Contents I. Introduction
Three centuries ago Sir Isaac Newton published in his ‘Treatise of Light’ [1] the concept of dispersion of light. The corpuscular theory by Newton was gradually succeeded over time by the wave theory, resulting in Maxwell's equations of electromagnetic waves [2]. But it was only in the early 19th century that quantitative measurement of dispersed light was recognized and standardized by Joseph von Fraunhofer's discovery of the dark lines in the solar spectrum (1817) [3] and their interpretation as absorption lines on the basis of experiments by Bunsen and Kirchhoff [4]. The term spectroscopy was first used in the late 19th century and provides the empirical foundations for atomic and molecular physics [5]. Following this, astronomers began to use spectroscopy for determining radial velocities of stars, clusters, and galaxies and stellar compositions [6]. Advances in technology and increased awareness of the potential of spectroscopy in the 1960s to 1980s lead to the first analytical methods [7, 8], the inclusion of ‘additional’ bands in multispectral imagers (e.g., the 2.09–2.35 µm band in Landsat for the detection of hydrothermal alteration minerals as proposed by A.F.H. Goetz), as well as first imaging spectrometer concepts and instruments [9]–12]. Significant recent progress was achieved when in particular airborne imaging spectrometers became available on a wider basis [13–17] helping to prepare for spaceborne imaging spectrometer activities [18]. However, it lasted until the late 1990s until first imaging spectrometers were launched in space. However, true imaging spectrometers, satisfying the definition given in section II are still sparse nowadays (e.g., CHRIS/PROBA, Hyperion, MERIS).
