3. Absorption

Absorption is the process by which incident radiation is taken in by a medium.

Absorption refers to how certain materials take in (or absorb) energy from incoming radiation, such as light or heat. When radiation hits a material, some of it is absorbed rather than reflected or transmitted. This absorbed energy is often transformed into internal energy, which can later be emitted as heat.

Think of absorption like a sponge soaking up water. Just as a sponge takes in water and fills up, materials can absorb different forms of energy from radiation and 'fill up' with internal energy.

A portion of the absorbed radiation is converted into internal heat energy, which may be subsequently emitted at longer thermal infrared wavelengths.

When a material absorbs radiation, some of that energy doesn't just disappear; it changes form. The energy can turn into heat, causing the material to become warmer. Eventually, this heat can be released as thermal radiation, which is typically longer in wavelength compared to the original absorbed radiation.

Consider how a black shirt feels hotter in the sun than a white shirt. The black shirt absorbs more sunlight (radiation), turning it into heat, which is then radiated back into the environment as infrared energy.

Absorption of UV in the atmosphere is mainly due to electronic transitions of atomic and molecular oxygen and nitrogen. The primary gases that are responsible for the atmospheric absorption of energy are ozone, water vapor, and carbon dioxide.

The atmosphere absorbs ultraviolet (UV) radiation largely due to the interaction between incoming UV photons and the electrons in atmospheric gases like oxygen and nitrogen. Ozone, water vapor, and carbon dioxide are crucial in absorbing energy, particularly in UV and infrared wavelengths, thereby preventing harmful radiation from reaching the Earth's surface.

Imagine applying sunscreen before going out in the sun. Just like sunscreen absorbs harmful UV rays and prevents them from damaging your skin, gases in the atmosphere absorb these rays to protect living organisms on Earth.

Ozone in the stratosphere absorbs about 99% of the harmful solar UV radiation, and eventually protects us from diseases like skin cancer.

Ozone, a form of oxygen, is concentrated in the stratosphere and plays an essential role in absorbing the majority of the sun's harmful UV radiation. Without this ozone layer, life on Earth would be significantly threatened by increased UV exposure, leading to higher incidences of skin cancer, cataracts, and other health issues.

Think of the ozone layer like a giant umbrella in the sky that protects us from sunburn. Just as rain won't reach you when you're under an umbrella, harmful UV rays are mostly blocked by ozone, allowing for safer exposure to sunlight.

There is very little absorption of EMR in the visible part of the spectrum. The absorption in the infrared (IR) region is mainly due to water vapor (H₂O) and carbon dioxide (CO₂) molecules.

In the visible spectrum, we experience minimal absorption, which is why we can see light effectively. However, in the infrared region, water vapor and carbon dioxide significantly absorb radiation, leading to heat retention in the atmosphere. This process is critical for maintaining Earth's temperature and influencing climate.

Think of how a car parked in the sun gets hot inside. The sun’s rays enter through the windows (minimal visibility absorption), but heat cannot escape effectively (IR absorption), raising the temperature inside the vehicle.

In microwave radiation, there is no absorption, and that’s why it is able to penetrate through the atmosphere.

Microwave radiation has longer wavelengths compared to visible light and infrared, allowing it to travel through atmospheric obstacles without being absorbed. This property is significant in communication and remote sensing technologies, enabling data transmission even in poor weather conditions.

Consider a tall building and how light might be blocked by it—but sound waves (like those from a radio) can often travel around or through gaps, allowing you to hear even if you can't see the source. Microwaves work in a similar way!

Absorption reduces the solar radiance, and may alter the apparent spectral signature of the target being observed.

As absorption occurs in the atmosphere, it diminishes the intensity of solar radiation that reaches the Earth’s surface, affecting how we perceive different surfaces or materials. This can lead to changes in the 'signature' or characteristics that sensors observe, complicating data interpretation in remote sensing.

Think of taking a photograph through tinted glasses. The tint changes how the colors are captured, making some appear darker or lighter than they actually are. Atmospheric absorption has a similar effect, altering how the reflected light is perceived by sensors on satellites.

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