The Observatory

I have often wondered why the place where atmospheric measurements are regularly made has traditionally been called an ‘observatory’, since the atmosphere is a gas and therefore invisible. Perhaps in the pre-instrument era, human observers just looked at the sky and noted whatever they could observe with their eyes. We know from history that meteorological observatories were set up at or evolved out of astronomical observatories and so perhaps a common nomenclature got applied to both. But even today, the name observatory remains popularly used to denote places that are not capable of making observations in the literal sense. For example, the Orbiting Carbon Observatory (OCO) is a NASA mission dedicated to the global measurement of atmospheric carbon dioxide which is an invisible constituent of air. The India-based Neutrino Observatory (INO) is a proposed particle physics research project to primarily study atmospheric neutrinos in a deep cave near Thevaram in Tamil Nadu. What is popularly known in the U. K. and elsewhere as a Public Health Observatory (PHO) is just a public health and wellness monitoring project. The WHO has a Global Health Observatory (GHO) that keeps a watch on global health-related issues and the incidence of diseases.

So a meteorological observatory is where we do not really see much but only measure quite a lot! In fact, all the basic atmospheric variables have to be measured with instruments. Only some properties of the atmosphere like temperature and humidity and the prevailing wind can be felt by human senses, while the pressure of the atmospheric column cannot even be felt. The power of the wind can be harnessed although it cannot be seen. Only the colour of the sky, the clouds, precipitation, lightning, and some optical phenomena such as the rainbow or lunar halo, can be perceived by the human eye, or observed so to say.

Presently, there are just a few tasks left that are required to be performed only by human observers at an observatory. For example, the tracking of pilot balloons with the aid of an optical theodolite is still done globally by human observers and remains a simple and inexpensive method of deriving the wind speed and direction at various levels. Measurement of visibility, which is a measure of air quality and transparency and is very important for aviation, is still best done by the human eye. Even automatic instruments that record visibility at airports and on runways have to calibrated and checked against visual observations.

The Human Eye and the Sun and Stars

The region of the electromagnetic spectrum with which we are most concerned in real life is the region of visible light, to which the human eye is very sensitive. This is precisely the wavelength range in which the sun and stars emit their strongest radiation. It is hard for me to imagine that a characteristic of the entire universe and an infinitesimal feature of the human anatomy, so distant and unrelated, could have evolved on their own and got matched with each other by sheer coincidence. I can only regard it as a fundamental and essential element of a Grand Design. Had this matching not been deliberately executed, the human eye would have been rendered useless and human beings deprived of the faculty of sight. What a pathetic situation that would have been! Humankind would have forever lived in the Dark Ages!

Remote Sensing

Remote sensing has been defined in various ways, but it is basically the process of observing an object in wavelengths that the human eye cannot perceive. The term has also developed a strong association with satellites, although aircrafts can be used for the same purpose. Remote sensing has applications in many diverse areas, ranging from monitoring of earth resources to medical diagnosis, but the basic principles are the same.

The visible spectrum consists of the seven colours familiar to us which are identified by their wavelength. The visible wavelength region is, however, an extremely small part of the whole spectrum. It is only in recent times that we are getting familiar with other wavelength regions of the spectrum and using them in various applications, as FM radio stations, mobile phones, satellite television or microwave ovens become more and more a part of our daily life. Radiation of wavelengths shorter than violet is called ultra-violet (UV) radiation. This has very high energy that can break chemical bonds, ionize molecules, damage skin cells or cause cancer. However, most of the UV radiation coming from the sun is absorbed by the layer of atmospheric ozone which resides in the stratosphere, and shields life on earth from its harmful effects. X-rays have wavelengths that are even shorter than UV. Gamma rays have yet shorter wavelengths it is more convenient to express their magnitude in terms of their energy levels. X-rays and gamma rays have great penetration power and have applications in astronomy, radioactivity and other fields. Towards the other end of the visible spectrum, radiation which has wavelength higher than red is called infra-red (IR). Radiation with still longer wavelengths are called millimetre waves, followed by microwaves and radio waves.

With the help of satellites that measure infrared radiation leaving the atmosphere we can ‘see’ clouds even at night and can measure the temperature of the earth and cloud tops. The most significant achievement of satellite remote sensing is that we can now monitor global weather round the clock. We can spot cloud formations at night, see the development of thunderstorms and severe weather any time of the day, or keep a watch on tropical cyclones threatening to strike the coast by night.

Microwave remote sensing has enabled us to see through clouds, measure large scale rainfall, estimate the winds in a severe hurricane and a host of other applications. Lidar-based remote sensing has allowed us to examine the interior structure of clouds, and study the properties of atmospheric aerosols among other things.

Remote sensing has indeed opened up before us a whole new world that was so far invisible to us.

The Bible (John 20:19-29) gives an account of how Jesus, after his resurrection, appeared before his disciples and greeted them and showed them his hands and side. The disciples were overjoyed when they saw him, but Thomas, one of the twelve disciples, was not there at that time. When the other disciples told him that they had seen the Lord, Thomas refused to believe. He said to them, “Unless I see the nail marks in his hands and put my finger where the nails were, and put my hand into his side, I will not believe.” A week later, Jesus appeared before his disciples once again, and this time Thomas was present. Jesus said to him, “Put your finger here; see my hands. Reach out your hand and put it into my side. Stop doubting and believe.” Thomas could only say, “My Lord and my God!” Then Jesus told him, “Because you have seen me, you have believed; blessed are those who have not seen and yet have believed.”

Is it necessary to see first in order to believe? No. The Bible further elaborates on this issue in another place. “What is faith?”, it asks, and the answer that follows says, “Faith gives substance to our hopes and makes us certain of realities we do not see” (Hebrews 11:1, NEB 1961).

Except for the changing colour of the sky, and the beauty and fury of clouds and precipitation, there is little else in the atmosphere that we can actually see. However, in the manner of faith, meteorological measurements and satellite-based remote sensing techniques help us to visualize the realities of the atmosphere that we are not able to perceive with our own vision.