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At least 253 records · Page 14

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NASA NTRS1977

Land use/land cover mapping (1:25000) of Taiwan, Republic of China by automated multispectral interpretation of LANDSAT imagery

Three methods were tested for collection of the training sets needed to establish the spectral signatures of the land uses/land covers sought due to the difficulties of retrospective collection of representative ground control data. Computer preprocessing techniques applied to the digital images to improve the final classification results were geometric corrections, spectral band or image ratioing and statistical cleaning of the representative training sets. A minimal level of statistical verification was made based upon the comparisons between the airphoto estimates and the classification results. The verifications provided a further support to the selection of MSS band 5 and 7. It also indicated that the maximum likelihood ratioing technique can achieve more agreeable classification results with the airphoto estimates than the stepwise discriminant analysis.

Sung, Q. C.↗

NASA NTRS1995

Effects of long term space environment exposure on optical substrates and coatings

At the time of our Second LDEF Post-Retrieval Symposium report, we had completed cleaning and measuring the post flight spectral performance of all of the samples except for the fused silica substrate with an antireflection (SiO2/TiO2) coating. As was documented in that report, after cleaning, all of the samples returned to their original pre-flight performance, with the exception of the fused silica anti-reflectance coated sample, which had significant degraded performance. All normal methods of removing the contaminant from the surface of this sample failed except for oxygen plasma etch. At the time of the previous report, we had only exposed the sample to three hours of plasma etch. We have since continued the plasma etch for a total of 32 hours, after which time, the transmission of the sample almost reached its pre-flight values. The peak areas of the transmission curves remained shifted approximately 150 nm. Of interest is the fact that the control samples, which hadn't flown, did not exhibit any spectral shifting. In summary, after the 6 yr exposure to the space environment, all of the coatings and substrates returned to their pre-flight performance after cleaning, with the exception of the antireflection coated fused silica sample. On this sample, the spectral transmission curves shifted approximately 150 nm.

Vallimont, John↗

NASA NTRS1981

Training site statistics from Landsat and Seasat satellite imagery registered to a common map base

Landsat and Seasat satellite imagery and training site boundary coordinates were registered to a common Universal Transverse Mercator map base in the Newport Beach area of Orange County, California. The purpose was to establish a spatially-registered, multi-sensor data base which would test the use of Seasat synthetic aperture radar imagery to improve spectral separability of channels used for land use classification of an urban area. Digital image processing techniques originally developed for the digital mosaics of the California Desert and the State of Arizona were adapted to spatially register multispectral and radar data. Techniques included control point selection from imagery and USGS topographic quadrangle maps, control point cataloguing with the Image Based Information System, and spatial and spectral rectifications of the imagery. The radar imagery was pre-processed to reduce its tendency toward uniform data distributions, so that training site statistics for selected Landsat and pre-processed Seasat imagery indicated good spectral separation between channels.

Clark, J.↗

NASA NTRS1987

Velocimetry with refractive index matching for complex flow configurations, phase 1

The feasibility of obtaining detailed velocity field measurements in large Reynolds number flow of the Space Shuttle Main Engine (SSME) main injector bowl was demonstrated using laser velocimetry and the developed refractive-index-matching technique. An experimental system to provide appropriate flow rates and temperature control of refractive-index-matching fluid was designed and tested. Test results are presented to establish the feasibility of obtaining accurate velocity measurements that map the entire field including the flow through the LOX post bundles: sample mean velocity, turbulence intensity, and spectral results are presented. The results indicate that a suitable fluid and control system is feasible for the representation of complex rocket-engine configurations and that measurements of velocity characteristics can be obtained without the optical access restrictions normally associated with laser velocimetry. The refractive-index-matching technique considered needs to be further developed and extended to represent other rocket-engine flows where current methods either cannot measure with adequate accuracy or they fail.

Thompson, B. E.↗

NASA NTRS2000

Improvements To Progressive Wave Tube Performance Through Closed-Loop Control

This report documents recent improvements to the acoustic and thermal control systems of the Thermal Acoustic Fatigue Apparatus (TAFA), a progressive wave tube test facility at the NASA Langley Research Center, Hampton, Virginia. A brief summary of past acoustic performance is given first to serve as a basis for comparison with the new performance data using a multiple-input, closed-loop, narrow-band controller. Performance data in the form of test section acoustic power spectral densities and coherence are presented in three of six facility configurations for a variety of input spectra. Tested spectra include uniform, two cases of pink noise, three cases of narrow-band random, a simulated launch payload bay environment for an expendable launch vehicle, and a simulated external acoustic load for the aft section of a reusable launch vehicle. In addition, a new closed-loop temperature controller and thermocouple data acquisition system are described.

Rizzi, Stephen A.↗

NASA NTRS1994

Compression of multispectral Landsat imagery using the Embedded Zerotree Wavelet (EZW) algorithm

The Embedded Zerotree Wavelet (EZW) algorithm has proven to be an extremely efficient and flexible compression algorithm for low bit rate image coding. The embedding algorithm attempts to order the bits in the bit stream in numerical importance and thus a given code contains all lower rate encodings of the same algorithm. Therefore, precise bit rate control is achievable and a target rate or distortion metric can be met exactly. Furthermore, the technique is fully image adaptive. An algorithm for multispectral image compression which combines the spectral redundancy removal properties of the image-dependent Karhunen-Loeve Transform (KLT) with the efficiency, controllability, and adaptivity of the embedded zerotree wavelet algorithm is presented. Results are shown which illustrate the advantage of jointly encoding spectral components using the KLT and EZW.

Shapiro, Jerome M.↗

NASA NTRS1979

Spatial-frequency response of the Limb Infrared Monitor of the Stratosphere /LIMS/ radiometer

The Limb Infrared Monitor of the Stratosphere (LIMS), an experiment on the Nimbus-7 satellite, is designed to scan the earth's limb vertically and measure spectral emission profiles of trace atmospheric gases believed to be important in processes controlling the stratospheric ozone distribution. Experiment objectives are reviewed and several analyses and measurements are described which were performed to determine the adequacy of the system for satisfying these objectives. Adequate spatial-frequency response for all the spectral channels is required to provide, through inversion of the measured limb-radiance profiles, important information about the temperature, structure, and composition of the atmosphere. From the LIMS design-model data, the MTF was calculated for the optical system, the detector field mask, the electronics, and the overall system, for each channel. The signal output performance of the instrument was predicted from the system MTF data model input radiance data for each channel. MTF measurements made on the flight sensor confirmed the analytical results. The predictions indicate that the instrument can satisfy the basic measurement objectives of the experiment.

Wilson, R. G.↗

NASA NTRS1984

Vegetation and soils field research data base: Experiment summaries

Understanding of the relationships between the optical, spectral characteristics and important biological-physical parameters of earth-surface features can best be obtained by carefully controlled studies over fields and plots where complete data describing the condition of targets are attainable and where frequent, timely spectral measurement can be obtained. Development of a vegetation and soils field research data base was initiated in 1972 at Purdue University's Laboratory for Applications of Remote Sensing and expanded in the fall of 1974 by NASA as part of LACIE. Since then, over 250,000 truck-mounted and helicopter-borne spectrometer/multiband radiometer observations have been obtained of more than 50 soil series and 20 species of crops, grasses, and trees. These data are supplemented by an extensive set of biophysical and meteorological data acquired during each mission. The field research data form one of the most complete and best-documented data sets acquired for agricultural remote sensing research. Thus, they are well-suited to serve as a data base for research to: (1) quantiatively determine the relationships of spectral and biophysical characteristics of vegetation, (2) define future sensor systems, and (3) develop advanced data analysis techniques.

Biehl, L. L.↗

NASA NTRS1979

A new spectral synthesis procedure for multivariable regulators

A method for selecting a multivariable state feedback controller that simultaneously achieves an a priori specification on closed loop eigenvalues and good mode mixing is presented. The problem is solved by projecting a desired modal matrix onto a constraint set containing the null space of the closed-loop state matrix, while assuring that the projection is in the null space. The feedback matrix follows immediately in the formulation. An example involving a helicopter hover controller is presented.

Maynard, R. A.↗

NASA NTRS1973

The muscle spindle as a feedback element in muscle control

The muscle spindle, the feedback element in the myotatic (stretch) reflex, is a major contributor to muscular control. Therefore, an accurate description of behavior of the muscle spindle during active contraction of the muscle, as well as during passive stretch, is essential to the understanding of muscle control. Animal experiments were performed in order to obtain the data necessary to model the muscle spindle. Spectral density functions were used to identify a linear approximation of the two types of nerve endings from the spindle. A model reference adaptive control system was used on a hybrid computer to optimize the anatomically defined lumped parameter estimate of the spindle. The derived nonlinear model accurately predicts the behavior of the muscle spindle both during active discharge and during its silent period. This model is used to determine the mechanism employed to control muscle movement.

Andrews, L. T.↗

NASA NTRS1979

The charge injection device /CID/ as a stellar tracking sensor

A 128 x 128 element CID imager was operated in a simulated stellar trackling environment and evaluated for temporal and pattern noise and spectral response over a temperature range of -40 C to +25 C. The test devices were fabricated on long-lifetime bulk silicon material and utilized very thin upper-level polysilicon electrodes for enhanced spectral response. A standard microcomputer was used to generate all control signals and to collect and process performance data. The results of this program were used to predict the performance of a 400 x 400 CID array designed specifically for stellar-tracking.

Burke, H. K.↗

NASA NTRS1983

Navier-Stokes solution on the CYBER-203 by a pseudospectral technique

A three-level, time-split, mixed spectral/finite difference method for the numerical solution of the three-dimensional, compressible Navier-Stokes equations has been developed and implemented on the Control Data Corporation (CDC) CYBER-203. This method uses a spectral representation for the flow variables in the streamwise and spanwise coordinates, and central differences in the normal direction. The five dependent variables are interleaved one horizontal plane at a time and the array of their values at the grid points of each horizontal plane is a typical vector in the computation. The code is organized so as to require, per time step, a single forward-backward pass through the entire data base. The one-and two-dimensional Fast Fourier Transforms are performed using software especially developed for the CYBER-203.

Lambiotte, J. J.↗

NASA NTRS1990

Brief state-of-the-art review on optical communications for the NASA ISES workshop

The current state of the art of optical communications is briefly reviewed. This review covers NASA programs, DOD and other government agency programs, commercial aerospace programs, and foreign programs. Included is a brief summary of a recent NASA workshop on optical communications. The basic conclusions from all the program reviews is that optical communications is a technology ready to be accepted but needed to be demonstrated. Probably the most advanced and sophisticated optical communications system is the Laser Intersatellite Transmission Experiment (LITE) system developed for flight on the Advanced Communications Technology Satellite (ACTS). Optical communications technology is available for the applications of data communications at data rates in the under 300 MBits/sec for nearly all applications under 2 times GEO distances. Applications for low-earth orbiter (LEO) to ground will allow data rates in the multi-GBits/sec range. Higher data rates are limited by currently available laser power. Phased array lasers offer technology which should eliminate this problem. The major problem of cloud coverage can probably be eliminated by look ahead pointing, multiple ground stations, and knowledge of weather conditions to control the pointing. Most certainly, optical communications offer a new spectral region to relieve the RF bands and very high data communications rates that will be required in less than 10 years to solve the communications problems on Earth.

Hendricks, Herbert D.↗

NASA NTRS2016

The Muscles Treasury Survey. I. Motivation and Overview

Ground- and space-based planet searches employing radial velocity techniques and transit photometry have detected thousands of planet-hosting stars in the Milky Way. With so many planets discovered, the next step toward identifying potentially habitable planets is atmospheric characterization. While the Sun-Earth system provides a good framework for understanding the atmospheric chemistry of Earth-like planets around solar-type stars, the observational and theoretical constraints on the atmospheres of rocky planets in the habitable zones (HZs) around low-mass stars (K and M dwarfs) are relatively few. The chemistry of these atmospheres is controlled by the shape and absolute flux of the stellar spectral energy distribution (SED), however, flux distributions of relatively inactive low-mass stars are poorly understood at present. To address this issue, we have executed a panchromatic (X-ray to mid-IR) study of the SEDs of 11 nearby planet-hosting stars, the Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems (MUSCLES) Treasury Survey. The MUSCLES program consists visible observations from Hubble and ground-based observatories. Infrared and astrophysically inaccessible wavelengths (EUV and Lyalpha) are reconstructed using stellar model spectra to fill in gaps in the observational data. In this overview and the companion papers describing the MUSCLES survey, we show that energetic radiation (X-ray and ultraviolet) is present from magnetically active stellar atmospheres at all times for stars as late as M6. The emission line luminosities of C IV and Mg II are strongly correlated with band-integrated luminosities and we present empirical relations that can be used to estimate broadband FUV and XUV (is equivalent to X-ray + EUV) fluxes from individual stellar emission line measurements. We find that while the slope of the SED, FUV/NUV, increases by approximately two orders of magnitude form early K to late M dwarfs (approximately equal 0.01-1), the absolute FUV and XUV flux levels at their corresponding HZ distances are constant to within factors of a few, spanning the range 10-70 erg per (sq cm) s in the HZ. Despite the lack of strong stellar activity indicators in their optical spectra, several of the M dwarfs in our sample show spectacular UV flare emission in their light curves. We present an example with flare/quiescent ultraviolet flux ratios of the order of 100:1 where the transition region energy output during the flare is comparable to the total quiescent luminosity of the star E(sub flare)(UV) approximately 0.3 L(sub *) delta (t) (delta t = 1 s). Finally, we interpret enhanced L(line)/L(sub Bol) ratios for C IV and N V as tentative observational evidence for the interaction of planets with large planetary mass-to-orbital distance ratios (M(sub plan)/A(sub plan)) with the transition regions of their host stars.

Infrared and astrophysically inaccessible waveleng↗

NASA NTRS1989

Automated frequency domain system identification of a large space structure

This paper presents the development and experimental results of an automated on-orbit system identification method for large flexible spacecraft that yields estimated quantities to support on-line design and tuning of robust high performance control systems. The procedure consists of applying an input to the plant, obtaining an output, and then conducting nonparametric identification to yield the spectral estimate of the system transfer function. A parametric model is determined by curve fitting the spectral estimate to a rational transfer function. The identification method has been demonstrated experimentally on the Large Spacecraft Control Laboratory in JPL.

Yam, Y.↗

NASA NTRSDate not supplied

Micro-Spectrometer for Resource Mapping in Extreme Environments

Measurements and analyses of resources within permanently shadowed craters and along steep embankments on extraterrestrial surfaces pose extreme challenges since astronauts and rovers cannot access them. However, these areas offer the potential for the greatest scientific returns. Researchers at the NASA Langley Research Center (LaRC) invented a deployable wireless micro-spectrometer that can access those challenging areas and deliver telemetry data to a receiver safely outside those extreme environments. The micro-spectrometers are designed for deployment by an astronaut, a rover, or a lander flying overhead. This device can also be installed on rover tires, under the astronaut’s shoes, or on a cane stick. The bullet-like, expendable micro-spectrometer can penetrate into soil to spectrally identify the components of soil, such as water, He-3, or other minerals. The signals from the soil assay data are transmitted to a mother station through a telemetry system. This LaRC developed micro-spectrometer bullet consists of micro-spectrometer optics with an all-imbedded, burst-mode, light-emitting-diode ultraviolet (LED UV) light source, a super-capacitor with control electronics, and telemetry electronics. Prototypes have been fabricated to demonstrate a spectral assay of soil components. Further maturation of this technology would be necessary for demonstrations on the Moon.

micro-spectrometer↗

NASA NTRS1993

Evolution of miniature detectors and focal plane arrays for infrared sensors

Sensors that are sensitive in the infrared spectral region have been under continuous development since the WW2 era. A quest for the military advantage of 'seeing in the dark' has pushed thermal imaging technology toward high spatial and temporal resolution for night vision equipment, fire control, search track, and seeker 'homing' guidance sensing devices. Similarly, scientific applications have pushed spectral resolution for chemical analysis, remote sensing of earth resources, and astronomical exploration applications. As a result of these developments, focal plane arrays (FPA) are now available with sufficient sensitivity for both high spatial and narrow bandwidth spectral resolution imaging over large fields of view. Such devices combined with emerging opto-electronic developments in integrated FPA data processing techniques can yield miniature sensors capable of imaging reflected sunlight in the near IR and emitted thermal energy in the Mid-wave (MWIR) and longwave (LWIR) IR spectral regions. Robotic space sensors equipped with advanced versions of these FPA's will provide high resolution 'pictures' of their surroundings, perform remote analysis of solid, liquid, and gas matter, or selectively look for 'signatures' of specific objects. Evolutionary trends and projections of future low power micro detector FPA developments for day/night operation or use in adverse viewing conditions are presented in the following test.

Watts, Louis A.↗

NASA NTRS1994

Lossless Compression and Rate Control for the Galileo NIMS Experiment

The Galileo Near-Infrared Mapping Spectrometer (NIMS) is a sophisticated multi-spectral instrument that was developed to study the spatial/compositional aspects of the atmosphere of Jupiter and the surfaces of it's satellites. Since its original development, the communication capability of the Galileo spacecraft has been severly reduced as the result of a failure of ground controllers to open the main antenna. The data rate which will be available for all instruments at the first Jupiter encounter in 1995 has been reduced by several orders of magnitude (even after recent numerous improvements to data link efficiency.).

data compression NIMS instrument Galileo↗