Infrared radiation is detected and converted to electrical signals by either thermal detectors or photon detectors. Development of focal plane arrays based on these processes continues with progress achieved in increased uniformity for photon detectors and increased sensitivity for thermal detectors. The current state of development for several materials for infrared focal plane arrays is discussed and recent developments reviewed. Applications and requirements for infrared focal plane arrays are described.
The application of advances in a variety of disciplines, has made significant impact on the area of optical sensing technology. This impact has not evolved so much from new optical designs, component prescriptions, or revolutionary coating designs, although there have been substantial innovations in certain areas. Instead, progress has resulted from the combined mix of a variety of ideas including the areas of advanced materials and material forming processes, coatings that do their job more efficiently, the application of computer control to manufacturing, wavefront correction, and alignment, as well as the collection, integration, and display of relevant data in a format that makes possible interpretation at-a-glance.
This paper is a review of present state-of-the-art and future technologies for infrared scene projection, including both target and background simulators. We will address the need to develop appropriate figures of merit for comparison and evaluation of these test methods. Test methods we will review and compare include: raster-scanned laser, liquidcrystal light valve, deformable membrane, reflective deformable-mirror spatial light modulators, thermal emitter arrays, and infrared halftone transparencies.
Optical techniques have been investigated for information processing since 1950's. This paper provides a unified view of different approaches to optical information processing and computing. Such a view serves to bring out interrelations (similarities and differences) between seemingly different topics and will thereby identify a common technological infrastructure for this broad discipline. The emerging technology of "Smart Pixels" is also discussed and a framework for organizing different "Smart Pixel" approaches presented.
The computational power of current high-performance computers is increasingly limited by data storage and retrieval rates rather than the processing power of the central processing units. No single existing memory technology can combine the required fast access and large data capacity. Instead, a hierarchy of serial access memory devices has provided a performance continuum which allows a balanced system design. Conventional memory technology can only marginally support the needs of high performance computers in terms of required capacity, data rates, access times and cost. Significant gaps in secondary and tertiary storage have emerged which make storage hierarchy design increasingly difficult. This paper reviews a radically different approach to data storage using the parallelism and three dimensionality of optical storage. 3-D optical storage has the potential to significantly alter the present hierarchy and fill the pressing need for high performance secondary and tertiary storage systems.
We discuss how one optical processor (a correlator) can be used for all levels of scene analysis (low, medium, and high-level computer vision). This is achieved by the use of different filter functions for the different levels of a hierarchical inference system. New optical processor filter research that allows such flexibility is advanced and examples of each of these filters are provided. For large class problems, feature extracted from each region of interest in a scene are fed to a neural net processor which performs recognition. New algorithms for optical neural net classifiers are also required. We conclude that present hardware optical correlator advances can significantly benefit from such processing.
The attitude control and navigation systems of future advanced spacecraft will be characterized by a high degree of autonomy, very high accuracy, efficient commandability, and fast fault recovery. These characteristics are incompatible with the constraints of conventional star sensors which mandate a-priori definition of all onboard attitude fixes and work only if attitude uncertainties remain small. With the availability of accurate, anti-blooming capable CCDs, fast microprocessors, high density memory chips, and star pattern recognition algorithms, it is now feasible to fabricate miniature Autonomous Star Trackers (ASTs) capable of (1) determining their attitude rapidly and reliably while having no a-priori attitude knowledge, (2) autonomous attitude updating, and (3) providing their attitude at rates up to typically 40 Hz. In addition to providing the functionality needed for future missions, ASTs can also be exploited to improve the reliability, mass, power, and cost of spacecraft and reduce the cost of operating them.
This paper describes star identification schemes used in the past, it discusses a number of star pattern recognition algorithms, and provides the main characteristics of current CCD star trackers. A number of specific functions enabled or enhanced by an AST are described including fast attitude acquisition, rapid fault recovery, attitude safing, gyroless/cheap-gyro attitude control, autonomous target acquisition by astronomy telescopes, autonomous optical navigation, and precision pointing to terrestrial targets. The AST being developed at Lockheed uses a fast, memory-efficient, and highly robust star pattern recognition algorithm based on matching groups of stars. The algorithm, which is also applicable to star scanners, is described along with a realistic simulation program for testing its performance. It is shown that an AST with an 11.3 degree FOV diameter, a database of 4100 guide stars, a 25 MHz MC68030 class microprocessor, and 800 Kbytes of memory will be capable of determining its attitude in 0.45 seconds with a success rate greater than 99.98% when using an optimal guide star selection method. Compute time and memory are found to be inversely proportional to the FOV area. The paper also reports on AST development by other organizations in a number of countries.
Proc. SPIE 10269, Laser remote sensing in atmospheric sciences, aviation safety, aeronautical research, and experiments from space platforms and high-flying aircraft, 102690B (16 November 1992); doi: 10.1117/12.161575
Traditionally, the term laser remote sensing has been associated with active, optical measurements of the Earth’s atmosphere, lands, and oceans. In this paper, we concentrate our overview of laser remote sensing upon the Earth’s atmosphere in three disciplines: Atmospheric sciences, aviation safety, and aeronautical research. In atmospheric sciences, laser remote sensing has played a prominent role in the measurement of clouds, aerosols, the planetary boundary layer, chemical species, metals and ions, and in atmospheric dynamics in the temporal tracking of physical parameters and the direct measurement of atmospheric winds. Quite recently, laser remote sensing has been especially effective in correlative studies from ground and airborne platforms related to scientific studies in the eruption of Mount Pinatubo, and in following the dispersion of associated aerosols in the atmosphere, both in latitude and longitude. Laser remote sensing has also been very effective in studies related to the formation of the ozone hole, in the antarctic and arctic regions. Range-resolved measurements of atmospheric ozone have been made which track “in real time” the formation of the ozone hole and its subsequent dissipation. Laser measurements of the depolarization ratio of backscattering from particulates in the region of the ozone hole where Polar Stratospheric Clouds (PSC’s) form have provided unique information on the physics of the PSC’s and on the dynamics of the formation of the ozone hole phenomena. It is quite clear that laser remote sensing has proven to be an invaluable measurement technique for these types of chemistry investigations. The range-resolved measurement of atmospheric water vapor, correlated to the height of the planetary boundary layer and the distribution of aerosols over land and oceans, has also been demonstrated quite recently to be a unique measurement provided by laser remote sensing from aircraft. When this technique is developed from high flying aircraft and/or satellites, a major measurement technique will be available for the study of the hydrological cycle, globally. Soon, we should be seeing range-resolved measurements of atmospheric water vapor (50 meters) from a high-flying aircraft, with an accuracy better than 10 percent, as a routine measurement in atmospheric sciences. The historical evolution of laser remote sensing from the initial ground-based measurements of atmospheric aerosols in the early 1960’s to the sophisticated measurements from aircraft of today represent a unique evolution of technology in lasers and electrooptics, coupled to persistent attention to sound engineering development of a unique technique. For this paper, I have asked Dr. William B. Grant, a pioneer in laser remote sensing of the atmosphere, to provide this section entitled “Laser Remote Sensing in Atmospheric Sciences.“
The maturation in the state-of-the-art of optical components is enabling increased applications for the technology. Most notable is the ever-expanding market for fiber optic data and communications links, familiar in both commercial and military markets. The inherent properties of optics and photonics, however, have suggested that components and processors may be designed that offer advantages over more commonly considered digital approaches for a variety of airborne sensor and signal processing applications. Various academic, industrial, and governmental research groups have been actively investigating and exploiting these properties of high bandwidth, large degree of parallelism in computation (e.g., processing in parallel over a two-dimensional field), and interconnectivity, and have succeeded in advancing the technology to the stage of systems demonstration. Such advantages as computational throughput and low operating power consumption are highly attractive for many computationally intensive problems. This review covers the key devices necessary for optical signal and image processors, some of the system application demonstration programs currently in progress, and active research directions for the implementation of next-generation architectures.
This review covers the optical design of passive remote sensing optical instruments. The review concentrates on the design of spacebome multispectral cameras and imaging spectrometers. The major designs that have been produced over the past ten years are discussed, and new designs for future imaging spectrometers are presented.
MODIS, a 36 band (0.42 - 14.24 micrometer) moderate resolution imaging spectroradiometer is the keystone sensor for the 15 year (1998-2013) Earth Observing System (EOS). MODIS sensors on both the AM and PM EOS spacecraft will each collect data from the entire globe every two days. This data will be used to generate numerous scientific products which will enhance knowledge of changes in the global climate system due to both natural and anthropogenic causes.
MODIS, under development by the Santa Barbara Research Center (SBRC), Goleta, California, and the EOS Project at the Goddard Space Flight Center (GSFC), Greenbelt, Maryland, will include bands with spatial resolutions of 250, 500 or 1,000 meters at nadir, SNR’s as large as several thousand, onboard spatial, spectral and radiometric calibration, solar and lunar radiometric stability monitoring, knowledge of pixel location to less than 500 meters (including spacecraft errors) and radiometric accuracy of 5 percent or less for the 19 reflected solar bands and 1 percent or less for the 17 thermal emission bands. Polarization sensitivity will be limited to less than two percent for bands with wavelengths less than 2.2 micrometers.
Hughes Aircraft Co. has been involved with laser range finders and laser radars for over 20 years. This paper tries to summarize some of the typical laser radar sensors and applications in the last few years. The first half of the paper is to give a brief analytical description of the current issues in designing a modem ladar. The second half gives a review of laser sensors that have been developed by Hughes and by other companies highlighting some of the key features of those sensors.