James A. Smith

Johns Hopkins University, Baltimore, Maryland, United States

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Publications (21)22.79 Total impact

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    ABSTRACT: In this paper, we present our first results towards understanding high temporal frequency thermal infrared response from a dense grass canopy. The model is driven by slowly varying, time-averaged meteorological conditions and by high frequency measurements of local and within canopy profiles of relative humidity and wind speed, and compared to high frequency thermal infrared observations. Previously, we have employed three-dimensional ray tracing to compute the intercepted and scattered solar and IR radiation fluxes and for final scene rendering. For the turbulent fluxes, simple resistance models for latent and sensible heat with one-dimensional profiles of relative humidity and wind speed are used. Our modeling approach has proven successful in capturing the directional and diurnal variation in background thermal infrared signatures. We hypothesize that at these scales, where the model is typically driven by time-averaged, local meteorological conditions, the primary source of thermal variance arises from the spatial distribution of sunlit and shaded foliage elements within the canopy and the associated radiative interactions. In recent experiments, we have begun to focus on the high temporal frequency response of plant canopies in the thermal infrared at 1 sec to 5 min intervals. At these scales, we hypothesize turbulent mixing plays a more dominant role. Our results indicate that in the high frequency domain, the vertical profile of temperature change is tightly coupled to the within canopy wind speed. In the results reported here, the canopy cools from the top down with increased wind velocities and heats from the bottom up at low wind velocities.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
    No preview · Article · Aug 2004
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    ABSTRACT: This report reviews, evaluates, and recommends atmospheric, environmental, and geophysical models that use physics to aid in understanding the impact that the natural environment has on the sensors that are commonly applied to the mine detection problem (either surface or buried). The report lists important predictive high-resolution atmospheric, environmental, and geophysical models. Priority models are evaluated to indicate their strengths and weaknesses. The report recommends areas needing further development to fill the gaps in predicting the effects of critical environmental factors on developing mine detection sensors.
    Full-text · Article · Feb 2004
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    Ballard · Jerrell R · James A. Smith · George G. Koenig
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    ABSTRACT: In this paper, we present our first results towards understanding high temporal frequency thermal infrared response from a dense plant canopy and compare the application of our model, driven both by slowly varying, time-averaged meteorological conditions and by high frequency measurements of local and within canopy profiles of relative humidity and wind speed, to high frequency thermal infrared observations. Previously, we have employed three-dimensional ray tracing to compute the intercepted and scattered radiation fluxes and for final scene rendering. For the turbulent fluxes, we employed simple resistance models for latent and sensible heat with one-dimensional profiles of relative humidity and wind speed. Our modeling approach has proven successful in capturing the directional and diurnal variation in background thermal infrared signatures. We hypothesize that at these scales, where the model is typically driven by time-averaged, local meteorological conditions, the primary source of thermal variance arises from the spatial distribution of sunlit and shaded foliage elements within the canopy and the associated radiative interactions. In recent experiments, we have begun to focus on the high temporal frequency response of plant canopies in the thermal infrared at 1 second to 5 minute intervals. At these scales, we hypothesize turbulent mixing plays a more dominant role. Our results indicate that in the high frequency domain, the vertical profile of temperature change is tightly coupled to the within canopy wind speed In the results reported here, the canopy cools from the top down with increased wind velocities and heats from the bottom up at low wind velocities. .
    Full-text · Article · Feb 2004 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: We compare images from the Enhanced Thematic Mapper Plus (ETM+) sensor on Landsat-7 and the Advanced Land Imager (ALI) instrument on Earth Observing One (EO-1) over a test site in Rochester, New York. The site contains a variety of features, ranging from water of varying depths, deciduous/coniferous forest, and grass fields, to urban areas. Nearly coincident cloud-free images were collected one minute apart on 25 August 2001. We also compare images of a forest site near Howland, Maine, that were collected on 7 September, 2001. We atmospherically corrected each pair of images with the Second Simulation of the Satellite Signal in the Solar Spectrum (6S) atmosphere model, using aerosol optical thickness and water vapor column density measured by in situ Cimel sun photometers within the Aerosol Robotic Network (AERONET), along with ozone density derived from the Total Ozone Mapping Spectrometer (TOMS) on the Earth Probe satellite. We present true-color composites from each instrument that show excellent qualitative agreement between the multispectral sensors, along with grey-scale images that demonstrate a significantly improved ALI panchromatic band. We quantitatively compare ALI and ETM+ reflectance spectra of a grassy field in Rochester and find < or equal to 6% differences in the visible/near infrared and approx. 2% differences in the short wave infrared. Spectral comparisons of forest sites in Rochester and Howland yield similar percentage agreement except for band 1, which has very low reflectance. Principal component analyses and comparison of normalized difference vegetation index histograms for each sensor indicate that the ALI is able to reproduce the information content in the ETM+ but with superior signal-to-noise performance due to its increased 12-bit quantization.
    No preview · Article · Feb 2004 · Optical Engineering
  • Ballard · Jerrell R · James A. Smith
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    ABSTRACT: The tree canopy characterization presented herein provided ground and tree canopy data for different types of tree canopies in support of EO-1 reflective and thermal infrared validation studies. These characterization efforts during August and September of 2001 included stem and trunk location surveys, tree structure geometry measurements, meteorology, and leaf area index (LAI) measurements. Measurements were also collected on thermal and reflective spectral properties of leaves, tree bark, leaf litter, soil, and grass. The data presented in this report were used to generate synthetic reflective and thermal infrared scenes and images that were used for the EO-1 Validation Program. The data also were used to evaluate whether the EO-1 ALI reflective channels can be combined with the Landsat-7 ETM+ thermal infrared channel to estimate canopy temperature, and also test the effects of separating the thermal and reflective measurements in time resulting from satellite formation flying.
    No preview · Article · Oct 2002
  • Jr. Jerrell R. Ballard · James A. Smith
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    ABSTRACT: This paper describes our hyperspectral reflectance modeling of a forest canopy based on measured input parameters and comparison with Earth Observing - 1 (EO-1) Advanced Land Imager (ALI) and Hyperion data. The model uses a high resolution, three-dimensional (3D) ray-tracing approach to estimate the intercepted and scattered solar radiation at multiple narrow wavelength bands. We present the comparisons of the effects of woody biomass, leaf litter, and clumping on reflectance signatures. The experimental data used for the model were collected in a hardwood forest canopy in Rochester, New York. Model calculations also are compared to a more simplified, low-resolution D model and a simple, multi-layer differential equation model.
    No preview · Article · Aug 2002 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: We present a comparison of images from the ETM+ sensor on Landsat-7 and the ALI instrument on EO-1 over a test site in Rochester, NY. The site contains a variety of features, ranging from water of varying depths, deciduous/coniferous forest, grass fields, to urban areas. The nearly coincident cloud-free images were collected just one minute apart on 25 August, 2001. We atmospherically corrected each image with the 6S atmosphere model, using aerosol optical thickness and water vapor column density measured by a Cimel sun photometer within the Aerosol Robotic Network (Aeronet), along with ozone density derived from NCEP data. We present three-color composites from each instrument that show excellent qualitative agreement. We present ETM+ and ALI reflectance spectra for water, grass, and urban targets. We make a more detailed comparison for our forest site, where we use measured geometric and optical properties as input to the SAIL canopy reflectance model, which we compare to the ETM+, ALI, and EO-1 Hyperion reflectance spectra.
    No preview · Article · Aug 2002 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: Independent component analysis (ICA) has shown success in blind source separation and channel equalization. Its applications to remotely sensed images have been investigated in recent years. Linear spectral mixture analysis (LSMA) has been widely used for subpixel detection and mixed pixel classification. It models an image pixel as a linear mixture of materials present in an image where the material abundance fractions are assumed to be unknown and nonrandom parameters. This paper considers an application of ICA to the LSMA, referred to as ICA-based linear spectral random mixture analysis (LSRMA), which describes an image pixel as a random source resulting from a random composition of multiple spectral signatures of distinct materials in the image. It differs from the LSMA in that the abundance fractions of the material spectral signatures in the LSRMA are now considered to be unknown but random independent signal sources. Two major advantages result from the LSRMA. First, it does not require prior knowledge of the materials to be used in the linear mixture model, as required for the LSMA. Second, and most importantly, the LSRMA models the abundance fraction of each material spectral signature as an independent random signal source so that the spectral variability of materials can be described by their corresponding abundance fractions and captured more effectively in a stochastic manner
    Full-text · Article · Mar 2002 · IEEE Transactions on Geoscience and Remote Sensing
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    ABSTRACT: Data assimilation methods applied to hydrologic models can incorporate spatially distributed maps of near surface temperature, especially if such measurements can be reliably inferred from satellite observations. Uncalibrated thermal IR imagery sometimes is scaled to temperature units to obtain such observations using the assumption that dense forest canopies are close to air temperature. For fully leafed deciduous forest canopies in the summer, this approximation is usually valid within 2C. In a leafless canopy, however, the materials views are thick boles and branches and the forest floor, which can store heat and yield significantly higher variations. Winter coniferous forests are intermediate with needles and branches being the predominant viewed materials. The US Dept of Energy's Multispectral Thermal Imager (MTI) is an experimental satellite with the capability to perform quantitative scene measurements in the reflective and thermal infrared region respectively. Its multispectral thermal IR capability enables quantitative surface temperature retrieval if pixel emissivity is known. MTI is pointable and targets multiple times in the winter and spring of 2001 at the Howland, Maine AmeriFlux research site operated by the University of Maine. Supporting meteorological and optical depth measurements also were made from three towers at the site. Directional thermal models of forest woody materials and needles are driver by the surface measurements and compared to satellite data to help evaluate the relationship between air temperature and satellite thermal measurements as a function of look angles, day and night.
    No preview · Article · Jan 2002 · Proceedings of SPIE - The International Society for Optical Engineering
  • James A. Smith · Ballard, Jerrell R., Jr
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    ABSTRACT: For simple homogeneous canopies, we predict canopy thermal infrared hot spot variations of 2 degreesC at the surface with respect to nadir viewing. Dependence on leaf size is weak as long as the ratio of leaf size to canopy height is maintained. However, the angular width of the hot spot increases as the ratio of leaf diameter to canopy height increases. Atmospheric effects minimize but do not eliminate the TIR hot spot at satellite altitudes. (C) 2001 society of Photo-Optical Instrumentation Engineers.
    No preview · Article · Aug 2001 · Optical Engineering
  • James A. Smith · S.M. Goltz
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    ABSTRACT: The authors describe a simple model to calculate brightness temperature and surface-energy balance for a forest-canopy system. The root mean-square (RMS) error in brightness temperature was 2.5°C. The corresponding RMS errors for net radiation, latent, and sensible heat were 38.9, 30.7, and 41.1 W m<sup>-2</sup> respectively
    No preview · Article · Dec 1999 · IEEE Transactions on Geoscience and Remote Sensing
  • James A. Smith · Jerrell R. Ballard
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    ABSTRACT: Satellite observations of agricultural and other plant canopies in the thermal and near IR regime have generally been at spatial scales of tens to hundreds of meters. Advances in sensor technology will extend our capabilities for IR measurements from space to yield improved spatial resolutions. We explore the variability in brightness temperature and the covariation of the normalized difference vegetation index (NDVI) with brightness temperature as a function of viewing geometry and changing spatial resolution. Using 3D models for both canopy reflectance and thermal infrared exitance, we employ a theoretical analysis for an agricultural scene. The directional viewing effects and correlation between the NDVI and brightness temperature are found to be scale independent and in agreement with experiment. Directional anisotropy in brightness temperature and NDVI are calculated to be less than 7 to 12% respectively for zenith view angles less than 30 deg. but range up to 22 to 40% for zenith view angles of 60 deg. Analysis of variation in local standard deviations with spatial resolution shows a maximum peak corresponding to crop row spacing with rapid fall-off at larger scales.
    No preview · Article · Aug 1999 · Optical Engineering
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    ABSTRACT: Satellite observations of agricultural and other plant canopies in the thermal IR regime have generally been at spatial scales of tens to hundreds of meters. Use of the thermal IR at higher resolutions is confounded by the mixture problem and other associated scaling issues. Advances in sensor technology will extend our capabilities for IR measurements to shorter wavelengths and yield improved spatial resolutions. However, experience with aircraft remote sensing observations has indicated that care must be exercised in understanding the interaction effects of viewing geometry at these higher resolutions. The utilization and scaling of observables with multi-resolution remote sensing data sets remain a difficult problem. At high spatial resolution the three-dimensional character of scene components contained within a pixel must be considered. In this paper, we explore the variability in brightness temperature and the co-variation of NDVI with brightness temperature as a function of viewing geometry and changing spatial resolution. Using three- dimensional models for both canopy reflectance and thermal IR exitance, we employ a theoretical analysis for an agricultural scene where previous comparisons and measurements were available.
    No preview · Article · Dec 1998 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: We present a simple, three-dimensional vegetation canopy thermal infrared exitance model for agricultural scenes. Computer graphics and ray-tracing techniques are used to estimate three-dimensional canopy view factors and scene shadows. The view factors are used to weight the individual contributions of soil and vegetation emission computed by steady-state energy budget formulations. We compare the three- dimensional model results to a one-dimensional formulation for an agricultural test site from the Hydrologic Atmospheric Pilot Experiment and Modelisation du Bilan Hydrique. The root mean square error is daylight brightness temperature for the one dimensional model was 2.5 degrees Celsius and 2.0 degrees Celsius for the three dimensional model.
    No preview · Article · Dec 1997 · Proceedings of SPIE - The International Society for Optical Engineering
  • James A. Smith · Jerrell R. Ballard · Jeffrey A. Pedelty
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    ABSTRACT: We present a theoretical study of the effects of three- dimensional canopy structure on directional thermal infrared exitance. A physics-based model employing steady-state energy budget formulations is used to compute scene element temperatures. Two approaches are then used to combine soil and vegetation contributions to the composite scene response. One method uses a plane-parallel abstraction of canopy architecture to estimate canopy view factors for weighting of soil and vegetation emission terms. The second approach employs computer graphics and rendering techniques to estimate 3-D canopy view factors and scene shadows. Both approaches are applied to a test agricultural scene and compared with available measurements. The models correctly estimate hemispherically averaged thermal infrared exitance to within experimental error with root-mean-square errors of 15.3 W m-2 for the 1-D model and 12.5 W m-2 for the 3-D model. However, the 1-D model systematically underestimates exitance at high sun angles. Explicit modeling of canopy 3-D row structure indicates potential directional anisotropy in brightness temperature of up to 14 degrees Celsius.
    No preview · Article · Nov 1997 · Optical Engineering
  • James A. Smith · Jeffrey A. Pedelty
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    ABSTRACT: We present a new approach for estimating land surface fluxes using remote sensing optical and thermal IR observations. We employ an artificial neural network and train it with a radiosity reflectance model. We then apply the network without retraining to extract geometrical view factors from AVIRIS imagery. We use the retrieved view factors and in- situ meteorological data to drive a surface energy balance model. Theoretical directional view factors were retrieved with an average absolute error of 15 percent. Hemispherical view factors were retrieved with a root mean square error of 6 percent. Surface net radiation estimated using the AVIRIS imagery and the surface energy balance model varied form 520 W m-2 to 650 W m-2 and are consistent with tower measurements. The retrieved view factors may also be used to model mixed pixel response for directional thermal IR data.
    No preview · Conference Paper · Aug 1997
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    ABSTRACT: Land surface temperature and emissivity products are currently being derived from satellite and aircraft remote sensing data using a variety of techniques to correct for atmospheric effects. Implicit in the commonly employed approaches is the assumption of isotropy in directional thermal infrared exitance. The authors' theoretical analyses indicate angular variations in apparent infrared temperature will typically yield land surface temperature errors ranging from 1 to 4°C unless corrective measures are applied
    No preview · Article · Aug 1997 · IEEE Transactions on Geoscience and Remote Sensing
  • Lee K. Balick · James A. Smith
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    ABSTRACT: Models of surface temperatures of two land surface types based on their energy budgets were developed to simulate the effects of environmental factors on thermal radiant exitance. The performance of these models is examined in detail. One model solves the non-linear differential equation for heat diffusion in solids using a set of submodels for surface energy budget components. The model performance is examined under three desert conditions thought to be a strong test of the submodels. The accuracy of the temperature predictions and submodels is described. The accuracy of the model is generally good but some discrepancies between some of the submodels and measurements are noted. The sensitivity of the submodels is examined and is seen to be strongly controlled by interaction and feedback among energy components that are a function of surface temperature. The second model simulates vegetation canopies with detailed effects of surface geometry on radiant transfer in the canopy. Foliage solar absorption coefficients are calculated using a radiosity approach for a three layer canopy and long wave fluxes are modeled using a view factor matrix. Sensible and latent heat transfer through the canopy are also simulated using nearby meteorological data but heat storage in the canopy is not included. Simulations for a coniferous forest canopy are presented and the sensitivity of the model to environmental inputs is discussed.
    No preview · Article · Jan 1995 · Proceedings of SPIE - The International Society for Optical Engineering
  • James A. Smith · S.M. Goltz
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    ABSTRACT: A steady-state thermal radiance model to compute thermal exitance and energy balance within forest canopies is described. The model treats fully leafed canopies as discrete ensembles of leaves partitioned into slope-angle and height classes. Short-wave energy flux absorbed within the canopy is estimated by solving simplified radiosity equations. Sensible heat exchange is estimated using a logarithmic wind profile above the canopy and a modified exponential profile within the canopy. The latent heat boundary layer resistance is estimated from site-specific measurements summarizing the effects of solar irradiance, air temperature, and vapor pressure deficit on stomatal conductance. Example comparisons for a dense spruce-fir forest study site in central Maine are given. For clear days the resulting root mean square error in modeled versus measured canopy temperatures was 1.2°C. Corresponding errors in latent and sensible heat flux energy budget terms were 30 and 32 W/m<sup>-2</sup>, respectively. For partly cloudy days the root mean square error in predicted temperature was 1.0°C and corresponding errors in latent and sensible heat were 40 and 110 W/m<sup>-2</sup>
    No preview · Article · Oct 1994 · IEEE Transactions on Geoscience and Remote Sensing
  • James A. Smith
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    ABSTRACT: Standard regression methods applied to canopies within a single homogeneous soil type yield good results for estimating leaf area index (LAI) but perform unacceptably when applied across soil boundaries. In contrast, the neural network reported generally yielded absolute percentage errors of <30%. The network was applied, without retraining, to a sample of Landsat TM data for an agriculture/forestry study site
    No preview · Article · Oct 1993 · IEEE Transactions on Geoscience and Remote Sensing