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NASA NTRS1984

Comparison of the information content of data from the LANDSAT 4 Thematic Mapper and the multispectral scanner

Evaluation of information contained in data from the visible and near-IR channels of LANDSAT 4 TM and MSS for five agricultural scenes shows that the TM provides a significant advance in information gathering capability as expressed in terms of bits per pixel or bits per unit area. The six reflective channels of the TM acquire 18 bits of information per pixel out of a possible 48 bits, while the four MSS channels acquire 10 bits of information per pixel out of a possible 28 bits. Thus the TM and MSS are equally efficient in gathering information (18/48 to approximately 10/28), contrary to the expected tendency toward lower efficiency as spatial resolution is improved and spectral channels are added to an observing system. The TM thermal IR data appear to be of interest mainly for mapping water bodies, which do not change temperature during the day, for assessing surface moisture, and for monitoring thermal features associated with human activity.

Price, J. C.↗

NASA NTRS1984

Spectral Characterization of the LANDSAT-4 MSS Sensors

Relative spectral response data for the LANDSAT-4 and LANDSAT-4 backup multispectral scanner subsystems (MSS), the protoflight and flight models are presented and compared to similar data for the LANDSAT 1, 2 and 3 scanners. Channel (six channels per band) outputs for soil and soybean targets were simulated and compared within each band and between scanners. The principal differences between the spectral responses of the LANDSAT-4 scanners and previous scanners are discussed. The simulated LANDSAT-4 scanner outputs were 3 to 10 percent lower in the red band and 3 to 11 percent higher in the first near-IR band than previous scanners for the soybeans targets. The LANDSAT-4 scanners were generally more uniform from channel to channel within bands than previous scanners. In the upper-band edge of the red band of the protoflight scanner, one channel was markedly different (12 nm) from the rest. For a soybeans target, this nonuniformity resulted in a within-band difference of 6.2 percent in simulated outputs between channels.

Markham, B. L.↗

NASA NTRS1984

Comparison of the information content of data from the LANDSAT-4 Thematic Mapper and the Multispectral Scanner

Simultaneous data acquisition by the LANDSAT-4 Thematic Mapper (TM) and the multispectral scanner (MSS) permits the comparison of the two types of image data with respect to engineering performance and data applications. The information contained in five matching scenes in agricultural areas is evaluated for the visible and near-IR channels, leading to the conclusion that the TM provides a significant advance in information gathering capability as expressed in terms of either bits per pixel or bits per unit area.

Price, J. C.↗

NASA NTRS1983

The extreme LMC supergiant HD 38489 - An optical and ultraviolet study

Near-IR, optical, and UV observations covering the 1200-7000 A range are combined in the present study of the extremely luminous B star HD 38489 = S134, which is found to be an evolved B star of 80-90 solar masses and 70 solar radii, with a T(eff) of 25,000 K. Its mass loss, at 0.00001 solar masses/year, is comparable to that of galactic stars, and additional similarities are noted to stars of the Hubble-Sandage class and to the 6-20 range is suggested, and a model envelope is derived.

Shore, S. N.↗

NASA NTRS1984

Far-infrared observations of a star-forming region in the Corona Australis dark cloud

A high-resolution far-IR (40-250-micron) survey of a 0.9-sq-deg section of the core region of the Corona Australis dark cloud (containing very young stellar objects such as T Tauri stars, Herbig Ae and Be stars, Herbig-Haro objects, and compact H II regions) is presented. Two extended far-IR sources were found, one associated with the Herbig emission-line star R CrA and the other with the irregular emission-line variable star TY CrA. The two sources have substantially more far-IR radiation than could be expected from a blackbody extrapolation of their near-IR fluxes. The total luminosities of these sources are 145 and 58 solar luminosity, respectively, implying that the embedded objects are of intermediate or low mass. The infrared observations of the sources associated with R CrA and TY CrA are consistent with models of the evolution of protostellar envelopes of intermediate mass. However, the TY CrA source appears to have passed the evolutionary stage of expelling most of the hot dust near the central source, yielding an age of about 1 Myr.

Cruz-Gonzalez, I.↗

NASA NTRS1984

VW Hyi - The white dwarf revealed

Nonsimultaneous IUE, optical, and near-IR observations of VW Hyi at quiescence are presented. Using these and UV data from other investigations, a broad feature in the ultraviolet is identified with L-alpha absorption. The presence and width of the line imply that (1) the white dwarf in VW Hyi is directly visible in the UV and (2) the effective temperature of this star is approximately 18,000 + or - 2000 K for log g = 8. The continuum observations, combined with the J and K photometry of Sherrington et al., (1980), can be fit with a combination of this relatively cool white dwarf and a steady-state disk model with an accretion rate of 10 to the -11th solar masses/yr. Additional observations of the hump in the optical light curve can be reasonably fit by a 12,000-K blackbody. Such a source is consistent with the hump being a minor contribution to the system's overall continuum distribution shortward of 2000 A and longward of about 1 micron.

Mateo, M.↗

NASA NTRS1984

Saturn's satellites - Near-infrared spectrophotometry (0.65-2.5 microns) of the leading and trailing sides and compositional implications

Water ice absorptions at 2.0, 1.5, and 1.25 microns are noted in near-IR spectra of Tethys, Dione, Rhea, Iapetus, and Hyperion, and the weak 1.04-micron ice absorption, which is detected for Rhea and Dione, is studied to establish band depth upper limits. The leading-trailing side 1.04-micron ice band depth differences on Saturn's satellites are similar to those for the Galilean satellites, indicating possible surface modification by magnetospheric charged particle bombardment. Limits are obtained for the amounts of particulates, trapped gases, and ammonium hydroxide on the surface. With the exception of the dark side of Iapetus, the surfaces of all of Saturn's satellites are nearly pure ice water.

Steele, A.↗

NASA NTRS1984

Spring wheat-leaf phytomass and yield estimates from airborne scanner and hand-held radiometer measurements

An attempt has been made to relate hand-held radiometer measurements, and airborne multispectral scanner readings, with both different wheat stand densities and grain yield. Aircraft overflights were conducted during the tillering, stem extension and heading period stages of growth, while hand-held radiometer readings were taken throughout the growing season. The near-IR/red ratio was used in the analysis, which indicated that both the aircraft and the ground measurements made possible a differentiation and evaluation of wheat stand densities at an early enough growth stage to serve as the basis of management decisions. The aircraft data also corroborated the hand-held radiometer measurements with respect to yield prediction. Winterkill was readily evaluated.

Aase, J. K.↗

NASA NTRS1984

Structure of the Uranian rings. I - Square-well model and particle-size constraints

A least squares fitting is added to the diffraction model for the Uranian rings and the model is then used to determine the relative optical depths of the rings at visible and near-IR wavelengths. Light transmission is assumed constant on a scale of a few radial km in the rings. The amount of starlight passing through the rings is calculated from occultations with account taken of a monolayer ring, diffraction effects, and multiple ring layers. A diffracted occultation profile is generated with consideration given to the angular diameter of the star, the impulse response of the detector, and atmospheric aberrations. Calculation procedures which remove noise are outlined and results are compared with the observational data base. The wavelength dependence of optical depth is formulated. It is shown that occultation data do not support the presence of a large fraction of submicron particles. No optical depth variations are projected for 0.88-2.2 microns wavelengths. Unchopped data are needed to verify the model predictions.

Elliot, J. L.↗

NASA NTRS1984

The EUV spectrum of H2O by electron impact

The vacuum ultraviolet (VUV) spectrum of H2O produced by electron impact at 200 eV is presented. A total of 25 spectral features are identified at a resolution of 0.5 nm over the wavelength range from 40 to 280 nm. Absolute emission cross-sections were obtained for each of the features. The differences of the features are all attributed to the various excited states of the dissociation products, H, O and O(+). The Lyman-alpha feature is the brightest for electron-induced fluorescence of H2O from the UV to the near-IR, and had a cross-section of 6.3 (+ or - 1.0 x 10 to the -18th) sq cm at 200 eV. The Lyman-alpha feature contributed 74 percent of the total measured emission cross-section in the EUV.

Ajello, J. M.↗

NASA NTRS1985

Far-infrared observations of two southern H II regions - RCW 122 and G 351.6-1.3

The luminosities in excess of 1,000,000 solar luminosities obtained in the present 1-arcmin resolution mapping of the two southern H II regions RCW 122 and G 351.6-1.3 requires the presence of OB star clusters. A luminosity/unit mass of the associated cloud of about 6 solar luminosities/solar mass is obtained by combining near-IR, far-IR, and CO-emission properties for RCW 122, and it is determined that the emitting dust grains are amorphous silicate-like. G 351.6-1.3 has very similar properties, although the fraction of 1-25 micron luminosity corrected for silicate absorption is about five times less than for RCW 122.

Mcbreen, B.↗

NASA NTRS1984

Measuring spectra of arid lands

The principles, instrumentation and data acquisition and interpretation techniques employed in multispectral remote sensing for geological applications are surveyed. Sensing is based on exact measurements of electromagnetic radiation interacting with atoms and molecules in the sensed scene. Absorbed radiation can be used to identify elements in the near-IR bands and emitted or reflected energy can be sensed in the mid- and far-IR. Sunlight normally serves as the exciting source. Wavelength absorptance and emittance characteristics are distinct for the various elements and molecules such as transition metal ions, water, carbonates, etc. The bands for identifying different materials are determined in the laboratory, followed by ground truth field tests. Several hand-held radiometers and spectrometers have been developed for the field trials. Each instrument usually has a limited detection range and serves for developing a data base for subtle distinctions among contiguous minerals with similar radiometric signatures. The data serve for calibrating first airborne and then satellite sensors, e.g., the Landsat MSS and Thematic Mapper. Instruments are also being tested using the Orbiter as the test platform.

Kahle, A. B.↗

NASA NTRS1984

The effects of the diffuse radiation fields due to multiple scattering and thermal reradiation by dust on the dynamics and thermodynamics of a dusty cometary atmosphere

A self-consistent model of a dirty, clathrate cometary nucleus is extended to account for diffuse radiation fields caused by multiple scattering and thermal reradiation of the solar continuum by dust. The model is configured to fit conditions expected for the various spacecraft which will encounter Halley's comet at 0.89 AU. The atmosphere is assumed a chemically reactive dust-gas mixture in quasi-steady spherically symmetric expansion. The effect of electron-neutral ion collisions is accounted for, along with rate constants of the various species of clathrate ice particles and radiative transfer of the solar input in the UV, visible and near-IR intervals. The opacity of the circumnuclear dust is projected to be an order of magnitude greater than previous estimates, which severely impacts the potential visibility of the nucleus to the cameras of the flyby satellites.

Marconi, M. L.↗

NASA NTRS1984

The detection of the FlPi(u)-XlSigma(+)g system of diatomic carbon toward X Persei

The 0-0 vibrational band of the F1Pi(u)-X1Sigma(+)g electronic system of C2 has been detected with the IUE in the interstellar medium along the line of sight toward X Per. A column density of 3 (+ or - 1) x 10 to the 12th/f(00) per sq cm was derived by a profile fitting method. The lower limit for 0-0 band oscillator strength was determined from a comparison of the upper limits of observations of the A-X and D-X systems, and an excitation temperature of 40 K was also obtained from the profile fitting. A statistical calculation of the level population with radiative pumping shows that the 0-0 band profile corresponds to a range of values for kinetic temperature, density, and near-IR radiation. An upper limit of 50 K for kinetic temperature was determined from the statistical equilibrium analysis.

Lien, D. J.↗

NASA NTRS1984

Recent developments in lithologic mapping using remote sensing data

Major development trends noted in remote sensing scanners are toward greater spatial and spectral resolution, as well as the acquisition of data over a broader portion of the electromagnetic spectrum. Attention is presently given to representative samples of the product of two new-generation satellite sensors, the Landsat-4 Thematic Mapper and SPOT, as well as the status of airborne scanner research aimed at the exploration of multispectral data in the thermal IR wavelength region (which encompasses the diagnostic spectral features of silicates and carbonates). Testing is underway for scanners having spectral bands as narrow as 0.01 micron in the visible and near-IR, which will be capable of identifying specific minerals.

Abrams, M.↗

NASA NTRS1985

Colors of reflection nebulae. II - The excitation of extended red emission

New BVI color-difference measurements are reported for the reflection nebulae NGC 7023, NGC 2068, and CED 201. The data are obtained through BVI imaging with a CCD detector and are analyzed together with previously published measurements for the reflection nebula NGC 2023. All four nebulae are substantially redder in the (V, I) range than expected on the basis of dust scattering alone, a result of the presence of extended emission in the I band. The relative strength of the I excess reaches a maximum in nebular regions where the color in the (B, V) range is bluest. These facts are interpreted in terms of a model which explains the extended I emission as a luminescence process excited by UV radiation from the illuminating star(s). Model fits identify the wavelength region between 1800 and 2500 A of the illuminating star's spectrum as the source of the energy of excitation. It appears possible that the 2200 A band in the dust-extinction curve is a gate for the excitation energy, and it is likely that the I excess emission and the extended near-IR emission recently discovered in reflection nebulae are similar in nature and origin.

Witt, A. N.↗

NASA NTRS1985

Osmium coated diffraction grating in the Space Shuttle environment - Performance

Samples coated with osmium were flown on the early Shuttle test flights, and on the return of these samples, the osmium coating was found to have disappeared, evidently due to the oxidation of the material in the atomic oxygen atmosphere. An instrument flown on the Spacelab 1 mission comprised an array of five spectrometers covering the extreme ultraviolet (EUV) to near-IR wavelengths. The EUV spectrometer contained an osmium-coated reflective grating located fairly deep within the instruments. Here, results of an assessment of the reflectivity and stability of the osmium surface over the course of the ten-day mission are reported. It is concluded that the osmium reflective coating remained stable relative to the spectrometer coated with MgF2 over the course of the mission. In addition, the ratio of sensitivity of these two spectrometers did not change in any major way from the time of the laboratory calibration until the time of flight two years later. Any changes are within the 50-percent calibration uncertainty.

Torr, M. R.↗

NASA NTRS1984

Visible and shortwave infrared focal planes for remote sensing instruments

The development of solid-state sensor technology for multispectral linear array (MLA) instruments is described. A buttable four-spectral-band linear-format CCD and a buttable two-spectral band linear-format short-wave IR CCD have been designed, and first samples have been demonstrated. In addition, first-sample four-band interference filters have been fabricated, and hybrid packaging technology is being developed. Based on this development work, the design and construction of focal planes for a Shuttle sortie MLA instrument have begun. This work involves a visible and near-IR focal plane with 2048 pixels x 4 spectral bands and a short-wave IR focal plane with 1024 pixels x 2 spectral bands.

Tower, J. R.↗