Mast Camera (Mastcam)

Instrument Overview

Introduction

The Mast-mounted Cameras (Mastcams) are two instrument suite of imaging systems on the Mars Science Laboratory rover's Remote Sensing Mast (RSM).

Objectives

The Mastcam primary objective is to characterize and determine details of the history and processes recorded in geologic material at the MSL site, particularly as they pertain to habitability. Mastcam will acquire panoramic, stereo, color, multispectral (400-1100 nm), and selected mosaics, zoom (close-up) images, and high-definition video observations to address the following specific objectives:

1. Observe Landscape Physiography and Processes. Provide a full description of the topography, geomorphology, and geologic setting of the MSL landing site, and the nature of past and present geologic processes at the site.
2. Examine the Properties of Rocks. Observe rocks (outcrops and clasts 3-4 mm) and the results of interaction of rover hardware with rocks to help determine morphology, texture, structure, mineralogy, stratigraphy, rock type, history/ sequence, depositional, diagenetic, and weathering processes for these materials.
3. Study the Properties of Fines. Examine martian fines (clasts <4 mm) to determine the processes that acted on these materials and individual grains within them, including physical and mechanical properties, the results of interaction of rover hardware with fines, plus stratigraphy, texture, mineralogy, and depositional processes.
4. View Frost, Ice, and Related Processes. Characterize frost or ice, if present, to determine texture, morphology, thickness, stratigraphic position, and relation to regolith and, if possible, observe changes over time; also examine ice-related (e.g., periglacial) geomorphic features.
5. Document Atmospheric and Meteorologic Events and Processes. Observe clouds, dust-raising events, properties of suspended aerosols (dust, ice crystals), and (using the video capability) eolian transport of fines.
6. Support and Facilitate Rover Operations, Analytical Laboratory Sampling, Contact Instrument Science, and Other MSL Science. To assist rover navigation, acquire images that help determine the location of the Sun, horizon features, and provide information pertinent to rover trafficability (e.g., hazards at hundreds of meters distance). For MSL science instruments, provide data that help the MSL science teams identify materials to be collected for, and characterize samples before delivery to, the MSL Analytical Laboratory; help teams identify and document materials to be examined by the Contact Instruments; and acquire images that support other MSL instruments that may need them.

Instrument Details

The Mastcams are two cameras with different focal lengths and different science color filters. One camera, referred to as the M-34 has a 34 mm focal length, f/8 lens that illuminates a 15 degree x 20 degree FOV over 1200 x 1600 pixels with slight corner vignetting. A typical image is likely to be 1152 x 1536 pixels owing to JPEG encoding constraints. The other camera, referred to as M-100, has a 100 mm focal length, f/10 lens that illuminates a 5.1 degree x 6.8 degree, 1200 x 1600 pixel FOV. Both cameras can focus from closer than 2.1 m (nearest view to the surface) and to infinity. The M-100 IFOV is 7.4 x 10^-5 radians, yielding 7.4 cm/pixel scale at 1 km distance and ~150 micron/pixel scale at 2 m distance. The M-34 IFOV is 2.2 x 10^-4 radians, giving a pixel scale of 450 micron at 2 m distance and 22 cm at 1 km. A strict definition of in focus is used for these cameras wherein the optical blur circle is less than or equal to 1 pixel.

Each camera has an 8 Gbyte internal buffer that permits it to store about 4,200 raw frames. Each is capable of losslessly compressing the images, or applying lossy JPEG compression, in realtime during acquisition and storage, or during readout of the buffer. A full-scale mosaic of 360 degrees x 80 degrees imaged in 3 science color filters with greater than or equal to 20% overlap between adjacent images with lossless compression is about 6.6 GBytes; with minimally lossy JPEG compression, less than or equal to 2.5x (3.2 bits/pixel), a mosaic including all science filters could be acquired. This is much more than can be sent back to Earth under normal communication limitations. Subframing of images is also available during image acquisition but not after and pixel summing is not available. Color 144 x 192 pixel thumbnail images can be created and compressed during readout, or from previously acquired raw or compressed images. Mosaics of thumbnail images from the M-34 can be used to synthesize wider-angle FOVs.

Both Mastcams are color imagers. Integrated over each detector is a RGB pattern filter. A broadband (IR cutoff) filter through which RGB imaging will occur is included in one of the 8 filter positions within each camera's filter wheel. Both cameras also have a narrow band filter with 10^5 neutral density attenuation to image the sun. The filters are distributed between the 34 mm and 100 mm cameras to ensure each can address some of the compositional objectives of the investigation should the other camera fail. The science filters are imaged through the RGB filter array; for some science filters, the throughput in some pixels of the unit cell will be poorer than in other pixels, but beyond 700 nm, all three Bayer colors have nearly identical throughput (i.e., they have large IR leaks, that we are using to our advantage). In-flight calibration uses the MER Pancam spare target with magnets mounted beneath the 4 color chips and white and gray surfaces to provide dust-free spots (following the approach of the Phoenix SSI team).

Mastcam hardware and internal processing permits a wide range of operational flexibility. Each camera is capable of acquiring images at very high frame rates compared to previous missions, including 720p high definition video (720 x 1280 pixel) at ~8 frames per second, and full science frames at somewhat greater than 4.5 fps. Traverse of the full focus range requires between 45 and 60 seconds, but autofocus around a known focus position can be accomplished much faster. Changes to consecutive filter positions takes 5-8 seconds, and between 30 and 45 seconds to rotate the filter wheel a full 360 degrees. Mosaic acquisition is paced by the time it takes the rover RSM to move and for motion induced vibration to settle (greater than or equal to 5 seconds between movements). The cameras include auto- and command-focus capability and auto- and command-exposure control. Radiometric accuracy is better than 10-15%, and precision 5-8%. Exposure times are expected to vary from a few tens of msec to a couple hundred msec, depending on filter bandpass and desired signal-to-noise ratio.

Reference: [MALINETAL2010]