The Aerospace Corporation’s sensitive Mako thermal infrared imaging spectrometer, which operates between 7.6 and 13.2 microns at a spectral sampling of 44 nm, and flies in a DeHavilland DHC-6 Twin Otter, has undergone significant changes over the past year that have greatly increased its performance. A comprehensive overhaul of its electronics has enabled frame rates up to 3255 Hz and noise reductions bringing it close to background-limited. A replacement diffraction grating whose peak efficiency was tuned to shorter wavelength, coupled with new AR coatings on certain key optics, has improved the performance at the short wavelength end by a factor of 3, resulting in better sensitivity for methane detection, for example. The faster frame rate has expanded the variety of different scan schemes that are possible, including multi-look scans in which even sizeable target areas can be scanned multiple times during a single overpass. Off-nadir scanning to ±56.4° degrees has also been demonstrated, providing an area scan rate of 33 km<sup>2</sup>/minute for a 2-meter ground sampling distance (GSD) at nadir. The sensor achieves a Noise Equivalent Spectral Radiance (NESR) of better than 0.6 microflicks (μf, 10<sup>-6</sup> W/sr/cm<sup>2</sup>/μm) in each of the 128 spectral channels for a typical airborne dataset in which 4 frames are co-added. An additional improvement is the integration of a new commercial 3D stabilization mount which is significantly better at compensating for aircraft motions and thereby maintains scan performance under quite turbulent flying conditions. The new sensor performance and capabilities are illustrated.
A new airborne thermal infrared imaging spectrometer, "Mako", with 128 bands in the thermal infrared covering 7.8 to
13.4 microns, has recently completed its engineering flight trials. Results from these flights, which occurred in
September 2010 and included two science flights, are presented. The new sensor flies in a Twin Otter aircraft and
operates in a whiskbroom mode, giving it the ability to scan to ±40° around nadir. The sensor package is supported on a
commercial 3-axis-stabilized mount which greatly reduces aircraft-induced pointing jitter. The internal optics and focal
plane array are operated near liquid helium temperatures, which in conjunction with a fast f/1.25 spectrometer enables
low noise performance despite the sensor's small (0.55 mrad) pixel size and the high frame rate needed to cover large
whisk angles. Besides the large-area-coverage scan mode (20 km<sup>2</sup> per minute at 2-meter GSD from 12,500 ft. AGL), the
sensor features a scan mirror pitch capability that enables both a high-sensitivity mode (longer integration times using
frame summing, covering a smaller spatial region) and a multiple-look mode (multiple looks at a smaller region in a
single aircraft overpass, for discriminating plume motion, for example).
We report progress on a high-performance, long-wavelength infrared hyperspectral imaging system for airborne
research. Based on a f/1.25 Dyson spectrometer and 128x128 arsenic doped silicon blocked impurity band array, this
system has significantly higher throughput than previous sensors. An agile pointing/scanning capability permits the
additional signal to be allocated between increased signal-to-noise and broader area coverage, creating new opportunities
to explore LWIR hyperspectral phenomenology.
The design of any modern imaging system is the end result of many trade studies, each seeking to optimize image quality within real world constraints such as cost, schedule and overall risk. Image chain analysis - the prediction of image quality from fundamental design parameters - is an important part of this design process. At The Aerospace Corporation we have been using a variety of image chain analysis tools for many years, the Parameterized Image Chain Analysis & Simulation SOftware (PICASSO) among them. In this paper we describe our PICASSO tool, showing how, starting with a high quality input image and hypothetical design descriptions representative of the current state of the art in commercial imaging satellites, PICASSO can generate standard metrics of image quality in support of the decision processes of designers and program managers alike.
The design of any modern imaging system is the end result of many trade studies, each seeking to optimize image
quality within real world constraints such as cost, schedule and overall risk. Image chain analysis - the prediction of
image quality from fundamental design parameters - is an important part of this design process. At The Aerospace
Corporation we have been using a variety of image chain analysis tools for many years, the <i>Parameterized Image Chain
Analysis & Simulation SOftware (PICASSO)</i> among them. In this paper we describe our PICASSO tool, showing how,
starting with a high quality input image and hypothetical design descriptions representative of the current state of the art
in commercial imaging satellites, PICASSO can generate standard metrics of image quality in support of the decision
processes of designers and program managers alike.
In this paper, we studied the imaging effects of pixel spatial-sampling and scan-velocity mismatch in 2D visible image sensors. these effects were examined experimentally by projecting bar pattern sequences of varying spatial frequency on two different devices and by comparing their outputs with the results of a corresponding imaging simulation. Beat patterns and aliased spatial frequencies were observed by imaging the bar pattern sequences onto an area CMOS `active pixel' sensor. Image phase reversal effects were observed by inducing a systematic mismatch between the scan velocity of a bar pattern `sunburst' areal image and the corresponding velocity of the clocked image charge in a time-delay-and-integration CCD image sensor. The visual image effects of an analog-to-digital converter's (ADC) pixel amplitude quantization, specifically integral nonlinearity (INL) and differential nonlinearity (DNL) were studied using two very different input images. The INL and DNL patterns, obtained from measurements on a 14-bit, video ADC were scaled and then imbedded in the response characteristics of these two images. Various scaling of these INL and DNL patterns were used. the results obtained show artifacts varying in impact from insignificant to clearly degrading.
Recent advances in Interferometric Fiber Optic Gyroscope (IFOG) technology have enabled these devices to equal, and in some respects exceed, the performance of the floated, spinning wheel rate integrating gyroscope. However, their ability to perform in a space radiation environment has been a significant concern. Test results are presented addressing the effects of space radiation on the performance of a high precision pointing grade IFOG. Proton-induced degradation of the optical components of an IFOG is evaluated based on testing performed at the Harvard Cyclotron Laboratory (HCL). Rationale is provided for using the HCL proton accelerator as a reasonable simulation of the space environment. An analysis is presented which prioritizes the component-level dose tests based on expected radiation sensitivities. The evaluation addresses both total dose (to about 12 krad) and dose rate effects. Testing was performed at the component level as well as the system level with an expanded version of a closed-loop operational IFOG. Primary concerns include permanent attenuation and spectral transmission (wavelength) sensitivity to total dose, and angle random walk and bias stability degradation as a function of dose rate. Component level results are presented for a superfluorescent light source, integrated optics chip (IOC), coupler, and polarization maintaining fiber coils. Closed-loop transient noise results are evaluated based on dose rate testing of the IOC, coupler, and fiber coil.