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Results for “canopy conductance”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Shortwave infrared detection of vegetation

The potential of short wave infrared (SWIR) measurements in vegetation discrimination is further substantiated through a discussion of field studies and an examination of the physical bases which cause SWIR measurements to vary with the vegetation type observed. The research reported herein supported the AGRISTARS program objective to incorporate TM measurements in the analysis of agricultural activity. Field measurements on corn and soybeans in Iowa were conducted, and the mean and variance of canopy reflectance were computed for each observation date. The Suits canopy reflectance model was used to evaluate possible explanations of the observed corn/soybeans reflectance patterns /39/. The SWIR measurements were shown to effectively discriminate corn and soybeans on the basis of leaf absorption properties.

Goward, S. N.↗
NASA NTRS2013

Integrating Solar Induced Fluorescence and the Photochemical Reflectance Index for Estimating Gross Primary Production in a Cornfield

The utilization of remotely sensed observations for light use efficiency (LUE) and tower-based gross primary production (GPP) estimates was studied in a USDA cornfield. Nadir hyperspectral reflectance measurements were acquired at canopy level during a collaborative field campaign conducted in four growing seasons. The Photochemical Reflectance Index (PRI) and solar induced chlorophyll fluorescence (SIF), were derived. SIF retrievals were accomplished in the two telluric atmospheric oxygen absorption features centered at 688 nm (O2-B) and 760 nm (O2-A). The PRI and SIF were examined in conjunction with GPP and LUE determined by flux tower-based measurements. All of these fluxes, environmental variables, and the PRI and SIF exhibited diurnal as well as day-to-day dynamics across the four growing seasons. Consistent with previous studies, the PRI was shown to be related to LUE (r2 = 0.54 with a logarithm fit), but the relationship varied each year. By combining the PRI and SIF in a linear regression model, stronger performances for GPP estimation were obtained. The strongest relationship (r2 = 0.80, RMSE = 0.186 mg CO2/m2/s) was achieved when using the PRI and SIF retrievals at 688 nm. Cross-validation approaches were utilized to demonstrate the robustness and consistency of the performance. This study highlights a GPP retrieval method based entirely on hyperspectral remote sensing observations.

cornfield↗
NASA NTRS1974

Influence of configuration details on the subsonic characteristics of a space shuttle orbiter design

An investigation was conducted in the Langley low-turbulence pressure tunnel of a model of a space shuttle orbiter design in order to determine the influence of minor configuration geometric details on the aerodynamic characteristics at subsonic speeds. A plane wing was tested with a small planform fillet; a twisted wing was tested with both a small and a large planform fillet. Tailored attitude-control propulsion-system wing-tip and body pods, trisegmented elevons, and canopy effects were also investigated. The tests were conducted at angles of attack from -3 deg to 24 deg for sideslip angles of 0 deg and 6 deg and at a Mach number of 0.25.

Decker, J. P.↗
NASA NTRS1993

Estimation of surface heat and moisture fluxes over a prairie grassland. IV - Impact of satellite remote sensing of slow canopy variables on performance of a hybrid biosphere model

Numerical experiments are conducted using the Ex-BATS model of Crosson and Weng (1993), which is an adaptation the Dickinson (1983, 1984) and Dickinson et al. (1986) biosphere model BATS. The purpose of these experiments is the assessment of the Ex-BATS performance when using remotely sensed data for the estimation of three key canopy variables retrieved from NOAA-AVHRR measurements: the total surface albedo, the leaf area index (LAI), and the nondiurnally varying component of stomatal resistance, r(s). The results of the simulations, which cover the entire FIFE 1987 time period, show that the satellite retrievals of r(s) are only 20 to 30 percent less accurate than the idealized results of the control experiment. The performance of the model which used satellite retrieval of the surface albedo and LAI was essentially equivalent to the hypothetical version.

Crosson, William L.↗
NASA NTRS1971

Static and dynamic load measurements in aerospace decelerator canopy fabrics with metal foil strain gages.

A test program was conducted to determine the feasibility of using conventional metal foil strain gages to measure load-time relationships on thin fabric membranes while these membranes were loaded under simulated aerodynamic decelerator conditions. Uniaxial and biaxial tests were made at fabric strain levels up to about 10%. Loadings were made both statically and dynamically, with the fastest load time being 0.015 second for zero to full load on uniaxial test specimens. For the biaxial tests, plane strain conditions were assumed, and by using experimentally determined strain-load relationships, principal loads were determined from the perpendicularly oriented strain-gage pairs. Although the complex stress-strain behavior of decelerator fabrics prevents the attainment of normally expected strain-gage accuracy, utilization of the techniques described can lead to meaningful measurements for the decelerator stress analyst.

Hoffman, I. S.↗
NASA NTRS1984

Steady state stresses in ribbon parachute canopies

An experimental study of the steady state stresses in model ribbon parachute canopies is presented. The distribution of circumferential stress was measured in the horizontal ribbons of two parachutes using Omega sensors. Canopy pressure distributions and overall drag were also measured. Testing was conducted in the University of Minnesota Low-Speed Wind Tunnel at dynamic pressures ranging from 1.0 to 1.5 inches of water. The stresses in the parachute canopies were calculated using the parachute structural analysis code, CANO. It was found that the general shape of the measured and calculated stress distributions was fairly similar; however, the measured stresses were somewhat less than the calculated stresses.

Garrard, W. L.↗
NASA NTRS1984

Transonic wind-tunnel investigation of the Galileo Probe parachute configuration

Wind-tunnel tests have been made of 1/4-scale and 1/2-scale models of the Galileo Probe conical ribbon-parachute at flight conditions. For the Galileo mission, the parachute is deployed behind a blunt shape at transonic speed. The investigation was initiated to verify the solutions to the delayed main-parachute opening with squidding that was observed in the 1982 Galileo Probe system balloon drop test. In addition to varying model scale, the forebody shape, angle of attack, dynamic pressure, Mach number, and canopy trailing distance behind the forebody were varied to determine their effect on parachute performance. Both steady-state and deployment tests were conducted. Parachute drag was measured and was seen to degrade severely at canopy trailing distances of 5.5 and 7 forebody diameters. Performance was shown to be good at the trailing distances of 9 and 11 diameters. A second balloon drop test demonstrated the desired parachute performance at the system level.

Corridan, R. E.↗
NASA NTRS1973

Advances in modeling aerodynamic decelerator dynamics.

The Viking entry vehicle uses a lines-first type of deployment in which the parachute, packed in a deployment bag, gets ejected rearward from the vehicle by a mortar. As the bag moves rearward, first the lines are unfurled and then the canopy. An analysis of the unfurling process is conducted, giving attention to longitudinal and rotational dynamics. It is shown that analytical modeling of aerodynamic systems provides significant information for a better understanding of the physics of the deployment process.

Whitlock, C. H.↗
NASA NTRS1982

Review of approaches to the investigation of the scattering properties of material media

An attempt is made to identify gaps in the current understanding of the backscattering properties of natural media, with attention both to fundamental questions which relate to the physics of scattering from such media, and applications-related considerations of the extraction of data of interest to the user from a given sensor image output. It is suggested that experiments be conducted, and models developed, for the areas of canopy constituents' dielectric and attenuation properties, volume geometry, and emission characteristics, as well as backscattering properties.

Ulaby, F. T.↗
NASA NTRS1948

Experimental Pressure Distribution on Fuselage Nose and Pilot Canopy of Supersonic Airplane at Mach Number 1.90

An investigation of the pressure distribution on the fuselage nose and the pilot canopy of a supersonic airplane model has been conducted at a Mach number of 1.90 over a wide range of angles of attack and yaw. Boundary layer separation apparently occurred from the upper surface at angles of attack above 24 degrees and from the lower surface at minus 15 degrees. No separation from the sides of the fuselage was evident at yaw angles up to 12 degrees.

Wyatt, DeMarquis D.↗
NASA NTRS1980

Thermography for estimating near-surface soil moisture under developing crop canopies

Previous investigations of thermal infrared techniques using remote sensors (thermography) for estimating soil water content have been limited primarily to bare soil. Ground-based and aircraft investigations were conducted to evaluate the potential for extending the thermography approach to developing crop canopies. A significant exponential relationship was found between the volumetric soil water content in the 0-4 cm soil layer and the diurnal difference between surface soil temperature measured at 0230 and 1330 LST (satellite overpass times of NASA's Heat Capacity Mapping Mission - HCMM). Surface soil temperatures were estimated using minimum air temperature, percent cover of the canopy and remote measurements of canopy temperature. Results of the investigation demonstrated that thermography can potentially be used to estimate soil temperature and soil moisture throughout a complete growing season for a number of different crops and soils.

Heilman, J. L.↗
NASA NTRS1991

A fully polarimetric scattering model for a coniferous forest

For an elliptically polarized plane wave exciting a coniferous forested canopy a fully polarimetric scattering model has been developed to account for the size and orientation distributions of each forest constituent. A canopy is divided into three layers over a rough interface. The upper two layers represent the crown with its constituents (leaves, stems, and branches). The lower layer stands for the trunks and the rough interface is the canopy-ground interface. For a plane wave exciting the canopy, the explicit expressions for the bistatic scattering coefficient associated with each scattering mechanism are given. For an elliptically polarized incidence wave, the present model can be recast in a form suitable for polarimetric wave synthesis. The model validation is justified by comparing the measured and the calculated values of the backscattering coefficients for a linearly polarized incident wave. The comparison is made over a wide range of frequencies and incident angles. Numerical simulations are conducted to calculate the radar polarization signature of the canopy for different incident frequencies and angles.

Karam, M. A.↗
NASA NTRS1980

Experimental relations between airborne and ground measured wheat canopy temperatures

Experiments using ground-based measurements of canopy temperatures have shown that plant temperatures are good indicators of plant water stress, and thus are useful for assessing water requirements and predicting yields. An intensive 23-day airborne- and ground-measurement program was conducted in Phoenix, Arizona in 1977 to compare airborne-acquired wheat canopy temperatures with simultaneous ground measurements. For canopies that covered at least 85 percent of the soil surface, airborne measurements differed from ground measurements of plant temperature by less than 2 C. Regardless of the amount of plant cover, the airborne measurements were virtually identical to ground-nadir measurements, and thus represent a combination of plant temperature and solid background temperature.

Millard, J. P.↗
NASA NTRS2022

Yonkers Urban Development II: Leveraging NASA Earth Observations to Support Modeling Urban Cooling Interventions and Urban Heat Vulnerability in Yonkers, New York

The City of Yonkers, New York, located in Westchester County, is experiencing rising temperatures which are a growing threat to the health and safety of its residents. Furthermore, the risk of heat-related illnesses and mortality disproportionately affects neighborhoods in Yonkers historically subjected to race-based housing segregation. To better understand these inequities, Groundwork Hudson Valley and NASA DEVELOP collaborated for a second term to evaluate community-level heat vulnerability, landcover distribution, street-level thermal comfort, and modeled urban cooling interventions. This team applied 2019 5-year American Community Survey (ACS) data and social and biophysical heat vulnerability variables established by the New York State Department of Health (NYSDOH), along with land surface temperature (LST) data collected from Landsat 8 Thermal Infrared Sensor (TIRS), and ISS ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) to identify communities in Yonkers in need of prioritized cooling intervention at the census tract level. Data from the Real-Time Mesoscale Analysis (RTMA) provided relevant meteorological data for the ENVI-met model to conduct street-level thermal observations and model tree canopy cooling interventions in the Yonkers neighborhoods of Kimball and Old 7th Ward. The project results will support the prioritization and equitable distribution of cooling infrastructure in identified neighborhoods. Additionally, Groundwork Hudson Valley will use the analyses as a heat literacy tool to improve advocacy efforts and inform both residents and officials about how investment in deliberate modification to tree canopy cover improves the city’s thermal environment and helps mitigate extreme heat.

Tamara Barbakova↗
NASA NTRS1986

Effects of nitrogen fertilization on growth and reflectance characteristics of winter wheat

The use of remote sensing to determine seasonal changes in agronomic and spectral properties of winter wheat canopies with different levels of N fertilization is investigated. Field experiments were conducted at Purdue Agronomy Farm, West Lafayette, IN during the 1978-1979 and 1979-1980 growing season. Spectral reflectance, total leaf N concentration, leaf chlorophyll concentration, leaf are index (LAI), and fresh and dry phytomass are measured and analyzed. Three distinct wheat canopies are detected for the O, 60, and 120 kg N/ha levels of fertilization; it is observed that with an increase in N the reflectance in the visible, and middle IR wavelengths decrease, and the IR reflectance is increased. The canopies with 120 kg N/ha display the highest LAI, maintain green leaf area the longest, and increase in fresh and dry phytomass. The relationship between spectral and agronomic variables is examined; the effect of changing chlorophyll concentration and LAI on the reflectance is studied.

Hinzman, L. D.↗
NASA NTRS2012

The Photochemical Reflectance Index from Directional Cornfield Reflectances: Observations and Simulations

The two-layer Markov chain Analytical Canopy Reflectance Model (ACRM) was linked with in situ hyperspectral leaf optical properties to simulate the Photochemical Reflectance Index (PRI) for a corn crop canopy at three different growth stages. This is an extended study after a successful demonstration of PRI simulations for a cornfield previously conducted at an early vegetative growth stage. Consistent with previous in situ studies, sunlit leaves exhibited lower PRI values than shaded leaves. Since sunlit (shaded) foliage dominates the canopy in the reflectance hotspot (coldspot), the canopy PRI derived from field hyperspectral observations displayed sensitivity to both view zenith angle and relative azimuth angle at all growth stages. Consequently, sunlit and shaded canopy sectors were most differentiated when viewed along the azimuth matching the solar principal plane. These directional PRI responses associated with sunlit/shaded foliage were successfully reproduced by the ACRM. As before, the simulated PRI values from the current study were closer to in situ values when both sunlit and shaded leaves were utilized as model input data in a two-layer mode, instead of a one-layer mode with sunlit leaves only. Model performance as judged by correlation between in situ and simulated values was strongest for the mature corn crop (r = 0.87, RMSE = 0.0048), followed by the early vegetative stage (r = 0.78; RMSE = 0.0051) and the early senescent stage (r = 0.65; RMSE = 0.0104). Since the benefit of including shaded leaves in the scheme varied across different growth stages, a further analysis was conducted to investigate how variable fractions of sunlit/shaded leaves affect the canopy PRI values expected for a cornfield, with implications for 20 remote sensing monitoring options. Simulations of the sunlit to shaded canopy ratio near 50/50 +/- 10 (e.g., 60/40) matching field observations at all growth stages were examined. Our results suggest in the importance of the sunlit/shaded fraction and canopy structure in understanding and interpreting PRI.

Cheng, Yen-Ben↗
NASA NTRS2011

Canopy Spectral Invariants: Application to Classification of Forest Types from Hyperspectral Data - Part 2

Many studies have been conducted to demonstrate the ability of hyperspectral data to discriminate plant dominant species. Most of them have employed the use of empirically based techniques, which are site specific, requires some initial training based on characteristics of known leaf and/or canopy spectra and therefore may not be extendable to operational use or adapted to changing or unknown land cover. In this paper we propose a physically based approach for separation of dominant forest type using hyperspectral data. The radiative transfer theory of canopy spectral invariants underlies the approach, which facilitates parameterization of the canopy reflectance in terms of the leaf spectral scattering and two spectrally invariant and structurally varying variables - recollision and directional escape probabilities. The methodology is based on the idea of retrieving spectrally invariant parameters from hyperspectral data first, and then relating their values to structural characteristics of three-dimensional canopy structure. Theoretical and empirical analyses of ground and airborne data acquired by Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) over two sites in New England, USA, suggest that the canopy spectral invariants convey information about canopy structure at both the macro- and micro-scales. The total escape probability (one minus recollision probability) varies as a power function with the exponent related to the number of nested hierarchical levels present in the pixel. Its base is a geometrical mean of the local total escape probabilities and accounts for the cumulative effect of canopy structure over a wide range of scales. The ratio of the directional to the total escape probability becomes independent of the number of hierarchical levels and is a function of the canopy structure at the macro-scale such as tree spatial distribution, crown shape and size, within-crown foliage density and ground cover. These properties allow for the natural separation of dominant forest classes based on the location of points on the total escape probability vs the ratio log-log plane.

Schull, M. A.↗
NASA NTRS1999

Effects of CO2 on stomatal conductance: do stomata open at very high CO2 concentrations?

Potato and wheat plants were grown for 50 d at 400, 1000 and 10000 micromoles mol-1 carbon dioxide (CO2). and sweetpotato and soybean were grown at 1000 micromoles mol-1 CO2 in controlled environment chambers to study stomatal conductance and plant water use. Lighting was provided with fluorescent lamps as a 12 h photoperiod with 300 micromoles m-2 s-1 PAR. Mid-day stomatal conductances for potato were greatest at 400 and 10000 micromoles mol-1 and least at 1000 micromoles mol-1 CO2. Mid-day conductances for wheat were greatest at 400 micromoles mol-1 and least at 1000 and 10000 micromoles mol-1 CO2. Mid-dark period conductances for potato were significantly greater at 10000 micromoles mol-1 than at 400 or 1000 micromoles mol-1, whereas dark conductance for wheat was similar in all CO2 treatments. Temporarily changing the CO2 concentration from the native 1000 micromoles mol-1 to 400 micromoles mol-1 increased mid-day conductance for all species, while temporarily changing from 1000 to 10000 micromoles mol-1 also increased conductance for potato and sweetpotato. Temporarily changing the dark period CO2 from 1000 to 10000 micromoles mol-1 increased conductance for potato, soybean and sweetpotato. In all cases, the stomatal responses were reversible, i.e. conductances returned to original rates following temporary changes in CO2 concentration. Canopy water use for potato was greatest at 10000, intermediate at 400, and least at 1000 micromoles mol-1 CO2, whereas canopy water use for wheat was greatest at 400 and similar at 1000 and 10000 micromoles mol-1 CO2. Elevated CO2 treatments (i.e. 1000 and 10000 micromoles mol-1) resulted in increased plant biomass for both wheat and potato relative to 400 micromoles mol-1, and no injurious effects were apparent from the 10000 micromoles mol-1 treatment. Results indicate that super-elevated CO2 (i.e. 10000 micromoles mol-1) can increase stomatal conductance in some species, particularly during the dark period, resulting in increased water use and decreased water use efficiency.

NASA Discipline Life Support Systems↗