Robert Louis Marcialis

Imager for Mars Pathfinder (IMP) image calibration

The Imager for Mars Pathfinder returned over 16,000 high-quality images from the surface of Mars. The camera was well-calibrated in the laboratory, with <5% radiometric uncertainty. The photometric properties of two radiometric targets were also measured with 3% uncertainty. Several data sets acquired during the cruise and on Mars confirm that the system operated nominally throughout the course of the mission. Image calibration algorithms were developed for landed operations to correct instrumental sources of noise and to calibrate images relative to observations of the radiometric targets. The uncertainties associated with these algorithms as well as current improvements to image calibration are discussed.

The size, shape, density, and Albedo of Ceres from its occultation of BD+8°471

The occultation of BD+8°471 by Ceres on 13 November 1984 was observed photoelectrically at 13 sites in Mexico, Florida, and the Caribbean. These observations indicate that Ceres is an oblate spheroid having an equatorial radius of 479.6±2.4 km and a polar radius of 453.4±4.5 km. The mean density of this minor planet is 2.7 g/cm3±5%, and its visual geometric albedo is 0.073. While the surface appears globally to be in hydrostatic equilibrium, firm evidence of real limb irregularities is seen in the data.

The Surface Composition of Charon: Tentative Identification of Water Ice

The 3 March 1987 Charon occultation by Pluto was observed in the infrared at 1.5, 1.7, 2.0, and 2.35 micrometers. Subtraction of fluxes measured between second and third contacts from measurements made before and after the event has yielded individual spectral signatures for each body at these wavelengths. Charons surface appears depleted in methane relative to Pluto. Constancy of flux at 2.0 micrometers throughout the event shows that Charon is effectively black at this wavelength, which is centered on a very strong water absorption band. Thus, the measurements suggest the existence of water ice on Plutos moon.

A two-spot albedo model for the surface of Pluto

This paper summarizes the work of Marcialis (1983, 1984). A finite-element approach has been used to generate synthetic light curves of an unevenly bright, rotating sphere. Application to the Pluto-Charon system shows that two circular spots (46 and 28 deg in radius, both at south latitude 23 deg, separated by 134 deg in longitude) with albedos half that of the surrounding terrain can accurately reproduce six available photoelectric light curves between 1953 and 1982. A dark equatorial band (extending from south latitude 69 deg to anywhere between 50 and 65 deg north latitude) can be invoked to explain the secular dimming. Constraints on this equatorial band, which may alternatively be viewed as two polar caps, are such that to date its dimensions are not uniquely determined. However, polar caps with albedos near unity serve quite well to explain the 40-percent dimming of Pluto since its discovery in 1930. Hardies 1964 photoelectric observations are presented for the first time in tabular form.

The MVACS Robotic Arm Camera

The Robotic Arm Camera (RAC) is one of the key instruments newly developed for the Mars Volatiles and Climate Surveyor payload of the Mars Polar Lander. This lightweight instrument employs a front lens with variable focus range and takes images at distances from 11 mm (image scale 1:1) to infinity. Color images with a resolution of better than 50 μm can be obtained to characterize the Martian soil. Spectral information of nearby objects is retrieved through illumination with blue, green, and red lamp sets. The design and performance of the camera are described in relation to the science objectives and operation. The RAC uses the same CCD detector array as the Surface Stereo Imager and shares the readout electronics with this camera. The RAC is mounted at the wrist of the Robotic Arm and can characterize the contents of the scoop, the samples of soil fed to the Thermal Evolved Gas Analyzer, the Martian surface in the vicinity of the lander, and the interior of trenches dug out by the Robotic Arm. It can also be used to take panoramic images and to retrieve stereo information with an effective baseline surpassing that of the Surface Stereo Imager by about a factor of 3.

The MVACS Surface Stereo Imager on Mars Polar Lander

The Surface Stereo Imager (SSI), a stereoscopic, multispectral camera on the Mars Polar Lander, is described in terms of its capabilities for studying the Martian polar environment. The cameras two eyes, separated by 15.0 cm, provide the camera with range-finding ability. Each eye illuminates half of a single CCD detector with a field of view of 13.8° high by 14.3° wide and has 12 selectable filters between 440 and 1000 nm. The ƒ/18 optics have a large depth of field, and no focusing mechanism is required; a mechanical shutter is avoided by using the frame transfer capability of the 528×512 CCD. The resolving power of the camera, 0.975 mrad/pixel, is the same as the Imager for Mars Pathfinder camera, of which it is nearly an exact copy. Specially designed targets are positioned on the Lander; they provide information on the magnetic properties of windblown dust, and radiometric standards for calibration. Several experiments beyond the requisite color panorama are described in detail: contour mapping of the local terrain, multispectral imaging of interesting features (possibly with ice or frost in shaded spots) to study local mineralogy, and atmospheric imaging to constrain the properties of the haze and clouds. Eight low-transmission filters are included for imaging the Sun directly at multiple wavelengths to give SSI the ability to measure dust opacity and potentially the water vapor content. This paper is intended to document the functionality and calibration of the SSI as flown on the failed lander.

CVF spectrophotometry of Pluto: Correlation of composition with Albedo

Abstract Time-resolved spectrophotometry of the Pluto-Charon system was obtained on 6 nigths in March and April of 1988. The observations include about one-third of the 6.4-day lightcurve, centered around minimum light, and span the wavelength region from 0.96 to 2.65 μm. The spectra reveal night-to-night variations in depths of methane absorptions throughout this region. Band depths vary such that their equivalent width is least near minimum light. One obvious interpretation is that dark regions on the planet are depleted in methane relative to bright areas, at least for the hemisphere observed. Our results are consistent with the observations of M.W. Buie and U. Fink (1987, Icarus 70, 483–498) but in conflict with those of S.R. Sawyer (1989, Bull. Amer. Astron. Sci. 21, 986, Abstract). The near-infrared spectrum of Pluto appears to be dominated by surface frost; atmospheric methane contributes much less to the overall spectral signature. We see evidence that Plutos dark equatorial regions tend to be redder than those of more moderate albedo.

DIRTCam in the desert: The Silver Lake field test of the Robotic Arm Camera

The Robotic Arm Camera (RAC) is a panchromatic imager included as part of the Mars Volatiles and Climate Surveyor (MVACS) science experiment on Mars Polar Lander and on the Mars 2001 lander. It is designed to take both panoramic and microscopic images in order to gather data on the morphology and mineralogy of surface materials. In order to demonstrate these capabilities, a field test was conducted at Silver Lake playa in the Mojave Desert. The test consisted of going to a remote site unknown to the science team and providing that team with a data set of RAC panoramic, anaglyph, and microscopic images similar to what would be available during an actual landing. With only this information the science team attempted a determination of the position and the geology of the field test site. Using panoramic and anaglyph images provided by RAC, in conjunction with overflight images simulating data from a descent camera, the landing site for the field test was determined within 50 m of the actual site as lying near both a playa and an alluvial fan. Images of samples from the surface and within the trench revealed grain morphology, texture, and mineralogy indicating a soil dominated by quartz and feldspar, interspersed with a minor mafic component. Grain-size distribution was bimodal, with small, rounded to subrounded grains dominant at lower depths and larger, more angular grains more plentiful near the surface. This mineralogy is confirmed by the geology of the site and the data provided by the descent images and mid-IR measurements. RAC has demonstrated its ability to image the local geology and identify the major mineralogic components of an unknown site. These abilities will be crucial in understanding both the macroscopic and the microscopic geology of future Mars landing sites. This test also has demonstrated the crucial link between RAC data and complementary data sets such as context images and compositional data that can support the mineralogic observations made by RAC.