Ball Aerospace & Technologies Corp. has combined the results of recent advances in CMOS imaging sensor, signal
processing and embedded computing technologies to produce a new high performance military video camera. In this
paper we present the design features and performance characteristics of this new, large format camera which was
developed for use in military airborne intelligence, surveillance and reconnaissance (ISR), targeting and pilotage
applications. This camera utilizes a high sensitivity CMOS detector array with low read noise, low dark current and
large well capacity to provide high quality image data under low-light and high intra-scene dynamic range illumination
conditions. The camera utilizes sensor control electronics and an advanced digital video processing chain to maximize
the quality and utility of the digital images produced by the CMOS device. Key features of this camera include: rugged,
small physical size, wide operating temperature range, low operating power, high frame rate and automatic gain control
for all-light-level applications. This camera also features a novel pixel decimation filter to provide custom image sizes
and video output formats.
Low-light-level video cameras have benefited from rapid advances in digital technology during the past two decades. In legacy cameras, the video signal was processed using analog electronics which made real-time, nonlinear processing of the video signal very difficult. In state-of-the-art cameras, the analog signal is digitized directly from the sensor and processed entirely in the digital domain, enabling the application of advanced processing techniques to the video signal in real time. In fact, all aspects of modern low-light television cameras are controlled via digital technology, resulting in various enhancements that surpass analog electronics.
In addition to video processing, large-scale digital integration in these low-light level cameras enables precise control of the image intensifier and image sensor, facilitating large inter-scene dynamic range capability, extended intra-scene dynamic range and blooming control. Digital video processing and digital camera control are used to provide improved system-level performance, including nearly perfect pixel response uniformity, correction of blemishes, and electronic boresight. Compact digital electronics also enable comprehensive camera built-in-test (BIT) capability which provides coverage for the entire camera--from photons into the sensor to the processed video signal going out the connector.
Individuals involved in the procurement of present and future low-light-level cameras need to understand these advanced camera capabilities in order to write accurate specifications for their advanced video system requirements. This paper provides an overview of these modern video system capabilities along with example specification text.
Video cameras have increased in usefulness in military applications over the past four decades. This is a result of many advances in technology and because no one portion of the spectrum reigns supreme under all environmental and operating conditions. The visible portion of the spectrum has the clear advantage of ease of information interpretation, requiring little or no training. This advantage extends into the Near IR (NIR) spectral region to silicon cutoff with little difficulty. Inclusion of the NIR region is of particular importance due to the rich photon content of natural night illumination. The addition of color capability offers another dimension to target/situation discrimination and hence is highly desirable. A military camera must be small, lightweight and low power. Limiting resolution and sensitivity cannot be sacrificed to achieve color capability. Newly developed electron-multiplication CCD sensors (EMCCDs) open the door to a practical low-light/all-light color camera without an image intensifier. Ball Aerospace & Technologies Corp (BATC) has developed a unique color camera that allows the addition of color with a very small impact on low light level performance and negligible impact on limiting resolution. The approach, which includes the NIR portion of the spectrum along with the visible, requires no moving parts and is based on the addition of a sparse sampling color filter to the surface of an EMCCD. It renders the correct hue in a real time, video rate image with negligible latency. Furthermore, camera size and power impact is slight.
Image intensifiers (I2) have gained wide acceptance throughout the Army as the premier nighttime mobility sensor for the individual soldier, with over 200,000 fielded systems. There is increasing need, however, for such a sensor with a video output, so that it can be utilized in remote vehicle platforms, and/or can be electronically fused with other sensors. The image-intensified television (I2TV), typically consisting of an image intensifier tube coupled via fiber optic to a solid-state imaging array, has been the primary solution to this need. I2TV platforms in vehicles, however, can generate high internal heat loads and must operate in high-temperature environments. Intensifier tube dark current, called "Equivalent Background Input" or "EBI", is not a significant factor at room temperature, but can seriously degrade image contrast and intra-scene dynamic range at such high temperatures. Cooling of the intensifier's photocathode is the only practical solution to this problem. The US Army RDECOM CERDEC Night Vision & Electronic Sensors Directorate (NVESD) and Ball Aerospace have collaborated in the reported effort to more rigorously characterize intensifier EBI versus temperature. NVESD performed non-imaging EBI measurements of Generation 2 and 3 tube modules over a large range of ambient temperature, while Ball performed an imaging evaluation of Generation 3 I2TVs over a similar temperature range. The findings and conclusions of this effort are presented.
The Multiband Imaging Photometer for Spitzer (MIPS) provides long wavelength capability for the mission, in imaging bands at 24, 70, and 160 microns and measurements of spectral energy distributions between 52 and 100 microns at a spectral resolution of about 7%. By using true detector arrays in each band, it provides both critical sampling of the Spitzer point spread function and relatively large imaging fields of view, allowing for substantial advances in sensitivity, angular resolution, and efficiency of areal coverage compared with previous space far-infrared capabilities. The Si:As BIB 24 micron array has excellent photometric properties, and measurements with rms relative errors of 1% or better can be obtained. The two longer wavelength arrays use Ge:Ga detectors with poor photometric stability. However, the use of 1.) a scan mirror to modulate the signals rapidly on these arrays, 2.) a system of on-board stimulators used for a relative calibration approximately every two minutes, and 3.) specialized reduction software result in good photometry with these arrays also, with rms relative errors of less than 10%.
We describe the ground testing and characterization of the Multiband Imaging Photometer for SIRTF (MIPS). This instrument is a camera with three focal plane arrays covering broad spectral bands centered at 24 μm, 70 μm, and 160 μm. The instrument features a variety of operation modes that permit accurate photometry, diffraction-limited imaging, efficient mapping, and low resolution spectral energy distribution determinations. The observational philosophy of MIPS relies heavily on the frequent use of internal relative calibration sources as well as a high level of redundancy in the data collection. We show that by using this approach, users of MIPS can expect very sensitive, highly repeatable observations of astronomical sources. The ground characterization program for MIPS involved a number of facilities including test dewars for focal-plane level testing, a specialized cryostat for instrument-level testing, and tests in the flight SIRTF Cryo-Telescope Assembly
We describe the test approaches and results for the Multiband Imaging Photometer for SIRTF. To verify the performance within a `faster, better, cheaper' budget required innovations in the test plan, such as heavy reliance on measurements with optical photons to determine instrument alignment, and use of an integrating sphere rather than a telescope to feed the completed instrument at its operating temperature. The tests of the completed instrument were conducted in a cryostat of unique design that allowed us to achieve the ultra-low background levels the instrument will encounter in space. We controlled the instrument through simulators of the mission operations control system and the SIRTF spacecraft electronics, and used cabling virtually identical to that which will be used in SIRTF. This realistic environment led to confidence in the ultimate operability of the instrument. The test philosophy allowed complete verification of the instrument performance and showed it to be similar to pre-integration predictions and to meet the instrument requirements.
The Multiband Imaging Photometer for SIRTF (MIPS) provides the space IR telescope facility (SIRTF) with imaging, photometry, and total power measurement capability in broad spectral bands centered at 24, 70, and 160 micrometers , and with low resolution spectroscopy between 50 and 95 micrometers . The optical train directs the light from three zones in the telescope focal plane to three detector arrays: 128 by 128 Si:As BIB, 32 by 32 Ge:Ga, and 2 by 20 stressed Ge:Ga. A single axis scan mirror is placed at a pupil to allows rapid motion of the field of view as required to modulate above the 1/f noise in the germanium detectors. The scan mirror also directs the light into the different optical paths of the instrument and makes possible an efficient mapping mode in which the telescope line of sight is scanned continuously while the scan mirror freezes the image motion on the detector arrays. The instrument is designed with pixel sizes that oversample the telescope Airy pattern to operate at the diffraction limit and, through image processing, to allow superresolution beyond the traditional Rayleigh criterion. The instrument performance and interface requirements, the design concept, and the mechanical, optical, thermal, electrical, software, and radiometric aspects of MIPS are discussed in this paper. Solutions are shown to the challenge of operating the instrument below 3K, with focal plane cooling requirements done to 1.5K. The optical concept allows the versatile operations described above with only a single mechanism and includes extensive self-test and on- board calibration capabilities. In addition, we discuss the approach to cryogenic end-to-end testing and calibration prior to delivery of the instrument for integration into SIRTF.
Wildfire is the array and instrument controller currently used in the infra-red instrumentation at National Optical Astronomy Observatories. Wildfire is a high performance, versatile transputer based controller which handles the clocking and readout of two-dimensional arrays along with all other aspects of instrument control. The system was originally designed to support the present generation of 256 X 256 infra-red arrays. This paper discusses the upgrade plan for Wildfire which is required to read out the newly developed 1 K X 1 K InSb arrays.
The Wildfire Instrument Controller is currently being used in four IR instruments at the Kitt Peak National Observatory. Wildfire is a high performance, versatile transputer based controller which manages the clocking and readout of the 2D arrays along with all other aspects of instrument control. Wildfire utilizes high speed fiber optic links for communication between its two components: the electronics mounted on the instrument and the digital signal processor located in the computer room. This paper is a systems level discussion of the hardware and software that make up the Wildfire Instrument Controller. We present an overview of the system operation along with measured performance data. We also discuss how the Wildfire system can be easily expanded to provide the higher level of performance required for high speed readout of the next generation 1024 by 1024 pixel IR arrays.
The Cryogenic Spectrometer (CRSP) is a longslit astronomical spectrograph which has been in service at Kitt Peak National Observatory since 1988, utilizing a 58 x 62 Santa Barbara Research Corporation InSb array in the dispersive focal plane. We have recently completed an extensive upgrade to the instrument which includes: installation of a SBRC 256 x 256 InSb array in the focal plane. CRSP is thus the first astronomical IR spectrograph to utilize the new 256 x 256 InSb focal plane. By comparison to the 62 x 58 focal plane, the 256 x 256 array has significantly less dark current (<1 e/s vs 50 e/s) and lower read noise (30 vs 350 electrons for a single read), resulting in improved performance for low background observations. In addition, the smaller pixels yield plate scales which are well- suited to sampling the typical seeing at Kitt Peak. This yields significant gains in the reduction of systematic errors associated with the extraction of point-source spectra against the challenging background of the IR night sky, which is dominated by emission lines of OH and by thermal emission from telluric absorption lines at wavelengths > 2.3 micrometers .
The Cryogenic Optical Bench (COB) is a 1-4 (mu) IR array camera with multiple cold spectral and spatial filtering capabilities which can be combined in a variety of configurations. The array is driven by a transputer based high speed data system using fiber optic links and dedicated processors. We describe the instrument functions and the mechanical, optical, electronic, and cryogenic implementation. COB is a facility instrument at Kitt Peak National Observatory, available for use by scientists worldwide on the basis of scientific merit.
The Simultaneous Quad-Color Infrared Imaging Device (SQIID) is the first of a new generation of infrared instruments to be put into service at the Kitt Peak National Observatory (KPNO). The camera has been configured to be modular in design and to accept new innovations in detector format as they become available. Currently the camera is equipped with four 256 x 256 platinum silicide arrays with 30 micron pixels for each of the four bands J (1.1-1.4 microns), H (1.5-1.8 microns), K (2.0-2.4 microns), and L' (3.52-4.12 microns). The optics of the instrument have been designed to accept detector arrays as large as 512 x 512, or an equivalent field size of 12.4 mm x 12.4 mm. The instrument is cooled with a pair of closed cycle cryogenic coolers, which are mechanically aligned and electrically phased to eliminate vibration. In addition, a transputer based electronics system has been incorporated to facilitate fast frame rates, co-add frames, and ease the data handling burden.