FIFI-LS (the Field Imaging Far Infrared Line Spectrometer for SOFIA) was successfully commissioned in 2014 during six flights on SOFIA. The observed wavelengths are set by rotating reflective gratings. In flight these gratings and their rotating mechanisms are exposed to vibrations. To quantify these vibrations, an acceleration sensor was placed on the exterior of the instrument. Simultaneously, the angle sensor of the grating was read out to analyze the movement of the grating. Based on this data, lab measurements were conducted to evaluate the effect of the vibrations on the image quality of FIFI-LS. The submitted paper will present the measured data and show the results of the analysis.
KEYWORDS: Observatories, Spectroscopy, Data archive systems, Advanced distributed simulations, X-rays, Data centers, Analytical research, Current controlled current source, Data analysis, Databases
Observing on the Stratospheric Observatory for Infrared Astronomy (SOFIA) requires a strategy that takes the specific circumstances of an airborne platform into account. Observations of a source cannot be extended or shortened on the spot due to flight path constraints. Still, no exact prediction of the time on source is available since there are always wind and weather conditions, and sometimes technical issues. Observations have to be planned to maximize the observing efficiency while maintaining full flexibility for changes during the observation. The complex nature of observations with FIFI-LS - such as the interlocking cycles of the mechanical gratings, telescope nodding and dithering - is considered in the observing strategy as well. Since SOFIA Cycle 3 FIFI-LS is available to general investigators. Therefore general investigators must be able to define the necessary parameters simply, without being familiar with the instrument, still resulting in efficient and flexible observations. We describe the observing process with FIFI-LS including the integration time estimate, the mapping and dithering setup and aspects of the scripting for the actual observations performed in flight. We also give an overview of the observing scenarios, which have proven to be useful for FIFI-LS.
The Field-Imaging Far-Infrared Line-Spectrometer (FIFI-LS) entered service on the Stratospheric Observatory for
Infrared Astronomy (SOFIA) on March 2014.
Exact pointing of the instrument is important. The SOFIA telescope provides an absolute pointing stability of 1” rms,
which is sufficient for FIFI-LS. The instrument boresight relative to the telescope reference system is established with
accuracy better than 1”. FIFI-LS has a built-in rotating K-Mirror to derotate the instrument field of view. Perfect
alignment of the optical axis of the K-Mirror and the optical axis of the optical systems in both instrument channels is
practically impossible. The remaining offsets result in a dependence of the instrument boresight on the K-Mirror
position. Therefore a boresight calibration model is established for each channel. With these models the instrument
boresight is calculated and transferred to the telescope control software. Achieving precise calibration of the boresight
has been an ongoing process including the first optical models of the instrument, measurements in different laboratories
and finally measurements during the commissioning flight series. In this paper, the approach used to calibrate FIFI-LS’s
boresight is explained. This includes the model used and an overview of the laboratory, as well as the in-flight
measurements leading to the calibrated boresight model.
The Stratospheric Observatory for Infrared Astronomy (SOFIA) is the world’s largest airborne observatory, featuring a
2.5 meter effective aperture telescope housed in the aft section of a Boeing 747SP aircraft. SOFIA’s current instrument
suite includes: FORCAST (Faint Object InfraRed CAmera for the SOFIA Telescope), a 5-40 μm dual band
imager/grism spectrometer developed at Cornell University; HIPO (High-speed Imaging Photometer for Occultations), a
0.3-1.1μm imager built by Lowell Observatory; GREAT (German Receiver for Astronomy at Terahertz Frequencies), a
multichannel heterodyne spectrometer from 60-240 μm, developed by a consortium led by the Max Planck Institute for
Radio Astronomy; FLITECAM (First Light Infrared Test Experiment CAMera), a 1-5 μm wide-field imager/grism
spectrometer developed at UCLA; FIFI-LS (Far-Infrared Field-Imaging Line Spectrometer), a 42-200 μm IFU grating
spectrograph completed by University Stuttgart; and EXES (Echelon-Cross-Echelle Spectrograph), a 5-28 μm highresolution
spectrometer designed at the University of Texas and being completed by UC Davis and NASA Ames
Research Center. HAWC+ (High-resolution Airborne Wideband Camera) is a 50-240 μm imager that was originally
developed at the University of Chicago as a first-generation instrument (HAWC), and is being upgraded at JPL to add
polarimetry and new detectors developed at Goddard Space Flight Center (GSFC). SOFIA will continually update its
instrument suite with new instrumentation, technology demonstration experiments and upgrades to the existing
instrument suite. This paper details the current instrument capabilities and status, as well as the plans for future
instrumentation.
KEYWORDS: Telescopes, Sensors, Human-machine interfaces, Astronomy, Computing systems, Observatories, Signal to noise ratio, Electronics, Signal processing, Signal detection
We describe observational operations and data reduction for the science instrument FIFI-LS (Field Imaging Far Infrared
Line Spectrometer) onboard SOFIA (Stratospheric Observatory for Infrared Astronomy). First, the observation strategy
is explained, which plans all the various observing modes and parameters based on the targets and the limitations of the
observatory and instrument. Next, the observations must be created in a format readable by instrument control software,
via a system of algorithms. Once the observations have been planned and prepared, they must be scheduled, executed
and analysed, and this process is outlined. The data reduction system which processes the results from these
observations, beginning from retrieving raw data, to obtaining a FITS file data cube readable by analysis programs, is
described in detail.
The Field Imaging Far Infrared Line Spectrometer (FIFI-LS) obtains spectral data within two wavelength ranges. The observed wavelengths are set by rotating the two diffraction gratings to specific angles. This paper describes on the grating assemblies, designed to rotate and stabilize the gratings. First the assembly itself and its special environment inside FIFI-LS is explained. Then a method is layed out how to monitor the performance of the drive and how to detect upcoming failures before they happen. The last chapter is dedicated to first inflight measurements of the position stability of the grating.
FIFI-LS is the German far-infrared integral field spectrometer for the SOFIA airborne observatory. The instrument offers
medium resolution spectroscopy (R ~ a few 1000) in the far-infrared with two independent spectrometers covering 50-110
and 100-200 μm. The integral field units of the two spectrometers obtain spectra covering concentric square fields-of-views
sized 3000and 6000, respectively. Both spectrometers can observe simultaneously at any wavelength in their ranges making
efficient mapping of far-infrared lines possible.
FIFI-LS has been commissioned at the airborne observatory SOFIA as a PI instrument in spring 2014. During 2015,
the commissioning as facility instrument will be complete and the SOFIA observatory will take over the operation of
FIFI-LS. The instrument can already be used by the community. Primary science cases are the study of the galactic and
extra-galactic interstellar medium and its processes.
In this presentation, the capabilities of FIFI-LS on the SOFIA telescope will be explained and how they are used by the
offered observing modes. The remaining atmosphere and the warm telescope create a high background situation, which
requires a differential measurement technique. This is achieved by SOFIA’s chopping secondary mirror and nodding the
telescope. Depending on the source size, different observing modes may be used to observe a source. All modes use spatial
and spectral dithering. The resulting data products will be 3D-data cubes.
The observing parameters will be specified using AOTs, like the other SOFIA instruments, and created via the tool
SSPOT which is similar to the Spitzer Space Telescope SPOT tool. The observations will be done in service mode, but
SOFIA invites a few investigators to fly onboard SOFIA during (part of) their observations.
The Stratospheric Observatory for Infrared Astronomy (SOFIA) is an airborne observatory, carrying a 2.5 m telescope onboard a heavily modified Boeing 747SP aircraft. SOFIA is optimized for operation at infrared wavelengths, much of which is obscured for ground-based observatories by atmospheric water vapor. The SOFIA science instrument complement consists of seven instruments: FORCAST (Faint Object InfraRed CAmera for the SOFIA Telescope), GREAT (German Receiver for Astronomy at Terahertz Frequencies), HIPO (High-speed Imaging Photometer for Occultations), FLITECAM (First Light Infrared Test Experiment CAMera), FIFI-LS (Far-Infrared Field-Imaging Line Spectrometer), EXES (Echelon-Cross-Echelle Spectrograph), and HAWC (High-resolution Airborne Wideband Camera). FORCAST is a 5–40 μm imager with grism spectroscopy, developed at Cornell University. GREAT is a heterodyne spectrometer providing high-resolution spectroscopy in several bands from 60–240 μm, developed at the Max Planck Institute for Radio Astronomy. HIPO is a 0.3–1.1 μm imager, developed at Lowell Observatory. FLITECAM is a 1–5 μm wide-field imager with grism spectroscopy, developed at UCLA. FIFI-LS is a 42–210 μm integral field imaging grating spectrometer, developed at the University of Stuttgart. EXES is a 5–28 μm high-resolution spectrograph, developed at UC Davis and NASA ARC. HAWC is a 50–240 μm imager, developed at the University of Chicago, and undergoing an upgrade at JPL to add polarimetry capability and substantially larger GSFC detectors. We describe the capabilities, performance, and status of each instrument, highlighting science results obtained using FORCAST, GREAT, and HIPO during SOFIA Early Science observations conducted in 2011.
FIFI-LS (Field-Imaging Far-Infrared Line Spectrometer) is an imaging spectrograph for SOFIA comprised of two
medium resolution (R~2200) grating spectrometers feeding two 16x25 pixel detector arrays, which enable simultaneous
line observations across two wavelength ranges (42-110 μm and 110-210μm) each across a field of view of 5x5 pixel.
FIFI-LS will be the extragalactic spectroscopic workhorse for SOFIA. FIFI-LS has enough sensitivity to observe a
substantial sample of nearby galaxies. It also has the right combination of wavelength range and spatial resolution to
carry out unique new observations beyond those possible with Herschel, Spitzer, ISO and IRAS. As the effective
sensitivity of FIFI-LS is only about a factor of 3-5 lower than the PACS spectrometer onboard Herschel, mainly due to
an enhanced multiplexing advantage, FIFI-LS will build upon recent exciting scientific results and spearhead the post-
Herschel far-infrared era.
FIFI-LS is scheduled for commissioning onboard SOFIA in early 2014. An account on the instrument and its current
stratus will be presented.
FIFI LS is the German far-infrared integral field spectrometer for the SOFIA airborne observatory. The instrument consists
of two independent integral field spectrometers for two different wavelength bands (45-110 μm and 100-200 μm). A
dichroic filter enables simultaneous observation of two different spectral lines in the same field-of view. This allows very
efficient mapping of extended regions with FIFI LS in many important far-infrared cooling lines with line ratios sensitive to
temperature and density.
FIFI LS will become a facility instrument for SOFIA. In the next two years it will become a fully commissioned facility
instrument. After its commission, FIFI LS will be available for general observing with a large science potential. In this
paper, we will also discuss the science of FIFI LS.
FIFI-LS is a Field-Imaging Line Spectrometer designed for the SOFIA airborne observatory. The instrument will
operate in the far infrared (FIR) wavelength range from 42 to 210 μm. Two spectrometers operating between
42-110 μm and 110-210 μm allow simultaneous and independent diffraction limited 3D imaging over a field of
view of 6" × 6" and 12" × 12" respectively. We have developed a telescope simulator to test the imaging and
spectral performance of FIFI-LS in the FIR. Here, we present the telescope simulator as well as the performance
verification of FIFI-LS using the simulator. Finally we compare the measurements with the theoretical expected
performance of FIFI-LS.
FIFI LS is a far-infrared integral field spectrometer for the SOFIA airborne observatory. The instrument is designed to maximize the observing efficiency by simultaneous and nearly independent imaging of the field-of-view in two medium spectral resolution bands. We present a summary of the FIFI LS design and the current status of instrument development. Its unique features as the large far-infrared photoconductor detectors, its integral field concept, and control system will be highlighted. Special attention will be given to the Extended Observing Opportunity Program, which will allow general access to FIFI LS on SOFIA.
FIFI LS is a Field-Imaging Line Spectrometer designed for the SOFIA airborne observatory. The instrument will operate in the far infrared wavelength range between 42 to 210 microns. Two spectrometer bands from 42 - 110 microns ('blue' channel) and 110 - 210 microns ('red' channel) allow simultaneous and independent diffraction limited 3D imaging over a field of view of 6 x 6 and 12 x 12 arcseconds respectively. Both spectrometer channels use Littrow mounted diffraction gratings, a set of anamorphic collimators, and a reflective integral field unit. Two large scale 25 x 16 pixel Ge:Ga detector arrays are utilized, axially stressed in the red channel and only slightly stressed in the blue channel. The spectral resolution of the instrument varies between R = 1400 to 6500 depending on wavelength. The sensitivity of the instrument will allow background limited performance over the entire wavelength range. We present test results for the components in the optical path of FIFI LS including grating efficiencies, filter characteristics, detector performance, and optical throughput. Based on our measurements we characterized and optimized the overall system performance to maximize observing efficiency - one of the major instrument design criteria.
FIFI LS is a far-infrared integral field spectrometer for the SOFIA airborne observatory. The instrument is designed to maximize the observing efficiency by simultaneous and nearly independent imaging of the field of view in two medium spectral resolution bands. Both spectral channels - covering a wavelength range of 42 to 110 microns and 110 to 210 microns respectively - allow diffraction limited spectral imaging. Reflective image slicers rearrange the 5x5 pixel field of view into the 1x25 pixel entrance slit of a grating spectrograph. Littrow mounted gratings with anamorphic collimators are used for spectral multiplexing with a spectral resolution between R = 1400 - 6500, depending on observing wavelength. Each spectral band employs two large format 25x16 pixel Ge:Ga detector arrays, axially stressed for the long wavelength band to achieve a longer wavelength response and slightly stressed for the short wavelength band. For each of the 25 spatial pixels, we are able to cover a velocity range of approximately 1500 km/s around a selected far-infrared line. This arrangement provides good spectral coverage with high responsivity. We present a summary of the FIFI LS design and the current status of instrument integration.
We are building the Field-Imaging Far-Infrared Line Spectrometer (FIFI LS) for the US-German airborne observatory SOFIA. The detector read-out system is driven by a clock signal at a certain frequency. This signal has to be provided and all other sub-systems have to work synchronously to this clock. The data generated by the instrument has to be received by a computer in a timely manner. Usually these requirements are met with a real-time operating system (RTOS).
In this presentation we want to show how we meet these demands differently avoiding the stiffness of an RTOS. Digital I/O-cards with a large buffer separate the asynchronous working computers and the synchronous working instrument. The advantage is that the data processing computers do not need to process the data in real-time. It is sufficient that the computer can process the incoming data stream on average. But since the data is read-in synchronously, problems of relating commands and responses (data) have to be solved: The data is arriving at a fixed rate. The receiving I/O-card buffers the data in its buffer until the computer can access it. To relate the data to commands sent previously, the data is tagged by counters in the read-out electronics. These counters count the system's heartbeat and signals derived from that. The heartbeat and control signals synchronous with the heartbeat are sent by an I/O-card working as pattern generator. Its buffer gets continously programmed with a pattern which is clocked out on the control lines. A counter in the I/O-card keeps track of the amount of pattern words clocked out. By reading this counter, the computer knows the state of the instrument or knows the meaning of the data that will arrive with a certain time-tag.
FIFI LS is a far-infrared integral field spectrometer for SOFIA that
maximizes observing efficiency by spectrally imaging fields in two
medium velocity resolution bands simultaneously and nearly independently. Although the two observing bands, Red (110-210 microns) and Blue (42-110 microns), share some common fore-optics, the Field-Imaging Far-Infrared Line Spectrometer (FIFI LS) can observe diffraction-limited spectra at R = 1400 to 6500, depending on wavelength, with two separate Littrow mounted spectrometers. To further increase the observing efficiency, we employ an integral field technique that allows multiplexing spatially. This is achieved by utilizing slicer mirrors to optically re-arrange the 2D field into a single slit for a standard long slit spectrometer. Effectively,
a 5 × 5 pixel spatial field of view is imaged to a 25 × 1 pixel slit and dispersed to a 25 × 16 pixel, 2D detector array. The detectors are two large format Ge:Ga arrays, axially stressed in the Red channel to achieve a longer wavelength response and slightly stressed in the Blue channel. Overall, for each of the 25 spatial pixels in each band, the instrument can cover a velocity range of approximately 1500 km/s with an estimated sensitivity of 2 × x 10-15 W Hz1/2 per pixel. This arrangement provides good spectral coverage with high responsivity. With this scheme FIFI LS will have advantages over single-slit spectrometers in detailed morphological studies of the heating and cooling of galaxies, star formation, the ISM under low-metalicity conditions as found in dwarf galaxies, active galactic nuclei and their environment, starbursts, and merging/interacting galaxies.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.