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CoMIC: A Compact Multicolor Imaging CameraSunip Mukherjee
Department of Physics and Applied Physics
This work was supported by the UMass Lowell Center for Space Science and Technology.
Design Highlights• 1U CubeSat compatible
• 8 Watts power usage
• 30° field of view (FOV)
• 0.1° angular resolution
• High optical throughput• 400 nm-900 nm operating
range• Can be used with very
narrow band interference filters
• Exposures as low as 1ms
AbstractWe describe the constructionand features of a compactmulticolor imaging camera(CoMIC) that can be used forremote sensing in 400-900 nmwavelength range. Theinstrument accommodates amosaic of optical filters thatallow only certain wavelengthsof light allowing CoMIC toimage different segments of ascene in different wavelengths,then scanned in a push-broomfashion to image a large areain multiple colors. The choiceof colors are determined by thechemical species or reaction tobe observed: sodium andpotassium doublet emission inthis prototype.
Future Plans• Customizable filter mosaic, along with
the compact form factor and ruggeddesign makes it ideal for applicationssuch as aeronomy (study of upperatmosphere), to surface remotesensing (agriculture, oil and gasexploration etc) in the visible to nearinfrared range with a large number ofsignatures.
• Higher resolution with a smaller FOVor vice-versa with minor modificationsto the existing design to extend rangeof applications.
• Planned weather balloon flight tomeasure airglow over a 24-hour periodto augment existing instruments thatmeasure airglow.
Push-Broom ScanningAs the name indicates, push-broom scanning(or on-track scanning) uses a line ofdetectors perpendicular to the direction ofscanning. In the case of CoMIC, the field-of-view (FOV) is divided into segments ofdifferent colors, and scanning is performedperpendicular to the segments so that onepoint is imaged under all color segments inthe instrument.
Scan direction
Left: Push-broom scanning concept is described(courtesy: Harris Geospatial); Right: Filter mosaicused in CoMIC, with possible scan direction. Thefour colors correspond to 500 nm, 589 nm, 770nm and 700 nm from left to right.
Design PrincipleThe instrument is designed around the 1U-CubeSat form factor thatrestricts its mass and volume within a 1.4 kg, 10 cm cube. The filtermosaic that lends CoMIC its ability to image in multiple colors requirenear-normal incidence of light for optimal operation. This is achieved byplacing the filter mosaic at a telecentric image plane. The filter plane isthen reimaged onto a charge-coupled detector (CCD) array usingmultiple lenses. The telecentric configuration allows the use of verynarrow band filters in the instrument.
Left: Protype instrument in a 3D-printed chassis; Right: Optical design layoutof the instrument.
Data Acquisition• Obtains optimally bright
images through automaticexposure control
• Prototype instrument has fourfilter panes: 589 nm forsodium, 700 nm forpotassium, 500 nm and 700nm for background continuum
Scan direction
1 ms exposure taken by CoMIC on a sunny day.The four filter patches are indicated in the figureusing false colors. The white ellipse indicates to atree under the 700 and 770 nm patches; dark treesunder all filters but 770nm demonstrates lowabsorbance by chlorophylls beyond 700 nm.
This scene is observed by CoMIC,whose output is displayed on theright.
Back of the Detector
Entrance Pupil
Camera Lens
Camera Electronics