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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 127 records · Page 7
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NASA NTRS2022

Determining the Primary Sources of Uncertainty in Retrieval of Marine Remote Sensing Reflectance From Satellite Ocean Color Sensors

Uncertainties in the retrieval of the remote sensing reflectance, R_rs, from Ocean Color (OC) satellite sensors have a strong impact on the performance of algorithms for the estimation of chlorophyll-a, mineral concentrations, and inherent optical properties (IOPs). The uncertainties are highest in the blue bands. The total radiance measured at the top of the atmosphere captures the instantaneous state of the atmosphere-ocean system: the in-water conditions, sky and Sun glint reflected from the wind-roughened ocean surface, as well as light scattered from molecules and aerosols in the atmosphere. Each of these components has associated uncertainties, and when combined with the additional uncertainties from the instrument noise and the atmospheric correction process, they contribute to the total uncertainty budget for the retrieved R_rs. We analyzed the contribution of each component uncertainties to the total R_rs uncertainties in SNPP-VIIRS level 2 products, taking advantage of the spectral differences between the components. We examined multiple scenes in the open ocean and coastal waters at spatial resolutions ranging from 2250 to 5250 m by comparing the retrieved R_rs to in situ measurements made at several AERONET-OC sites and at the MOBY site. It was shown that uncertainties associated with the molecular (Rayleigh) scattering play the most significant role, while the contributions of other components are usually smaller. Uncertainties in Rayleigh scattering are primarily attributed to the variability of Rayleigh optical thickness (ROT) with a standard deviation of approximately 1.5% of ROT, which can largely explain the frequency of negative R_rs retrievals as observed using the current standard atmospheric correction process employed by NASA. Variability of the sky light reflected from the ocean surface in some conditions also contributed to uncertainties in the blue; water variability proportional to R_rs had a very pronounced peak in the green at coastal sites.

remote sensing reflectance↗
NASA NTRS1974

Bistatic sea state radar monitoring system and applications to marine geodesy

The bistatic scattering of high frequency radio waves can be used to observe directional ocean-wave spectra. This makes it possible to measure RMS wave heights. An experimental aircraft system for such measurements is discussed. The system utilizes a surface transmitter and an airborne receiver. Questions of high frequency scattering from the ocean surface are considered along with surface spectrum measurements.

Ruck, G. T.↗
NASA NTRS1986

The interaction of light with phytoplankton in the marine environment

In many regions of the ocean, the phytoplankton population dominates both the attenuation and scattering of light. In other regions, non-phytoplankton contributions to the absorption and scattering may change the remote sensing reflectance and thus affect the ability to interpret remotely sensed ocean color. Hence, variations in the composition of both the phytoplankton population and of the non-phytoplankton material in the water can affect the optical properties of the sea. The effects of these contributions to the remote sensing reflectance and the submarine light field are modeled using scattering and absorption measurements of phytoplankton cultures obtained at the Friday Harbor Laboratory of the University of Washington. These measurements are used to develop regional chlorophyll algorithms specific to the summer waters of Puget Sound for the Coastal Zone Color Scanner, Thematic Mapper and future Ocean Color Imager, and their accuracies are compared for high chlorophyll waters with little or no Gelbstoff, but with variable detrital and suspended material.

Carder, Kendall L.↗
NASA NTRS1989

Aerosol analysis with the Coastal Zone Color Scanner - A simple method for including multiple scattering effects

A method for studying aerosols over the ocean using Nimbus-7 CZCS data is proposed which circumvents having to perform radiative transfer computations involving the aerosol properties. The method is applied to the CZCS band 4 at 670 nm, and yields the total radiance (L sub t) backscattered from the top of a stratified atmosphere containing both stratospheric and tropospheric aerosols and the the Rayleigh scattered radiance (L sub r). The radiance which the aerosol would produce in the single scattering approximation is retrieved from (L sub t) - (L sub r) with an error of not greater than 5-7 percent.

Gordon, Howard R.↗
NASA NTRS1985

A General-applications Direct Global Matrix Algorithm for Rapid Seismo-acoustic Wavefield Computations

A new matrix method for rapid wave propagation modeling in generalized stratified media, which has recently been applied to numerical simulations in diverse areas of underwater acoustics, solid earth seismology, and nondestructive ultrasonic scattering is explained and illustrated. A portion of recent efforts jointly undertaken at NATOSACLANT and NORDA Numerical Modeling groups in developing, implementing, and testing a new fast general-applications wave propagation algorithm, SAFARI, formulated at SACLANT is summarized. The present general-applications SAFARI program uses a Direct Global Matrix Approach to multilayer Green's function calculation. A rapid and unconditionally stable solution is readily obtained via simple Gaussian ellimination on the resulting sparsely banded block system, precisely analogous to that arising in the Finite Element Method. The resulting gains in accuracy and computational speed allow consideration of much larger multilayered air/ocean/Earth/engineering material media models, for many more source-receiver configurations than previously possible. The validity and versatility of the SAFARI-DGM method is demonstrated by reviewing three practical examples of engineering interest, drawn from ocean acoustics, engineering seismology and ultrasonic scattering.

Schmidt, H.↗
NASA NTRS1986

Imaging radar polarimetry from wave synthesis

It was shown that it is possible to measure the complete scattering matrix of an object using data acquired on a single aircraft pass, and can combine the signals later in the data processor to generate radar images corresponding to any desired combination of transmit and receive polarization. Various scattering models predict different dependence on polarization state of received power from an object. The imaging polarimeter permits determination of this dependence, which is called the polarization signature, of each point in a radar image. Comparison of the theoretical predictions and observational data yield identification of possible scattering mechanisms for each area of interest. It was found that backscatter from the ocean is highly polarized and well-modeled by Bragg scattering, while scattering from trees in a city park possesses a considerable unpolarized component. Urban regions exhibit the characteristics expected from dihedral corner reflectors and their polarization signatures are quite different from the one-bounce Bragg model.

Zebker, Howard A.↗
NASA NTRSDate not supplied

TPSAS-NF1676L-34796-DND

The recently completed 2015-2017 EVS-2 mission NAAMES (The North Atlantic Aerosols and Marine Ecosystems Study) provides a unique set of airborne remote sensing and ship-based in situ measurements in a remote and under-sampled region of the Earth?s ocean. The NASA SABOR (Ship-Aircraft Bio-Optical Research) campaign was conducted during the summer of 2014, also in the Atlantic Ocean, out of the Chesapeake Bay and in the eastern coastal region of the United States. For both campaigns, the NASA GISS Research Scanning Polarimeter, a multi-angle, multi-spectral polarimeter measured the upwelling polarized radiances from aircraft. And for both campaigns, ship-based in situ measurements of the ocean were collected jointly with the aircraft measurements. We present results from the new RSP-MAPP (1) that is based on optimal estimation and that can retrieve simultaneous aerosol microphysical properties (including effective radius, single-scattering albedo, and real refractive index) and ocean color products using accurate radiative transfer, Mie calculations, and the DP (Detritus Plankton) series of accurate, numerically efficient ocean bio-optical models. The RSP-MAPP algorithm was applied to data collected during SABOR and NAAMES to retrieve aerosol microphysics and ocean products for all Aerosols-Above-Ocean (AAO) scenes. The RSP-MAPP products are compared against i) collocated aerosol extinction and backscatter profiles collected by the NASA LaRC airborne High Spectral Resolution Lidar (HSRL-1), including lidar depth profiles of the ocean diffuse attenuation coefficient and the hemispherical backscatter coefficient, and ii) collocated ship-based in situ measurements of the ocean.

Snorre Stamnes↗
NASA NTRS2015

An Innovative Concept for Spacebased Lidar Measurement of Ocean Carbon Biomass

Beam attenuation coefficient, c, provides an important optical index of plankton standing stocks, such as phytoplankton biomass and total particulate carbon concentration. Unfortunately, c has proven difficult to quantify through remote sensing. Here, we introduce an innovative approach for estimating c using lidar depolarization measurements and diffuse attenuation coefficients from ocean color products or lidar measurements of Brillouin scattering. The new approach is based on a theoretical formula established from Monte Carlo simulations that links the depolarization ratio of sea water to the ratio of diffuse attenuation Kd and beam attenuation C (i.e., a multiple scattering factor). On July 17, 2014, the CALIPSO satellite was tilted 30Âdeg off-nadir for one nighttime orbit in order to minimize ocean surface backscatter and demonstrate the lidar ocean subsurface measurement concept from space. Depolarization ratios of ocean subsurface backscatter are measured accurately. Beam attenuation coefficients computed from the depolarization ratio measurements compare well with empirical estimates from ocean color measurements. We further verify the beam attenuation coefficient retrievals using aircraft-based high spectral resolution lidar (HSRL) data that are collocated with in-water optical measurements.

Hu, Yongxiang↗
NASA NTRS2008

Improving Coastal Ocean Color Validation Capabilities through Application of Inherent Optical Properties (IOPs)

Understanding how the different components of seawater alter the path of incident sunlight through scattering and absorption is essential to using remotely sensed ocean color observations effectively. This is particularly apropos in coastal waters where the different optically significant components (phytoplankton, detrital material, inorganic minerals, etc.) vary widely in concentration, often independently from one another. Inherent Optical Properties (IOPs) form the link between these biogeochemical constituents and the Apparent Optical Properties (AOPs). understanding this interrelationship is at the heart of successfully carrying out inversions of satellite-measured radiance to biogeochemical properties. While sufficient covariation of seawater constituents in case I waters typically allows empirical algorithms connecting AOPs and biogeochemical parameters to behave well, these empirical algorithms normally do not hold for case I1 regimes (Carder et al. 2003). Validation in the context of ocean color remote sensing refers to in-situ measurements used to verify or characterize algorithm products or any assumption used as input to an algorithm. In this project, validation capabilities are considered those measurement capabilities, techniques, methods, models, etc. that allow effective validation. Enhancing current validation capabilities by incorporating state-of-the-art IOP measurements and optical models is the purpose of this work. Involved in this pursuit is improving core IOP measurement capabilities (spectral, angular, spatio-temporal resolutions), improving our understanding of the behavior of analytical AOP-IOP approximations in complex coastal waters, and improving the spatial and temporal resolution of biogeochemical data for validation by applying biogeochemical-IOP inversion models so that these parameters can be computed from real-time IOP sensors with high sampling rates. Research cruises supported by this project provides for collection and processing of seawater samples for biogeochemical (pigments, DOC and POC) and optical (CDOM and POM absorption coefficients) analyses to enhance our understanding of the linkages between in-water optical measurements (IOPs and AOPs) and biogeochemical constituents and to provide a more comprehensive suite of validation products.

Mannino, Antonio↗
NASA NTRS1986

Calibration of satellite sensors after launch

A simple and accurate method for the postflight calibration of satellite Visible Infrared Spin-Scan Radiometers (VISSR) is presented, and the results of inflight testing are reported. The calibration source for the VISSR with its effective wavelength of 610 nm is the radiance of sunlight, measured in calibrated reflectance units, scattered by the atmospheric gas above ocean which is far from land. Only the lowest 20 percent of the full-scale VISSR response is calibrated. VISSR testing aboard two geostationary operational evironmental satellites between 1980 and 1983 showed significant calibration coefficient variations of only + or - 12 percent and + or - 2 percent. Good agreement was found between values of aerosol optical thickness measured by VISSR and those measured from the ground.

Fraser, R. S.↗
NASA NTRS1993

Data fusion with artificial neural networks (ANN) for classification of earth surface from microwave satellite measurements

A data fusion system with artificial neural networks (ANN) is used for fast and accurate classification of five earth surface conditions and surface changes, based on seven SSMI multichannel microwave satellite measurements. The measurements include brightness temperatures at 19, 22, 37, and 85 GHz at both H and V polarizations (only V at 22 GHz). The seven channel measurements are processed through a convolution computation such that all measurements are located at same grid. Five surface classes including non-scattering surface, precipitation over land, over ocean, snow, and desert are identified from ground-truth observations. The system processes sensory data in three consecutive phases: (1) pre-processing to extract feature vectors and enhance separability among detected classes; (2) preliminary classification of Earth surface patterns using two separate and parallely acting classifiers: back-propagation neural network and binary decision tree classifiers; and (3) data fusion of results from preliminary classifiers to obtain the optimal performance in overall classification. Both the binary decision tree classifier and the fusion processing centers are implemented by neural network architectures. The fusion system configuration is a hierarchical neural network architecture, in which each functional neural net will handle different processing phases in a pipelined fashion. There is a total of around 13,500 samples for this analysis, of which 4 percent are used as the training set and 96 percent as the testing set. After training, this classification system is able to bring up the detection accuracy to 94 percent compared with 88 percent for back-propagation artificial neural networks and 80 percent for binary decision tree classifiers. The neural network data fusion classification is currently under progress to be integrated in an image processing system at NOAA and to be implemented in a prototype of a massively parallel and dynamically reconfigurable Modular Neural Ring (MNR).

Lure, Y. M. Fleming↗
NASA NTRS1995

Effects of Raman scattering on the water-leaving radiance

The contribution of Raman scattering to the water-leaving radiance is examined using Monte Carlo simulations. Exit angle information is retained, allowing a comparison of different satellite viewing directions. Chlorophyll values of 0.0, 0.01, 0.1, and 1.0 mg Chl/cu m are simulated. Little directional variability is found, with the exception of the direct solar backscatter direction. The wavelength variability is greatest for low chlorophyll concentrations and is negligible for 1.0 mg Chl/cu m. At 550 nm the Raman contribution ranges from approximately 18% of the total water-leaving radiance for pure water to 3% for 1.0 mg Chl/cu m. At 440 nm the range is from 6% to 2%, indicating that Raman scattering will impact radiance ratios for ocean color satellite algorithms.

Waters, Kirk J.↗
NASA NTRS1995

In situ phytoplankton absorption, fluorescence emission, and particulate backscattering spectra determined from reflectance

An inverse model was developed to extract the absortion and scattering (elastic and inelastic) properties of oceanic constituents from surface spectral reflectance measurements. In particular, phytoplankton spectral absorption coefficients, solar-stimulated chlorophyll a fluorescence spectra, and particle backscattering spectra were modeled. The model was tested on 35 reflectance spectra obtained from irradiance measurements in optically diverse ocean waters (0.07 to 25.35 mg/cu m range in surface chlorophyll a concentrations). The universality of the model was demonstrated by the accurate estimation of the spectral phytoplankton absorption coefficents over a range of 3 orders of magnitude (rho = 0.94 at 500 nm). Under most oceanic conditions (chlorophyll a less than 3 mg/cu m) the percent difference between measured and modeled phytoplankton absorption coefficents was less than 35%. Spectral variations in measured phytoplankton absorption spectra were well predicted by the inverse model. Modeled volume fluorescence was weakly correlated with measured chl a; fluorescence quantum yield varied from 0.008 to 0.09 as a function of environment and incident irradiance. Modeled particle backscattering coefficients were linearly related to total particle cross section over a twentyfold range in backscattering coefficents (rho = 0.996, n = 12).

Roesler, Collin S.↗
NASA NTRS1996

Multiwavelength Comparison of Modeled and Measured Remote Tropospheric Aerosol Backscatter Over Pacific Ocean

Aerosol concentrations and size distributions in the middle and upper troposphere over the remote Pacific Ocean were measured with a forward scattering spectrometer probe (FSSP) on the NASA DC-8 aircraft during NASA's Global Backscatter Experiment (GLOBE) in May-June 1990. The FSSP size channels were recalibrated based on refractive index estimates from flight-level aerosol volatility measurements with a collocated laser optical particle counter (LOPC). The recalibrated FSSP size distributions were averaged over 100-s intervals, fitted with lo-normal distributions and used to calculate aerosol backscatter coefficients at selected wavelengths. The FSSP-derived backscatter estimates were averaged over 300-s intervals to reduce large random fluctuations. The smoothed FSSP aerosol backscatter coefficients were then compared with LOPC-derived backscatter values and with backscatter measured at or near flight level from four lidar systems operating at 0.53, 1.06, 9.11, 9.25, and 10.59 micrometers. Agreement between FSSP-derived and lidar-measured backscatter was generally best at flight level in homogeneous aerosol fields and at high backscatter values. FSSP data often underestimated low backscatter values especially at the longer wavelengths due to poor counting statistics for larger particles (greater than 0.8 micrometers diameter) that usually dominate aerosol backscatter at these wavelengths. FSSP data also underestimated backscatter at shorter wavelengths when particles smaller than the FSSP lower cutoff diameter (0.35 micrometers) made significant contributions to the total backscatter.

Cutten, D. R.↗
NASA NTRS2011

Earth as an Extrasolar Planet: Earth Model Validation Using EPOXI Earth Observations

The EPOXI Discovery Mission of Opportunity reused the Deep Impact flyby spacecraft to obtain spatially and temporally resolved visible photometric and moderate resolution near-infrared (NIR) spectroscopic observations of Earth. These remote observations provide a rigorous validation of whole disk Earth model simulations used to better under- stand remotely detectable extrasolar planet characteristics. We have used these data to upgrade, correct, and validate the NASA Astrobiology Institute s Virtual Planetary Laboratory three-dimensional line-by-line, multiple-scattering spectral Earth model (Tinetti et al., 2006a,b). This comprehensive model now includes specular reflectance from the ocean and explicitly includes atmospheric effects such as Rayleigh scattering, gas absorption, and temperature structure. We have used this model to generate spatially and temporally resolved synthetic spectra and images of Earth for the dates of EPOXI observation. Model parameters were varied to yield an optimum fit to the data. We found that a minimum spatial resolution of approx.100 pixels on the visible disk, and four categories of water clouds, which were defined using observed cloud positions and optical thicknesses, were needed to yield acceptable fits. The validated model provides a simultaneous fit to the Earth s lightcurve, absolute brightness, and spectral data, with a root-mean-square error of typically less than 3% for the multiwavelength lightcurves, and residuals of approx.10% for the absolute brightness throughout the visible and NIR spectral range. We extend our validation into the mid-infrared by comparing the model to high spectral resolution observations of Earth from the Atmospheric Infrared Sounder, obtaining a fit with residuals of approx.7%, and temperature errors of less than 1K in the atmospheric window. For the purpose of understanding the observable characteristics of the distant Earth at arbitrary viewing geometry and observing cadence, our validated forward model can be used to simulate Earth s time dependent brightness and spectral properties for wavelengths from the far ultraviolet to the far infrared.brightness

Robinson, Tyler D.↗
NASA NTRS2000

Aerosol Radiative Forcing in Asian Continental Outflow

Aerosols in elevated layers were sampled with FSSP-probes and wire impactors over the Pacific ocean aboard the NASA DC-8 aircraft. Analyses of particle size and morphology identifies two distinctly different aerosol types for cases when the mid-visible extinctions exceed 0.2/km. Smaller sizes (effective radii of 0.2 um) and moderate absorption (mid-visible single scattering albedo of.935) are typical for urban-industrial pollution. Larger sizes (effective radii of 0.7 um) and weak absorption (mid-visible single scattering albedo of 0.985) identify dust. This aerosol classification is in agreement with its origin as determined by airmass back trajectory analysis. Based on lidar vertical profiling, aerosol dominated by dust and urban-industrial pollution above 3km were assigned mid-visible optical depths of 0.50 and 0.27, respectively. Radiative transfer simulations, considering a 50% cloud-cover below the aerosol layers, suggest (on a daily tP C)C> basis) small reductions (-4W/m2) to the energy budget at the top of the atmosphere for both aerosol types. For c' 0 dust, more backscattering of sunlight (weaker solar absorption) is compensated by a stronger greenhouse effect due to larger sizes. Forced reductions to the energy budget at the surface are 12W/m2 for both aerosol types. In contrast, impacts on heating rates within the aerosol layers are quite different: While urban-industrial aerosol warms the layer (at +0.6K/day as solar heating dominates), dust cools (at -0.5K/day as infrared cooling dominates). Sensitivity tests show the dependence of the aerosol climatic impact on the optical depth, particle size, absorptivity, and altitude of the layers, as well as clouds and surface properties. Climatic cooling can be eliminated (1) for the urban-industrial aerosol if absorption is increased to yield a mid-visible single scattering albedo of 0.89, or if the ocean is replaced by a land surface; (2) for the dust aerosol if the effective radius is increased from 0.7 to 1.2 um. The removal of low-level clouds doubles the cooling at the top of the atmosphere to about -8W/m2.

Pueschel, R.↗