Flight operations at Patna's Jayaprakash Narayan International Airport will now be safer even when the visibility is poor.

India Meteorological Department (IMD) has installed Drishti - an indigenously developed transmissometer that will record exact visibility readings for pilots even when visibility is less than 2,000m.

The system started functioning at Patna airport from last week.

A transmissometer helps the pilot to land and take-off safely, especially when visibility is poor. Visibility condition at the Patna airport has always been a concern because of the short stretch of the runway. It did not have any digital machinery to measure readings before Drishti.

"A transmissometer has been installed adjacent to the runway near the touchdown point for flights," said airport assistant general manager (air traffic management) Santosh Kumar. "It has three components - a sensor, a receiver and a transmitter. There is a gap of 30m between the receiver and transmitter. The censor records visibility readings and the data is continuously sent to the air-traffic controller."

Senior officials at Patna airport said the runway visibility range was three to five kilometres but it reduced considerably in case of dense cloud cover during monsoon or fog in winter. This leads to cancellation and diversion of flights.

Sources said two transmissometers were initially proposed to be installed at the airport - one at each end of the runway. "Considering the short stretch of the runway at Patna airport, one transmissometer was considered sufficient to serve the purpose," said Ashish Sen, director of Patna meteorological centre.

Council of Scientific and Industrial Research-National Aerospace Laboratories (CSIR-NAL) designed Drishti for the India Meteorological Department. They signed an agreement on May 20, 2014 for the joint production of Drishti. Sources said it costs just one-third the price of an imported transmissometer and gives more accurate readings. Transmissometers have been made mandatory at all airports according to International Civil Aviation Organisation (ICAO) and World Meteorological Organisation guidelines.

Twenty-seven airports across the country will be equipped with Drishti transmissiometers. Patna airport features in the first phase among eight.

Aviation experts were happy with the technology. They said such advanced equipment will ensure safe operation of flights. "The present system where we take rough readings to assess visibility is not accurate," said an aviation scientist in the city who is settled in the US at present. "The modern day aviation industry needs a better system to record visibility. The practice is unsafe because majority of the accidents in the aviation sector are linked to bad weather."

Every airport in the country has an airport meteorological office that provides it with weather related information. This includes visibility condition and forecast required for flight planning and operations to the air-traffic controller. The controller then conveys information to other locations.

According to the guidelines of ICAO, equipment such as transmissometers and instrument landing system (ILS) are used to ascertain the visibility.

Patna airport's ILS lacks a transmissometer. The meteorological office issues rough visibility readings and a detailed scientific map to the airport.