Engineering topics

Smith, G. L.

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

At least 19 records

NASA NTRS2011

Clouds and Earth Radiant Energy System (CERES), a Review: Past, Present and Future

The Clouds and Earth Radiant Energy System (CERES) project s objectives are to measure the reflected solar radiance (shortwave) and Earth-emitted (longwave) radiances and from these measurements to compute the shortwave and longwave radiation fluxes at the top of the atmosphere (TOA) and the surface and radiation divergence within the atmosphere. The fluxes at TOA are to be retrieved to an accuracy of 2%. Improved bidirectional reflectance distribution functions (BRDFs) have been developed to compute the fluxes at TOA from the measured radiances with errors reduced from ERBE by a factor of two or more. Instruments aboard the Terra and Aqua spacecraft provide sampling at four local times. In order to further reduce temporal sampling errors, data are used from the geostationary meteorological satellites to account for changes of scenes between observations by the CERES radiometers. A validation protocol including in-flight calibrations and comparisons of measurements has reduced the instrument errors to less than 1%. The data are processed through three editions. The first edition provides a timely flow of data to investigators and the third edition provides data products as accurate as possible with resources available. A suite of cloud properties retrieved from the MODerate-resolution Imaging Spectroradiometer (MODIS) by the CERES team is used to identify the cloud properties for each pixel in order to select the BRDF for each pixel so as to compute radiation fluxes from radiances. Also, the cloud information is used to compute radiation at the surface and through the atmosphere and to facilitate study of the relationship between clouds and the radiation budget. The data products from CERES include, in addition to the reflected solar radiation and Earth emitted radiation fluxes at TOA, the upward and downward shortwave and longwave radiation fluxes at the surface and at various levels in the atmosphere. Also at the surface the photosynthetically active radiation and ultraviolet radiation (total, UVA and UVB) are computed. The CERES instruments aboard the Terra and Aqua spacecraft have served well past their design life times. A CERES instrument has been integrated onto the NPP platform and is ready for launch in 2011. Another CERES instrument is being built for launch in 2014, and plans are being made for a series of follow-on missions.

Smith, G. L.↗

NASA NTRS2001

Gamma-Weighted Discrete Ordinate Two-Stream Approximation for Computation of Domain Averaged Solar Irradiance

An algorithm is developed for the gamma-weighted discrete ordinate two-stream approximation that computes profiles of domain-averaged shortwave irradiances for horizontally inhomogeneous cloudy atmospheres. The algorithm assumes that frequency distributions of cloud optical depth at unresolved scales can be represented by a gamma distribution though it neglects net horizontal transport of radiation. This algorithm is an alternative to the one used in earlier studies that adopted the adding method. At present, only overcast cloudy layers are permitted.

Kato, S.↗

NASA NTRS1997

Bidirectional Reflectance Functions for Application to Earth Radiation Budget Studies

Reflected solar radiative fluxes emerging for the Earth's top of the atmosphere are inferred from satellite broadband radiance measurements by applying bidirectional reflectance functions (BDRFs) to account for the anisotropy of the radiation field. BDRF's are dependent upon the viewing geometry (i.e. solar zenith angle, view zenith angle, and relative azimuth angle), the amount and type of cloud cover, the condition of the intervening atmosphere, and the reflectance characteristics of the underlying surface. A set of operational Earth Radiation Budget Experiment (ERBE) BDRFs is available which was developed from the Nimbus 7 ERB (Earth Radiation Budget) scanner data for a three-angle grid system, An improved set of bidirectional reflectance is required for mission planning and data analysis of future earth radiation budget instruments, such as the Clouds and Earth's Radiant Energy System (CERES), and for the enhancement of existing radiation budget data products. This study presents an analytic expression for BDRFs formulated by applying a fit to the ERBE operational model tabulations. A set of model coefficients applicable to any viewing condition is computed for an overcast and a clear sky scene over four geographical surface types: ocean, land, snow, and desert, and partly cloudy scenes over ocean and land. The models are smooth in terms of the directional angles and adhere to the principle of reciprocity, i.e., they are invariant with respect to the interchange of the incoming and outgoing directional angles. The analytic BDRFs and the radiance standard deviations are compared with the operational ERBE models and validated with ERBE data. The clear ocean model is validated with Dlhopolsky's clear ocean model. Dlhopolsky developed a BDRF of higher angular resolution for clear sky ocean from ERBE radiances. Additionally, the effectiveness of the models accounting for anisotropy for various viewing directions is tested with the ERBE along tract data. An area viewed from nadir and from the side give two different radiance measurements but should yield the same flux when converted by the BDRF. The analytic BDRFs are in very good qualitative agreement with the ERBE models. The overcast scenes exhibit constant retrieved albedo over viewing zenith angles for solar zenith angles less than 60 degrees. The clear ocean model does not produce constant retrieved albedo over viewing zenith angles but gives an improvement over the ERBE operational clear sky ocean BDRF.

Manalo-Smith, N.↗

NASA NTRS1995

Clouds and the Earth's Radiant Energy System (CERES) algorithm theoretical basis document: Geolocation, calibration, and ERBE-like analyses (subsystems 1-3) - volume 2

The theoretical bases for the Release 1 algorithms that will be used to process satellite data for investigation of the Clouds and Earth's Radiant Energy System (CERES) are described. The architecture for software implementation of the methodologies is outlined. Volume 2 details the techniques used to geolocate and calibrate the CERES scanning radiometer measurements of shortwave and longwave radiance to invert the radiances to top-of-the-atmosphere (TOA) and surface fluxes following the Earth Radiation Budget Experiment (ERBE) approach, and to average the fluxes over various time and spatial scales to produce an ERBE-like product. Spacecraft ephemeris and sensor telemetry are used with calibration coefficients to produce a chronologically ordered data product called bidirectional scan (BDS) radiances. A spatially organized instrument Earth scan product is developed for the cloud-processing subsystem. The ERBE-like inversion subsystem converts BDS radiances to unfiltered instantaneous TOA and surface fluxes. The TOA fluxes are determined by using established ERBE techniques. Hourly TOA fluxes are computed from the instantaneous values by using ERBE methods. Hourly surface fluxes are estimated from TOA fluxes by using simple parameterizations based on recent research. The averaging process produces daily, monthly-hourly, and monthly means of TOA and surface fluxes at various scales. This product provides a continuation of the ERBE record.

Wielicki, B. A.↗

NASA NTRS1994

Radiation budget measurements for the eighties and nineties

The Earth Radiation Budget Experiment (ERBE) consisted of a scanning radiometer and non-scanning radiometers on each of three spacecraft. These instruments began flying in October 1984. The nonscanning radiometers continue to operate, providing broadband radiation measurements of the Earth's outgoing longwave radiation and reflected solar radiation, in addition to measurements of the solar output. The Clouds and Earth Radiant Energy System (CERES) features a scanning radiometer, which is an improved version of the ERBE scanning radiometer, and will fly on the Tropical Rainfall Measurement Mission and Earth Observation System platforms in the late nineties. The CERES project will provide not only radiant fluxes at the 'top of the atmosphere' (TOA), but also at the surface and will compute radiant flux divergence through the atmosphere.

Smith, G. L.↗

NASA NTRS1993

Earth radiation budget - Results of outgoing longwave radiation from Nimbus-7, NOAA-9, and ERBS satellites

Outgoing longwave radiation (OLR) data from Nimbus-7 ERB wide field-of-view instruments are compared with results from the ERBE instruments aboard the NOAA-9 and NOAA-10 satellites. Over most regions of the globe, the agreement between the two sets of OLR results is generally to within 8 W/sq m. There are larger differences at higher latitudes and regions concentrated over land and desert. Results of daytime and nighttime differences suggest that the shortwave channels may be at fault due to their different design for Nimbus-7 and NOAA-9. Some of the differences may also be related to different viewing geometry of the two satellites.

Bess, T. D.↗

NASA NTRS1992

Annual and interannual variations of earth-emitted radiation based on a 10-year data set

The method of empirical orthogonal functions (EOFs) was applied to a 10-yr data set of outgoing longwave radiation. Spherical harmonic functions are used as a basis set for producing equal area map results. The first EOF accounts for 66 percent of the variance. After that, each EOF accounts for only a small variance, forming a slowly converging series. The first two EOFs describe mainly the annual cycle. The third EOF is primarily the semiannual cycle although many other EOFs also contain significant semiannual parts. These results reaffirm those based on a shorter data set. In addition, a much stronger spring/fall mode was found in the central equatorial Pacific Ocean for the second EOF than was found earlier. The fourth EOF describes much of the 1976 to 1977 and 1982 to 1983 ENSO phenomena. There is typically a gap in the spectrum between a semiannual peak and the annual cycle for all but the first EOF. A semiannual OLR dipole straddles the Asian-Australian monsoon track.

Bess, T. D.↗

NASA NTRS1992

Comparison of 18 months of longwave radiation results from Nimbus-7 and the ERBE NOAA-9 and NOAA-10 satellites

The outgoing longwave radiation (OLR) data from ERBE wide-field-of-view (WFOV) and scanning sensor are compared with Nimbus-7 WFOV results. Monthly averaged OLR data from the ERBE WFOV instruments aboard the NOAA-9 and NOAA-10 polar orbiting satellites during the 3-year overlap period with Nimbus-7 are deconvolved using spherical harmonics. Results of a comparison of the data sets are presented on regional, zonal, and global scales in the spatial domain and on a monthly scale in the time domain.

Bess, T. D.↗

NASA NTRS1991

Shortwave wide-field-of-view results from the Earth Radiation Budget Experiment

The deconvolution (DCN) and numerical filter (NF) techniques of analyzing nonscanning radiometer measurements are evaluated by comparison with scanning radiometer results for monthly mean maps of albedo and absorbed solar radiation. Both techniques successfully enhance the resolution of the monthly mean product. The numerical filter albedo adheres closer to the scanning radiometer in the zonal average than does the DCN albedo. Zonal rms's, however, show that the DCN albedo is about 1 percent better than the NF in the Southern Hemisphere, but in the Northern Hemisphere the NF is better by up to 2 percent.

Rutan, David↗

NASA NTRS1991

Spatial variability of outgoing longwave radiation

Spatial distributions of day-to-day variations in the outgoing longwave radiation (OLR) are quantified by examining spatial variations in daily OLR data obtained from the Earth Radiation Budget Experiment scanning radiometer aboard the NOAA-9 meteorological satellite, in the form of daily maps and monthly radiation maps at 2.5 deg latitude-longitude scale. The results show that the variations of OLR during a month are markedly greater in the subtropics than they are in the mid and high altitudes. Results for October 1985 are presented.

Smith, G. L.↗

NASA NTRS1991

Scene identification probabilities for evaluating radiation flux errors due to scene misidentification

The scene identification probabilities (Pij) are fundamentally important in evaluations of the top-of-the-atmosphere (TOA) radiation-flux errors due to the scene misidentification. In this paper, the scene identification error probabilities were empirically derived from data collected in 1985 by the Earth Radiation Budget Experiment (ERBE) scanning radiometer when the ERBE satellite and the NOAA-9 spacecraft were rotated so as to scan alongside during brief periods in January and August 1985. Radiation-flux error computations utilizing these probabilities were performed, using orbit specifications for the ERBE, the Cloud and Earth's Radiant Energy System (CERES), and the SCARAB missions for a scene that was identified as partly cloudy over ocean. Typical values of the standard deviation of the random shortwave error were in the order of 1.5-5 W/sq m, but could reach values as high as 18.0 W/sq m as computed from NOAA-9.

Manalo, Natividad D.↗

NASA NTRS1991

Spatial sampling errors for a satellite-borne scanning radiometer

The Clouds and Earth's Radiant Energy System (CERES) scanning radiometer is planned as the Earth radiation budget instrument for the Earth Observation System, to be flown in the late 1990's. In order to minimize the spatial sampling errors of the measurements, it is necessary to select design parameters for the instrument such that the resulting point spread function will minimize spatial sampling errors. These errors are described as aliasing and blurring errors. Aliasing errors are due to presence in the measurements of spatial frequencies beyond the Nyquist frequency, and blurring errors are due to attenuation of frequencies below the Nyquist frequency. The design parameters include pixel shape and dimensions, sampling rate, scan period, and time constants of the measurements. For a satellite-borne scanning radiometer, the pixel footprint grows quickly at large nadir angles. The aliasing errors thus decrease with increasing scan angle, but the blurring errors grow quickly. The best design minimizes the sum of these two errors over a range of scan angles. Results of a parameter study are presented, showing effects of data rates, pixel dimensions, spacecraft altitude, and distance from the spacecraft track.

Manalo, Natividad D.↗

NASA NTRS1991

Transfer function considerations for the CERES scanning radiometer

The Clouds and Earth's Radiant Energy System (CERES) scanning radiometer will determine the radiation budget of the Earth on a regional basis over a number of years. The error in the reconstructed field is used as a design criterion for selecting design parameters for the instrument. The reconstruction error is comprised of errors due to aliasing, blurring and radiance equivalent noise of the instrument, and can be evaluated in terms of the transfer function of the system.

Manalo, N.↗

NASA NTRS1990

Surface radiation budget in the Clouds and the Earth's Radiant Energy System (CERES) effort and in the Global Energy and Water Cycle Experiment (GEWEX)

The surface radiation budget (SRB) and the atmospheric radiative flux divergence (ARD) are vital components of the weather and climate system. The importance of radiation in a complex international scientific endeavor, the GEWEX of the World Climate Research Programme is explained. The radiative transfer techniques and satellite instrumentation that will be used to retrieve the SRB and ARD later in this decade with the CERES are discussed; CERES is a component of the Earth Observing System satellite program. Examples of consistent SRB and ARD retrievals made with Nimbus-7 and International Satellite Cloud Climatology Project data from July 1983 are presented.

Charlock, Thomas P.↗

NASA NTRS1990

Estimates of radiative flux divergence in the atmosphere from satellite data

Several options for the inference of the atmospheric radiative flux divergence (ARD) on the basis of satellite data are discussed. Attention is given to the clear-sky case and the cloudy-sky case. LW ARD profiles for different climatological regimes are presented and the effect of cloud base height on LW ARD divergence at various heights is illustrated.

Smith, G. L.↗

NASA NTRS1990

A satellite retrieval of the shortwave heating of the atmosphere and the surface - Relationship to the general circulation, interannual climate variability, and the cryosphere

Data from several Nimbus-7 instruments and monthly averaged, multilayer delta-Eddington radiative transfer calculations are used to estimate the full vertical profile of the SW heating in the surface and the atmosphere. The noontime physical profile of clouds, water vapor, and surface albedo is used to compute a daily, monthly averaged top-of-atmosphere albedo (TOA), which was produced with noontime Nimbus-7 data, and a profile of SW heating for the atmosphere and surface. The daily, monthly averaged TOA albedo for July 1983 is compared with the ERBE daily, monthly averaged TOA albedo for July 1985. The sensitivity of the vertical SW heating profiles to the retrieval input assumptions is shown.

Charlock, Thomas P.↗

NASA NTRS1990

Validation of Earth Radiation Budget Experiment scanning radiometer data inversion procedures

Validation techniques were implemented in the inversion of scanner radiometer data to assess the accuracy of the top of atmosphere radiant fluxes. An evaluation of SW radiant flux standard deviations for the same scene type shows that they contribute about 6.0 W/sq m for viewing zenith angles less than 55 deg and can reach values of up to 17.6 W/sq m for larger zenith angles in the backward scanning position. Three-channel intercomparison results, presented as color graphic displays and histograms, effectively validate the radiance measurements and the spectral factors. Along-track data were used to validate limb-darkening models and showed good agreement with current ERBE models. These validation techniques were found to be very effective in assessing the quality of the radiant fluxes generated by the ERBE inversion algorithm.

Manalo, Natividad D.↗

NASA NTRS1990

Space-time variations of outgoing longwave and shortwave reflected radiation

Hovmoller diagrams are used to examine radiation variations at synoptic space and time scales. These variations are quantified statistically via the application of correlations in the time-longitude domain. In higher latitudes where the outgoing LW radiation (OLR) and the SW reflected (SWR) radiation are independent of longitude, the 2D autocorrelation function shows that the maximum characteristic lengths are in the downstream direction. These characteristic lengths provide a good measure of zonally advected atmospheric phenomena. Also from the 2D autocorrelation functions, correlation speeds were determined, which match well with mean longitudinal wind directions and speeds. This indicates that the major time-varying features advect with the flow, rather than propagating in some other fashion.

Rutan, David↗