Imaging spectroscopy -- the acquisition of spectra for every point in an image -- is a powerful analytical method that enables remote material detection, identification, measurement, and monitoring for scientific discovery and application research. From mapping vegetation species on Earth to studying the composition of the intergalactic medium, spectrometers can be used to reveal physical, chemical, and biological properties and processes.
Since its inception in the late twentieth century, spectrometer technology has advanced to where we are now capable of using advanced spectroscopy to understand worlds from the micron scale to exoplanet distances. Spectroscopy provides access to information about molecules, atmospheric conditions, and composition, and it has been used on Earth and throughout the solar system to perform new science research. In the future, spectroscopy of exoplanets could provide the first evidence of life beyond Earth.
High-fidelity spectrometers with advanced detectors, optical designs, and computation systems are needed to derive information of value from remotely measured spectra. Current research focuses on several key topics:
- Versatility: Increasing both spectral range and swath width would enable future spectrometers to measure the global distribution of atmospheric gases on a daily basis. These versatile instruments would also help meet the mass and power constraints of future missions without compromising performance.
- Optical design: Improved diffraction gratings for tuning efficiency and reducing scattering and polarization sensitivity would lead to higher-quality spectral measurements.
- Real-time algorithms: Onboard cloud screening with negligible false alarms, for example, would lower buffering, transmission, analysis, and curation costs by eliminating unusable data.
In recent years, JPL has developed, tested, and delivered airborne, rover-type and space class imaging spectrometers. Our Moon Mineralogy Mapper spectrometer discovered evidence of low concentrations of water on the illuminated surface of the Moon and was successful at enabling scientists to derive mineralogical properties from its spectral measurements. This and a range of potential future mission for science and applications research has driven our interest in miniaturizing such a system for in situ use on other solar system bodies in the future.
Selected Research Projects
Europa Short-Wavelength Infrared Spectrometer
Research for the Europa Short-Wavelength Infrared Spectrometer (ESWIRS) is focused on identifying the spectroscopic and imaging capabilities required for compositional measurements and mapping contributions to Europa exploration science. In addition to developing and testing the key element of the ESWIRS along-track scan mirror subsystem, JPL is tasked with understanding the impact of radiation on ESWIRS spectra through test and analysis. Current efforts include the development and demonstration of on-instrument data radiation mitigation.
Mapping Imaging Spectrometer for Europa
The Mapping Imaging Spectrometer for Europa (MISE) was selected in May 2015 for the NASA mission to Europa. The MISE instrument will measure spectra from 0.8 to 5 μm with 10 nm spectral sampling and spatial sampling at geologic scales (25 m/pixel at 100 km) to reveal the geochemical tapestry of Europa. The two primary MISE science goals are (1) to assess the habitability of Europa’s ocean by understanding the inventory and distribution of surface compounds and (2) to investigate the geologic history of Europa’s surface and search for areas that are currently active. A prototype imaging spectrometer with flight-like slit, grating, order sorting filter, and focal plane array has successfully completed planetary protection bakeouts for dry heat microbial compatibility. The MISE prototype has been tested in three radiation beamlines and the data used to calibrate and validate radiation transport models and to develop algorithms for radiation noise suppression.
Hyperspectral Infrared Imager
Hyperspectral Infrared Imager (HyspIRI) is a visible to shortwave infrared (VSWIR) imaging spectrometer with more than 1000 cross-track elements, excellent slit uniformity, low polarization sensitivity, and low scattered light. The airborne campaign began collecting spectral measurements in the spring of 2013 for science research related to ecosystem composition, function, biochemistry, seasonality, structure, and modeling; coastal ocean phytoplankton functional types and habitats; urban land cover, temperature, and transpiration; surface energy balance; atmospheric characterization and local methane sources; and surface geology, resources, soils, and hazards. A primary goal of the campaign is to demonstrate the diverse science that could be enabled by a subsequent global HyspIRI space mission and to demonstrate and refine the data processing and science algorithms that would be used.
Ultra-Compact Imaging Spectrometer
Ultra-Compact Imaging Spectrometer (UCIS) is a first-of-its-kind imaging spectrometer weighing less than 3 kg and consuming less than 3 W. The system is light and flexible enough to be used in mass- and power-constrained in situ platforms while still satisfying stringent performance specifications. Future work includes developing an instrument that could be mounted on a rover mast for determining the mineralogy of the surrounding terrain and even guiding a rover toward closer examination of scientifically important targets. This instrument would have a mast-mounted total mass of 1.5 kg (with some additional electronics potentially located on the rover body) and would open up new ways of performing geologic exploration through its ability to collect wide-angle panoramas and produce high-quality, full-range diagnostic spectra for every pixel in the image. The system would acquire approximately 500,000 spectra in the time that previous rover instruments would acquire one.
Next-Generation Imaging Spectrometers
Next-Generation Imaging Spectrometers (NGIS) are currently used by the National Ecological Observatory Network and the Carnegie Institution of Washington to study, explore, and conserve ecosystems on large geographic scales. These high fidelity, high resolution VSWIR and VNIR imaging spectrometers have better than 95% cross-track IFOV uniformity.
Next-Generation Airborne Visible and Infrared Imaging Spectrometer
The Next-Generation Airborne Visible and Infrared Imaging Spectrometer (AVIRIS‑NG) instrument measures across the spectral range from 380 to 2510 nm at 5 nm spectral sampling with a calibrated, high-signal-to-noise-ratio spectrum measured for every spatial sample in the image. The system has been calibrated and deployed with a new high-rate data-capture system and a new real-time cloud-screening algorithm to support a methane-release experiment at the Department of Energy’s Rocky Mountain Oil Field Test Center. This instrument’s capability to detect and measure methane point sources is of interest for both greenhouse gas research and natural resource exploration, and the onboard cloud-screening algorithm is applicable for space imaging spectrometer missions.
Portable Remote Imaging Spectrometer
The Portable Remote Imaging Spectrometer (PRISM) instrument is operated by JPL as part of the Coral Reef Airborne Laboratory (CORAL), which makes high-density observations across ten coral reef regions in the Indian, Pacific, and Atlantic Oceans. Spectral images acquired by the PRISM instrument are processed and analyzed against values for biogeophysical forcings (e.g., sea surface temperature and carbonate chemistry) to produce a set of quantitative, empirical models that can be used to estimate current global reef condition and forecast reef condition under scenarios of predicted global change. With PRISM, CORAL offers the clearest, most extensive picture to date of the condition of a large portion of the world’s coral reefs from a uniform data set.