Engineering topics

Smith, G. L.

Publications and source records attributed to Smith, G. L..

At least 55 records · Page 3

NASA NTRS1985

The preparation and characterization of a lithium borate glass prepared by the gel technique

The preparation of an amorphous lithium borate gel by the metal organic procedure is described. In addition, a preliminary evaluation of the behavior of the gel upon heating is given. In particular the crystallization tendency of the gel is studied with the aid of DTA and X-ray diffraction, and the structural changes in the gel are monitored with the aid of IR spectroscopy. The glass produced from the lithium borate gel is compared to both the gel precursor material and a glass of similar composition prepared by conventional techniques. Specifically, the relevant water contents, crystallization behavior, and structural features are contrasted.

Weinberg, M. C.↗

NASA NTRS1985

Cloud bidirectional reflectance functions - A comparison of experimental and theoretical results

A comparison of bidirectional reflectance models developed by radiative transfer theory calculations with empirical models developed from Nimbus 7 Earth Radiation Budget (ERB) measurements indicates good overall comparison, with rms differences of about 10 percent for solar zenith angles lower than 60 deg. The results of these comparisons demonstrate that the theoretical model provides a good description of the reflected radiance fields of clouds as seen by satellite. A cloud model based on Geosynchronous Operational Environmental Satellite (GOES) data was also compared with the Nimbus 7 general cloud model, and it is found that bidirectional models which compare well with the Nimbus 7 ERB results can be reproduced using GOES data.

Stuhlmann, R.↗

NASA NTRS1984

Infrared parameterization and simple climate models

The geographical distribution of the annual mean and the annual cycle in surface temperature and satellite-observed IR is examined, and the spherical harmonic representation of the data fields is exploited to demonstrate how variances and covariances are dominated by the largest space and time scales. The geographical distribution of the annual cycle in the T and IR fields is explored; the strong imprint of the continents in both is clearly evident. The influence of the cloudiness of seasonal precipitation regimes on the IR annual cycle is also quite striking, especially over the subtropics. Analysis of the data shows that the simple form IR = A+BT (with A = 204 W/sq m and B = 1.93 W/sq m/K) explains 90 percent of the area-weighted variance in the annual mean and annual cycle of the zonally averaged IR field.

Short, D. A.↗

NASA NTRS1984

The earth radiation budget derived from the Nimbus 7 ERB experiment

The earth radiation budget as determined from the ERB experiment aboard the Nimbus-7 polar-orbiting satellite is presented in the form of time-latitude cross sections, hemispherically and globally averaged time plots, and annual global averages for the time period spanning November 1978 through October 1979. Comparisons are made between results derived from the fixed wide-field-of-view (WFOV) radiometers and those derived from the scanning narrow-field-of-view (NFOV) radiometers. While there is excellent agreement in regard to the spatial and temporal variations, the absolute magnitudes differ. The NFOV yields outgoing longwave fluxes and albedos that are about 4W/sq m and 2.5 percent, respectively, greater than those derived from the WFOV sensors. Also, limited simultaneous comparisons are made between ERB results and those from the AVHRR on the NOAA-7 operational satellite.

Jacobowitz, H.↗

NASA NTRS1984

A variational formulation for time-dependent climate models

A variational principle for time dependent diffusion problems is presented and is demonstrated by applying it to simple seasonal climate models. Two cases are treated. The first, a North-Coakley-type model with constant properties, is used as a tutorial example for the application of the technique. For the second case, heat capacity and thermal conductivity are considered to be latitude dependent in order to treat the effects of land/ocean distribution on the seasonal temperature distribution over the earth. The variational equations are derived and approximate analytical solutions are developed which delineate the influences of the physical asymmetries of the hemispheres in producing an asymmetric annual cycle.

Smith, G. L.↗

NASA NTRS1984

The crystallization behavior and kinetics of a barium fluorozirconate type glass

An investigation of the crystallization behavior of a Zr-Ba-La-Al-F glass which is subjected to isothermal heat treatments is presented. The number and nature of the crystalline phases which form and their nucleation sites are determined at three temperatures. Also, the growth rate and volume fraction of crystals which nucleate internally in the glass, when heated at 320 C, are determined as a function of time.

Neilson, G. F.↗

NASA NTRS1984

Method for estimating errors for radiation budget based on a scanning radiometer

The conduction of the Earth Radiation Budget Experiment (ERBE) will involve the utilization of three sets of instruments. Each set consists of a nonscanning package and a scanning radiometer. The instruments will fly on the NOAA F and G operational satellites and on a dedicated spacecraft, the Earth Radiation Budget Satellite (ERBS). The ERBS will be in a 57 deg inclination orbit and will precess around the earth to provide sampling of the diurnal cycle of regions between + or - 57 deg latitude. The primary function of the scanning radiometer is to provide measurements for the calculation of the earth-emitted and absorbed solar radiation at the top of the earth-atmosphere system, averaged over 250 x 250 km regions. The present paper is concerned with errors found in these regional averages. Attention is given to details regarding the problem, scene identification probabilities, scene identification error effects, total pixel error, and errors due to regional averaging.

Smith, G. L.↗

NASA NTRS1983

Annual cycle and spatial spectra of earth emitted radiation at large scales

Monthly averaged, resolution enhanced global distributions of the earth's emitted radiation, as measured by the Nimbus-6 Earth Radiation Budget (ERB) wide field of view radiometers, have been analyzed for 1 year of data from July 1975 to June 1976. These distributions are expressed in terms of spherical harmonic coefficients, and time and space variability of the emitted radiation field is studied in terms of these coefficients. The average annual distribution accounts for 78 percent of the space-time power, and the annual cycle accounts for 17 percent of the power. Spatial variations over the globe are described in terms of degree variance, and longitudinal variations are described in terms of spectral power as a function of latitude. The longitudinal spectra were found to vary strongly with time.

Smith, G. L.↗

NASA NTRS1983

Statistical theory for estimating sampling errors of regional radiation averages based on satellite measurements

The processes which determine the weather and climate are driven by the radiation received by the earth and the radiation subsequently emitted. A knowledge of the absorbed and emitted components of radiation is thus fundamental for the study of these processes. In connection with the desire to improve the quality of long-range forecasting, NASA is developing the Earth Radiation Budget Experiment (ERBE), consisting of a three-channel scanning radiometer and a package of nonscanning radiometers. A set of these instruments is to be flown on both the NOAA-F and NOAA-G spacecraft, in sun-synchronous orbits, and on an Earth Radiation Budget Satellite. The purpose of the scanning radiometer is to obtain measurements from which the average reflected solar radiant exitance and the average earth-emitted radiant exitance at a reference level can be established. The estimate of regional average exitance obtained will not exactly equal the true value of the regional average exitance, but will differ due to spatial sampling. A method is presented for evaluating this spatial sampling error.

Smith, G. L.↗

NASA NTRS1983

A comparison of experimental and theoretical bidirectional reflectance functions

Bidirectional reflectance models developed by radiative transfer theory calculations are compared with empirical models from Nimbus 7 ERB measurements for two cloud altitudes (medium height cloud tops at 3 km and high cloud tops at 9 km). For solar zenith angles less than 60 deg, the models agree to within 10 percent. For larger zenith angles, however, the differences between the models increase rapidly. These differences are attributed to three-dimensional cloud effects and to smearing effects associated with averaging measurements over finite solar zenith angle ranges. It is thus demonstrated, that the theoretical models provide a good description of the radiance fields of clouds as seen by the satellite.

Stuhlmann, R.↗

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 NTRS1981

An optimal numerical filter for wide-field-of-view measurements of earth-emitted radiation

A technique is described in which all data points along an arc of the orbit may be used in an optimal numerical filter for wide-field-of-view measurements of earth emitted radiation. The statistical filter design is derived whereby the filter is required to give a minimum variance estimate of the radiative exitance at discrete points along the ground track of the satellite. An equation for the optimal numerical filter is given by minimizing the estimate error variance equation with respect to the filter weights, resulting in a discrete form of the Wiener-Hopf equation. Finally, variances of the errors in the radiant exitance can be computed along the ground track and in the cross track directions.

Smith, G. L.↗

NASA NTRS1981

Deconvolution of wide-field-of-view satellite radiometer measurements of reflected solar radiation

An approach is presented by which the deconvolution of wide-field-of-view (WFOV) measurements of solar radiation reflected from earth is reduced from the solution of a two-dimensional integral equation to the solution of a set of one-dimensional integral equations. This reduces the storage needed for the required matrices by an order of magnitude and the computations by two orders of magnitude. Also, the theoretical and operational difficulties associated with the solution of ill-posed problems are greatly simplified by working with one-dimensional integral equations rather than with a two-dimensional integral equation.

Smith, G. L.↗

NASA NTRS1981

Deconvolution of wide field-of-view radiometer measurements of earth-emitted radiation. I - Theory

The theory of deconvolution of wide field-of-view (WFOV) radiometer measurements of earth-emitted radiation provides a technique by which the resolution of such measurements can be enhanced to provide radiant exitance at the top of the atmosphere with a finer resolution than the field of view. An analytical solution for the earth-emitted radiant exitance in terms of WFOV radiometer measurements is derived for the nonaxisymmetric (or regional) case, in which the measurements and radiant exitance are considered to be functions of both latitude and longitude. This solution makes it possible to deconvolve a set of WFOV radiometer measurements of earth-emitted radiation and obtain information with a finer resolution than the instantaneous field of view of the instrument. It is shown that there are tradeoffs involved in the selection between WFOV and scanning radiometers.

Smith, G. L.↗

NASA NTRS1981

Deconvolution of wide field-of-view radiometer measurements of earth-emitted radiation. II - Analysis of first year of Nimbus 6 ERB data

The theory of deconvolution considered by Smith and Green (1981) is applied to Nimbus 6 data in order to interpret the data with the maximum obtainable resolution. Attention is given to the data sample, sun-contaminated measurements, the measurement model, the deconvolution, the degree variance, the spherical harmonic coefficients, the geographical distribution of longwave radiation, time histories of zonal coefficients, and the effect of a grid system. Degree variance plots for 12 months of longwave radiation data show that the limit for a spherical harmonic representation of the Nimbus 6 wide field-of-view longwave data is 12th degree. The degree variance plots also reveal that most of the power is in the lower degree terms. Contour maps of the radiation field show the geographical distribution of earth emitted radiant exitance for each month.

Bess, T. D.↗

NASA NTRS1981

Time and space spectra of earth-emitted radiation at large scales

Several earth radiation instruments have been flown on spacecraft. The most recent of these instruments has been the Earth Radiation Budget (ERB) instrument aboard the Nimbus 6 and Nimbus 7 spacecraft. The ERB instrument includes two earth-viewing wide-field-of-view (WFOV) radiometers one of which measures total irradiance and the other measures shortwave (SW) irradiances. he difference between the two irradiances is the longwave (LW) or earth-emitted irradiance. The ERB instrument has been providing WFOV measurements since July 1975. These WFOV data are suitable for studying large-scale processes over spatial scales of thousands of kilometers. The present investigation is concerned with a study of the annual cycle of the distribution of the earth's LW radiation. This study is based on one year of WFOV data, from July 1975 through June 1976. The present investigation is an extension of the study by Bess and Smith (1979).

Bess, T. D.↗

NASA NTRS1980

Deconvolution and analysis of wide-angle longwave radiation data from Nimbus 6 Earth radiation budget experiment for the first year

One year of longwave radiation data from July 1975 through June 1976 from the Nimbus 6 satellite Earth radiation budget experiment is analyzed by representing the radiation field by a spherical harmonic expansion. The data are from the wide field of view instrument. Contour maps of the longwave radiation field and spherical harmonic coefficients to degree 12 and order 12 are presented for a 12 month data period.

Bess, T. D.↗

NASA NTRS1979

Estimating regional heat flux from scanning radiometer data

Method using matrix approach to determine best linear estimate of total flux consistent with condition of minimum variance proves useful in meteorological studies. It is useful for researchers studying options in scanner design such as scan pattern, scan rate, and radiometer field-of-view.

Bess, T. D.↗