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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

Uncertainty of Passive Imager Cloud Optical Property Retrievals to Instrument Radiometry and Model Assumptions: Examples from MODIS

The optical and microphysical structure of clouds is of fundamental importance for understanding a variety of cloud radiation and precipitation processes. With the advent of MODIS on the NASA EOS Terra and Aqua platforms, simultaneous global-daily 1 km retrievals of cloud optical thickness (COT) and effective particle radius (CER) are provided, as well as the derived water path (WP). The cloud product (MOD06/MYD06 for MODIS Terra and Aqua, respectively) provides separate retrieval datasets for various two-channel retrievals, typically a VISNIR channel paired with a 1.6, 2.1, and 3.7 m spectral channel. The MOD06 forward model is derived from on a homogeneous plane-parallel cloud. In Collection 5 processing (completed in 2007 with a modified Collection 5.1 completed in 2010), pixel-level retrieval uncertainties were calculated for the following non-3-D error sources: radiometry, surface spectral albedo, and atmospheric corrections associated with model analysis uncertainties (water vapor only). The latter error source includes error correlation across the retrieval spectral channels. Estimates of uncertainty in 1 aggregated (Level-3) means were also provided assuming unity correlation between error sources for all pixels in a grid for a single day, and zero correlation of error sources from one day to the next. I n Collection 6 (expected to begin in late summer 2013) we expanded the uncertainty analysis to include: (a) scene-dependent calibration uncertainty that depends on new band and detector-specific Level 1B uncertainties, (b) new model error sources derived from the look-up tables which includes sensitivities associated with wind direction over the ocean and uncertainties in liquid water and ice effective variance, (c) thermal emission uncertainties in the 3.7 m band associated with cloud and surface temperatures that are needed to extract reflected solar radiation from the total radiance signal, (d) uncertainty in the solar spectral irradiance at 3.7 m, and (e) addition of stratospheric ozone uncertainty in visible atmospheric corrections. A summary of the approach and example Collection 6 results will be shown.

Cloud Properties Observations↗
NASA NTRS1984

Optical properties of NH3 ice from the far infrared to the near ultraviolet

The optical constants (n(r), n(i)) for solid ammonia in the cubic phase from 0.14 to 200 microns are displayed in both graphical and tabular form. The refractive indices n(r) were obtained from previously published spectra of the absorption index n(i) by means of the Kramers-Kronig dispersion relation. Mie scattering parameters in the same spectral range are graphically illustrated for particle sizes from 1 to 100 microns. An application of these results to the atmosphere of the planet Jupiter is also presented.

Martonchik, J. V.↗
NASA NTRS1999

Optical Properties of Aerosols from Long Term Ground-Based Aeronet Measurements

AERONET is an optical ground-based aerosol monitoring network and data archive supported by NASA's Earth Observing System and expanded by federation with many non-NASA institutions including AEROCAN (AERONET CANada) and PHOTON (PHOtometrie pour le Traiteinent Operatonnel de Normalisation Satellitaire). The network hardware consists of identical automatic sun-sky scanning spectral radiometers owned by national agencies and universities purchased for their own monitoring and research objectives. Data are transmitted hourly through the data collection system (DCS) on board the geostationary meteorological satellites GMS, GOES and METEOSAT and received in a common archive for daily processing utilizing a peer reviewed series of algorithms thus imposing a standardization and quality control of the product data base. Data from this collaboration provides globally distributed near real time observations of aerosol spectral optical depths, aerosol size distributions, and precipitable water in diverse aerosol regimes. Access to the AERONET data base has shifted from the interactive program 'demonstrat' (reserved for PI's) to the AERONET homepage allowing faster access and greater development for GIS object oriented retrievals and analysis with companion geocoded data sets from satellites, LIDAR and solar flux measurements for example. We feel that a significant yet under utilized component of the AERONET data base are inversion products made from hourly principal plane and almucanter measurements. The current inversions have been shown to retrieve aerosol volume size distributions. A significant enhancement to the inversion code has been developed and is presented in these proceedings.

Holben, B. N.↗
NASA NTRS2010

Examining the Impact of Overlying Aerosols on the Retrieval of Cloud Optical Properties from Passive Remote Sensing

Haywood et al. (2004) show that an aerosol layer above a cloud can cause a bias in the retrieved cloud optical thickness and effective radius. Monitoring for this potential bias is difficult because space ]based passive remote sensing cannot unambiguously detect or characterize aerosol above cloud. We show that cloud retrievals from aircraft measurements above cloud and below an overlying aerosol layer are a means to test this bias. The data were collected during the Intercontinental Chemical Transport Experiment (INTEX-A) study based out of Portsmouth, New Hampshire, United States, above extensive, marine stratus cloud banks affected by industrial outflow. Solar Spectral Flux Radiometer (SSFR) irradiance measurements taken along a lower level flight leg above cloud and below aerosol were unaffected by the overlying aerosol. Along upper level flight legs, the irradiance reflected from cloud top was transmitted through an aerosol layer. We compare SSFR cloud retrievals from below ]aerosol legs to satellite retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) in order to detect an aerosol ]induced bias. In regions of small variation in cloud properties, we find that SSFR and MODIS-retrieved cloud optical thickness compares within the uncertainty range for each instrument while SSFR effective radius tend to be smaller than MODIS values (by 1-2 microns) and at the low end of MODIS uncertainty estimates. In regions of large variation in cloud properties, differences in SSFR and MODIS ]retrieved cloud optical thickness and effective radius can reach values of 10 and 10 microns, respectively. We include aerosols in forward modeling to test the sensitivity of SSFR cloud retrievals to overlying aerosol layers. We find an overlying absorbing aerosol layer biases SSFR cloud retrievals to smaller effective radii and optical thickness while nonabsorbing aerosols had no impact.

Coddington, O. M.↗
NASA NTRS2022

Arctic Biogeochemical and Optical Properties of Dissolved Organic Matter Across River to Sea Gradients

Arctic landscapes are warming and becoming wetter due to changes in precipitation and the timing of snowmelt which consequently alters seasonal runoff and river discharge patterns. These changes in hydrology lead to increased mobilization and transport of terrestrial dissolved organic matter (DOM) to Arctic coastal seas where significant impacts on biogeochemical cycling can occur. Here, we present measurements of dissolved organic carbon (DOC) and chromophoric DOM (CDOM) in the Yukon River-to-Bering Sea system and two river plumes on the Alaska North Slope which flow into the Beaufort Sea. Our sampling characterized optical and biogeochemical properties of DOM during high and low river discharge periods for the Yukon River-Bering Sea system. The average DOC concentration at the multiple Yukon River mouths ranged from a high of 10.36 mg C L-1 during the ascending limb of the 2019 freshet (late May), 6.4 mg C L-1 during the descending limb of the 2019 freshet (late June), and a low of 3.86 mg C L-1 during low river discharge in August 2018. CDOM absorption coefficient at 412 nm (aCDOM(412)) averaged 8.23 m-1, 5.07 m-1, and 1.9 m-1, respectively. Several approaches to model DOC concentration based on its relationship with CDOM properties demonstrated cross-system seasonal and spatial robustness for these Arctic coastal systems despite spanning an order of magnitude decrease in DOC concentration from the lower Yukon River to the Northern Bering Sea as well as the North Slope systems. “Snapshot” fluxes of DOC and CDOM across the Yukon River Delta to Norton Sound were calculated from our measurements and modeled water fluxes forced with upstream USGS river gauge data. Our findings suggest that during high river flow, DOM reaches the delta largely unaltered by inputs or physical and biogeochemical processing and that the transformations of Yukon River DOM largely occur in the plume. However, during low summer discharge, multiple processes including local precipitation events, microbial decomposition, photochemistry, and likely others can alter the DOM properties within the lower Yukon River and Delta prior to flowing into Norton Sound.

Arctic↗
NASA NTRS1974

Optical properties of particles in planetary atmospheres - Laboratory studies

The laboratory techniques employed for the determination of optical constants are discussed briefly. The values obtained for the real n and imaginary k parts of the refractive indices of water, ice, and liquid ammonia are presented graphically. Work currently in progress on solid ammonia and on sulphuric acid is discussed. Other approaches to studies of the properties of aerosols in planetary atmospheres are presented briefly.

Williams, D.↗
NASA NTRS1972

Changes in optical properties of the Surveyor 3 camera

The measurements made to analyze changes in the camera's optical performance involved the following areas: (1) spectral reflectance (specular), (2) gonioreflectance, (3) ellipsometry, (4) spectral transmission, (5) contrast and modulation transfer, and (6) photography (macro and micro).

Rennilson, J.↗
NASA NTRS2000

Comparison of Aerosol Optical Properties and Water Vapor Among Ground and Airborne Lidars and Sun Photometers During TARFOX

We compare aerosol optical thickness (AOT) and precipitable water vapor (PWV) measurements derived from ground and airborne lidars and Sun photometers during TARFOX (Tropospheric Aerosol Radiative Forcing Observational Experiment). Such comparisons are important to verify the consistency between various remote sensing measurements before employing them in any assessment of the impact of aerosols on the global radiation balance. Total scattering ratio and extinction profiles measured by the ground-based NASA/GSFC Scanning Raman Lidar (SRL) system, which operated from Wallops Island, Virginia (37.86 deg N, 75.51 deg W), are compared with those measured by the Lidar Atmospheric Sensing Experiment (LASE) airborne lidar system aboard the NASA ER-2 aircraft. Bias and rms differences indicate that these measurements generally agreed within about 10%. Aerosol extinction profiles and estimates of AOT are derived from both lidar measurements using a value for the aerosol extinction/backscattering ratio S(sub a)=60 sr for the aerosol extinction/backscattering ratio, which was determined from the Raman lidar measurements.

Ferrare, R.↗
NASA NTRS2000

Comparison of Aerosol Optical Properties and Water Vapor Among Ground and Airborne Lidars and Sun Photometers During TARFOX

We compare aerosol optical thickness (AOT) and precipitable water vapor (PWV) measurements derived from ground and airborne lidars and sun photometers during the Tropospheric Aerosol Radiative Forcing Observational Experiment. Such comparisons are important to verify the consistency between various remote sensing measurements before employing them in any assessment of the impact of aerosols on the global radiation balance. Total scattering ratio and extinction profiles measured by the ground-based NASA Goddard Space Flight Center scanning Raman lidar system, which operated from Wallops Island, Virginia (37.86 deg N, 75.51 deg W); are compared with those measured by the Lidar Atmospheric Sensing Experiment (LASE) airborne lidar system aboard the NASA ER-2 aircraft. Bias and root-mean-square differences indicate that these measurements generally agreed within about 10%. Aerosol extinction profiles and estimates of AOT are derived from both lidar measurements using a value for the aerosol extinction/backscattering ratio S(sub a) = 60 sr for the aerosol extinction/backscattering ratio, which was determined from the Raman lidar measurements. The lidar measurements of AOT are found to be generally within 25% of the AOT measured by the NASA Ames Airborne Tracking Sun Photometer (AATS-6). However, during certain periods the lidar and Sun photometer measurements of AOT differed significantly, possibly because of variations in the aerosol physical characteristics (e.g., size, composition) which affect S(sub a). Estimates of PWV, derived from water vapor mixing ratio profiles measured by LASE, are within 5-10% of PWV derived from the airborne Sun photometer. Aerosol extinction profiles measured by both lidars show that aerosols were generally concentrated in the lowest 2-3 km.

Ferrare, R.↗
NASA NTRS1990

Satellite material contaminant optical properties

The Air Force Wright Research and Development Center and the Arnold Engineering Development Center are continuing a program for measuring optical effects of satellite material outgassing products on cryo-optic surfaces. Presented here are infrared (4000 to 700 cm(-1)) transmittance data for contaminant films condensed on a 77 K geranium window. From the transmittance data, the contaminant film refractive and absorptive indices (n, k) were derived using an analytical thin-film interference model with a nonlinear least-squares algorithm. To date 19 materials have been studied with the optical contents determined for 13 of those. The materials include adhesives, paints, composites, films, and lubricants. This program is continuing and properties for other materials will be available in the future.

Wood, B. E.↗
NASA NTRS2011

MODIS Cloud Optical Property Retrieval Uncertainties Derived from Pixel-Level VNIR/SWIR Radiometric Uncertainties

Moderate Resolution Imaging Spectroradiometer (MODIS) retrievals of optical thickness and effective particle radius for liquid water and ice phase clouds employ a well-known VNIR/ SWIR solar reflectance technique. For this type of algorithm, we evaluate the quantitative uncertainty in simultaneous retrievals of these two cloud parameters to pixel-level radiometric calibration estimates and other fundamental (and tractable) error sources.

Platnick, S.↗
NASA NTRS1990

Structural and optical properties for typical solid mirror shapes

A method is developed to determine the weight, center of gravity, areal properties, and mass inertial properties for typical mirrors. A number of support conditions were considered to examine optical surface deflections, surface quality, and fundamental natural frequency for single- and double-arch mirror shapes. Structural performance estimates were made with the NASTRAN program, and optical performances were evaluated with the FRINGE program, using an SXA 40-in mirror. To show the behavior of element types from the NASTRAN program, finite element validity and sensitivity studies were performed in optical model applications. Material parameters, contoured back shapes, and support locations are shown to have significant effects on structural and optical performances. Optimal support locations and support points are given. Fundamental natural frequencies for some shapes are found with the closed-form solution. The plate models results may not be acceptable for determining real mirror optical performances.

Cho, Myung K.↗
NASA NTRS1991

Nonlinear optical properties of organic materials: A theoretical study

Replacement of electronic switching circuits in computing and telecommunication systems with purely optical devices offers the potential for extremely high throughput and compact information processing systems. The potential application of organic materials containing molecules with large nonresonant nonlinear effects in this area have triggered intensive research during the last decade. Interest on this area was due to two facts: (1) that many organic materials show nonlinearities that are orders of magnitude larger than those of conventional inorganic materials such as lithium niobate and potassium dihydrogen phosphate; and (2) that organic materials show much flexibility in terms of molecular designs. Some of the desirable characteristics that these materials should have are that they be transparent to the frequency of the incident laser and its second or third harmonic, that they have a high damage threshold, and, in the case of second-order effects, that their crystal structure or molecular orientation be accentric. Since polymeric assemblages can enhance the nonlinear response of organic molecules severalfold, efforts have been directed toward the synthesis of thin films with interpenetrating lattices of electroactive molecules. The goal of this theoretical investigation is to predict the magnitude of the molecular polarizabilities of organic molecules that could be incorporated into films. These calculations are intended to become a powerful tool to assist material scientists in screening for the best candidates for optical applications. The procedure that was developed for the present calculations is based on the static-field approach, and is a modification to the method developed by Dewar and Stewart, 1984 for calculating molecular linear polarizabilities.

Cardelino, Beatriz H.↗
NASA NTRS1993

Optical properties of CO2 ice and CO2 snow in the ultraviolet, visible, and infrared

The project was to measure the optical constants of CO2 ice in the spectral regions of weak absorption. Many previous measurements had been made by others in the strong absorption bands, but the weak regions had been poorly measured or not measured at all. In these regions the emissivity of CO2 frost and CO2 clouds is quite sensitive to particle sizes and to the value of the absorption coefficient, so the new measurements will have applications to energy budget and remote sensing of the Martian surface and atmosphere. During the time period covered by this grant, a method was developed for growing clear crystals of CO2, 4 cm in length. An apparatus was constructed for accurate measurement of spectral transmission through these crystals, for wavelengths 0.18-3.8 micrometers, covering the near-ultraviolet, visible, and near-infrared regions, bounded by the strong ultraviolet absorption and the 4.3-micrometer band. Our new best estimate of the spectral absorption coefficient (expressed as imaginary refractive index) is shown. It is a composite result of many measurements on dozens of crystals. Now that we have a good dataset for the shortwave absorption spectrum, the focus of the research has moved to the thermal infrared, for which a Fourier Transform interferometer has been adapted for use with C02-ice crystals.

Warren, Stephen↗