EM Radiance
Radiance is used to characterize diffuse emission and/or reflection of EM radiation, or to quantify emission of neutrinos and other particles. Historically, radiance is called “intensity” and spectral radiance is called “specific intensity”.
Radiance is useful because it indicates how much of the power emitted, reflected, transmitted or received by a surface will be received by an optical system looking at that surface from a certain view angle.
Spectral radiance expresses radiance as a function of frequency or wavelength. Radiance is the integral of the spectral radiance of all frequencies/wavelengths.
For radiation emitted by an ideal black body at a given temperature, spectral radiance is governed by Planck’s law, while the integral of radiance over the hemisphere into which it radiates, is governed by the Stefan–Boltzmann law.
Hyperspectral imaging collects and processes data from across the EM spectrum. Its goal is to obtain the spectrum for each pixel in the image of a scene, with the purpose of finding objects, identifying materials, or detecting processes.
The human eye sees visible light in three bands (red, green & blue). Spectral imaging divides the spectrum into many more bands. This technique of dividing images into bands can be extended beyond the visible.
In hyperspectral imaging, the recorded spectra have a fine wavelength resolution and cover a wide range of wavelengths.
Hyperspectral sensors use almost the entire EM spectrum. Objects leave unique ‘prints’ in the EM spectrum. These ‘spectral signatures‘ or ‘fingerprints’ enable identification of the materials that make up a scanned object.
Hyperspectral sensors and processing systems are used in surveillance, physics, astronomy, agriculture, biomedical imaging, and geosciences. A spectral signature for oil helps geologists find new oil fields.
