Imaging spectrometer with high spectral and spatial resolution and high signal-to-noise, will identify the moon's spectral fingerprint (Moon Mineralogy Mapper).

This picture shows an approximately true color image of areas of Altadena and Pasadena, CA (Airborne Visible InfraRed Imaging Spectrometer - AVIRIS).

The MIRI optics module.

The images produced by M3 can be thought of as a cube of information. The width is 600 pixels (each of which has a spatial resolution of 70 m at the instrument's altitude of 100 km), the length is an infinite strip along the spacecraft's orbital path (or wherever one chooses to "crop" the picture for an individual study), and the depth is 261 spectral channels.

For scientific analysis of materials composition and physical properties, imaging spectroscopy is often the next best thing to being there. In Solar System exploration, "being there" is often impossible, but "orbiting around" or "flying by" typically provides a platform from which the full electromagnetic spectrum of reflections or emissions from a surface may be sensed, with the right instruments.

In the visible and infrared wavelengths, imaging spectrometers are often the best way to remotely sense mineral composition, terrestrial bioecological parameters, and to quantitatively differentiate among different ices and ice types. The way molecules interact with light is measurable in the laboratory, and repeatable in the natural world, allowing detailed measurements to be made from afar at the limits of optical performance.

Light entering an instrument aperture is finely split and measured in hundreds of spectral components tightly associated with each area on the surface covered by a single image pixel. Getting the spatial and spectral information precisely registered together is the most difficult part. JPL's space flight imaging spectrometers lead the world in precise spatial/spectral and radiometric accuracy and calibration.

In the visible and infrared wavelengths, imaging spectrometers are often the best way to remotely sense mineral composition, terrestrial bioecological parameters, and to quantitatively differentiate among different ices and ice types. The way molecules interact with light is measurable in the laboratory, and repeatable in the natural world, allowing detailed measurements to be made from afar at the limits of optical performance.

Light entering an instrument aperture is finely split and measured in hundreds of spectral components tightly associated with each area on the surface covered by a single image pixel. Getting the spatial and spectral information precisely registered together is the most difficult part. JPL's space flight imaging spectrometers lead the world in precise spatial/spectral and radiometric accuracy and calibration.

Moon Mineralogy Mapper (M³)
The Moon Mineralogy Mapper is an imaging spectrometer with high spectral and spatial resolution, reliably uniform results, and a high signal-to-noise ratio.

The instrument will detect electromagnetic radiation with wavelengths from 430 to 3000 nanometers (0.43 to 3 microns), which covers visible light and the near-infrared. (Unlike previous lunar spectrometers, M³ will include the range from 2.5 to 3 microns, which is uniquely a marker for small amounts of OH and H2O.) This spectral region is dominated by solar reflection, as contrasted with the longer wavelengths of the thermal-infrared region, which is influenced primarily by heat radiated by the ground.

M³ will divide the approximately 2600-nm range to which it is sensitive into 261 discrete bands, each of which is only 10 nm wide. This is considered very high spectral resolution, and will enable M³ to detect the fine detail required for mineral identification.

Spatial resolution will be similarly high. From its vantage point 100 km above the lunar surface, M³ will be able to resolve features as small as 70 m in diameter.

Each picture M³ produces will show mountains, craters, or plains like a regular camera, but in a very narrow range of wavelengths (the 10-nm sliver of the spectrum that constitutes one spectral channel). It's like taking a picture using a filter that allows only one precise color of light through the lens.

But M³ will take 261 such pictures simultaneously, each in its own "color." To identify the spectral fingerprint of a particular portion of the lunar surface, one would plot the light intensity of each of the 261 channels, noting how bright each pixel is at each wavelength. Plotting this on a graph produces a spectrum. Each mineral has its own unique spectrum, identified by taking spectrographic readings in a laboratory. (Actually, since scientists will have an idea of what they are looking for, they will be able to limit their plotting to the relevant portions of the spectrum for a given mineral—up to a few dozen channels each time.)

M³ will sense the terrain beneath it through a strip of 600 spatial elements (pixels) oriented perpendicular to the direction of its flight around the Moon. As the instrument orbits the Moon, all 600 pixels will photograph the lunar surface simultaneously, producing an image 600 pixels wide and many kilometers long (along the endless path the instrument will fly).

Designed for simplicity, reliability, and accuracy, M³ uses a compact system of optics (the mirrors that collect and direct the light) known as an "Offner" design, which produces little or no distortion, either spatially or spectrally. And instead of mechanically scanning the scene as some systems do, M³ will use the "pushbroom" method in which the instrument passively sweeps the scene below as it flies, recording with the entire row of 600 pixels simultaneously.

Each of those 600 pixels, as mentioned above, will simultaneously record images in each of 261 spectral channels. So the product of M³'s measurements can be described as an "image cube" that is 600 pixels wide, infinitely long over time as the instrument flies (an "instantaneous snapshot" would be one pixel long), and 261 spectral channels deep.

M³ will employ two modes, global (mapping the entire surface) and target (zeroing in on features of special interest).

In global mode, the instrument will merge groups of pixels to reduce the data rate and accommodate the limited available downlink time. This will result in an effective spatial resolution of 140 nm and spectral resolution of 40 nm. Resolution will be at the maximum 70 m spatial and 10 nm spectral while in target mode, but data in this mode will be recorded for only six minutes at a time. Thus, the total amount of data transmitted in global and target modes will be the same.

The field of view (FOV) will be 40 km for both modes to allow contiguous orbit-to-orbit measurements at the equator that will minimize variations in lighting conditions. The instrument will use diffraction grating to separate sunlight into its constituent wavelengths, much as a prism does, and will maintain 12-bit precision and use only lossless compression throughout.Dr. Carle Peters from Brown University is the Principal Investigator for the Moon Mineralogy Mapper.