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The general linear camera calibration problem is formulated and several classification schemes for various subcases of this problem are developed. For each subcase, simple solutions are found that satisfy all necessary constraints. The results improve those already in the literature with respect to simplicity, efficiency, and coverage. However, the classification scheme is not exhaustive.
Photometry of the upper atmosphere of Venus from Mariner 10 on February 5, 1974 is discussed with respect to in-flight verification of camera linearity, shading, and absolute photometric calibration. Among photometric results are the following: (1) temporal brightness variations were observed in the UV greater than 10% over a few hours due to the rapid rotation of the upper atmosphere, (2) the observed terminator was 4 degrees past the geometric terminator due to detached haze layers at altitudes around 85 km, (3) there were no indications of cloud top elevation variations greater than a few hunderd meters, and (4) in the UV, the bright and dark regions both had low albedos in all scales, showing that the UV absorber is not confined just to dark markings.
The time between transitions in the video output of a camera is measured when registered at reticle marks on the vidicon faceplate. This device permits precision calibration of raster linearity of television camera tubes.
An algorithm is presented for correcting IUE low resolution spectral images obtained with the SWP camera for some of the non-linearity effects reported by Bohlin et al. (1980). The non-linearity problem, which affects SWP images processed at Goddard Space Flight Center in the period May 22, 1978 to July 7, 1979 and at VILSPA in the period June 14, 1978 to August 6, 1979, was essentially due to the use of an Intensity Transfer Function (ITF) that erroneously included a blank image in the 20 percent exposure level. The correction algorithm described here was adopted by the three IUE Agencies in November 1979 as being suitable for most IUE users. It has the advantages to be applicable to any kind of low resolution SWP spectra, to introduce errors which are usually less than the intrinsic photometric errors, and to be of simple application. The results obtained by applying the method to a representative set of spectra of both point and extended sources are reported. In addition, a new evaluation of linearity and reproducibility of the SWP spectral data is provided, based on the improved ITF.
One of the main difficulties encountered in the development of a multispectral scanner is the realization of an oscillating mechanical device. A magnetic device which is characterized by the absence of friction is presented. The main developments concern the analysis of magnetic forces. A preliminary project of a device which could be used in a satellite is presented.
Polarized K-coronal brightness (pB) of the solar corona can be measured by taking four successive coronal brightness images through a linear polarizer, by turning it through four successive angles in intervals of 45∘ and using a standard formula to measure pB from the total coronal brightness (TB) that contains both the polarized K- and the unpolarized F-coronal brightness. The question is: will the time-dependent, highly dynamic corona illuminate each pixel with the same brightness during the time it takes to take the four successive images? To mitigate this problem we now have the polarization camera, in which, each super-pixel is made up of four sub-pixels, and built in to these four sub-pixels is a polarization mask that contains four linear polarizers orientated at four angles 45∘ apart. This allows the measurement of pB to be made in a single exposure. Here, the question is: will the variations of the coronal brightness in the four adjacent sub-pixels in a super-pixel be sufficiently negligible to assume that they observe the same part of the corona? This article looks for answers to these two questions by conducting two synthetic experiments to measure the electron temperature in the plane of the sky on a spherically asymmetric model (SAM) corona by first using a linear polarizer, and then replacing it with a polarization camera and use statistical analyses to determine how well the measured temperature matched the true temperature for the two cases.
A study of the Stereosat mission, which may acquire analog/digital stereo image data of cartographic quality with linear array camera systems, is presented, with attention given to the Stereosat system and the mission parameters, the utilization of the Stereosat studies in order to indicate the nature and scope of the problems associated with recording image data of high geometric fidelity from spacecraft equipped with line array sensors, and the assessing of the possibilities of meeting the completeness and accuracy requirements of cartographic products. A 713-km circular, sun-synchronous, near polar orbit, with an inclination of 98.24 deg and a repeat cycle of 48 days is designed to insure global coverage of the earth's land masses during the three-year lifetime of the mission. Three cameras (fore, vertical, and aft looking), mounted so as to record stereotriplets for a 61.4 km wide swath at a nominal focal plane scale of 1:1,000,000, are considered. The IFOV of 15 m should be adequate for producing thematic and image maps at scales of 1:50,000 to 1:250,000. The value of the coverage to cartographers will be dictated by the accuracy of the digital image data, which is largely a function of satellite control.
A conductor-dielectric junction exposed to the space environment is a frequent spacecraft design feature. Due to spacecraft charging and/or solar array operation, the conductor can acquire a high potential with respect to the surrounding plasma. If this potential is positive the insulators adjacent to exposed conductors can collect current as if they were conductors themselves. This phenomenon, called snapover, results in a substantial increase in current collection, and may even result in a glow discharge if the potential is high enough. If a conductor has a negative potential, arcing can occur at the site of a junction. Both of these phenomena negatively affect spacecraft operation. To prevent negative consequences, the physical mechanisms of snapover and arc inception require investigation. In this paper, results are presented of an experimental and theoretical study of snapover, glow discharge, and arc phenomena for different materials immersed in argon or xenon plasmas. The effect of snapover is investigated for several metal-dielectric junctions: copper-teflon, copper-Kapton, copper-glass, aluminum-teflon, aluminum-Kapton, steel-teflon, anodized aluminum with pinholes, and copper-ceramics. I-V curves are measured and snapover inception voltages, essential parameters (increase in current and collection area due to secondary electrons), and glow discharge inception thresholds are determined. Optical spectra are obtained for glow discharges in both argon and xenon plasmas. These spectra provide information regarding atomic species entrapped in the glow region. Some spectral lines can be used to estimate plasma parameters in the discharge area. A video-camera and linear array were used to confirm that snapover inception is accompanied by very low intensity visible light emission. This result seems to be important for the estimate of the light pollution around spacecraft. Optical spectra (wavelengths 380-650 nm) of arcs are also obtained on a negatively biased chromic acid anodized aluminum plate immersed in low density argon and xenon plasmas. Analysis of these spectra confirms our earlier findings that aluminum atoms are ejected from the arc site. Moreover, it is found that chromium atoms are also quite abundant in the arc plasma. It is believed that the latter results contribute considerably to the understanding of processes of plasma contamination caused by arcing.
NASA's long term plan for Mars sample collection and return requires a highly streamlined approach for spectrally characterizing a landing site, documenting the mineralogical make-up of the site and guiding the collections of samples which represent the diversity of the site. Ideally, image data should be acquired at hundreds of VIS and IR wavelengths, in order to separately distinguish numerous anticipated species, using principal component analysis and linear unmixing. Cameras with bore-sighted point spectrometers can acquire spectra of isolated scene elements, but it requires 10(exp 2) to 10(exp 2) successive motions and precise relative pointing knowledge in order to create a single data cube which qualifies as a spectral map. These and other competing science objectives have to be accomplished within very short lander/rover operational lifetime (a few sols). True, 2-D imaging spectroscopy greatly speeds up the data acquisition process, since the spectra of all pixels in the scene are collected at once. This task can be accomplished with cameras that use electronically tunable acousto-optic tunable filters (AOTFs) as the optical tuning element. AOTFs made from TeO2 are now a mature technology, and operate at wavelengths from near-UV to about 5 microns. Because of incremental improvements in the last few years, present generation devices are rugged, radiation-hard and operate at temperatures down to at least 150K so they can be safely integrated into the ambient temperature optics of in-situ instruments such as planetary or small-body landers. They have been used for ground-based astronomy, and were also baselined for the ST-4 Champollion IR comet lander experiment (CIRCLE), prior to cancellation of the ST-4 mission last year. AIMS (for Acousto-optic Imaging spectrometer), is a prototype lander instrument which is being built at GSFC with support by the NASA OSS Advanced Technologies and Mission Studies, Mars Instrument Definition and Development Program (MIDP). AIMS is capable of tunable spectroscopic imaging of surface mineralogy, ices and dust between 0.5 and 2.4 microns, at a resolving power (lambda/delta lambda) which is typically several hundred. The design spatial resolution, similar to IMP and SSI, will allow mapping at scales down to about 1 cm.
We describe the imaging quality of the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) as measured during the ground calibration of the instrument. We describe the calibration techniques and report our results for the final configuration of HMI. We present the distortion, modulation transfer function, stray light,image shifts introduced by moving parts of the instrument, best focus, field curvature, and the relative alignment of the two cameras. We investigate the gain and linearity of the cameras, and present the measured flat field.
Design options are described for the multispectral linear arrays which will provide data and facilities beyond those obtained by LANDSAT 1, 2, 3, and D (the thematic mapper) are considered. The features, uses, and risks of a 10M fine resolution pointable imager, a 15M/30M dual resolution pointable imager, a 30M selectable spectral resolution pointing imager, a 30M electronically pointable multi-temporal sampler, and a 40M/80M mixed resolution imager are described. A large format camera scheduled for 1981 shuttle launch which can obtain high spatial ground resolution (approximately 10M), a relative position accuracy of plus or minus 14M, and a relative heightening accuracy, by virtue of stereographic coverage, of between 7 and 28M depending on the base-to-height ratio used. A potential problem of the system is that it will orbit in the shuttle.
A laser speckle strain measurement system with two-dimensional measurement capabilities has been built and tested for high temperature applications. The 1st and 2nd principle strains at a point on a specimen are calculated from three components of one-dimensional strain. Strain components are detected by cross-correlating reference and shifted speckle patterns recorded before and after straining the specimen. Speckle patterns are recorded by a linear photodiode array camera. Accurate strains have been measured at temperatures up to 650 C. Stable speckle correlations and linear stress-strain relations have been demonstrated up to 750 C. The resolution of the system is 15 microstrains, with a gauge length less than 1 mm.
A CCD camera was previously set up to record infrared images of the injector face of a small rocket combustor. Good semi-quantitative results were obtained but it was found that non-linearities in the camera system made accurate determinations of temperature difficult. A Pulnix CCD camera was purchased and calibrated. The system was calibrated for temperatures between 500 and 850 C. The best filter to use was found to be a BG850 glass filter. The actual calibrations are presented in the report. The system was to be used on a hydrogen oxygen system but the tests did not take place as scheduled. Attempts were made with a methane oxygen system but the carbon in the system interfered with the viewing of the injector face.
The development and current status of InSb line arrays for astronomy are reviewed. Instrument concepts are currently being developed for an infrared instrument for NASA's Space Telescope which would use such detectors for both spectroscopy and imaging. Preliminary performance measurements are given for a simple pushbroom camera, using a 128-element line array, designed for operation on the 24-inch Cassegrain telescope at the JPL Table Mountain Observatory. The design and construction of the camera are described.
Photodiode arrays used as image sensors in satellite remote imaging systems offer the advantages of geometric accuracy, precise registration of scene elements, enhanced operational reliability, and wide spectral response. Principles of photodiode-array operation are reviewed, and the latest developments in self-scanned array chip technology are described along with optical system requirements for multispectral coverage. Results of development efforts with a spaceborne solid-state multispectral camera based on linear sensing array technology are outlined to demonstrate the capabilities of this approach to multispectral sensing.
Cartographic products fall into a variety of classes: topographic maps that are concerned with planimetric information and elevations or heights; thematic maps, which might be used for geology, vegetation, water, or to display these subjects; digital elevation maps that would be produced from digital terrain data; and finally image maps. In terms of satellite applications, thematic maps and image maps are emphasized. The objectives are to consider, first, if resolution will be adequate for the identification of control and for the compilation of map products. Then, second, to define map accuracy standards and to determine the potential for meeting these standards with image data from the film camera, scanner and linear array systems of the 1980s.
This paper presents a new approach to depth from stereo in scenes with non-Lambertian surfaces. While these surfaces usually prove to be hard to incorporate in photo-consistency energy minimization, we retrieve additional information about their surface normals from applying a polarization-based approach that computes the degree and angle of polarization at each pixel. Therefore, we set up a stereo camera rig that captures four different rotations of a linear polarizer simultaneously for each camera. While most existing polarization-based approaches to shape reconstruction require a setup with known lighting, our approach uses arbitrary unpolarized illumination. We describe a regularization-based stereo approach that constrains specular surface normals in the scene to lie in the plane of their observed angle of polarization. We derive the mathematical foundations of this approach and present results on virtually generated stereo and real-world stereo imagery.
To unveil the complexity of the solar atmosphere, measurement of the magnetic field in the upper chromosphere and transition region is fundamentally important, as this is where the forces transition from plasma to magnetic field dominated. Measurements of the field are also needed to elucidate the energy transport from the lower atmospheric regions to the corona beyond. Such an advance in heliospheric knowledge became possible with the first flight of the international solar sounding rocket mission, CLASP. For the first time, linear polarization was measured in Hydrogen Lyman-Alpha at 121.60 nm in September 2015. For linear polarization measurements in this emission line, high sensitivity is required due to the relatively weak polarization signal compared to the intensity. To achieve this high sensitivity, a low-noise sensor is required with good knowledge of its characterization, including linearity. This work presents further refinement of the linearity characterization of the cameras flown in 2015. We compared the current from a photodiode in the light path to the digital response of the detectors. Pre-flight CCD linearity measurements were taken for all three flight cameras and calculations of the linear fits and residuals were performed. However, the previous calculations included a smearing pattern and a digital saturation region on the detectors which were not properly taken into account. The calculations have been adjusted and were repeated for manually chosen sub-regions on the detectors that were found not to be affected. We present a brief overview of the instrument, the calibration data and procedures, and a comparison of the old and new linearity results. The CLASP cameras will be reused for the successor mission, CLASP2, which will measure the Magnesium II h & k emission lines between 279.45 nm and 280.35 nm. The new approach will help to better prepare for and to improve the camera characterization for CLASP2.