A New Class of Imaging Spectrometer for Planetary Science

A NASA-funded Planetary Instrument Definition and Development Project (PIDDP) has led to the development of a new class of imaging spectrometer that combines the principal advantages of two traditional techniques used for imaging spectrometry: the signal collection advantage offered by the interferometric or Fourier Transform Spectrometer (FTS) class, and the no-moving-parts advantage offered by the dispersive and filter-array classes. This new class of imaging spectrometer, referred to as windowing interferometric, has no filters, no slit, and no moving parts. The advantage of having no moving parts provides high reliability, low cost, and allows the interferometer to be monolithic and therefore extremely rugged. The high signal collection ability of this instrument allows it to be miniaturized for use from a rover or small orbiter while still obtaining a high signal-to-noise ratio. The high signal collection ability also makes this approach ideal for missions to the outer planets. In order to put these advantages in perspective we have developed a comprehensive classification of imaging spectrometers, and a novel graphical technique for describing the principal of operation and relative signal collection abilities of the classes of imaging spectrometers. We divide imaging spectrometers into a matrix of classes based on their method of obtaining spatial information and their method of obtaining spectral information. Methods of acquiring spatial information include whiskbroom, pushbroom, staring, and a new class we refer to as windowing. We use the term windowing to describe the new class of instruments that employ a two-dimensional FOV which moves across the object in the along-track direction during each acquisition. The classifications by spectral approach include the familiar filtering, dispersive, and interferometric techniques. A novel graphical technique for comparing the classes of imaging spectrometers is to plot the transmittance as a function of the along-track spatial dimension and the wavelength. The temporal evolutions of these transmittance functions describe the methods of operation and provide ready insight into the relative signal collection abilities of the entire family of imaging spectrometers. We present the design of our demonstration instrument of the windowing interferometric class, and performance results obtained in laboratory and field testing.