# Thermal Infra-red Remote Sensing

## A few notes

• All bodies with temperature above 0 K emit radiation.
• 0 K = ‒273,15 °C
• A blackbody is a theoretical object that completely absorbs all wavelengths of electromagnetic radiation incident on it.
• When a blackbody is heated to a temperature above 0 K, it emits radiation.
• Blackbody radiation at temperatures comparable to the temperature of the earth’s surface (~300 K) is the thermal infrared (TIR)
• “Good absorbers are good emitters”, meaning that a blackbody emits 100% of the radiation it absorbs (so the absorbed radiation has no effect on the blackbody’s temperature)

### Basic principles

It is necessary that the reader understands the following principles.

 PRINCIPLE DESCRIPTION Planck’s Law of blackbody radiation Describes the electromagnetic radiation of a blackbody of a defined temperature Stefan-Boltzmann Law Calculates the total electromagnetic radiation as function of a blackbody’s temperature Wien’s Displacement Law Calculates the wavelength at which maximum spectral radiant exitance(emitted radiation) occurs Kirchhoff’s Law ➔Emittance at a given wavelength = absorbance at the same wavelength➔Blackbodies are theoretical; the behaviour of real objects can be described based on how close to being a blackbody they are.➔Emissivity (ε):◆ε = 1 ⇒ blackbody◆ε < 1 ⇒ real-life material

### Planck’s Law of blackbody radiation

• Created by Max Planck (1858–1947)
• Blackbody radiation can be calculated by the object’s (absolute) temperature according to the formula:
$M λ = 2 π h c 2 λ 5 e hc / λkT − 1$

where

• λ: wavelength
• Mλ: radiation at wavelength λ
• Τ: temperature (absolute temperature in K).

Therefore, at any given wavelength we can have a spectral radiant exitance curve (“radiation”) according to the absolute temperature:

(to be continued)