Solar and Infrared Radiation Measurements

10 Infrared Measurements

The world Infrared Standard Group has been operating continuously since 2003, showing an excellent relative stability between individual instruments of ±1 W m^–2.

Julian Gröbner

(2009)

10.1 Introduction

A body with a temperature above 0 K emits radiation. For the earth’s surface and atmospheric temperatures, this radiation is in the infrared (IR). The Stefan–Boltzmann law states that the power per unit area L emitted by a body of absolute temperature T is

$$L\text{=}\epsilon \sigma T^{\text{4}}\left(10.1\right)$$

In this equation σ is the Stefan–Boltzmann constant, equal to 5.670 x 10^–8 W m^–2 K^–4, and ε is the emissivity of the body. If the emitting body is a gray body, then the emissivity is < 1; for a black body, ε is equal to 1. For example, if a pyrgeometer, ...