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Sellers, P. J.

Publications and source records attributed to Sellers, P. J..

34 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

FIFE: Analysis and results - A review

This paper describes the first results of the data analysis carried out for the First International Satellite Surface Climatology Project Field Experiment (FIFE) conducted over a 15 x 15 km grasslands study area in the central United States. Preliminary results show that the energy and mass flux data collected at several diurnal cycles during different parts of the growing season are of high quality. It was found that the canopy radiometric brightness temperature measured in the 10.4-12.3 microns is linearly related to seasonal variations in canopy aerodynamic temperature, and, thus, may provide a useful measure of sensible heat flux from the surface. Airborne monitoring of the mass and heat flux in the atmospheric boundary layer were found to be adequate for studies of the energy and mass budgets above the test site.

Hall, F. G.↗
NASA NTRS1988

The first ISLSCP field experiment (FIFE)

The background and planning of the first International Satellite Land Surface Climatology Project (ISLSCP) field experiment (FIFE) are discussed. In FIFE, the NOAA series of satellites and GOES will be used to provide a moderate-temporal resolution coarse-spatial resolution data set, with SPOT and aircraft data providing the high-spatial resolution pointable-instrument capability. The paper describes the experiment design, the measurement strategy, the configuration of the site of the experiment (which will be at and around the Konza prairie near Manhattan, Kansas), and the experiment's operations and execution.

Sellers, P. J.↗
NASA NTRS1987

Extraction of spectral hemispherical reflectance (albedo) of surfaces from nadir and directional reflectance data

A radiative transfer model is used to investigate how the error of spectral hemispherical reflectance data obtained from nadir reflectance values varies with wavelength, solar zenith angle, leaf area index, and leaf orientation distribution. Several techniques employing multiple off-nadir view angles taken in azimuth planes are found to accurately infer spectral hemispherical reflectances, and to be well suited to sensor systems that scan in a known azimuth plane or view fore and aft in a known azimuth plane. The effects of errors in hemispherical reflectance on terrestrial energy budget and productivity calculations is also considered.

Kimes, D. S.↗
NASA NTRS1987

Hemispherical reflectance variations of vegetation canopies and implications for global and regional budget studies

The hemispherical reflectance (HR) variations of vegetation canopies are studied as a function of solar zenith angle, wavelength, and canopy characteristics (leaf area index, leaf orientation distribution, and leaf and soil optical properties). The radiative transfer model of Kimes (1984) is used to explain the radiative transfers that give rise to variations in the HR for various vegetation canopies as a function of sun angle. The results of this model are compared with those calculated from Sellers' (1985) analytical two-stream approximation. It is noted that the findings have significant implications for a wide range of global and regional energy budget studies.

Kimes, D. S.↗
NASA NTRS1987

Testing the Simple Biosphere model (SiB) using point micrometeorological and biophysical data

The suitability of the Simple Biosphere (SiB) model of Sellers et al. (1986) for calculation of the surface fluxes for use within general circulation models is assessed. The structure of the SiB model is described, and its performance is evaluated in terms of its ability to realistically and accurately simulate biophysical processes over a number of test sites, including Ruthe (Germany), South Carolina (U.S.), and Central Wales (UK), for which point biophysical and micrometeorological data were available. The model produced simulations of the energy balances of barley, wheat, maize, and Norway Spruce sites over periods ranging from 1 to 40 days. Generally, it was found that the model reproduced time series of latent, sensible, and ground-heat fluxes and surface radiative temperature comparable with the available data.

Sellers, P. J.↗
NASA NTRS1987

Canopy reflectance, photosynthesis, and transpiration. II - The role of biophysics in the linearity of their interdependence

The ability of satellite sensor systems to estimate area-averaged canopy photosynthetic and transpirative properties is evaluated. The near linear relationship between the simple ratio (SR) and normalized difference (ND) and the surface biophysical properties of canopy photosynthetically active radiation (PAR) absorption, photosynthesis, and bulk stomatal resistance is studied. The models utilized to illustrate the processes of canopy reflectance, photosynthesis, and resistance are described. The dependence of SR, the absorbed fraction of PAR, and canopy photosynthesis and resistance on total leaf area index is analyzed. It is noted that the SR and ND vegetation indices and vegetation-dependent qualities are near-linearly related due to the proportion of leaf scattering coefficient in visible and near IR wavelength regions. The data reveal that satellite sensor systems are useful for the estimation of photosynthesis and transpirative properties.

Sellers, P. J.↗
NASA NTRS1986

Satellite remote sensing of primary production

Leaf structure and function are shown to result in distinctive variations in the absorption and reflection of solar radiation from plant canopies. The leaf properties that determine the radiation-interception characteristics of plant canopies are directly linked to photosynthesis, stomatal resistance and evapotranspiration and can be inferred from measurements of reflected solar energy. The effects of off-nadir viewing and atmospheric constituents, coupled with the need to measure changing surface conditions, emphasize the need for multitemporal measurements of reflected radiation if primary production is to be estimated.

Tucker, C. J.↗
NASA NTRS1986

A brief description of the simple biosphere model (SiB)

A biosphere model for calculating the transfer of energy, mass, and momentum between the atmosphere and the vegetated surface of the Earth was designed for atmospheric general circulation models. An upper vegetation layer represents the perennial canopy of trees or shrubs, a lower layer represents the annual ground cover of grasses and other herbacious species. The local coverage of each vegetation layer may be fractional or complete but as the individual vegetation elements are considered to be evenly spaced, their root systems are assumed to extend uniformly throughout the entire grid-area. The biosphere has seven prognostic physical-state variables: two temperatures (one for the canopy and one for the ground cover and soil surface); two interception water stores (one for the canopy and one for the ground cover); and three soil moisture stores (two of which can be reached by the vegetation root systems and one underlying recharge layer into and out of which moisture is transferred only by hydraulic diffusion).

Sellers, P. J.↗
NASA NTRS1986

The first International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment - FIFE

The International Satellite Land Surface Climatology Project (ISLSCP) will verify the use of satellite data for the estimation of land-surface properties through field experiments using point measurements on the ground and areal measurements from aircraft overflights. It will study approaches for obtaining areal averages of the radiation, moisture, and heat fluxes made using remotely sensed data, by combining the surface point measurements of the fluxes with the aircraft areal observations using a surface energy balance model. Surface parameters to be estimated from aircraft observations include: surface radiation temperature, albedo, land cover or vegetation index, and surface soil moisture. The latter will be obtained using passive and active microwave approaches. The area-averages of the surface properties will be compared with satellite data. The First ISLSCP Field Experiment is planned for a site having relatively uniform vegetation cover in the central great plains of the U.S.A.

Schmugge, T. J.↗
NASA NTRS1986

A simple biosphere model (SiB) for use within general circulation models

A simple realistic biosphere model for calculating the transfer of energy, mass and momentum between the atmosphere and the vegetated surface of the earth has been developed for use in atmospheric general circulation models. The vegetation in each terrestrial model grid is represented by an upper level, representing the perennial canopy of trees and shrubs, and a lower level, representing the annual cover of grasses and other heraceous species. The vegetation morphology and the physical and physiological properties of the vegetation layers determine such properties as: the reflection, transmission, absorption and emission of direct and diffuse radiation; the infiltration, drainage, and storage of the residual rainfall in the soil; and the control over the stomatal functioning. The model, with prescribed vegetation parameters and soil interactive soil moisture, can be used for prediction of the atmospheric circulation and precipitaion fields for short periods of up to a few weeks.

Sellers, P. J.↗
NASA NTRS1986

The First International Satellite Land Surface Climatology Project (ISLSCP) field experiment FIFE

The purpose of ISLSCP is to verify the use of satellite data for the estimation of land-surface properties. This is to be done through a series of field experiments using a combination of point measurements on the ground and areal measurements from aircraft overflights. In addition to validating satellite estimates of surface properties, approaches for obtaining areal averages of the radiation, moisture, and heat fluxes from remotely sensed data are to be studied. The procedure for doing this is to combine the surface point measurements of the fluxes with the aircraft areal observations using a surface-energy-balance model. This should make it possible to interpolate between the point estimates of these fluxes and calculate area-averaged quantities. The surface parameters to be estimated from aircraft observations include: surface radiation temperature, albedo, land-cover or vegetation index, and surface soil moisture.

Schmugge, T. J.↗
NASA NTRS1985

Inferring hemispherical reflectance of the earth's surface for global energy budgets from remotely sensed nadir or directional radiance values

The relationship between directional reflectances spanning the entire reflecting hemisphere and hemispherical reflectance (albedo) and the effect of solar zenith angle and cover type on these relationships were investigated, using the results obtained from NOAA's 7/8 AVHRR ground-level reflectance measurements. Bands 1 (0.58-0.6B microns) and 2 (0.73-1. 1 microns) were used for reflectance measurements of 11 natural vegetation surfaces ranging from bare soils to dense vegetation canopies. The results show that errors in inferring hemispherical reflectance from nadir reflectance can be between 11 and 45 percent for all cover types and solar angles, depending on the viewing angles. A technique is described in which a choice of two specific view angles reduces this error to less than 6 percent for both bands and for all sun angles and cover types.

Kimes, D. S.↗
NASA NTRS1985

The First International Satellite Land-Surface Climatology Project (ISLSCP) Field Experiment (FIFE)

The International Satellite Land Surface Climatology Project (ISLSCP) will verify the use of satellite data for the estimation of land-surface properties through field experiments using point measurements on the ground and areal measurements from aircraft overflights. In addition to validating satellite estimates of surface properties, it studies approaches for obtaining areal averages of the radiation, moisture and heat fluxes made using remotely sensed data. The procedure suggested combines the surface point measurements of the fluxes with the aircraft areal observations using a surface energy balance model to interpolate between the point estimates of these fluxes and calculate area-averaged quantities. The surface parameters to be estimated from aircraft observations include: surface radiation temperature, albedo, land cover or vegetation index, and surface soil moisture (the latter to be obtained using passive and active microwave approaches). The area-averages of the surface properties are compared with satellite data where possible. The First ISLSCP Field Experiment is planned for l987 at a site having relatively uniform vegetation cover in the central great plains of the USA. for 1987 at a site having relatively uniform vegetation cover in the central great plains of the USA.

Schmugge, T. J.↗
NASA NTRS1983

Evaporation from a partially wet forest canopy

The results of experimental studies of water storage in a Sitka-spruce canopy are presented and analyzed in terms of model simulations of evaporation. Wet-branch cantilever deflection was measured along with meteorological data on three days in August, 1976, to determine the relationship of canopy evaporation to wind speed and (hence) aerodynamic resistance. Two versions of a simple unilayer model of sensible and latent heat transport from a partially wet canopy were tested in the data analysis: model F1 forbids the exchange of heat between wet and dry foliage surfaces; model F2 assumes that this exchange is highly efficient. Model F1 is found to give results consistent with the rainfall-interception model of Rutter et al. (1971, 1975, 1977), but model F2 gives results which are more plausible and correspond to the multilayer simulations of Sellers and Lockwood (1981) and the experimental findings of Hancock and Crowther (1979). It is inferred that the role of eddy diffusivity for water vapor is enhanced relative to momentum transport, and that the similarity hypothesis used in conventional models may fail in the near vicinity of a forest canopy.

Hancock, N. H.↗
NASA NTRS1983

On the design of an interactive biosphere for the GLAS general circulation model

Improving the realism and accuracy of the GLAS general circulation model (by adding an interactive biosphere that will simulate the transfers of latent and sensible heat from land surface to atmosphere as functions of the atmospheric conditions and the morphology and physiology of the vegetation) is proposed.

Mintz, Y.↗