Overview on the instrument configuration
Image: DLR RM-OS
Several imaging spectrometers have been designed to be combined with earth or planetary observation telescopes for wavelengths ranging from the ultraviolet to the thermal infrared. One pioneering solution was been presented by Offner in the early 1970's.
The standard Offner spectrometer is made of three spherical concentric elements. The primary and tertiary elements are reflecting mirrors. The secondary element is a curved grating for dispersion and could be the limiting stop of the system. This system has the great advantage of being simple, compact, and both spatially and spectrally uniform. This combination is free from spherical aberration, coma and distortion. One example of application is the infrared imaging spectrometer MERTIS.
The spectrometer MERTISemploys an uncooled microbolometer array that provides a short thermal time constant as well as very low noise equivalent temperature difference NETD. The measurements have a signal to noise ratio of at least 100. The array provides spectral separation and spatial resolution according to its two dimensional shape. The general instrument architecture comprises the sensor head including the optical elements and the TMA imaging optics, the detector and the driving electronics. This highly integrated measurement system is completed by a motor driven pointing unit device which orients the optical path to the planet and the calibration targets. It weighs less that 3.3 kg and could be implemented in high resolution telescopes as well as in large field imaging systems.
They can be applied to perform many different tasks such as accurate mapping of wide areas, object identification and recognition, process monitoring, environment assessment and management. Application areas include forestry, geology, agriculture, fire detection, security, oceanography, ecology and others.