# What is specific intensity anyway?

• OETN
In summary, the person is asking for help with a problem regarding the specific intensity of solar radiation at the surface of the Earth and in the direction of Earth from the solar surface. They mention that the values are not specific and provide a website they found through a Google search for "specific intensity".
OETN
Hi all,

I need a hand regarding this problem, just can't seem to find the start point. (It's a two parter):

What is the specific intensity of the radiation at the solar surface in the direction of Earth

What is the specific intensity of solar radiation at the surface of the Earth.

As you can see, isn't really specific on values so it would seem you have to quote any used values. Would be great if anyone could help.

ON

e possible explanation of specific intensity is that it is a measure of the amount of radiation (such as light or heat) that is emitted, transmitted, or received in a specific direction. It is a physical quantity that is used in the study of radiative transfer, which is the process of energy transfer through electromagnetic radiation. Specific intensity is typically measured in units of watts per square meter per steradian (W/m2/sr).

To answer the first part of your question, the specific intensity of radiation at the solar surface in the direction of Earth would depend on the wavelength or frequency of the radiation being emitted. The sun emits radiation across a wide range of wavelengths, from infrared to ultraviolet. The specific intensity would also depend on the distance between the sun and Earth, as the intensity of radiation decreases with distance.

For the second part of your question, the specific intensity of solar radiation at the surface of the Earth would again depend on the wavelength and distance. However, it would also be affected by factors such as the Earth's atmosphere, which can absorb and scatter some of the incoming radiation. This is why the specific intensity of solar radiation at Earth's surface is lower than at the solar surface.

To find specific intensity values for these scenarios, you would need to use equations that take into account the relevant variables, such as the Stefan-Boltzmann law for blackbody radiation. It is important to note that specific intensity can vary greatly depending on the specific conditions and context in which it is being measured. I hope this helps clarify the concept of specific intensity for you.

## 1. What is specific intensity and how is it measured?

Specific intensity is a physical quantity that measures the amount of energy emitted or absorbed by a source in a particular direction per unit time, per unit solid angle, and per unit area. It is usually denoted by the symbol I and has units of energy per unit time per unit solid angle per unit area (e.g. watts per square meter per steradian). It is typically measured using instruments such as spectrophotometers or radiometers.

## 2. How is specific intensity related to other radiative transfer properties?

Specific intensity is related to other radiative transfer properties such as flux and radiance. Flux is the total amount of energy flowing through a surface per unit time and radiance is the specific intensity per unit solid angle. Specific intensity is also related to optical depth, which is a measure of the amount of absorption and scattering of radiation as it travels through a medium.

## 3. What factors affect the specific intensity of a source?

The specific intensity of a source is affected by various factors such as the temperature of the source, its chemical composition, and its physical properties such as density and opacity. The distance between the source and the observer also plays a role in determining the specific intensity.

## 4. How is specific intensity used in different fields of science?

Specific intensity is a fundamental concept in many fields of science, including astrophysics, atmospheric science, and remote sensing. In astrophysics, it is used to study the emission and absorption of radiation from celestial objects. In atmospheric science, it is used to understand the transfer of solar and thermal radiation in the Earth's atmosphere. In remote sensing, it is used to interpret data from satellite sensors to study the Earth's surface and atmosphere.

## 5. How does specific intensity help us understand the behavior of light?

Specific intensity is a useful measure for understanding the behavior of light because it allows us to quantify the amount of radiation emitted or absorbed by a source in a particular direction. It also helps us understand the effects of absorption and scattering on the intensity of light as it travels through a medium. Additionally, specific intensity is used in radiative transfer equations, which are essential for predicting the behavior of light in various environments.

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