Visibility on the runway is extremely important for safe landing and take-off of an aircraft. Hence visual-range accessors are mandatory for all airport runways.

Till now the transmissometers used in Indian airports were imported. The requirement of a highly-accurate, cost-effective, low-maintenance, indigenous, state-of-the-art system on par with more-expensive imported systems prompted development of the Drishti transmissometer at CSIR-NAL.

Drishti at New Delhi Airport

Explore Circuits and Projects Explore Videos and Tutorials

Indigenous, economical and rugged
Drishti is the only indigenously-developed transmissometer of its kind available today. It costs just one-third the price of an imported system, yet gives more precise readings than it.


The device is rugged, has high mean time between failures and is nearly maintenance-free. In fact, the Drishti system installed in New Delhi airport in 2011 has never had a failure or maintenance issue to date!

Virtual instrumentation concept with a combination of modular hardware and software design has made serviceability easier, while weatherproof enclosures (IP65) for the electronics hardware make the system rugged. The availability of complete knowledge base to the component level allows cost-effective servicing and maintenance.

Modern design
Built on an industry-standard FPGA design platform, Drishti makes good use of virtual instrumentation concept. Miniaturised, highly-precise, modular optics with provision for manual and automatic alignment has been used in its design.


The use of electronic modulation technique for modulating lamp intensity and synchronous demodulation technique for improving signal-to-noise ratio make Drishti highly efficient. It is provided with landline and Wi-Fi communication from runway to air traffic control (ATC) room. It also features web-enabled remote accessibility for data and health monitoring of the system from anywhere in the country. The system facilitates automated measurement of RVR (50-2000 metres) and MOR (10-10,000 metres).

LED Streetlights With Unique Thermal Management

The system

Drishti, developed by CSIR-NAL for Indian Meteorological Department (IMD), meets the specifications for visibility measurement instruments set forth by ICAO and WMO. It has a field-programmable gate array (FPGA)-embedded hardware and web-enabled data acquisition software built in LabView environment.


It basically comprises of a transmitter (a lamp with spectral characteristics similar to runway lights) that sends collimated beam of light and a receiver (an optical detector and associated electronics photopically-corrected to match the human-eye response) that is set up at a characteristic distance to collect the transmitted beam.

Drishti is a 30-metre baseline system covering low and high visibility ranging from less than 25 metres to about 10,000 metres. It is suitable for installation in all categories of airport—CAT I, CAT II, CAT III A and CAT III B. It also has provision for varying the baseline anywhere between 15 metres to 75 metres as per international standards.

The instrument is set up parallel to airport runway. A detector collects the transmitted light beam and measures the attenuation of light intensity caused while traversing through the atmosphere. It works on the principle that, higher the attenuation factor, lower will be the visibility of the runway. Data from field site is transmitted to ATC room, which is usually located 4 to 5 kilometres away, through cable and Wi-Fi.

A multi-disciplinary field product, the success of which is attributed to the effective and efficient use of physics, material science and several engineering streams, such as electronics, computer science, communication, civil, environmental, structural, electrical and mechanical engineering.

There were several technical constraints the team had to overcome during the development of this product. Since Drishti is a field equipment, it should be capable of withstanding harsh environment conditions like rain, fog, lightning and climatic variations (extreme heat of about 55°C during summer and snow in winter). As safety of aircraft cannot be compromised, a real-time operating system that works round the clock was necessary. Also, the system should be rugged with high mean time between failures.

"Today We Are In A Phase Where Haptics Is Necessary"

The Drishti team was able to meet all these challenges successfully using virtual instrumentation concept. With a highly customisable application development software and modular electronics hardware, a user-defined system was developed. Increased reliability was achieved by reducing the part count to minimum. Eco-friendly, miniaturised, high-precision optics were used. The effects of weather and climate were offset by housing the electronics, mechanical hardware and the precision optics in environmentally-controlled enclosures.

Installed systems

After evaluating the performance of Drishti system in the critical fog season of December 2011 to February 2012, Indian Meteorological Department requested CSIR-NAL to install three more systems at Indira Gandhi International Airport, New Delhi, which is the most stringent and crucial airport of India to cover the requirement of 2012-13 fog season. In a record time of three weeks, the team developed the systems, installed them and received the International Class I certification.

F77_Box3Currently there are seven Drishti systems operating in three Indian international Airports—Indira Gandhi International Airport of New Delhi (five systems), Lucknow International Airport (one system) and NSCBI Airport of Kolkata (one system). A partnership agreement is signed with Indian Meteorological Department, who are the sole buyers, users and certifying agency for civilian airports, on 20th May 2014 and soon all the civilian airports of the country will have Drishti systems.

Copyrights, patents, awards and recognition
The Drishti system holds 14 copyrights. There are four patents and a trademark filed for Drishti under Intellectual Property Management Division (IPMD)—CSIR. Drishti has also been certified with International Class I NOTAM (Notice to Air Man).

The system has been recognised by various organisations and has won several prestigious awards like the Aeronautical Society of India Award for Indigenisation of Aeronautical Equipment, best innovation award of 2012 and 2013 by CSIR-NAL and IETE Diamond Jubilee Corporate Award for performance in Electronic Instruments & Instrumentation in 2013. It has also received NRDC Meritorious Invention 2012 award and IESA Technovation 2013 award for Most Innovative Product.

A Better Society, Thanks to Technology

The author is a technical correspondent at EFY