Honouring a pioneer

The Photosynthetic Bubbler that measures the rate of photosynthesis in acquatic plants, invented in 1924. - BY SPECIAL ARRANGEMENT

There are plans to showcase the brilliance of J.C. Bose when the General Assembly of International Radio Science Union meets in India next year, and it is a right move as his scientific achievements have not been recognised by the world at large.

THE centenary celebration of the patenting of the first galena single contact point coherer developed by Sir J. C. Bose in 1904 has two aspects. The first is that J.C. Bose was opposed to the commercial exploitation of any research product (and he wrote to Rabindranath Tagore on this point) and the patent application was submitted on his behalf by some of his friends. The second is that his legendary work - on the production, transmission, properties and applications of millimetre waves, which was the beginning of radio science - was done about a decade earlier. Between 1885 and 1901, J.C. Bose published a series of papers on this new topic in prestigious international journals. His originality and innovation at the dawn of radio science was, in the words of the Nobel Laureate Neville Mott, at least 60 years ahead of his time. In fact, it appears that he anticipated the existence of p-type and n-type semiconductors and also developments in such fields as microwave antenna design, application of semiconductor crystals and microwave optics.

However, the situation changed soon. Bose moved on to plant science. Sir Oliver Lodge, the British physicist, started concentrating on parapsychology. Heinrich Hertz, who confirmed the existence of electromagnetic waves, died in 1894. For years this promising area lay dormant. Also at the same time, the dramatic success of Guglielmo Marconi in achieving trans-Atlantic propagation in the longer wavelengths created a new communication pathway that holds scientific and commercial attention even today. The course of progress in radio science would have taken a different path had Bose or Lodge continued to do research in the area.

Millimetre waves now form a major part in communication and remote sensing. It is curious that Bose worked around 60 GHz (about 5 mm) in his effort to generate radio waves of very short wavelengths. Hertz produced radio waves around 66 cm, Lodge around 8 cm. It is curious because 5 mm waves are right in the middle of the oxygen absorption band. The band surrounding this frequency - 10 GHz to 100 GHz - and beyond (mm and sub-millimetre waves) - now provide specially secure communication systems and also remote sensing of the atmosphere. There are absorption lines because of the presence of water vapour, ozone and other trace species in the atmosphere. One can work in the window frequencies for communication or use those that have attenuation to monitor water vapour or ozone. Use of millimetre waves is in fact a major tool for monitoring atmospheric water vapour.

Bose would have been glad to see that in the past three decades the techniques he introduced have been successfully applied in many areas in India. In the early years, shortly after the Bangladesh war, the Indian Air Force launched a programme called ADGES to generate indigenous technology on radar and troposcatter systems with the help of the Indian Institutes of Technology, the National Physical Laboratories and Roorkee University. This effort provided new radar technologies as well as new information on the tropospheric medium. This created a new knowledge base and indigenous technologies. Furthermore, the Indian satellite Bhaskara used a number of radiometers at millimetre wavelengths for similar studies.

Other new applications have come up. One concerns radio remote sensing. For years the ionised regions of the upper atmosphere - the ionosphere - have been explored from satellites through radio waves. In later years these were extended to microwave and millimetre regions. Then there are those minor species in the atmosphere - water vapour, ozone, chlorine oxide - the concentrations of which, we now know, are changing because of human activities. A special role of this is in producing climate change. Millimetre technologies are providing a rare view of these changes. One can also monitor oceans and lands, soil moisture and weather-related parameters. Remote sensing extends to objects outside the earth - the sun, the galaxies, radio stars, early universe and so on. Also there is the new aspect of electromagnetic field and biological systems. An area of special concern is the biological effects of mobile communication. In all these, Indian scientists are active.

A new and increasingly dominant area using frequency at and around those Bose was working on is climate and radio wave propagation. The key aspects are water vapour and refractivity profiles (Global Positioning System and millimetre wave radiometer), rain rates (Tropical Rainfall Measuring Mission or TRMM, measuring tropical and subtropical rainfall) and lightning activities. Then there is the proposed India-French satellite Megha Tropique, expected to be launched in a few years. The key instruments include millimetre wave imagers and a water vapour sounder. Indian Satellite IRS-P4, already launched in 1999, has a multi-channel Scanning Microwave Radiometer (MSMR). This, combined with the TRMM satellite and Megha Tropique and Global Precipitation Mission (GPM) (when available), will have major impact on our understanding of tropical rainfall.

We have now strong evidence that atmosphere is getting increasingly loaded with aerosols (small particles). Some of these are in fact black carbon (constituents of the brown haze). Observations made from aircraft have shown that as the aerosol load increases, cloud droplets increase in number. When this happens, the size of the droplets decreases, and we can expect a decrease in rainfall. All these show the enormous influence Bose's work has in radio communication, in remote sensing, and now in global climate change monitoring. Bose undoubtedly was a major contributor to the beginning of radio science. It is difficult to understand why his name is not associated with Lodge, Augusto Righi and Marconi as successors to Maxell and Hertz, in the area of radio waves. It is a pity that his work was not taken further by his students and disciples. There are plans to dedicate to Bose's memory a special public lecture on 100 years of radio science and an exhibition of his extraordinary experiments at the next General Assembly of International Radio Science Union to be held in India in October 2005. This is the first time an assembly of this magnitude will be held in Asia.

Dr. A.P. Mitra, a Fellow of the Royal Society in London, is an Honorary Scientist of Eminence at the National Physical Laboratory, New Delhi.