The Mars Surveyor '98 Orbiter Color Imager (Mars Color Imager, or MARCI) consists of two cameras with unique optics and identical focal plane assemblies (FPA), Data Acquisition System (DAS) electronics, and power supplies, developed under Planetary Instrument Definition and Development Program (PIDDP) funding. Each camera is characterized by small physical size (~6 X 6 X 12 cm, including baffle, and < 500 gm), low power requirements (< 2.5 W, including power supply losses), and high science performance (1000 X 1000 pixel, low noise).
The Wide Angle (WA) camera will acquire daily global maps in five spectral bands, including two ultraviolet bands that quantitatively characterize atmospheric ozone, at resolutions no poorer than 7.2 km/pixel under the worst case downlink data rate. Under better downlink conditions, the WA will provide kilometer-scale global maps of atmospheric phenomena such as clouds, hazes, dust storms, and the polar hood. Limb observations will provide additional detail on atmospheric structure at 1/3 scale-height resolution. This experiment will complement PMIRR with great synergy.
The Medium Angle (MA) camera is designed to study selected areas of Mars at regional scale. Its 6deg. field-of-view (FOV), which covers 40 km at 40 m/pixel, was selected to permit all positions of the planet except the rotational poles to be accessible for image acquisitions every two mapping cycles (roughly 52 sols), based on the orbit parameters provided in the Proposal Information Package. Ten spectral channels between 425 nm and 1000 nm provide the ability to discriminate both atmospheric and surface features on the basis of composition.
Mission operations benefits greatly from use of capabilities (e.g. operations software), facilities, and personnel at Malin Space Science Systems (MSSS) that have been assembled as part of the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) operations effort. These resources greatly reduce operations cost and complexity, and can be shared with the MGS Mars Relay effort to further reduce cost.
MARCI addresses directly two of the three high level goals of the Mars Surveyor Program: Climate and Resources. Life, the third goal is addressed primarily through the environmental factors associated with the other two goals. MARCI is first and foremost an atmospherically-oriented experiment. Its daily, global, km-scale maps of atmospheric phenomena will be used directly to study martian meteorology. In addition to tracking atmospheric phenomena in space and time, the MARCI investigation will use ozone as a surrogate for water vapor, and cloud motions as a surrogate for wind measurements, to study the present global circulation. Wind streaks, polar deposits and other wind-shaped or modified landforms will be used to study past circulation relationships.
MARCI is secondarily a geological experiment, designed to begin to fill in gaps in knowledge about martian geology that will remain after Mars Global Surveyor. Chemical and mineralogical composition remain major gaps in understanding Mars; the MGS Thermal Emission Spectrometer (TES) begins to address these gaps, and the 2001 flight of the gamma ray spectrometer will as well. MARCI contributes to compositional studies primarily through measurement of reflectance properties dominated by weathering products. Observations at several spectral wavelengths will permit composition of adjacent surface materials to be discriminated. The high spatial resolution that MARCI affords at the expense of spectral detail complements the lower spatial, higher spectral resolution of TES. Its diurnal coverage near the poles, and roughly monthly repeat coverage elsewhere, permit searches for changes that reflect both climate and material. While not an imaging spectrometer, MARCI will be able to discriminate between many important weathering products derived from the volcanic rocks that clearly dominate the surface of Mars.
In addition, while the MARCI ozone observations are suitable to inferring atmospheric water variations, they provide a much stronger investigation of Mars atmospheric photochemistry when combined with direct water vapor measurements made by PMIRR. Current photochemical modeling is limited by the availability of simultaneous ozone and water profile measurements (e.g., Nair et al., 1994). The ability to measure both with detailed seasonal, vertical, and latitudinal information would provide, by far, the strongest observational constraints to date on Mars photochemistry.
Like PMIRR, MARCI is both a nadir and limb viewing instrument. The visible and UV limb profiles derived from MARCI data will complement the IR profiles extracted by PMIRR. The spatial resolution at the limb of the two data sets is roughly comparable (about 1/3 of a scale height), which should facilitate intercomparison.
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