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Lawless, James G.

Publications and source records attributed to Lawless, James G..

17 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

The reflection for dense plant canopies from the one-angle radiative transfer equation

An essential component of remote sensing of vegetation canopies from satellites is fundamental understanding. Since passive remote is driven by photons, the modeling of photon interactions with vegetation is a basic building block in that understanding. Several such photon transport models have been developed during the past two decades and continue to be developed. Different approaches have been followed including monte carlo, radiosity methods, geometric shadowing, and radiative transfer. In general, each approach has application for canopies with specific attributes. This presentation concerns the application of radiative transfer to dense vegetation canopies in which the soil does not participate. The approach taken here is novel in that a consistent theory for photon transport for non-rotationally invariant leaf scattering is developed in a canopy with a general leaf angle distribution (LAD). The theory is limited to the one-angle approximation (azimuthally averaged radiance) and is based on Chandrasekhar's analytical theory. While such a model is admittedly only approximate, it does fulfill a unique function in our search for understanding. In particular, the model is simple in its construct yet contains the essential features of canopy architecture that are mainly responsible for observed responses. Thus, this model will not only be a predictive tool but also an educational one. The mathematical setting is the radiative transfer equation in a dense (semiinfinite) canopy. The leaf scattering phase function is assumed to be Lambertian with different reflectance and transmittance. In addition, abaxial and adaxial differentiation is allowed which effectively destroys optical reciprocity. The analytical solution for the canopy BRDF is obtained by manipulation of the integral transport equation (a la Chandrasekhar) for a general LAD. With discretization of the. leaf angle, the resulting set of integral equations are solved iteratively including an acceleration procedure when the single scatter albedo is near one (in the NIR). Results will be compared to the LARS soybean canopy radiances as well as to broadleaf results from a recent Ames experiment.

Ganapol, B. D.↗
NASA NTRS1994

Global- to Micro-Scale Evolution of the Pinatubo Aerosol: Using Composite Data Sets to Build the Picture and Assess Consistency of Different Measurements

This paper brings together experimental. evidence required to build realistic models of the global evolution of physical, chemical, and optical properties of the aerosol resulting from the 1991 Pinatubo volcanic eruption. Such models are needed to compute the effects of the aerosol on atmospheric chemistry, dynamics, radiation, and temperature. Whereas there is now a large and growing body of post-Pinatubo measurements by a variety of techniques, some results are in conflict, and a self-consistent, unified picture is needed, along with an assessment of remaining uncertainties. This paper examines data from photometers, radiometers, impactors, optical counters/sizers, and lidars operated on the ground, aircraft, balloons, and spacecraft.

Russell, P. B.↗
NASA NTRS1994

Multiple View Zenith Angle Observations of Reflectance From Ponderosa Pine Stands

Reflectance factors (RF(lambda)) from dense and sparse ponderosa pine (Pinus ponderosa) stands, derived from radiance data collected in the solar principal plane by the Advanced Solid-State Array Spectro-radiometer (ASAS), were examined as a function of view zenith angle (theta(sub v)). RF(lambda) was maximized with theta(sub v) nearest the solar retrodirection, and minimized near the specular direction throughout the ASAS spectral region. The dense stand had much higher RF anisotropy (ma)dmurn RF is minimum RF) in the red region than did the sparse stand (relative differences of 5.3 vs. 2.75, respectively), as a function of theta(sub v), due to the shadow component in the canopy. Anisotropy in the near-infrared (NIR) was more similar between the two stands (2.5 in the dense stand and 2.25 in the sparse stand); the dense stand exhibited a greater hotspot effect than 20 the sparse stand in this spectral region. Two common vegetation transforms, the NIR/red ratio and the normalized difference vegetation index (NDVI), both showed a theta(sub v) dependence for the dense stand. Minimum values occurred near the retrodirection and maximum values occurred near the specular direction. Greater relative differences were noted for the NIR/red ratio (2.1) than for the NDVI (1.3). The sparse stand showed no obvious dependence on theta(sub v) for either transform, except for slightly elevated values toward the specular direction.

Johnson, Lee F.↗
NASA NTRS1994

Atmospheric Aerosols

Aerosols, defined as particles and droplets suspended in air, are always present in the atmosphere. They are part of the earth-atmosphere climate system, because they interact with both incoming solar and outgoing terrestrial radiation. They do this directly through scattering and absorption, and indirectly through effects on clouds. Submicrometer aerosols usually predominate in terms of number of particles per unit volume of air. They have dimensions close to the wavelengths of visible light, and thus scatter radiation from the sun very effectively. They are produced in the atmosphere by chemical reactions of sulfur-, nitrogen- and carbon-containing gases of both natural and anthropogenic origins. Light absorption is dominated by particles containing elemental carbon (soot), produced by incomplete combustion of fossil fuels and by biomass burning. Light-scattering dominates globally, although absorption can be significant at high latitudes, particularly over highly reflective snow- or ice-covered surfaces. Other aerosol substances that may be locally important are those from volcanic eruptions, wildfires and windblown dust.

Pueschel, R. F.↗
NASA NTRS1994

Plant Responses to Increased UV-B Radiation: A Research Project

Ozone decrease implies more ultraviolet-B (UV-B) radiation reaching the surface of the Earth. Increased UV-B radiation triggers responses by living organisms. Despite the large potential impacts on vegetation, little is known about UV-B effects on terrestrial ecosystems. Long-term ecological studies are needed to quantify the effects of increased UV radiation on terrestrial ecosystems, asses the risks, and produce reliable data for prediction. Screening pigments are part of one of the protective mechanism in plants. Higher concentrations of screening pigments in leaves may be interpreted as a response to increased UV radiation. If the screening effect is not sufficient, important molecules will be disturbed by incoming radiation. Thus, genetics, photosynthesis, growth, plant and leaf shape and size, and pollen grains may be affected. This will have an impact on ecosystem dynamics, structure and productivity. It is necessary to monitor selected terrestrial ecosystems to permit detection and interpretation of changes attributable to global climate change and depleted ozone shield. The objectives of this project are: (1) To identify and measure indicators of the effects of increased solar UV-B radiation on terrestrial plants; (2) to select indicators with the greatest responses to UV-B exposure; (3) to test, adapt or create ecosystem models that use the information gathered by this project for prediction and to enhance our understanding of the effects of increased UV-B radiation on terrestrial ecosystems. As a first step to achieve these objectives we propose a three-year study of forest and steppe vegetation on the North slope of the Brooks Range (within the Arctic circle, in Alaska), in the Saguaro National Monument (near Tucson, Arizona) and in the forests and steppes of Patagonia (Argentina). We selected (1) vegetation north of the Polar Circle because at 70N there is 8% risk of plant damage due to increased UV-B radiation; (2) the foothills of Catalina Mountains because there is anecdotal evidence of plant damage on the saguaros that has been linked to increased UV radiation, and (3) the forests of Nothofagus spp. and the steppe of Patagonia where the risk of plant damage at 35S is 5% and increases to as much as 15% at 55S due to increased UV-B radiation. Measurements of UV-B radiation impinging on the surface at 55S largely exceed the predicted UV-B radiation values at 50 latitude and 0% ozone depletion. Preliminary HPLC analyses of UV-B absorbing compounds in Nothofagus antartica, N. pumilio, N. betuloides and Rumex sp. in natural conditions show species-specific patterns. The spectrum of N. antartica grown at 38S differs significantly from that of N. antartica in natural conditions in Ushuaia (55S). These results suggest that the selected main area (Patagonia) is appropriate for assessing the problem and its magnitude and that Nothofagus is appropriate for our study.

DAntoni, H. L.↗
NASA NTRS1994

SIGMA: A Knowledge-Based Simulation Tool Applied to Ecosystem Modeling

The need for better technology to facilitate building, sharing and reusing models is generally recognized within the ecosystem modeling community. The Scientists' Intelligent Graphical Modelling Assistant (SIGMA) creates an environment for model building, sharing and reuse which provides an alternative to more conventional approaches which too often yield poorly documented, awkwardly structured model code. The SIGMA interface presents the user a list of model quantities which can be selected for computation. Equations to calculate the model quantities may be chosen from an existing library of ecosystem modeling equations, or built using a specialized equation editor. Inputs for dim equations may be supplied by data or by calculation from other equations. Each variable and equation is expressed using ecological terminology and scientific units, and is documented with explanatory descriptions and optional literature citations. Automatic scientific unit conversion is supported and only physically-consistent equations are accepted by the system. The system uses knowledge-based semantic conditions to decide which equations in its library make sense to apply in a given situation, and supplies these to the user for selection. "Me equations and variables are graphically represented as a flow diagram which provides a complete summary of the model. Forest-BGC, a stand-level model that simulates photosynthesis and evapo-transpiration for conifer canopies, was originally implemented in Fortran and subsequenty re-implemented using SIGMA. The SIGMA version reproduces daily results and also provides a knowledge base which greatly facilitates inspection, modification and extension of Forest-BGC.

Dungan, Jennifer L.↗
NASA NTRS1994

BIOME: An Ecosystem Remote Sensor Based on Imaging Interferometry

Until recent times, optical remote sensing of ecosystem properties from space has been limited to broad band multispectral scanners such as Landsat and AVHRR. While these sensor data can be used to derive important information about ecosystem parameters, they are very limited for measuring key biogeochemical cycling parameters such as the chemical content of plant canopies. Such parameters, for example the lignin and nitrogen contents, are potentially amenable to measurements by very high spectral resolution instruments using a spectroscopic approach. Airborne sensors based on grating imaging spectrometers gave the first promise of such potential but the recent decision not to deploy the space version has left the community without many alternatives. In the past few years, advancements in high performance deep well digital sensor arrays coupled with a patented design for a two-beam interferometer has produced an entirely new design for acquiring imaging spectroscopic data at the signal to noise levels necessary for quantitatively estimating chemical composition (1000:1 at 2 microns). This design has been assembled as a laboratory instrument and the principles demonstrated for acquiring remote scenes. An airborne instrument is in production and spaceborne sensors being proposed. The instrument is extremely promising because of its low cost, lower power requirements, very low weight, simplicity (no moving parts), and high performance. For these reasons, we have called it the first instrument optimized for ecosystem studies as part of a Biological Imaging and Observation Mission to Earth (BIOME).

Peterson, David L.↗
NASA NTRS1994

Direct Monitoring of Trace Atmospheric Species via Ion Trap Mass Spectrometry

There is an ever-increasing emphasis on the part of government agencies, academia, and industry on enhancing our understanding of atmospheric processes and assessing the impact of human activities on these processes. While issues such as the ozone hole and rising levels of greenhouse gases have received major attention. relatively little is known about the types, concentrations, sources, and sinks of hydrocarbons in the troposphere and stratosphere. Such information would be of tremendous utility in assessing the roles of various anthropogenic and biogenic processes on global carbon cycles. An ion trap mass spectrometer has been developed for monitoring trace levels of hydrocarbons in the atmosphere on NASA's DC-8 "flying laboratory". This aircraft is used to provide measurements in support of a number of "Mission to Planet Earth" activities and tropospheric chemistry experiments. In past missions, specific compounds have been monitored via highly specialized instrumentation, fast GO, or collection of whole air samples for subsequent ground-based analysis. The ion trap has several features. including small size. excellent sensitivity, and broad applicability, which make it highly atttrat:ive for atmospheric monitoring. The design of this instrument, its air sampling interface. and the various complications associated with aircraft-deployment will be described. Data showing the sensitivity of the instrument for detecting hydrocarbons at mixing ratios below one part-per-billion, and the use of MS/MS for direct, on-line, real-time monitoring will be presented.

Palmer, P. T.↗
NASA NTRS1994

Physical and Radiative Properties of Arctic Atmospheric Aerosols

Atmospheric aerosols sampled in the Arctic basin by impactors have been analyzed for the total aerosol and its black carbon fraction. The mass of black carbon aerosol in the lower troposphere is one percent (1 g black carbon in 100 g total aerosol), reduced to one part in 10(exp 4) in the stratosphere. The aerosol single scatter albedos vary between 1.0 in the stratosphere, currently dominated by high light scattering due to Pinatubo volcanic aerosol, and 0.94 in the lower troposphere. The aerosol has the potential to regionally warm the earth-atmosphere system because of the high surface albedo of snow-covered surfaces in the Arctic.

Pueschel, R. F.↗
NASA NTRS1994

Advanced Automation for Ion Trap Mass Spectrometry-New Opportunities for Real-Time Autonomous Analysis

The utility of MS/MS for both target compound analysis and the structure elucidation of unknowns has been described in a number of references. A broader acceptance of this technique has not yet been realized as it requires large, complex, and costly instrumentation which has not been competitive with more conventional techniques. Recent advancements in ion trap mass spectrometry promise to change this situation. Although the ion trap's small size, sensitivity, and ability to perform multiple stages of mass spectrometry have made it eminently suitable for on-line, real-time monitoring applications, advance automation techniques are required to make these capabilities more accessible to non-experts. Towards this end we have developed custom software for the design and implementation of MS/MS experiments. This software allows the user to take full advantage of the ion trap's versatility with respect to ionization techniques, scan proxies, and ion accumulation/ejection methods. Additionally, expert system software has been developed for autonomous target compound analysis. This software has been linked to ion trap control software and a commercial data system to bring all of the steps in the analysis cycle under control of the expert system. These software development efforts and their utilization for a number of trace analysis applications will be described.

Palmer, Peter T.↗
NASA NTRS1994

Low Ozone in the Marine Boundary Layer of the Tropical Pacific Ocean

Aircraft measurements of ozone, its key precursors, and a variety of chemical tracers were made in the troposphere of the western and central Pacific in October 1991. These data are presented and analyzed to examine the occurrence of low ozone concentrations in the remote marine boundary layer of the tropical and equatorial Pacific Ocean. The data from these flights out of Guam, covering an area extending from the equator to 20 N and from south of the Philippines to Hawaii, show average O3 concentrations as low as 8-9 ppb (ppb=10(exp-9)v/v) at altitudes of 0.3-0.5 km in the boundary layer. Individual measurements as low as 2-5 ppb were recorded. Low O3 concentrations do not always persist in space and time. High O3, generally associated with the transport of upper tropospheric air, was also encountered in the boundary layer. In practically all cases, O3 increased to values as large as 25-30 ppb within 2 km above the boundary layer top. Steady state model computations are used to suggest that these low O3 concentrations are a result of net photochemical O3 destruction in a low NO environment, sea-surface deposition, and extremely low net entrainment rates (1-2 mm per second) from the free troposphere. Day/night measurements of ethane, propane, gaseous and aerosol Cl suggest that daytime (morning) Cl atom concentrations in the vicinity of 10(exp 5) molecules per cubic centimeter may be present in the marine boundary layer. This Cl atom abundance can be rationalized only if sea salt aerosols can release free chlorine (Cl2) to the gas phase in the presence of sun light (and possibly O3). These Cl atom concentrations, however, are still insufficient and Cl (or Br) chemistry is not likely to be an important cause of the observed low O3.

Singh, Hanwant B.↗
NASA NTRS1994

Pinatubo Aerosol Evolution: Using Composite Data Sets to Build the Global- To Micro-Scale Picture and Assess Consistency of Different Measurements

This paper brings together experimental evidence required to build realistic models of the global evolution of physical, chemical, and optical properties of the aerosol resulting from the 1991 Pinatubo volcanic eruption. Such models are needed to compute the effects of the aerosol on atmospheric chemistry, dynamics, radiation, and temperature. Whereas there is now a large and crowing body of post-Pinatubo measurements by a variety of techniques, some results are in conflict, and a self-consistent, unified picture is needed, along with an assessment of remaining uncertainties. This paper examines, data from photometers, radiometers, impactors, optical counter/sizers, and lidars operated on the ground, aircraft, balloons, and spacecraft. Example data sources include: (1) Tracking sunphotometers and lidars at Mauna Loa Observatory (MLO) and on the DC-8. (2) Particle spectrometers and wire impactors on the ER-2 and DC-8. (3) Dustsondes (particle counter/sizers on balloons). and (3) SAGE II, SAM II, AVHRR, CLAES, and ISAMS sensors on a variety of satellites. We assess the mutual consistency of these disparate data sets and recommend 'consensus' properties and uncertainties in the process of developing a composite data set. Recommended properties include the spatial and temporal evolution of particle chemical composition, shape, wavelength-and temperature-dependent refractive index, size distribution, and optical depth spectra. Supporting references are cited and representative data shown.

Russell, Philip B.↗
NASA NTRS1994

Environmental Perturbations Caused by the Impacts of Comets and Asteroids on Earth

The extinction mechanisms proposed at the Cretaceous-Tertiary geological boundary are reviewed and related to the impact of asteroids or comets in general. For impact energies below 10(exp 4) Megatons (less than 6 x 10(exp 4) years; asteroid diameter less than 650 m), blast, earthquake, and fire may destroy local areas up to 10(exp 5) square m. Tidal waves could flood a kilometer inland over entire ocean basins. The energy range from 105 to 106 Megatons (less than 2 x 10(exp 6) years; asteroid diameter less than 3 km) is transitional. Dust lifted, sulfur released from within impacting asteroids, and soot from fires started by comets can produce climatologically significant optical depths of 10. At energies beyond 10(exp 7) Megatons, blast and earthquake damage is regional (10(exp 6) square cm). Tsunami cresting to 100 m and flooding 20 km inland will sweep the coastal zones of the world's oceans. Fires will be set globally. Light levels may drop so low from the smoke, dust and sulfate that vision is not possible. At energies approaching 10(exp 9) Megatons the ocean surface waters may be acidified by sulfur. The combination of these effects would be devastating.

Toon, Owen B.↗
NASA NTRS1991

Status report on the land processes aircraft science management operations working group

Since its inception three years ago, the Land Processes Aircraft Science Management Operations Working Group (MOWG) provided recommendations on the optimal use of the Agency's aircraft in support of the Land Processes Science Program. Recommendations covered topics such as aircraft and sensor usage, development of long-range plans, Multisensor Airborne Campaigns (MAC), program balance, aircraft sensor databases, new technology and sensor development, and increased University scientist participation in the program. Impacts of these recommendations improved the efficiency of various procedures including the flight request process, tracking of flight hours, and aircraft usage. The group also created a bibliography focused on publications produced by Land Processes scientists from the use of the aircraft program, surveyed NASA funded PI's on their participation in the aircraft program, and developed a planning template for multi-sensor airborne campaigns. Benefits from these activities are summarized.

Lawless, James G.↗
NASA NTRS1988

Physical/chemical closed-loop life support

Information on physical/chemical closed-loop life support systems are given in viewgraph form. Information is given on program objectives, the elements of a life support system, and Pathfinder program elements.

Lawless, James G.↗
NASA NTRS1984

Global Biology: An Interdisciplinary Scientific Research Program at NASA Ames Research Center

NASA has initiated new effort in Global Biology, the primary focus of which is to understand biogeochemical cycles. As part of this effort, an interdisciplinary team of scientists has formed at Ames Research Center to investigate the cycling of sulfur in the marine coastal zone and to study the cycling of nitrogen in terrestrial ecosystems. Both studies will use remotely sensed data, coupled with ground-based research, to identify and measure the transfer of major and minor biologically produced gases between these ecosystems and global reservoirs.

Lawless, James G.↗