The resolution of an imaging system can be quantified using the modulation transfer function (MTF) derived from an image with an edge feature. For Earth-viewing satellites, imaging an appropriate terrestrial edge feature is difficult when optical blur from the atmosphere contaminates the MTF. With a sharp edge and no atmosphere, our Moon has provided researchers with an alternative by deriving the line spread function from the lunar edge. The Moon’s surface, however, has features, e.g., craters and seas, that depart from clean step-like behavior, making curve fitting to the data difficult and diminishing the effectiveness of the method. We demonstrate an improvement in which a reflectance (albedo) map of the Moon, created from a mosaic of the U.S. Department of Defense/NASA Clementine images, is used to flatten the surface features before the edge spread function is measured. The objective is to improve the reliability of MTF measurements for on-orbit calibration of the National Oceanic and Atmospheric Administration/NASA Geostationary Operational Environmental Satellite (GOES) weather satellites and similar missions. The technique is applied to the reflective bands of the Advanced Baseline Imager on GOES-16 and GOES-17 weather monitoring satellites.
The Geostationary Operational Environmental Satellite R (GOES-R) series is the planned next generation of operational weather satellites for the United State’s National Oceanic and Atmospheric Administration. The first launch of the GOES-R series is planned for October 2016. The GOES-R series satellites and instruments are being developed by the National Aeronautics and Space Administration (NASA). One of the key instruments on the GOES-R series is the Advance Baseline Imager (ABI). The ABI is a multi-channel, visible through infrared, passive imaging radiometer. The ABI will provide moderate spatial and spectral resolution at high temporal and radiometric resolution to accurately monitor rapidly changing weather.
Initial on-orbit calibration and performance characterization is crucial to establishing baseline used to maintain performance throughout mission life. A series of tests has been planned to establish the post launch performance and establish the parameters needed to process the data in the Ground Processing Algorithm. The large number of detectors for each channel required to provide the needed temporal coverage presents unique challenges for accurately calibrating ABI and minimizing striping.
This paper discusses the planned tests to be performed on ABI over the six-month Post Launch Test period and the expected performance as it relates to ground tests.
We present both laboratory and telescope testing results describing the performance of the H4RG-10 CMOS-Hybrid
detector. The H4RG-10 is the largest visible hybrid array currently in existence and shows great potential for use in
future space missions. We report read noise, dark current, pixel connectivity, persistence, and inter-pixel
capacitance measurements for the temperature range 110-240 K. We report on quantitative astrometric and
qualitative photometric performance of the instrument based on observations made at USNO's Flagstaff Station
observatory and establish an upper limit to the astrometric performance of the detector. We discuss additional
testing and future work associated with improving detector performance.
CMOS-based focal planes have many potential advantages over CCDs for use in space for star mapping/star
tracking applications. These include more flexible readout circuitry and improved radiation tolerance. There are
also weaknesses, including noise performance, quantum efficiency, and potential systematics introduced by the
presence of circuitry on the photosensitive side of the detector. In this paper, we measure the effects of these sources
of error on centroiding and photometry for the HDTV (1k x 2k) SI-1920HD camera by observing stellar reference
fields using USNO's 8-inch Twin Astrograph telescope in Flagstaff, AZ. This camera serves as an archetype for the
entire family of related TIS detectors, including the 3k x 4k V12M and the 7.6k x 7.6k V59M. We determine an
upper limit for the astrometric centroiding performance for this class of detector to be ~1/30th of a pixel. There are
indications that better performance may be possible if improvements are made to the temperature control system
used for this first set of observations.
This paper presents the radiometric and noise characteristics of 12-bit SI-1920HD cameras built from the AltaSens ProCamHD 3560 FPA as a function of integration time and temperature. Our measurements are for two integration time regions: 1 to 50 millisecond, which is standard for video operation; and 1 to 240 seconds, of possible use for stellar observations. For 1 to 50 millisecond integration times, the cameras are extremely linear with a Gaussian-like dark frame. As we increased to seconds-long integration times, the camera initially remains radiometrically linear, but develops a dark frame with the vast majority of pixels at dn=5. Further increases in integration time eventually result in a saturated dark frame with all pixels at dn=4095. Reducing the operating temperature to -7.2°C increased the integration times at which the camera's two transitions occur by a factor of 20. The calibration parameters determined from our measurements were applied to the image data collected by Dorland et al. (these proceedings).
Provided the MTF has no holes, data from an unfilled aperture can be processed to form an image. The filled aperture always has higher signal-to-noise, but if that system is too large to build, then lower signal-to-noise may be better than no signal whatsoever. For constant collecting area, it is better to have fewer, larger telescopes and move them around to fill the MTF, but for many applications, e.g., the NASA/GSFC Stellar Imager, the change in the target during the reconfiguration time is a more significant limit than the signal-to-noise ratio. This drives the optical design towards a larger number of smaller apertures. Reconfiguring has higher signal to noise than snapshot imaging because different portions of the MTF are filled by different photons, thereby allowing better filtering. With this insight, we see that the signal-to-noise can also be improved by filling different portions of the MTF with different wavelengths. Furthermore, the use of multiple narrow bandwidths avoids the artifacts inherent in broadband synthesis. We have demonstrated that this works, although artifacts can form if the scene changes with wavelength. We will present results from algorithms developed for removing artifacts and for exploiting spectral diversity
Recent advances in large format detector arrays and holographic diffraction gratings have made possible the development of imaging spectrographs with high sensitivity and resolution, ideally suited for space-based remote sensing of earth resources. An optical system composed of dual spectrographs and a common fore-optic has been designed for the visible-near infrared (VNIR) and shortwave bands with 10-nm spectral resolution, providing 30-meter ground resolution from an altitude of 605 km. The spectrograph designs are based on a modified Offner 1-X relay with spherical mirrors and a convex spherical holographic grating for the secondary mirror. The fore-optic is a three-mirror anastigmatic telescope with a 360-mm focal length to match the pixel pitch of the respective 1024 X 1024 visible silicon CCD and SWIR HgCdTe FPAs. The primary advantages of this design are the relatively low f-number (f/3), large flat field (18 mm), and low distortion. Preliminary performance results of a VNIR testbed grating and spectrograph are presented and compared to the design predictions.
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