In this issue devoted to Infrared Astronomy Instruments, you will note that most of the instruments are designed for use at altitude, either in aircraft, balloons, probes or satellites. Such usage permits observation above the interfering atmosphere usually encountered during ground observations. Most of the water vapor is below the platform at 40,000 feet (~13 km) and most of the CO2 is below platforms at 120,000 feet (~40 km).
Two airborne observatories operated above much of the earth's atmosphere are providing effective platforms for infrared astronomical observations. A summary is given of the wide variety of instrumentation currently in use and continuing to be developed for these facilities. The classes of instruments include various far infrared photometers, filter wheel and grating spectrometers, Fourier transform spectrometers, Michelson and Fabry-Perot interferometers, a polarimeter, and a microwave line receiver.
Rocket-borne cryogenic cooled infrared telescopes have been used for infrared and submillimeter measurements of the celestial background, atmospheric and auroral emission spectra, multicolor observations of the interplanetary medium, H II region, galactic center region and the cosmic background. This paper reviews some of the technology developed for rocketborne cryogenically cooled infrared systems and outlines its potential applications for future satellite infrared systems.
The objective of the Infrared Astronomical Satellite (IRAS) is to produce an unbiased all-sky survey in the wavelength region between 8 and 120 um. Using a 60 cm diameter helium cooled telescope and detector arrays which are essentially zodiacal light background photon noise limited, heretofore unprecedented sensitivity can be achieved. The optical design, the focal plane layout and expected performance of the current design concept are discussed.
Many of the recent advances in infrared astronomy have been the result of improved performance of existing infrared detectors or the introduction of new detectors. This paper includes a brief examination of the background photon fluxes encountered in infrared astronomy and the effect on detector performance of the fluctuation in this background. The operating characteristics and limitations of thermal and photon detectors currently utilized in infrared astronomy are also discussed.
The Center for Astrophysics-University of Arizona balloon-borne, inertially-guided, 102 cm telescope was designed to perform photometry and high resolution mapping of far-infrared (40-250 um) celestial sources. To date the telescope has now been flown and successfully recovered a total of ten times. Six of the flights have produced useful astronomical data, resulting in more than 40 hours of observations of numerous objects, such as HII regions, dark clouds, molecular clouds, galaxies, the galactic center, planets, and an asteroid. Maps with a resolution of 1 arcmin FWHM have been achieved with absolute position accuracies of ±10 arc-sec. The rms noise equivalent flux density of the system is ~70 Jy/(Hz)1/2. From the launch site in Texas, sources as far south as -50 degrees declination have been observed.
We have developed a 41-inch balloon telescope for far-infrared astronomical observations. It is constructed entirely of aluminum alloy, including the optics, and incorporates several novel features. Two composite bolometers, operated at 1.7 K, with adjacent fields of view on the sky, allow us to carry out two-color photometry in the wavelength ranges 40-80 um and 80-400 um. The far-infrared payload flies on a stabilized balloon platform developed in the U.K. as a national facility by the Science Research Council. The maiden flight of both systems was launched in 1976 November. Despite problems with the stabilization system which prevented releasing the telescope from its stow position, we were able to scan a number of far-infrared sources. In-flight calibration, based on detections of both Venus and Saturn, indicates that the far-inqared noise-equivalent flux density* [areance] was ~130 Jy Hz -1/2 for the short wavelength channel and ~500 Jy Hz-1/2 for the long wavelength channel.
The field of infrared upconversion for astronomy is reviewed. The basic theory of upconversion is presented, along with a brief historical summary of upconversion techniques. Several investigators have employed upconverters in astronomical studies, but have met with only modest success. Upconversion will become a useful detection method for astronomy only if substantial but perhaps forseeable improvements can be realized.
An infrared spatial interferometer has been developed to extend the spatial resolution of astronomical observations beyond the diffraction limits of existing telescopes. It is the first such instrument to measure the angular diameters and shapes of circumstellar shells at wavelengths from 2 to 20 AM. As a result, the angular resolution of routine telescopic observations at 10 µm has been extended from ~1 arcsec to ~0.1 arcsec even though observations are often obtained in ~3 arcsec conditions of atmospheric "seeing."
With strong governmental support and broad-based public approval, the United States solar energy program has expanded rapidly in the last few years. In particular, we have traced the history and development of the solar tower from an idea in 1969 through first federal funding in 1973, to a program to initiate pilot plant construction in 1977. About 3,000 heliostats will reflect sunlight onto a central receiver in which 500°C steam will be generated to drive a turbo-generator. With this 10 MWe plant scheduled to feed electricity into a utility grid in 1980, a 50-100 MWe demonstration plant is proposed to be on line in 1985.
This paper describes a new image coding system which combines the detection and coding of visually significant edges in natural images. The edges are defined as amplitude discontinuities between different regions of an image. The edge detection system makes use of 3 x 3 masks, which are well suited for digital implementation. Edge angles are quantized to eight equally spaced directions, suitable for chain coding of contours. Use of an edge direction map improves the simple thresholding of gradient modulus images. The concept of local connectivity of the edge direction map is useful in improving the performance of this method as well as other edge operators such as Kirsch and Sobel. The concepts of an "edge activity index" and a "locally adaptive threshold" are introduced and shown to improve the performance even further.
Additional insight is obtained about changes in the human eye by noting the changes in the first order characteristics. Delano's y,y-bar diagram furnishes one of the best schemes for depicting these changes. In particular, the cardinal points are easy to locate and visualize. The effects of accommodation and of the correction of myopia with a spectacle lens are calculated and presented in the diagram.
This paper attempts an analytical treatment of flare light in microdensitometers by developing a model based on scattering from the air-glass interface. Verification of the model is conducted via a breadboard mockup on an optical table, and on an actual microdensitometer. It is, seen that the simple model predicts values for flare irradiance well within an order of magnitude. It is further shown that a sample trace is not only a convolution of the target with the projected sensor aperture but, to some extent, a convolution of the target with the irradiated area in the sample plane as well. Based on this analysis, it is shown that flare can be corrected for provided its magnitude is held constant. This requires that, during a full scan, the target always remains effectively within the irradiated area.
MTF-based simplified test conditions and proposed criteria for the evaluation of the image quality of fixed focal length lenses and zoom lenses for 35 mm cameras are described. Measurements are made for white light, in the infinite conjugate plane, on-axis and at two 0.7 field (15 mm off-axis) positions, at full aperture and f/8. The focus is set at full aperture for best MTF response at 30 mm-1 on-axis. The lenses are evaluated by exam-ining the MTF responses at 10 mm-1 and 30 mm-1. Previously proposed conditions and criteria for fixed focal length lenses are also described for reference.
Optical cross-correlation to determine relative signal displacements and degree of similarity between two signals is commonly implemented by matched filter techniques using absorption transparencies as inputs. The problems associated with absorption inputs include low correlation-signal intensities due to the light absorbing nature of the input and low signal-to-noise ratios. Without considerable preprocessing, positive correlation peak detection is not always readily achievable. These limitations are largely overcome by complex exponentiation of the inputs. For the optical analog this means phasing the input transparencies by a bleaching process to yield phase transparencies. The cross-correlation function of these complex exponentiated inputs has two striking properties. One, the correlation signal approaches a delta function. Two, the correlation signal is not affected by a difference in bias levels (average densities) of the two inputs in-asmuch as only differential phase differences are used for detecting correlation. This means constant phase shifts will not contaminate the correlation signal. Hence, extensive data preprocessing is not required. One- and two-dimensional digital simulation experiments were carried out to demonstrate these properties. Simulated density functions were defined by computer generated random numbers. Random noise distortions were added to study their impact on the correlation-signal shape and intensity. In order to have a standard for comparison, the commonly used (statistical) correlation coefficient was computed along with the correlation of the complex exponentiated inputs. The results indicate that complex exponentiation provides a means to obtain extremely reliable correlation peak positions having very high peak intensity and very high signal-to-noise ratio (SNR). Since the correlation function is a narrow well defined spike, a threshold detector can be employed for signal detection.