Dr. Jürgen Wolf Profile

Dr. Jürgen Wolf

at NASA Ames Research Ctr

SPIE Involvement:

Conference Program Committee | Author

Publications (48)

PROCEEDINGS ARTICLE | July 6, 2018

Towards a European Stratospheric Balloon Observatory: the ESBO design study

Proc. SPIE. 10700, Ground-based and Airborne Telescopes VII

KEYWORDS: Observatories, Telescopes, Astronomy, Stars, Sensors, Ultraviolet radiation, Far infrared, Spatial resolution

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PROCEEDINGS ARTICLE | July 6, 2018

Adding a second spectral channel to the SOFIA FPI+ science instrument

Proc. SPIE. 10702, Ground-based and Airborne Instrumentation for Astronomy VII

KEYWORDS: Near infrared, Telescopes, Optical filters, Beam splitters, Cameras, Sensors, Infrared radiation, Pluto

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The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a heavily modified Boeing 747SP aircraft, accommodating a 2.7 meter infrared telescope. This airborne observation platform operates at flight altitudes of up to 13.7 km (45,000 ft) and therefore allows a nearly unobstructed view of the visible and infrared universe at wavelengths between 0.3 µm and 1600 µm. The Focal Plane Imager (FPI+) is SOFIA’s main tracking camera. It uses a commercial, off-the-shelf camera with a thermoelectrically cooled EM-CCD. The back-illuminated sensor has a peak quantum efficiency greater than 95% at 550 nm and the dark current is as low as 0.01 e-/pix/sec. Since 2015, the FPI+ has been available to the community as a Facility Science Instrument, and can be used to observe stellar occultations by solar system objects such as dwarf planets, moons, asteroids, and comets, and transits of extra-solar planets. To date, SOFIA has conducted multi-channel observations of occultations, e.g. the occultation by Pluto in June of 2015 or the occultation by Triton in October 2017, using three instruments, HIPO and FLITECAM at the main instrument flange of the telescope, and the FPI+. This multi-wavelength sampling is important for enabling discrimination of particle sizes and constituents of hazes in the atmosphere of bodies such as Pluto and Triton, and the coma material of comets. Multi-wavelength observations also serve to allow us to place constraints on the chemical compositions of these formations. After the retirement of the two other instruments, the FPI+ is now SOFIA’s only remaining observing tool for occultations. In order to preserve some of the multi-color observing capability of the platform, we here discuss the addition of a second spectral channel to the FPI+. In a first upgrade step, a beamsplitter will split the incoming light and send it to two EMCCD cameras, one working in the ”blue”, e.g. SLOAN g’ band, and the other working in the ”red”, e.g. SLOAN i’ or z’ band. In a second upgrade step, the ”red” channel could be equipped with a NIR camera in order to provide a wider wavelength separation of the two bands. This will however require a modified dichroic coating on the tertiary (Nasmyth) mirror of the SOFIA telescope. This paper presents a preliminary design study of the opto-mechanical configuration of the dual channel FPI+.

PROCEEDINGS ARTICLE | September 14, 2016

Deutsches SOFIA Institut (DSI) at the SOFIA Science Center: engineering and scientific contributions to the airborne observatory

Proc. SPIE. 9973, Infrared Remote Sensing and Instrumentation XXIV

KEYWORDS: Observatories, Telescopes, Mirrors, Stars, Imaging systems, Cameras, Calibration, Space telescopes, Aluminum, Electroluminescent displays

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PROCEEDINGS ARTICLE | August 9, 2016

Development of the FPI+ as facility science instrument for SOFIA cycle four observations

Proc. SPIE. 9908, Ground-based and Airborne Instrumentation for Astronomy VI

KEYWORDS: Observatories, Observatories, Telescopes, Mirrors, Stars, Imaging systems, Cameras, Sensors, Diagnostics, Space telescopes, Pluto

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The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a heavily modified Boeing 747SP aircraft, accommodating a 2.5m infrared telescope. This airborne observation platform takes astronomers to flight altitudes of up to 13.7 km (45,000ft) and therefore allows an unobstructed view of the infrared universe at wavelengths between 0.3 m and 1600 m. SOFIA is currently completing its fourth cycle of observations and utilizes eight different imaging and spectroscopic science instruments. New instruments for SOFIAs cycle 4 observations are the High-resolution Airborne Wideband Camera-plus (HAWC+) and the Focal Plane Imager (FPI+). The latter is an integral part of the telescope assembly and is used on every SOFIA flight to ensure precise tracking on the desired targets. The FPI+ is used as a visual-light photometer in its role as facility science instrument. Since the upgrade of the FPI camera and electronics in 2013, it uses a thermo-electrically cooled science grade EM-CCD sensor inside a commercial-off-the-shelf Andor camera. The back-illuminated sensor has a peak quantum efficiency of 95% and the dark current is as low as 0.01 e-/pix/sec. With this new hardware the telescope has successfully tracked on 16th magnitude stars and thus the sky coverage, e.g. the area of sky that has suitable tracking stars, has increased to 99%. Before its use as an integrated tracking imager, the same type of camera has been used as a standalone diagnostic tool to analyze the telescope pointing stability at frequencies up to 200 Hz (imaging with 400 fps). These measurements help to improve the telescope pointing control algorithms and therefore reduce the image jitter in the focal plane. Science instruments benefit from this improvement with smaller image sizes for longer exposure times. The FPI has also been used to support astronomical observations like stellar occultations by the dwarf planet Pluto and a number of exoplanet transits. Especially the observation of the occultation events benefits from the high camera sensitivity, fast readout capability and the low read noise and it was possible to achieve high time resolution on the photometric light curves. This paper will give an overview of the development from the standalone diagnostic camera to the upgraded guiding/tracking camera, fully integrated into the telescope, while still offering the diagnostic capabilities and finally to the use as a facility science instrument on SOFIA.

PROCEEDINGS ARTICLE | August 8, 2016

A high-sensitivity EM-CCD camera for the open port telescope cavity of SOFIA

Proc. SPIE. 9906, Ground-based and Airborne Telescopes VI

KEYWORDS: Telescopes, Fluctuations and noise, Imaging systems, Cameras, Interfaces, Quantum efficiency, Fourier transforms, CCD cameras, Target acquisition, Prototyping

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The Stratospheric Observatory for Infrared Astronomy (SOFIA) has three target acquisition and tracking cameras. All three imagers originally used the same cameras, which did not meet the sensitivity requirements, due to low quantum efficiency and high dark current. The Focal Plane Imager (FPI) suffered the most from high dark current, since it operated in the aircraft cabin at room temperatures without active cooling. In early 2013 the FPI was upgraded with an iXon3 888 from Andor Techonolgy. Compared to the original cameras, the iXon3 has a factor five higher QE, thanks to its back-illuminated sensor, and orders of magnitude lower dark current, due to a thermo-electric cooler and “inverted mode operation." This leads to an increase in sensitivity of about five stellar magnitudes.

The Wide Field Imager (WFI) and Fine Field Imager (FFI) shall now be upgraded with equally sensitive cameras. However, they are exposed to stratospheric conditions in flight (typical conditions: T≈-40° C, p≈ 0:1 atm) and there are no off-the-shelf CCD cameras with the performance of an iXon3, suited for these conditions. Therefore, Andor Technology and the Deutsches SOFIA Institut (DSI) are jointly developing and qualifying a camera for these conditions, based on the iXon3 888. These changes include replacement of electrical components with MIL-SPEC or industrial grade components and various system optimizations, a new data interface that allows the image data transmission over∼30m of cable from the camera to the controller, a new power converter in the camera to generate all necessary operating voltages of the camera locally and a new housing that fulfills airworthiness requirements. A prototype of this camera has been built and tested in an environmental test chamber at temperatures down to T=-62° C and pressure equivalent to 50 000 ft altitude. In this paper, we will report about the development of the camera and present results from the environmental testing.

PROCEEDINGS ARTICLE | August 8, 2016

Computer-aided star pattern recognition with astrometry.net: in-flight support of telescope operations on SOFIA

Proc. SPIE. 9913, Software and Cyberinfrastructure for Astronomy IV

KEYWORDS: Observatories, Telescopes, Stars, Detection and tracking algorithms, Imaging systems, Cameras, Calibration, Pattern recognition, Space telescopes, Electroluminescent displays

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PROCEEDINGS ARTICLE | July 27, 2016

Pointing and control system performance and improvement strategies for the SOFIA Airborne Telescope

Proc. SPIE. 9906, Ground-based and Airborne Telescopes VI

KEYWORDS: Telescopes, Mirrors, Cameras, Sensors, Control systems, Electroluminescence, Ray tracing, Finite element methods, Gyroscopes, Motion estimation

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SPIE Journal Paper | July 7, 2015

First exoplanet transit observation with the Stratospheric Observatory for Infrared Astronomy: confirmation of Rayleigh scattering in HD 189733 b with the High-Speed Imaging Photometer for Occultations

Mandushev, Georgi , Dunham, Edward , Collins, Peter , Angerhausen, Daniel , Mandell, Avi , Becklin, Eric , Hamilton, Ryan , Logsdon, Sarah , McElwain, Michael , McLean, Ian , Pfüller, Enrico , Savage, Maureen , Shenoy, Sachindev , Vacca, William , Van Cleve, Jeffrey , Wolf, Jürgen

JATIS Vol. 1 Issue 03

KEYWORDS: Exoplanets, Observatories, Photometry, Stars, Data modeling, Infrared astronomy, Rayleigh scattering, Signal to noise ratio, Point spread functions, Planets

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PROCEEDINGS ARTICLE | August 4, 2014

Characterization of InGaAs-based cameras for astronomical applications using a new VIS-NIR-SWIR detector test bench

Proc. SPIE. 9145, Ground-based and Airborne Telescopes V

KEYWORDS: Telescopes, Indium gallium arsenide, Cameras, Sensors, Calibration, Quantum efficiency, Lamps, Interference (communication), Photodiodes, Monochromators

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PROCEEDINGS ARTICLE | August 4, 2014

Upgrade of the SOFIA target acquisition and tracking cameras

Proc. SPIE. 9145, Ground-based and Airborne Telescopes V

KEYWORDS: Observatories, Telescopes, Mirrors, Stars, Imaging systems, Cameras, CCD cameras, Space telescopes, Computer aided design, CCD image sensors

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PROCEEDINGS ARTICLE | July 22, 2014

Environmental testing for new SOFIA flight hardware

Proc. SPIE. 9145, Ground-based and Airborne Telescopes V

KEYWORDS: Telescopes, Mirrors, Safety, Imaging systems, Lenses, Cameras, Sensors, Fourier transforms, Optical testing, Temperature metrology

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PROCEEDINGS ARTICLE | July 18, 2014

Evolution of the SOFIA tracking control system

Proc. SPIE. 9152, Software and Cyberinfrastructure for Astronomy III

KEYWORDS: Observatories, Telescopes, Optical filters, Imaging systems, Cameras, Image processing, Computing systems, Control systems, Signal processing, Computer architecture

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PROCEEDINGS ARTICLE | September 27, 2012

Upgrade of the SOFIA target acquisition and tracking cameras