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NASA NTRS1979

Methane band limb-brightening on Uranus

Area scanner measurements of the brightness distributions of Uranus at 6300 and 7250 A are presented. At the former wavelength, which is characteristic of continuum radiation, the observed limb-darkening is consistent with the results of Stratoscope observations. At the latter wavelength, in the center of a strong methane absorption band, the planet shows substantial limb-brightening as has been reported by other investigators. The limb-brightening and geometric albedo of Uranus in this methane band can be explained in terms of a clear atmospheric model in which the methane partial pressure above the saturation level is equal to its equilibrium vapor pressure. This conclusion is relatively insensitive to the methane mixing ratio below the saturation level. The presence of a high-altitude, conservatively, isotropically scattering haze of optical thickness 0.1, such as that previously proposed as a possible cause of the 7250-A limb-brightening, would produce a geometric albedo at this wavelength that is substantially larger than the value observed for Uranus.

Pilcher, C. B.↗

NASA NTRS1981

Solar limb brightening at 350 microns

The NASA Infrared Telescope Facility at Mauna Kea was used to observe the intensity profile of the quiet solar limb in the 300-400 micron continuum. A significant resolved brightening of several percent over the outer 60 arcsec of the solar limb in this band is found. However, the magnitude of the brightening is considerably less than that indicated by earlier observations of a total solar eclipse in integrated sun-moon radiation by Beckman, Lesurf, and Ross (1975) in the 1.2 mm continuum. More recent ground-based observations indicate that the magnitude of solar limb brightening at 800 microns and at 1.3 mm is stronger than that at 350 microns. This may be regarded as an indication that the hot material which produces the brightening at the extreme limb, thought to consist in part of chromospheric spicules, is optically thin in the 350 micron continuum.

Lindsey, C.↗

NASA NTRS1982

Submillimeter extensions of the solar limb determined from observations of the total eclipse of 1981 July 31

First results are presented of observations of a lunar occultation of the solar limb made from the Kuiper Airborne Observatory in the 30 micrometr, 50 micrometer, 100 micrometer, and 200 micrometer continuum during the total solar eclipse of 1981 July 31. The solar limb was extended at the longer wavelengths up to 1000 km higher than predicted from smooth plane-parallel chromospheric models. Results at both second and third contact show the infrared limb extensions to be approximately 0".8, 1"5, 2".5 and 3".0 above the visible limb in the observed bands, respectively. A possible interpretation proposes chromospheric fine structure inhomogeneities of greater density than presently incorporated in models of the middle chromosphere.

Lindsey, C.↗

NASA NTRS1983

Development of limb volume measuring system

The mechanisms underlying the reductions in orthostatic tolerance associated with weightlessness are not well established. Contradictory results from measurements of leg volume changes suggest that altered venomotor tone and reduced blood flow may not be the only contributors to orthostatic intolerance. It is felt that a more accurate limb volume system which is insensitive to environmental factors will aid in better quantification of the hemodynamics of the leg. Of the varous limb volume techniques presently available, the ultrasonic limb volume system has proven to be the best choice. The system as described herein is free from environmental effects, safe, simple to operate and causes negligible radio frequency interference problems. The segmental ultrasonic ultrasonic plethysmograph is expected to provide a better measurement of limb volume change since it is based on cross-sectional area measurements.

Bhagat, P. K.↗

NASA NTRS1984

Facular Limb-darkening Functions for Irradiance Modeling

The limb darkening function of faculae is an important factor in estimating facular contributions to solar irradiance variations. The existing photometric data is reviewed and a synthetic limb darkening function for faculae was generated which was compared with the limb darkening functions currently in use for irradiance modeling. The excess facular flux ranges from 0.017 to 0.0349 of the solar photospheric flux for the various representations. The present limitation appears to be the lack of comprehensive photometric data. The representations are especially varied near the limb, where photometry is most difficult. Synoptic data on calcium plage areas is used as a substitute for facular areas in modeling. Based upon the existing data, the present best value for the effect of faculae on the solar constant is given by delta s/s = 3.9 x 10(-8) A (sub plage prime) for an active region near disk center, where A (sub plage) is the calcium plage area in millionths of a solar hemisphere.

Hirayama, T.↗

NASA NTRS1983

Effect of limb darkening functions variations on deconvolution of wide-field-of-view measurements of earth emitted radiation

A solution is presented to the problem of deconvolving wide field of view measurements of earth-emitted radiation for the case of limb-darkening functions which are geographically dependent. The method of linear perturbations is used and the effects of limb-darkening function variations at various scales are evaluated. A simple model for the geographical variation of the limb-darkening function based on the radiant exitance is introduced. It is shown that the effect of these variations on the global average radiant exitance vanishes identically, and is insignificant for large spatial scales. For wave numbers six through twelve, the limb-darkening effects are small but possibly significant. At wave numbers greater than twelve, the noise due to meteorological variability dominates for an orbit altitude of 1100 km. The smallness of these effects is due to the smoothness of the monthly averaged radiant exitance field.

Smith, G. L.↗

NASA NTRS1989

Limb-darkening functions as derived from along-track operation of the ERBE scanning radiometer for January 1985

During January 1985, the scanning radiometer aboard the Earth Radiation Budget Satellite was operated to scan along-track. These data have been analyzed to produce limb-darkening functions for Earth emitted radiation, which relate the radiance in any given direction to the radiant exitance. Limb-darkening functions are presented in tabular form and shown as figures for 10 day cases and 12 night cases, corresponding to various scene types and latitude zones. The scene types were computed using measurements within 10 deg of zenith. The limb-darkening functions have values of 1.03 to 1.09 at zenith, with 1.06 being typical. It is found that latitude causes a variation on the order of 1 percent, except for zenith angles greater than 70 deg. These limb-darkening models are about 2 percent higher at zenith than the models derived from Nimbus 7 data.

Smith, G. Louis↗

NASA NTRS1988

Effects of immobilization on rat hind limb muscles under non-weight-bearing conditions

The effect of stretched and unstretched immobilization of a hind limb on the concentration and the metabolism of proteins in the hind-limb muscles of rats was investigated. The animals were divided into three groups: (1) weight-bearing controls, (2) tail-cast-suspended, and (3) suspended, with one hind limb immobilized with the ankle in dorsiflexion (30-40 deg angle) and the other freely moving. It was found that unloading the hind limbs for 6 days by tail cast suspension caused soleus to atrophy and reduced growth of the gastrocnemius and plantaris muscles; unloading resulted in a higher degradation rate and lower synthesis rate in both in vitro and in vivo. Chronic stretch of the unloaded soleus not only prevented its atrophy but led to significant hypertrophy, relative to weight-bearing controls, with increases in both the sarcoplasmic and myofibrillar protein fractions. Immobilizing one ankle in dorsiflexion prevented the inhibition of growth in the plantaris and gastrocnemius muscles due to unloading.

Jaspers, Stephen R.↗

NASA NTRS1988

Observations from 1982 of facular limb darkening and excess solar oblateness

Observations of facular regions on 35 days during 1982 obtained with the Extreme Limb Photometer are reported. The data were obtained at a wavelength of 0.53 microns with two apertures, No. 1 covering 36 arcsec and No. 2 covering 11 arcsec, inwards from the limb. The mean contrast of the faculae closer to the limb (aperture 2) is 1.51 + or - 0.23 times that from aperture No. 1. This contrast ratio can be fit to a 1/ms curve. These results are consistent with those from 1975 and 1979 observations and may be consistent with the facular limb-darkening function determined by Libbrecht and Kuhn (1984, 1985) if the data are normalized by the area of the solar surface. However, no calibrations or corrections are required to obtain the mean facular contrast presented here.

Chapman, G. A.↗

NASA NTRS1991

Telescope beam-profile diagnostics and the solar limb

The basic method is described for determining the solar limb brightness profile properly corrected for spurious limb darkening caused by the far wings of the resolving beams encountered in large far-infrared and radio telescopes. When the far wings of the beam can be independently measured this problem is usually amenable to standard deconvolution procedures. Under a broad range of well-defined cases, solutions to the deconvolution problem are unique to within the discrimination provided by the core of the beam profile. The theory is applied to solar limb scans made recently on the James Clerk Maxwell Telscope to show solar limb brightening in 850 micron radiation.

Lindsey, Charles A.↗

NASA NTRS1992

Photon escape probabilities from resolved sources - Application to solar C III limb emission

Monodirectional effective escape probabilities, involving line-of-sight-integrated escape factors, are calculated for the highly anisotropic source represented by C III emission at the solar limb as a concrete example of the application of such probabilities. Predicted intensity variations of C III lines with limb distance are obtained using a spherical shell model, showing several interesting features which may be observable with appropriate instruments. Among these are expected enhancements of extreme ultraviolet lines at 884.5 and 1308.7 A, and local limb-brightening and limb-darkening effects in optically thick lines, which may provide sensitive constraints on the solar C III emission distribution. Comparisons are made with available observations.

Kastner, S. O.↗

NASA NTRS1993

Altitude profile of aerosols on Mars from measurements of its thermal radiation on limb

Measurements of the thermal (range 7 - 13 micrometers) radiation of Mars with the high space resolution (approximately 2 km) were made by the TERMOSKAN experiment of the Phobos mission. Some of the results were published earlier but only the surface radiation was analyzed in detail. However some part of these measurements was made near the limb of the planet. The atmosphere gives an important input here in the planetary thermal radiation. Beyond the limb the atmosphere is the only source. The task of this work is to estimate some characteristics of the atmosphere using brightness profiles of the thermal radiation near the limb. An appropriate model of the temperature profile T(h) is necessary for such an analysis. A set of T(h) models (nominal, maximal and minimal) was defined using various sources including MARSGRAM, Viking-1 lander data, its theoretical considerations and boundary layer models. On the next step the possible input of the atmospheric gaseous emissions (wing of CO2 15 micrometer band) was estimated. It was found that even for the maximal T(h) this input is no more than a few percents of the measured radiation beyond the limb. Consequently the aerosols are responsible for almost all measured emission. The analysis of the observed profile showed that these aerosols have two components: (1) exponential with the scale height about 10 km and (2) some layered structure (two layers with maxima about 23 and 33 km consisted probably of ice).

Moroz, V. I.↗

NASA NTRS1994

Six-degree-of-freedom parallel minimanipulator with three inextensible limbs

A Six-Degree-of-Freedom Parallel-Manipulator having three inextensible limbs for manipulating a platform is described. The three inextensible limbs are attached via universal joints to the platform at non-collinear points. Each of the inextensible limbs is also attached via universal joints to a two-degree-of-freedom parallel driver such as a five-bar linkage, a pantograph, or a bidirectional linear stepper motor. The drivers move the lower ends of the limbs parallel to a fixed base and thereby provide manipulation of the platform. The actuators are mounted on the fixed base without using any power transmission devices such as gears or belts.

Tahmasebi, Farhad↗

NASA NTRS1993

New limb-darkening coefficients for modeling binary star light curves

We present monochromatic, passband-specific, and bolometric limb-darkening coefficients for a linear as well as nonlinear logarithmic and square root limb-darkening laws. These coefficients, including the bolometric ones, are needed when modeling binary star light curves with the latest version of the Wilson-Devinney light curve progam. We base our calculations on the most recent ATLAS stellar atmosphere models for solar chemical composition stars with a wide range of effective temperatures and surface gravitites. We examine how well various limb-darkening approximations represent the variation of the emerging specific intensity across a stellar surface as computed according to the model. For binary star light curve modeling purposes, we propose the use of a logarithmic or a square root law. We design our tables in such a manner that the relative quality of either law with respect to another can be easily compared. Since the computation of bolometric limb-darkening coefficients first requires monochromatic coefficients, we also offer tables of these coefficients (at 1221 wavelength values between 9.09 nm and 160 micrometer) and tables of passband-specific coefficients for commonly used photometric filters.

Van Hamme, W.↗

NASA NTRS1994

Non-local thermodynamic equilibrium limb radiance from O3 and CO2 in the 9-11 micrometer spectral region

Satellite remote sensing of mesospheric and thermospheric O3 abundance in the terrestrial atmosphere often uses 9-11 micrometer thermal emission. In this paper, we apply a line-by-line non-local thermodynamic equilibrium (non-LTE) radiance model to this spectral region and investigate the conditions of LTE breakdown and the effect that this has on the limb radiance measured by an i.r. sounder. Monochromatic and band-integrated radiance calculations have been performed for limb view tangent heights between 55 and 105 km under daytime and nighttime conditions. Non-LTE emission from both O3 and CO2 are shown to be important with the divergence of radiance from LTE values and the diurnal variation being band dependent. We have shown that the contribution of the CO2 bands to the Limb Infrared Monitor of the Stratosphere O3 channel is significant for daytime conditions at tangent heights above about 60 km. A study has been made to choose O3 sounding channel spectral passbands for the High Resolution Dynamics Limb Sounder. High resolution calculations are required to determine those spectral intervals that will filter radiance from selected bands and characterize their non-LTE behavior. This will allow for improved O3 retrievals above 70 km and non-LTE studies.

Edwards, David P.↗

NASA NTRS1996

Calibration of the Microwave Limb Sounder on the Upper Atmosphere Research Satellite

The Microwave Limb Sounder (MLS) is a three-radiometer, passive, limb emission instrument onboard the Upper Atmosphere Research Satellite (UARS). Radiometric, spectral and field-of-view calibrations of the MLS instrument are described in this paper. In-orbit noise performance, gain stability, spectral baseline and dynamic range are described, as well as use of in-flight data for validation and refinement of prelaunch calibrations. Estimated systematic scaling uncertainties (3 sigma) on calibrated limb radiances from prelaunch calibrations are 2.6% in bands 1 through 3, 3.4% in band 4, and 6% in band 5. The observed systematic errors in band 6 are about 15%, consistent with prelaunch calibration uncertainties. Random uncertainties on individual limb radiance measurements are very close to the levels predicted from measured radiometer noise temperature, with negligible contribution from noise and drifts on the regular in-flight gain calibration measurements.

Jarnot, R. F.↗

NASA NTRS2002

Description and Sensitivity Analysis of the SOLSE/LORE-2 and SAGE III Limb Scattering Ozone Retrieval Algorithms

The SOLSE (Shuttle Ozone Limb Sounding Experiment) and LORE (Limb Ozone Retrieval Experiment) instruments are scheduled for reflight on Space Shuttle flight STS-107 in July 2002. In addition, the SAGE III (Stratospheric Aerosol and Gas Experiment) instrument will begin to make limb scattering measurements during Spring 2002. The optimal estimation technique is used to analyze visible and ultraviolet limb scattered radiances and produce a retrieved ozone profile. The algorithm used to analyze data from the initial flight of the SOLSE/LORE instruments (on Space Shuttle flight STS-87 in November 1997) forms the basis of the current algorithms, with expansion to take advantage of the increased multispectral information provided by SOLSE/LORE-2 and SAGE III. We also present detailed sensitivity analysis for these ozone retrieval algorithms. The primary source of ozone retrieval error is tangent height misregistration (i.e., instrument pointing error), which is relevant throughout the altitude range of interest, and can produce retrieval errors on the order of 10-20 percent due to a tangent height registration error of 0.5 km at the tangent point. Other significant sources of error are sensitivity to stratospheric aerosol and sensitivity to error in the a priori ozone estimate (given assumed instrument signal-to-noise = 200). These can produce errors up to 10 percent for the ozone retrieval at altitudes less than 20 km, but produce little error above that level.

Loughman, R.↗

NASA NTRS2002

Convergence of limb, visceral, and vertical semicircular canal or otolith inputs onto vestibular nucleus neurons

The major goal of this study was to determine the patterns of convergence of non-labyrinthine inputs from the limbs and viscera onto vestibular nucleus neurons receiving signals from vertical semicircular canals or otolith organs. A secondary aim was to ascertain whether the effects of non-labyrinthine inputs on the activity of vestibular nucleus neurons is affected by bilateral peripheral vestibular lesions. The majority (72%) of vestibular nucleus neurons in labyrinth-intact animals whose firing was modulated by vertical rotations responded to electrical stimulation of limb and/or visceral nerves. The activity of even more vestibular nucleus neurons (93%) was affected by limb or visceral nerve stimulation in chronically labyrinthectomized preparations. Some neurons received non-labyrinthine inputs from a variety of peripheral sources, including antagonist muscles acting at the same joint, whereas others received inputs from more limited sources. There was no apparent relationship between the spatial and dynamic properties of a neuron's responses to tilts in vertical planes and the non-labyrinthine inputs that it received. These data suggest that non-labyrinthine inputs elicited during movement will modulate the processing of information by the central vestibular system, and may contribute to the recovery of spontaneous activity of vestibular nucleus neurons following peripheral vestibular lesions. Furthermore, some vestibular nucleus neurons with non-labyrinthine inputs may be activated only during particular behaviors that elicit a specific combination of limb and visceral inputs.

NASA Discipline Developmental Biology↗