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At least 1,351 records · Page 75

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NASA NTRS1981

Development of rotation sample designs for the estimation of crop acreages

The idea behind the use of rotation sample designs is that the variation of the crop acreage of a particular sample unit from year to year is usually less than the variation of crop acreage between units within a particular year. The estimation theory is based on an additive mixed analysis of variance model with years as fixed effects, (a sub t), and sample units as a variable factor. The rotation patterns are decided upon according to: (1) the number of sample units in the design each year; (2) the number of units retained in the following years; and (3) the number of years to complete the rotation pattern. Different analytic formulae for the variance of (a sub t) and the variance comparisons in using a complete survey of the rotation patterns.

Lycthuan-Lee, T. G.↗

NASA NTRS1981

Sample selection in foreign similarity regions for multicrop experiments

The selection of sample segments in the U.S. foreign similarity regions for development of proportion estimation procedures and error modeling for Argentina, Australia, Brazil, and USSR in AgRISTARS is described. Each sample was chosen to be similar in crop mix to the corresponding indicator region sample. Data sets, methods of selection, and resulting samples are discussed.

Malin, J. T.↗

NASA NTRS1982

Estimating acreage by double sampling using LANDSAT data

Double sampling techniques employing LANDSAT data for estimating the acreage of corn and soybeans was investigated and evaluated. The evaluation was based on estimated costs and correlations between two existing procedures having differing cost/variance characteristics, and included consideration of their individual merits when coupled with a fictional 'perfect' procedure of zero bias and variance. Two features of the analysis are: (1) the simultaneous estimation of two or more crops; and (2) the imposition of linear cost constraints among two or more types of resource. A reasonably realistic operational scenario was postulated. The costs were estimated from current experience with the measurement procedures involved, and the correlations were estimated from a set of 39 LACIE-type sample segments located in the U.S. Corn Belt. For a fixed variance of the estimate, double sampling with the two existing LANDSAT measurement procedures can result in a 25% or 50% cost reduction. Double sampling which included the fictional perfect procedure results in a more cost effective combination when it is used with the lower cost/higher variance representative of the existing procedures.

Pont, F.↗

NASA NTRS1982

Acoustic levitating apparatus for submillimeter samples

A hemispherical focusing radiator has been employed to generate ultrahigh intensity sound waves in a gaseous medium at the center of curvature of the radiator (focal point) at 75, 107, and 163 kHz. A volumetric force is produced by optimally placing a reflector in the vicinity of the focal point to levitate samples of submillimeter sizes. It has been demonstrated that a sample with a specific gravity of 19.3 can be levitated with this apparatus. The lateral positional wandering of the sample in the force well is estimated at less than 5% of the dimension of the sample size used.

Lee, M. C.↗

NASA NTRS1982

Sampling errors in the estimation of empirical orthogonal functions

Empirical Orthogonal Functions (EOF's), eigenvectors of the spatial cross-covariance matrix of a meteorological field, are reviewed with special attention given to the necessary weighting factors for gridded data and the sampling errors incurred when too small a sample is available. The geographical shape of an EOF shows large intersample variability when its associated eigenvalue is 'close' to a neighboring one. A rule of thumb indicating when an EOF is likely to be subject to large sampling fluctuations is presented. An explicit example, based on the statistics of the 500 mb geopotential height field, displays large intersample variability in the EOF's for sample sizes of a few hundred independent realizations, a size seldom exceeded by meteorological data sets.

North, G. R.↗

NASA NTRS1982

Ambient airborne solids concentrations including volcanic ash at Hanford, Washington sampling sites subsequent to the Mount St. Helens eruption

Airborne solids concentrations were measured on a near daily basis at two Hanford, Washington sites after the eruption of Mount St. Helens on May 18, 1980. These sites are about 211 km east of Mount St. Helens. Collected airborne solids included resuspended volcanic ash plus normal ambient solids. Average airborne solids concentrations were greater at the Hanford meteorological station sampling site which is 24 km northwest of the Horn Rapids dam sampling site. These increased concentrations reflect the sampling site proximity to greater ash fallout depths. Both sites are in low ash fallout areas although the Hanford meteorological station site is closer to the greater ash fallout areas. Airborne solids concentrations were decreased by rain, but airborne solids concentrations rapidly increased as surfaces dried. Airborne concentrations tended to become nearly the same at both sampling sites only for July 12 and 13.

Sehmel, G. A.↗

NASA NTRS1982

Estimation of the sugar cane cultivated area from LANDSAT images using the two phase sampling method

A two phase sampling method and the optimal sampling segment dimensions for the estimation of sugar cane cultivated area were developed. This technique employs visual interpretations of LANDSAT images and panchromatic aerial photographs considered as the ground truth. The estimates, as a mean value of 100 simulated samples, represent 99.3% of the true value with a CV of approximately 1%; the relative efficiency of the two phase design was 157% when compared with a one phase aerial photographs sample.

Parada, N. D. J.↗

NASA NTRS1983

The window of visibility: A psychological theory of fidelity in time-sampled visual motion displays

Many visual displays, such as movies and television, rely upon sampling in the time domain. The spatiotemporal frequency spectra for some simple moving images are derived and illustrations of how these spectra are altered by sampling in the time domain are provided. A simple model of the human perceiver which predicts the critical sample rate required to render sampled and continuous moving images indistinguishable is constructed. The rate is shown to depend upon the spatial and temporal acuity of the observer, and upon the velocity and spatial frequency content of the image. Several predictions of this model are tested and confirmed. The model is offered as an explanation of many of the phenomena known as apparent motion. Finally, the implications of the model for computer-generated imagery are discussed.

Watson, A. B.↗

NASA NTRS1983

The Antaeus Project - An orbital quarantine facility for analysis of planetary return samples

A design is presented for an earth-orbiting facility for the analysis of planetary return samples under conditions of maximum protection against contamination but minimal damage to the sample. The design is keyed to a Mars sample return mission profile, returning 1 kg of documented subsamples, to be analyzed in low earth orbit by a small crew aided by automated procedures, tissue culture and microassay. The facility itself would consist of Spacelab shells, formed into five modules of different sizes with purposes of power supply, habitation, supplies and waste storage, the linking of the facility, and both quarantine and investigation of the samples. Three barriers are envisioned to protect the biosphere from any putative extraterrestrial organisms: sealed biological containment cabinets within the Laboratory Module, the Laboratory Module itself, and the conditions of space surrounding the facility.

Sweet, H. C.↗

NASA NTRS1983

A quarantine protocol for analysis of returned extraterrestrial samples

A protocol is presented for the analysis at an earth-orbiting quarantine facility of return samples of extraterrestrial material that might contain (nonterrestrial) life forms. The protocol consists of a series of tests designed to determine whether the sample, conceptualized as a 1-kg sample of Martian soil, is free from nonterrestrial biologically active agents and so may safely be sent to a terrestrial containment facility, or it exhibits biological activity requiring further (second-order) testing outside the biosphere. The first-order testing procedure seeks to detect the presence of any replicating organisms or toxic substances through a series of experiments including gas sampling, analysis of radioactivity, stereomicroscopic inspection, chemical analysis, microscopic examination, the search for metabolic products under growth conditions, microbiologicl assays, and the challenge of cultured cells with any agents found or with the extraterrestrial material as is. Detailed plans for the second-order testing would be developed in response to the actual data received from primary testing.

Bagby, J. R.↗

NASA NTRS1983

Composition of bulk samples and a possible pristine clast from Allan Hills A81005

Abundances of thirty-five elements were determined in two bulk samples and a white clast in the Allan Hills A81005 meteorite. High siderophile element content indicates that the sample is a regolith breccia. An Fe/Mn ratio of 77 in this meteorite eliminates parent bodies of known differentiated meteorites as the source of ALHA 81005. The incompatible elements are very similar to those found in most lunar highlands rocks, and provide very strong evidence that the sample is lunar in origin. The clast sample has the trace element pattern of a lunar anorthosite and is very low in KREEP and siderophile elements. It may be a fragment of a pristine lunar rock.

Boynton, W. V.↗

NASA NTRS1983

Comet nucleus sample return mission

A comet nucleus sample return mission in terms of its relevant science objectives, candidate mission concepts, key design/technology requirements, and programmatic issues is discussed. The primary objective was to collect a sample of undisturbed comet material from beneath the surface of an active comet and to preserve its chemical and, if possible, its physical integrity and return it to Earth in a minimally altered state. The secondary objectives are to: (1) characterize the comet to a level consistent with a rendezvous mission; (2) monitor the comet dynamics through perihelion and aphelion with a long lived lander; and (3) determine the subsurface properties of the nucleus in an area local to the sampled core. A set of candidate comets is discussed. The hazards which the spacecraft would encounter in the vicinity of the comet are also discussed. The encounter strategy, the sampling hardware, the thermal control of the pristine comet material during the return to Earth, and the flight performance of various spacecraft systems and the cost estimates of such a mission are presented.

Source record↗

NASA NTRS1983

Conic sectors for sampled-data feedback systems

The conic-sector analysis of the closed-loop stability and robustness of a multivariable-analog-system controller based on sampled-data feedback compensation is investigated. Conic sectors and sampled-data feedback systems are defined, and the existence of a conic sector containing a sampled-data operator is established mathematically. An example is presented to prove that the conic sector is computable and gives sufficient conditions of closed-loop stability. A procedure for determining sampled-data-operator gain is also derived.

Thompson, P. M.↗

NASA NTRS1983

Optical effects module and passive sample array

The Optical Effects Module (OEM) has the objective to monitor the effects of the deposition and adhesion of both molecular species and particles on optical surfaces in the Shuttle cargo bay environment. The OEM performs inflight measurements of the ultraviolet (253.7 nm) transmittance and diffuse reflectance of five optical samples at regular intervals throughout the orbital mission. Most of the obtained results indicates or implies the absence of a significant accumulation of contamination other than particulates on the samples. The contaminant species (or particulates) adhering to the samples of the Passive Sample Array (PSA) were identified by means of Auger and X-ray energy dispersive analyses. The elements silicon, chlorine, and phosphorus were discovered.

Linton, R. C.↗

NASA NTRS1985

Ultrahigh-Vacuum Sample-Transfer System

Ultrahigh-vacuum (UHV) sample-transfer system developed features short-term (less than 30 minutes) transfer of samples from atmospheric pressure into sample manipulator within UHV analysis system without significantly degrading system pressure. New system is austere approach to sample transfer, involving no automation. Total cost of system is factor of 10 less than commercially available instruments.

Outlaw, R.↗

NASA NTRS1984

Study of proton and neutron activation of metal samples in low Earth orbit

The analysis of the gamma-ray spectra taken from samples flown in Spacelab 1; the search for and review of neutron and proton activation cross-sections needed to analyze the results of the Long Duration Exposure Facility (LDEF) activation measurements; additional calculations of neutron induced activation for the LDEF samples; the data analysis plan for the LDEF and Spacelab 2 samples; the measurement of relevant cross-sections with activation of samples of V, Co, In, and Ta at the Indiana University Cyclotron Facility; and the preparation of an extended gamma-ray calibration source through the development of a proper technique to accurately deposit equal quantities of radioactive material onto a large number of point on the source are discussed.

Laird, C. E.↗

NASA NTRS1984

Mossbauer spectroscopy and X-ray diffraction of samples from the Santa Catharina iron meteorite

Conversion electron Mossbauer spectroscopy (CEMS) of samples from the Santa Catharina iron meteorite shows the presence of the ordered iron-nickel phase with 50% Ni, tetrataenite, and of the paramagnetic iron-nickel phase with 25% Ni. The FeNi phase with 50% Ni amounts to 70% of the iron-nickel alloys. Futhermore, the CEM spectra show the presence of small peaks from one or more spinel compounds. These small peaks are more pronounced when regions near the rim of the samples are analyzed. The X-ray diffraction of different areas of the samples, both optically dark and optically light areas, shows the presence of a diffraction pattern from a single f.c.c. lattice with a lattice parameter of a=3.58A This means that the two different Fe-Ni phases seen in the CEMS analysis occupy the same lattice. The X-ray photographs also show the presence of super-structure reflections from the ordered FeNi phase, and that the orientation of the f.c.c. lattice is the same within the whole sample.

Roy-Poulsen, H.↗

NASA NTRS1984

Sample return from a comet flyby

Sample collection and return to the Earth from a fast fly through of a cometary coma is the simplest sample return mission possible from any extraterrestrial body. The mission can provide valuable laboratory samples from a known cometary body and it can do it at low cost, within our lifetimes. The method and the merits of the sample collection process from a comet flyby are discussed.

Brownlee, D. E.↗