National Weather Service Forecast Offices in the Western U.S. receive satellite images from the GOES West geostationary satellite every half hour, both day and night. These pictures are used for diagnosing and forecasting weather patterns. They serve to enhance centralized computer guidance and make possible more timely short range forecasts (zero to twelve hours). A variety of image types are received, including infrared and visible images with various enhancements. In recent months water vapor charts have been made available routinely to the forecaster. These charts have proven useful in diagnosing the structure of mid-tropospheric flow patterns over the data sparse eastern Pacific. Several examples of satellite pictures will be shown and their use in weather forecasting demonstrated. Future needs of the field forecaster, such as looping capability, will also be discussed.
Recently the British have unveiled details of a new Mercury Cadmium Telluride (HgCdTd) "SPRITE" detector that performs time delay and integration within the material itself. The detector has been applied to a new serial/parallel TV compatible high performance thermal imager, the IR-18. This paper introduces the concept of the SPRITE detector and analyzes and explains its unique features. It then describes how the detector is applied to the IR-18. A video tape or movie will be shown of IR-18 imagery with afocal telescopes having different magnifications. The IR-l8 is currently manufactured by Barr & Stroud Ltd, Glasgow, Scotland. Magnavox is the exclusive distributor in the U.S.
Twenty-three years ago G. E. Pugh and then later Leonard Schiff independently suggested the possibility of performing two new tests of Einstein's General Theory of Relativity by observations on orbiting gyroscopes. The experiment calls for the development of a free precession gyroscope with drift-rates less than 10-11 deg/hour, many orders of magnitude below the performance of typical inertial navigation instruments. A team of physicists and engineers at Stanford University have developed under NASA support a gyroscope that appears to have the required performance characteristics making use of a combination of novel cryogenic and space physics techniques. The gyro is an electrically suspended sphere, spun up initially by means of gas jets to a speed of 200 Hz and then allowed to coast freely in a 10-9 torr vacuum. The orientation of the spin axis of the gyroscope is read out by observing the direction of the "London moment" in the rota-ting superconductor with the aid of SQUID (Superconducting QUantum Interference Device) magnetometers.
The small helium-cooled infrared telescope (Spacelab IRT) is a multiband instrument capable of highly sensitive observations from space. The experiment consists of a cryogenically cooled, very well baffled telescope with a ten channel focal plane array. During the Spacelab 2 flight of the Space Shuttle, this instrument will make observations between 5 and 120 μm wavelength that will be background limited by the expected zodiacal emission. Design considerations necessitated by this level of performance are discussed in this paper. In particular, the operation of a very sensitive focal plane array in the space environment is described. The Spacelab IRT will be used to map the extended, low-surface brightness celestial emission. During the seven day length of the mission better than 70% sky coverage is expected. The instrument will also be used to measure the infrared contamination environment of the Space Shuttle. This information will be important in the development of the next generation of infrared astronomical instruments. The performance of the Spacelab IRT, in particular its sensitivity to the contamination environment is detailed.
A liquid helium-cooled infrared spectrometer for the 16 to 50μm range is described. The instrument has six detectors, three each of Si:Sb and Ge:Ga and two diffraction gratings mounted back-to-back. Cold preoptics are used to match the spectrometer to the telescope. In its nominal configuration the system resolution is 0.03μm from 16 to 30μm and 0.07μm from 28 to 50μm. A cooled filter wheel is used to change order sorting filters. The gratings are driven by a steel band and gear train operating at 40 K. The detector outputs are amplified by a TIA, employing a matched pair of JFET's operating at ~70° K inside the Dewar. The external warm electronics include a gain stage for the TIA and D.C.-coupled gating circuit to remove charged-particle (cosmic-ray secondary)-induced noise spikes. The gating circuit reduces the overall system noise by a factor of two when the spectrometer is used on NASA's Kuiper Airborne Observatory. Sample spectra are presented and the deglitcher performance is illustrated.
One of the major problems confronting future spaceborne Earth observation missions is the tremendous volume of data that must be handled. The communication links will become overloaded if all data collected are relayed to ground-based stations for processing. Less than 1 percent of the collected data are analyzed. This is due to cloud cover, unwanted data, data taken at the wrong tine, etc. including a "smart" sensor on board that could recognize clouds and generic Earth-features would permit collection of only desirable data. This would eliminate overloading the communications links and considerably reduce the ground-based data analysis costs. This paper discusses developments in remote sensing Earth-feature classification that can help solve the data-deluge problem.
A next logical step in the progression of state-of-the-art detector systems for use in astronomical observations is seen to be the development of an intensified charge-coupled device (ICCD) system, involving the incorporation of a thinned backside-illuminated CCD as the anode of a Space Telescope design Digicon tube. This concept extends the demonstrated fundamental photon counting accuracy, low background, sensitivity, and stability of the Digicon to the two-dimensional capabilities of CCDs. In particular, the CCD-Digicon combination enables (1) the use of magnetic deflection in order to take full advantage of the basic resolution elements in the system and to enhance the uniformity of elemental response, and (2) charge pulse centroiding to substantially increase the number of effective detector resolution elements without straining manufacturing techniques as would be required to produce such amounts of physical array cells. Results of recent investigations into the feasibility and characteristics of these techniques are presented.
Two key reasons for pursuing the development of mosaic focal planes are reviewed and it is shown that rapid frame repetition rate is the only requirement that can be solved no other way than through mosaic focal planes. With the view that spaceborne mosaic focal plane sensors are necessarily "smart sensors" requiring a lot of onboard processing just to function, it is pointed out that various artificial intelligence techniques may be the most appropriate to incorporate in the data processing. Finally, a novel mosaic focal plane design is proposed, termed a virtual mosaic focal plane, in response to other system constraints.
The general features of an FM-CW range imaging sensor using a commercial waveguide C02 laser are described. The basic principles of FM-CW radar are reviewed, and laboratory measurements of the frequency stability and range resolution obtained with diffuse targets are presented.
A small remote sensing payload (3 Kg.) is being flown on a low altitude (500 KM) Rohini Satellite to be launched by India in middle of 1982. The sensor comprises of two solid-state cameras having resolution of 1Km with 250Km swath, using photodiode array in Red and IR bands. The scan motion is provided by the spin of the satellite. The sensor utilises smart technique for reduction of data content to be transmitted to ground by incorporating onboard feature classification algorithms.
The coordinate transformation assembly (CTA) is a non-contact electro-optical device designed to link the angular coordinates between two remote platforms to a high degree of accuracy. Each assembly, which is compact and without moving parts, consists of two units: the transmitter and the receiver. The transmitter consists of one polarizing beamsplitter and two laser diodes with polarized output. The receiver consists of a polarizing beam-splitter, two lenses, a dual-axis photodetector and a regular photodetector. The angular roll is measured about the line-of-sight between two assemblies using a polarizing sensing method. Accuracy is calculated to be better than 0.01 degrees with a signal-to-noise ratio of 35 db. Pitch and yaw are measured relative to the line-of-sight at each assembly by locating a laser spot in the field-of-view of a dual-axis photodetector located in the focal plane of a small lens. The coordinate transformation parameter most difficult to obtain is the roll coordinate because high resolution involves observing a small variation in the difference of two strong signals. Under such an arrangement, any variation in source strength or detector sensitivity will cause an error. In the scheme devised for the CTA, this source of error has been eliminated through a paring and signal processing arrangement wherein the detector sensitivity and the source intensity are made common to the paired measurements and thus eliminated. The ±0.01 degree accuracy of the angular roll as well as the pitch and yaw measurements over ±2 degrees angular range has been demonstrated. An attractive feature of the CTA is that paired assemblies can be deployed to relay coordinates around corners and over extended distances.
NOAA-AVHRR data is being used to monitor global vegetation type and condition and to study various environmental factors in addition to performance of meteorological functions. The AVHRR instrument has ±54° as a maximum scan angle limits and it is necessary to be aware of the effects of sun-target-sensor geometry at extreme scan angles to be able to properly interpret the satellite images. In order to interpret the images for vegetation type and condition analysis it is necessary to calibrate back to the nadir view position. Both simulation studies and empirical investigations with digital scanner data have been performed in order to sufficiently understand the effects of scan angle and sun angle, as well as the effects of atmospheric scattering, to eventually perform adequate calibrations. Not suprisingly, the effects are large and studies are continuing to provide improved calibrations. It is the results of these investigations which we describe in this paper.
The object of this work was to develop analytical tools for, describing errors associated with mosaic array centroiding. As an example of a current problem, a Monte Carlo simulation of a point source tracking problem was implemented. Then for a given noise and image model, the accuracy of the image tracking was evaluated. In general the various causes for error in the centroid estimate were pixel geometry, device and background noise, and energy spillage outside window. Both mean errors (bias) and distribution about the mean (variance) were studied. The conclusions were: Various sources of centroid estimation errors were developed. A Monte Carlo simulation of track position estimation was evaluated for various scenarios. Multiple measurements could be shown to provide resolution of a fraction of a pixel.
The problem of characterizing detection system performance presents the following dilemma: On the one hand, if the system is good, then performance failures will be extremely rare events. But on the other hand, if the occurrence of rare events is to be characterized, then reliance entirely on Monte Carlo simulation would require an enormous number of runs, and the expense would be prohibitive. Algebraic models contribute a complementary approach to circumvent the problem. Such models can augment the simulation approach in a variety of ways. This paper discusses several such models, focussing particularly on models for detection probability and false alarm rate. Numerical results confirming specific models are presented.
The increased complexity of scientific and earth-operational spacecraft, and the need for rapid dissemination of the resulting data, has produced a severe data management problem. In particular, multispectral-imaging missions impose a significant burden on the present ground processing facilities since they generate vast quantities of high-speed data. One solution to the image data processing problem is to implement onboard processors capable of transmitting useful information rather than raw data, thus reducing ground processing requirements and the turnaround time for users. NASA is currently investigating the feasibility of performing high-speed data processing on board the spacecraft. As a part of this effort, Martin Marietta is under contract to develop an adaptable data system for real-time image processing, the Information Adaptive System (IAS). The IAS, with the necessary test and support equipment, will be demonstrated in a laboratory environment to examine the operational performance of this system in terms of a potential onboard processor. The key system design features are speed, programmability, and adaptability as a function of operator commands or image parameters in the data stream. The processing functions included within the IAS architecture are radiometric correction, data packetization, data-set selection, distortion/coefficient processing, and adaptive system control. Each of these functions will be described in this paper with the test support and demonstration equipment.
Nonvolatile memory for data and control programs is required for advanced remote sensor systems. Simultaneous storage for data processing and data accumulation will provide versatile sensor control and optimized data link buffering. Bubble domain technology offers significant reliability and functional advantages for meeting these complicated high density memory requirements. Bubble operational capability includes multifunctional block and serial access, first-in/first-out storage, simultaneous read/write, asynchronous data rates, and expandable capacities. Several bubble device technologies have emerged in recent years. Permalloy gap devices are available commercially, while more recent device technologies such as ion implant and self-structured current accessed are in research stages. The newer device concepts are aimed at increasing storage density and data rates while minimizing power and cost. A flexible system concept is analyzed which is compatible with all of these bubble device technologies. Detailed estimates of memory system characteristics are discussed for each type of bubble device. System capacity, weight, and volume tradeoffs are dependent on the basic device data site period and on the device packaging scheme. Data rate and power dissipation are coupled to device technology, data site period, and also the device packaging scheme. Permalloy gap, ion implant, and self-structured current access systems appear to respectively offer capacities of up to 108, 109, and 1010 bits and power per unit data rate efficiencies of 140, 60, and 2 w/Mbps. Immediate term (1-2 years) systems are feasible only in permalloy gap technology. Barring unforeseen developments, near term (3-5 years) system development is expected to employ ion implant devices and longer term (7-9 years) system development could exploit self-structured current accessed devices.
Linescanner sensor signal acquisition was investigated as part of the NASA Multi-spectral Linear Array (MLA) design study program. This paper presents a hybrid analog and digital approach which resulted from that investigation. As part of the signal acquisition, the analog signals are converted to digital form and processed to compensate for detector nonuniformity. This method requires only an 8 bit A to D converter to compensate for bias and gain nonuniformity and still provide nearly 8 bit resolution and accuracy in the output signal. This resulted from having control of the A to D conversion range and by using on board calibration measurements with a much higher accuracy than needed in the actual data. Very little accuracy was lost as a result of the bias and gain compensation. The paper describes this advanced approach along with the calibration algorithm used to achieve such performance.