The researchers at Shiv Nadar University in Gautam Buddha Nagar, Uttar Pradesh, showed the methodology by conducting extensive trials on foggy winter mornings. They chose 10 red LED lights as the light source. The light source was then varied by altering the current flowing through the LEDs at a rate of around 15 cycles per second.
The researchers kept a camera 150 meters away from the LEDs. The image was recorded by the camera and transferred to a desktop computer. The characteristics of the source were then extracted using computer methods and knowledge of the modulation frequency. This is known as 'demodulation.' To obtain a clear image, the image has to be demodulated at a rate equal to the rate of modulation of the light source.
Using the modulation-demodulation process, the researchers witnessed a significant improvement in image quality. The length of time it takes the computer to complete the procedure is determined by the size of the image. "The computational time for a 2160 × 2160 image is about 20 milliseconds," says Bapan Debnath, PhD scholar at RRI and co-author of the paper. That's about the size of the image with the LEDs. In 2016, his colleagues estimated the rate.
The researchers repeated the experiment several times, noting the progress each time. When the fog intensity fluctuated during the observation, they did not see a significant improvement in image quality. There was a high breeze in this case, and they noticed fog trails throughout the area. The density of water droplets in the air changed with time, making the modulation-demodulation process less efficient.
The researchers then altered the experimental design. They created an external substance, a piece of cardboard held 20 cm away from the LEDs, to reflect the light to the camera. The cardboard was 75 meters away from the camera. The camera captured the modulated light reflected from the cardboard as it traveled through the fog.
They demonstrated how their methodology still considerably enhanced the image quality. When they repeated the experiment in bright sunlight, they discovered that after demodulating the source, the image quality was good enough to discern the LEDs from the brightly reflected sunlight.
How the discovery helps?
The team's research has provided a way for boosting image quality without the use of significant computations. The team from the Raman Research Institute (RRI), Bengaluru, an autonomous institute of the Department of Science and Technology; Space Applications Centre, Indian Space Research Organisation, Ahmedabad; Shiv Nadar University, Gautam Buddha Nagar; and Université Rennes and Université Paris-Saclay, CNRS, France, modulated and demodulated the light source at the observer's end to achieve sharpness. The findings were published in the journal 'OSA Continuum.'
The technology is inexpensive, requiring only a few LEDs and a standard desktop computer capable of executing the process in less than a second. The technology can improve airplane-landing tactics by providing the pilot with a clear view of beacons on the runway, which is far superior to relying just on reflected radio waves, as is now the case.
In rail, marine, and road transportation, the technique can help uncover obstructions in the path that would otherwise be concealed by fog, as well as aid in the detection of lighthouse beacons. More research is needed to demonstrate the usefulness in such real-world scenarios. The team is looking into whether the methodology can be used to moving sources.
