requirements
- Mounting arrangement
- Cable lengths and routing
- Surge and lightning protection
- Calibration requirements
- Maintenance access
- Spare parts requirements
- Required documentation
- Applicable airport authority requirements
Standards, References and Documents
Standards and References
- ICAO Annex 3 – Meteorological Service for International Air Navigation
- ICAO Annex 14, Volume I – Aerodrome Design and Operations
- ICAO Doc 9328 – Manual of Runway Visual Range Observing and Reporting Practices
- WMO-No. 8 – Guide to Instruments and Methods of Observation
- ICAO Annex 3, Appendix 3 – technical specifications for observations and reports (RVR assessment, averaging and reporting)
- ICAO Doc 9837 – Manual on Automatic Meteorological Observing Systems at Aerodromes
- Applicable FAA requirements for RVR and visibility measurement systems
- DGCA India requirements and the meteorological authority (IMD) requirements for aerodrome observing systems
- Airport-specific technical specifications
- Manufacturer installation and maintenance manuals
Documentation
- Technical datasheet and product catalogue
- System configuration
- Installation, operation and maintenance manuals
- Wiring diagrams and mounting details
- Communication/interface documentation
- Calibration or verification documentation
- Factory and site acceptance test documentation
- Recommended spare parts list
- Preventive maintenance schedule
Confirm the applicable edition and exact compliance requirements during project design and procurement. Numerical values on this page (reporting steps, averaging periods, sensor positions) are general ICAO guidance and are not a substitute for the current Annex 3, Doc 9328 and DGCA/IMD requirements.
Selection Based on Your Runway and Systems
We support visibility measurement projects with equipment selection based on the actual runway, meteorological, electrical, communication and integration requirements, so the solution integrates reliably with the airport's meteorological and operational infrastructure.
RVR / Transmissometer — Frequently Asked Questions
What is an RVR / transmissometer system?
It provides automated measurement of atmospheric visibility for airport meteorological monitoring and runway visual range assessment. An optical measurement path determines atmospheric extinction, and the processed data goes to an airport weather observation system, RVR display, ATIS interface or other approved reporting infrastructure.
How does a transmissometer work?
It measures the attenuation of light travelling through a defined atmospheric path between an optical transmitter and receiver at a known separation. Fog, mist, dust, smoke and other suspended matter reduce the light reaching the detector, and the equipment processes this attenuation into a visibility parameter.
How is RVR calculated from the transmissometer reading?
The transmissometer measures transmittance (T) over a fixed baseline (L), from which the extinction coefficient is σ = −ln(T) / L and meteorological optical range follows as MOR ≈ 3 / σ. RVR is then calculated for the pilot viewing conditions: by day from the extinction coefficient and background luminance (Koschmieder), and at night from the extinction coefficient and runway light intensity (Allard).
Why does RVR depend on the runway light brightness step?
At night and in low light the processor needs the actual runway light brightness step from the CCR or lighting control system. If the step reaching the RVR processor does not match the step set on the CCR, the reported RVR will be wrong, so commissioning must verify this interface end to end and re-verify it after any change to the lighting control system or CCR replacement.
Can a forward-scatter sensor be used instead of a transmissometer?
Many airports use forward-scatter visibility sensors as the RVR input, which ICAO Doc 9328 recognises alongside transmissometers. A transmissometer measures over a fixed baseline, whereas a forward-scatter sensor measures a small sample volume. Select the type from the airport RVR requirement, the runway category and the aviation authority approval basis.
Where should RVR sensors be located?
Establish the exact location from the applicable airport design criteria. Typical ICAO guidance puts sensors close to the runway, of the order of 120 m from the centreline or less, at about 2.5 m height, with the touchdown-zone sensor about 300 m from the threshold. Check these figures against Annex 3 Appendix 3 and Doc 9328 for your edition. Equipment within the operational area should be frangibly mounted.
What are the typical RVR reporting rules?
General ICAO guidance gives a reported range of approximately 50 m to 2,000 m, with steps of 25 m below 400 m, 50 m from 400 to 800 m and 100 m above 800 m, and averaging of one minute for local reports and ATS displays and ten minutes for METAR/SPECI. RVR is required on CAT II/III runways. Confirm against the current Annex 3, Doc 9328 and DGCA/IMD requirements before using these as a specification.
Why is optical alignment important?
Transmissometer performance depends heavily on correct optical alignment. Confirm the mounting positions and mechanical stability of both structures, align the optical axes per the manufacturer procedure, check the path for obstructions, confirm signal strength and stability, record the results and repeat verification after major structural work or equipment relocation.
What is the role of the background luminance sensor?
It measures ambient light for the day and night computation of RVR. It is usually mounted separately from the transmissometer with a clear view of the sky and no shadow or reflected light. A wrong day or night changeover can point to a dirty, shaded or faulty sensor.
What maintenance and troubleshooting does it need?
Periodic optical inspection, alignment verification, window and lens cleaning, diagnostic review, communication testing and calibration or verification using manufacturer-approved procedures. For unstable measurement check contamination and alignment, for no data check supply and communication, and if RVR does not change with the lighting brightness setting check the CCR feedback and the processor step table.
Which standards apply to RVR systems?
References include ICAO Annex 3 and its Appendix 3, ICAO Annex 14 Volume I, ICAO Doc 9328, ICAO Doc 9837, WMO-No. 8, and DGCA India and IMD requirements for aerodrome observing systems. Confirm the applicable edition for the project. See also the Wind & Visibility Display page for presenting RVR to operations staff.
What should I confirm before ordering?
Confirm the runway and installation location, required visibility measurement range, RVR requirement, number of measurement positions, optical path arrangement, accuracy, data outputs, communication interface, AWOS and ATIS integration, compatibility with the existing RVR processor, power supply, environmental requirements, mounting, surge and lightning protection, calibration and documentation.
Procurement Information for Indian Projects
Indian public tenders commonly ask for the documents below. State which ones your tender requires when you send the enquiry, so they are covered in the quotation.
- Manufacturer / OEM authorisation
- Country of origin and local-content declaration (for Make in India purchase preference)
- Type-test and routine-test certificates, and the FAA / ICAO / IEC compliance documents named in the specification
- Datasheets, drawings and installation instructions
- Warranty, delivery period and spares support
- GeM catalogue or tender-portal requirements, where applicable
Request RVR System Requirements Review
Planning a new RVR installation, replacing an existing transmissometer, or upgrading an airport weather monitoring system? Share your runway configuration, required RVR measurement points, existing equipment, communication interface and airport integration requirements. We can help identify the appropriate transmissometer, RVR processing architecture, mounting arrangement, interfaces and supporting equipment.
Engineering Note
An RVR / transmissometer installation should be treated as part of the complete airport meteorological measurement and reporting system. Sensor selection alone does not establish RVR compliance. RVR is calculated from transmittance, background luminance and the runway light intensity in use, and the sensor positions must represent the touchdown zone, midpoint and stop-end as required for the runway category.
Final equipment selection should consider the runway operational category, sensor location, optical measurement arrangement, runway lighting information, processing architecture, reporting requirements, applicable aviation regulations and the manufacturer's current technical documentation.
Product Disclaimer
Product availability, configuration, dimensions, electrical characteristics, photometric performance, certifications and compliance status depend on the selected manufacturer and project specification. The technical values published on this page should not be treated as a substitute for the manufacturer's current approved Technical Data Sheet.
Final selection shall be based on the approved project specification, applicable aviation standards, authority requirements, manufacturer documentation and site conditions. Use of this page is also subject to the Legal Notice, Disclaimer & Terms of Use.
Standards and editions referenced on this site are listed on the Standards Reference page.