urn:nasa:pds:context:instrument:cirs.co 1.0 1.7.0.0 Product_Context 2016-10-01 1.0 extracted metadata from PDS3 catalog and modified to comply with PDS4 Information Model urn:nasa:pds:context:instrument_host:spacecraft.co::1.0 instrument_to_instrument_host Calcutt, S.B., F.W. Taylor, P.A.R. Ade, V.G. Kunde, and D.E. Jennings, The Composite Infrared Spectrometer, J. Brit. Interplan Soc., Vol. 45, pp. 811-816, 1992. reference.CALCUTTETAL1992 Flasar, F.M., V.G. Kunde, M.M. Abbas, R.K. Achterberg, P. Ade, A. Barucci, B. Bezard, G.L. Bjoraker, J.C. Brasunas, S.B. Calcutt, R. Carlson, C.J. Cesarsky, B.J. Conrath, A. Coradini, R. Courtin, A. Coustenis, S. Edberg, S. Edgington, C. Ferrari, T. Fouchet, D. Gautier, P.J. Gierasch, K. Grossman, P. Irwin, D.E. Jennings, E. Lellouch, A.A. Mamoutkine, A. Marten, J.P. Meyer, C.A. Nixon, G.S. Orton, T.C. Owen, J.C. Pearl, R. Prange, F. Raulin, P.L. Read, P.N. Romani, R.E. Samuelson, M.E. Segura, M.R. Showalter, A.A. Simon-Miller, M.D. Smith, J.R. Spencer, L.J. Spilker, and F.W. Taylor, Exploring the Saturn System in the Thermal Infrared: The Composite Infrared Spectrometer, Space Sci. Rev., Vol. 115, pp. 169-297, doi:10.1007/s11214-004-1454-9, 2004. reference.FLASARETAL2004B Kunde, V.G., P.A.R. Ade, R.D. Barney, D. Bergman, J.-F. Bonnal, R. Borelli, D. Boyd, J.C. Brasunas, G. Brown, S.B. Calcutt, F. Carroll, R. Courtin, J. Cretolle, J.A. Crooke, M.A. Davis, S. Edberg, R. Fettig, M. Flasar, D.A. Glenar, S. Graham, J.G. Hagopian, C.F. Hakun, P.A. Hayes, L. Herath, L. Horn, D.E. Jennings, G. Karpati, C. Kellebenz, B. Lakew, J. Lindsay, J. Lohr, J.J. Lyons, R.J. Martineau, A.J. Martino, M. Matsumura, J. McCloskey, T Melak, G. Michel, A. Morell, C. Mosier, L. Pack, M. Plants, D. Robinson, L. Rodriguez, P. Romani, W.J. Schaefer, S. Schmidt, C. Trujillo, T. Vellacott, K. Wagner, and D. Yun, Cassini Infrared Fourier Spectroscopic Investigation, SPIE Vol. 2803, pp. 162-177, doi:10.1117/12.253416, 1996. reference.KUNDEETAL1996 Martin, D.H., and E. Puplett, Polarized Interferometric Spectrometry for the Millimeter and Submillimeter Spectrum, Infrared Physics, Vol 10, pp. 105-109, doi:10.1016/0020-0891(70)90006-0, 1969. reference.MARTIN-PUPLETT1969 COMPOSITE INFRARED SPECTROMETER Spectrometer not applicable not applicable INSTRUMENT OVERVIEW =================== The instrument was designed, built and tested by an international partnership, led by NASA Goddard Space Flight Center (GSFC) and including the CEN/Saclay and Observatoire de Paris-Meudon in France, Queen Mary and Westfield College of the University of London, the University of Oxford, and the Universitat Karlsruhe, Germany. The principal investigator is M. Flasar (GSFC). The final design has evolved considerably since the original conception (KUNDEETAL1996). A description of the flight model of the instrument is given here; the reader is referred to technical publications in the literature (CALCUTTETAL1992, KUNDEETAL1996) for further technical details. Telescopes: Primary Secondary ---------- Diameter (cm): 50.8 7.6 F-number: F/6 Interferometers: Mid-IR Far-IR --------------- Type: Michelson Polarising Spectral Range (cm-1): 10--600 600--1400 Spectral Resolution (\cm ): 0.5--20 0.5--20 Integration time (s): 50--2 50--2 Focal Planes:* FP1 FP3 FP4 ------------ Spectral Range: 10--600 600--1100 1100-1400 Detectors: Thermopile Photoconductive Photovoltaic (dual) (1X10 array) (1X10 array) Pixel FOV (mrad): 4.3 0.27 0.27 Pixel A_Omega (cm^2): 2.4X10^-2 1.5X10^-4 1.5X10^-4 Peak D-star (cm Hz^{1/2} W^{-1}): 4X10^{9} 2X10^{10} 7X10^{11} Temperature (K): 170 74--92 74--92 CIRS Instrument Technical Specification. *In the original proposal, the far-IR was covered by two focal planes, with FP1 covering 10--300 cm-1 and FP2 covering 300--600 cm-1. These were later combined into a single focal plane 1, covering the full range 10--600 cm-1. The table summarises the principal instrument parameters. The optics assembly is comprised of a telescope, relay optics, and a pair of interferometers, covering the mid and far-IR spectral regions. Both interferometers share a common scan mechanism, as does a reference interferometer which controls the sampling rate and mirror movement. The other main components of CIRS are the detectors, the electronics assembly, and the passive radiative cooler. The entire instrument is maintained at 170K, except for the mid-IR detectors which are at ~80K. The berylium telescope is a Cassegrain type, consisting of a 50.8 cm F/6 paraboloidal primary and a 7.6 cm hyperboloidal secondary, the same sizes as used by the Voyager Infrared Interferometer Spectrometer (IRIS). The primary mirror has a gold-enhanced surface for low-scattering. The beam then passes to two field stops, where one part of the field is relayed to the far-IR interferometer and the other to the mid-IR interferometer, via collimators and folding mirrors (see figures cirs_optics and cirs_mechanical). A shutter may be commanded into the light path of the mid-IR fore-optics for internal calibration. The far-infrared interferometer (FIR) is of the Martin-Puplett type (MARTIN&PUPLETT1969), which uses wire-grid polarisers to split, recombine and analyse the radiation. This technique takes advantage of nearly ideal-response wire-grid polarisers, which have reflection and transmission co-efficients approaching 100% for both linear planes of polarisation, and over a wide spectral range. The 2-micron centre to centre wire spacing used in CIRS gives good response from 0--300 cm-1 and then decreasing response to 600 cm-1. The far-infrared focal plane assembly (FP1) uses two thermopile detectors to measure the final transmitted and reflected beams at the polariser-analyser, however if one fails the interferometer can still operate, albeit with a lower efficiency. The 4.3 mrad diameter field of view (FOV) of the FIR detector is the same as the IRIS detector. CIRS represents an improvement however in terms of spectral range (10--200 cm-1 now being accessible) and also in throughput, due to the greater efficiency of the polarising grids over conventional mirrors in the far-IR. The mid-infrared interferometer (MIR) is a conventional Michelson design which has a KBr beamsplitter and cube-corner retroreflectors. A germanium lens focuses the recombined beams onto the mid-IR focal plane, which covers the range 600--1400 cm-1 using two photodetector arrays. The FP3 array of 1X10 photoconductive detectors measures from 600--1100 cm-1, which includes prominent bands of acetylene, ethane, propane and nitriles. The FP4 array of 1X10 photovoltaic detectors covers 1100--1400 cm-1. This range includes the important 1304 cm-1 band of methane. CIRS sensitivity is improved substantially over the IRIS instrument in the MIR due to the use of cooled HgCdTe detectors rather than a thermopile. The mid-infrared focal plane is thermally isolated from the rest of the instrument by a tripod of low-conductance titanium alloy supports. At the rear of the focal plane, a flexible copper link connects to a cold finger, which extends from the passive radiative cooler. This patch is of aluminium honeycomb painted with conductive black paint, which radiates to a 2-pi field of view of deep space. The temperature of the mid-IR focal plane can be set via ground control to temperatures between 70 and 90K, by balancing the cooling effect of the patch with the application of a small heater, to an accuracy of 0.1K. This improved sensitivity allows for a much smaller FOV: each pixel has a 0.273 mrad square field of view, (c.f. Voyager IRIS 4.3 mrad) although the response across this field is not flat. The spatial response is given elsewhere in the documentation (CIRS_FOV_Overview.pdf). This much smaller FOV allows for much higher spatial resolution on the limb than IRIS, with a resolution of less than one scale height in the stratospheres of both Saturn and Titan. The relative sizes and alignment of the FIR and MIR fields of view is depicted in figure (cirs-fov). Due to constraints on the available mass for electronics, the ten detectors on each of the mid-IR focal planes may not be used at once. Instead, five from each array can be used simultaneously, in one of four modes (see figure modes): odd detectors, even detectors, reduced field of view (centre detectors only), or reduced resolution mode. This allows considerable versatility in operation. Both the FIR and the MIR interferometers share a common scan mechanism and Reference Interferometer (RI), which is a red light laser (785 nm) diode source. This provides the reference fringes used to create timing signals for data logging, and for feedback control of the mirror speed. The scan time is set in units of 1/8 second (=1 RTI) from 2--52s, which takes the mechanism to the maximum mirror travel distance of 1.04cm. The scan time controls the spectral resolution, from 20--0.5 cm-1. CIRS also provides an option for co-adding two consecutive interferograms in an on-board buffer before downlink, which halves the data rate. To enable this, the zero path difference (ZPD) of each interferogram must be determined on board, which requires an additional white light interferogram to be produced for reference. A white light source is provided in the RI for this purpose, which is an LED of centre wavelength 870nm and FWHM 70nm, and shares the optics with the laser. Decontamination heaters are also provided which can increase the instrument temperature to ~270K to drive off contaminants which may have condensed on the optics or detectors.