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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Results of Airborne Backscatter Measurements During the Surface Wave Dynamics Experiment

Ocean backscatter data over a wide variety of oceanic and atmospheric conditions were obtained by the Jet Propulsion Laboratory NUSCAT Ku-band scatterometer during the Surface Wave Dynamics Experiment (SWADE). Thirty hours of backscatter data were collected in ten flights by NUSCAT on the NASA Ames C130 aircraft during an intensive observation period (IOP) of SWADE in the winter of 1991. The SWADE experimental area, off the coast of Virginia and Maryland, was deployed with an array of buoys providing appropriate in-situ measurements to correlate with the radar backscatter for incidence angles from 10ø to 60ø at both horizontal and vertical polarizations.

Airborne↗
NASA NTRS1999

Dust Optical Properties derived from Sun/Sky Measurements and Satellite Data

We derive the optical properties of dust originating from the Sahara and nearby regions using a combination of ground based and satellite measurements. The AErosol ROBotic NETwork (AERONET) sun/sky radiances from Cap Verde and Sede Boker are used together with Landsat TM data over Senegal and the Atlantic Ocean. The data introduce a cascade of increasing complexity of dust optical properties: The sky aureole radiance is sensitive mainly to the dust size distribution; the TM data over the ocean at 150 deg scattering angle are also sensitive to the spectral refractive index from 470 to 2,210 nm. The TM data over the land measure the balance between the dust scattering and absorption of light reflected by the bright surface, thus very sensitive to dust spectral absorption. Sky radiance at scattering angle of 120 deg, add sensitivity to the dust nonsphericity. Preliminary results, indicative of the ambient dust in the entire atmospheric column, show that dust is less absorbing and with smaller nonspherical properties than anticipated from in situ measurements. Dust is dominated by particles with effective radius of 2 to 2.5 micron, refractive index for wavelengths less then 1 micron of 1.53-0.001i and nonsphericity that increases the phase function at 120 deg above that of spheres by 1.8 and 1.7 at 673 nm down to 1.2 and 1.3 for 1020 nm for Cap Verde and Sede Boker respectively. No significant nonsphericity effect is noticed for scattering angle of 150 deg. This agrees with a mixture of 30% and 45% respectively of Mishchenko et al (JGR, 102, 1997: plate 5 on page 16,841) "polydisperse equiprobable shape mixture of prolate and oblate spheroids with aspect ratios ranging from 1.4 to 2.21, with the rest being spherical particles.

Kaufman, Yoram J.↗
NASA NTRS1987

Theory and observations of cometary ionospheres

The basic physical and chemical processes responsible for the makeup of cometary ionospheres are discussed in the framework of relevant in situ measurements on the Halley and Giacobini-Zinner comets, as well as recent theoretical models of cometary ionospheres. Special attention is given to physical processes responsible for the formation of the contact surface (CS), which is that surface where the magnetic field becomes zero or extremely small and which separates the field-free ionosphere and the magnetized plasma on the outside. Results of in situ observations indicate that the plasma just outside the CS is just as ionospheric in nature as the 'classical' ionospheric plasma residing within this surface. An expression for the magnetic field in this region is derived.

Cravens, T. E.↗
NASA NTRS2000

OCTS And Seawifs Bio-Optical Algorithm and Product Vaildattion and Intercomparison in US Coastal Waters

Monitoring the health of U.S. coastal waters is an important goal of the National Oceanic and Atmospheric Administration (NOAA). Satellite sensors are capable of providing daily synoptic data of large expanses of the U.S. coast. Ocean color sensor, in particular, can be used to monitor the water quality of coastal waters on an operational basis. To appraise the validity of satellite-derived measurements, such as chlorophyll concentration, the bio-optical algorithms used to derive them must be evaluated in coastal environments. Towards this purpose, over 21 cruises in diverse U.S. coastal waters have been conducted. Of these 21 cruises, 12 have been performed in conjunction with and under the auspices of the NASA/SIMBIOS Project. The primary goal of these cruises has been to obtain in-situ measurements of downwelling irradiance, upwelling radiance, and chlorophyll concentrations in order to evaluate bio-optical algorithms that estimate chlorophyll concentration. In this Technical Memorandum, we evaluate the ability of five bio-optical algorithms, including the current SeaWiFS algorithm, to estimate chlorophyll concentration in surface waters of the South Atlantic Bight (SAB). The SAB consists of a variety of environments including coastal and continental shelf regimes, Gulf Stream waters, and the Sargasso Sea. The biological and optical characteristics of the region is complicated by temporal and spatial variability in phytoplankton composition, primary productivity, and the concentrations of colored dissolved organic matter (CDOM) and suspended sediment. As such, the SAB is an ideal location to test the robustness of algorithms for coastal use.

Brow, Chirstopher↗
NASA NTRS2012

Determination of the Heliospheric Radial Magnetic Field from the Standoff Distance of a CME-Driven Shock Observed by the Stereo Spacecraft

We report on the determination of radial magnetic field strength in the heliocentric distance range from 6 to 120 solar radii (R-solar) using data from Coronagraph 2 (COR2) and Heliospheric Imager I (HI1) instruments on board the Solar Terrestrial Relations Observatory spacecraft following the standoff-distance method of Gopalswamy & Yashiro. We measured the shock standoff distance of the 2008 April 5 coronal mass ejection (CME) and determined the flux-rope curvature by fitting the three-dimensional shape of the CME using the Graduated Cylindrical Shell model. The radial magnetic field strength is computed from the Alfven speed and the density of the ambient medium. We also compare the derived magnetic field strength with in situ measurements made by the Helios spacecraft, which measured the magnetic field at the heliocentric distance range from 60 to 215 R-solar.We found that the radial magnetic field strength decreases from 28 mG at 6 R-solar to 0.17 mG at 120 R-solar. In addition, we found that the radial profile can be described by a power law.

CMEs↗
NASA NTRS2002

Summary of Quantitative Interpretation of Image Far Ultraviolet Auroral Data

Direct imaging of the magnetosphere by instruments on the IMAGE spacecraft is supplemented by simultaneous observations of the global aurora in three far ultraviolet (FUV) wavelength bands. The purpose of the multi-wavelength imaging is to study the global auroral particle and energy input from thc magnetosphere into the atmosphere. This paper describes provides the method for quantitative interpretation of FUV measurements. The Wide-Band Imaging Camera (WIC) provides broad band ultraviolet images of the aurora with maximum spatial and temporal resolution by imaging the nitrogen lines and bands between 140 and 180 nm wavelength. The Spectrographic Imager (SI), a dual wavelength monochromatic instrument, images both Doppler-shifted Lyman alpha emissions produced by precipitating protons, in the SI-12 channel and OI 135.6 nm emissions in the SI-13 channel. From the SI-12 Doppler shifted Lyman alpha images it is possible to obtain the precipitating proton flux provided assumptions are made regarding the mean energy of the protons. Knowledge of the proton (flux and energy) component allows the calculation of the contribution produced by protons in the WIC and SI-13 instruments. Comparison of the corrected WIC and SI-13 signals provides a measure of the electron mean energy, which can then be used to determine the electron energy fluxun-. To accomplish this reliable modeling emission modeling and instrument calibrations are required. In-flight calibration using early-type stars was used to validate the pre-flight laboratory calibrations and determine long-term trends in sensitivity. In general, very reasonable agreement is found between in-situ measurements and remote quantitative determinations.

Frey, H. U.↗
NASA NTRSDate not supplied

Probing the Lower-Thermosphere-Ionosphere In-situ with Small Spacecraft

The LTI at Earth spans the altitude range of about 90km to 200km. These altitudes do not lendthemselves easily to exploration by neither balloons nor orbiting spacecraft. As a consequence,only few in-situ measurements from the region exist, provided by sounding rocket campaignsand a few low-dipping Atmospheric Explorer missions in the 1970s. This has left a critical needfor simultaneous and co-located measurements of comprehensive sets of physical parametersto characterize both the neutral and plasma constituents. Such observations with extensivecoverage in time and space are crucial to advancing our understanding of the energetics, dy-namics, and chemistry of this complex region of the Earth’s atmosphere. Not all observablesare accessible through remote sensing so novel approaches and technological solutions are calledfor to obtain the needed in-situ measurements.Over the last decade, small spacecraft systems have proven their capability to provide someof these observations. Miniaturized instruments for electric and magnetic fields as well as forplasma and neutral gas densities, composition, and winds have been developed and proven inspace along with a large number of small satellite systems. Huge progress is also seen in thedevelopment of small satellite technology in support of large constellations. This paper willreview some of the main developments and discuss their relevance and potential for explorationof the LTI.

Aeronomy↗
NASA NTRS1981

Utilization of remote sensing in Alaska permafrost studies

Permafrost related features such as: aufeis, tundra, thaw lakes and subsurface ice features were studied. LANDSAT imagery was used to measure the extent and distribution of aufeis in Arctic Slope rivers over a period of 7 years. Interannual extent of large aufeis fields was found to vary significantly. Digital LANDSAT data were used to study the short term effects of a tundra fire which burned a 48 sq km area in northwestern Alaska. Vegetation regrowth was inferred from Landsat spectral reflectance increases and compared to in-situ measurements. Aircraft SAR (Synethic Aperture Radar) imagery was used in conjunction with LANDSAT imagery used in conjunction with LANDSAT imagery to qualitatively determine depth categories for thaw lakes in northern Alaska.

Hall, D. K.↗
NASA NTRS2015

Evaluation of a Model-Based Groundwater Drought Indicator in the Conterminous U.S.

Monitoring groundwater drought using land surface models is a valuable alternative given the current lack of systematic in situ measurements at continental and global scales and the low resolution of current remote sensing based groundwater data. However, uncertainties inherent to land surface models may impede drought detection, and thus should be assessed using independent data sources. In this study, we evaluated a groundwater drought index (GWI) derived from monthly groundwater storage output from the Catchment Land Surface Model (CLSM) using a GWI similarly derived from in situ groundwater observations. Groundwater observations were obtained from unconfined or semi-confined aquifers in eight regions of the central and northeastern U.S. Regional average GWI derived from CLSM exhibited strong correlation with that from observation wells, with correlation coefficients between 0.43 and 0.92. GWI from both in situ data and CLSM was generally better correlated with the Standard Precipitation Index (SPI) at 12 and 24 month timescales than at shorter timescales, but it varied depending on climate conditions. The correlation between CLSM derived GWI and SPI generally decreases with increasing depth to the water table, which in turn depends on both bedrock depth (a CLSM parameter) and mean annual precipitation. The persistence of CLSM derived GWI is spatially varied and again shows a strong influence of depth to groundwater. CLSM derived GWI generally persists longer than GWI derived from in situ data, due at least in part to the inability of coarse model inputs to capture high frequency meteorological variability at local scales. The study also showed that groundwater can have a significant impact on soil moisture persistence where the water table is shallow. Soil moisture persistence was estimated to be longer in the eastern U.S. than in the west, in contrast to previous findings that were based on models that did not represent groundwater. Assimilation of terrestrial water storage data from the Gravity Recovery and Climate Experiment (GRACE) satellite mission improved the correlation between CLSM based regional average GWI and that based on in situ data in six of the eight regions. Practical issues regarding the application of GRACE assimilated groundwater storage for drought detection are discussed. An important conclusion of this study is that model parameters that control the depth to the water table, including bedrock depth, strongly influence the evolution and persistence of simulated groundwater and require careful configuration for drought monitoring.

Evaluation↗
NASA NTRS2014

Evaluation of a Model-Based Groundwater Drought Indicator in the Conterminous U.S.

Monitoring groundwater drought using land surface models is a valuable alternative given the current lack of systematic in situ measurements at continental and global scales and the low resolution of current remote sensing based groundwater data. However, uncertainties inherent to land surface models may impede drought detection, and thus should be assessed using independent data sources. In this study, we evaluated a groundwater drought index (GWI) derived from monthly groundwater storage output from the Catchment Land Surface Model (CLSM) using a GWI similarly derived from in situ groundwater observations. Groundwater observations were obtained from unconfined or semi-confined aquifers in eight regions of the central and northeastern U.S. Regional average GWI derived from CLSM exhibited strong correlation with that from observation wells, with correlation coefficients between 0.43 and 0.92. GWI from both in situ data and CLSM was generally better correlated with the Standard Precipitation Index (SPI) at 12 and 24 month timescales than at shorter timescales, but it varied depending on climate conditions. The correlation between CLSM derived GWI and SPI generally decreases with increasing depth to the water table, which in turn depends on both bedrock depth (a CLSM parameter) and mean annual precipitation. The persistence of CLSM derived GWI is spatially varied and again shows a strong influence of depth to groundwater. CLSM derived GWI generally persists longer than GWI derived from in situ data, due at least in part to the inability of coarse model inputs to capture high frequency meteorological variability at local scales. The study also showed that groundwater can have a significant impact on soil moisture persistence where the water table is shallow. Soil moisture persistence was estimated to be longer in the eastern U.S. than in the west, in contrast to previous findings that were based on models that did not represent groundwater. Assimilation of terrestrial water storage data from the Gravity Recovery and Climate Experiment (GRACE) satellite mission improved the correlation between CLSM based regional average GWI and that based on in situ data in six of the eight regions. Practical issues regarding the application of GRACE assimilated groundwater storage for drought detection are discussed. An important conclusion of this study is that model parameters that control the depth to the water table, including bedrock depth, strongly influence the evolution and persistence of simulated groundwater and require careful configuration for drought monitoring.

hydrology↗
NASA NTRSDate not supplied

Discovery of hydrated Clasts with Very High Abundance of Ferromagnesian 160-Rich Olivine: Inner or Outer Solar System origin?

Olivine is one of the major minerals in chondritic meteorites and occurs in all chondritic components, including amoeboid olivine aggregates (AOAs), forsterite-bearing Type B (FoB) Ca, Al-rich inclusions (CAIs), chondrules, and matrices. As a result, olivines could preserve chemical and isotopic characteristics of their formation environments. There are significant variations in oxygen isotopic compositions of chondritic olivine. Forsteritic olivine in AOAs and FoB-CAIs has solar-like 16O-rich compositions (D17O ~ -23±2‰); the former condensed from an 16O-rich gas of ~solar composition, whereas the latter crystallized from remelted condensates in an isotopic similar gaseous reservoir. Olivine phenocrysts in chondrules are significantly 16O-depleted compared to CAIs and AOAs: D17O ranges from ~ -7 to +3‰. Only rare relict olivines in chondrules have CAI/AOA-like 16O-rich compositions; these grains most likely represent fragments of CAIs and AOAs incompletely melted during chondrule formation. Olivine in matrices of weakly metamorphosed meteorites is extremely fine-grained (<100 nm) and has predominantly forsteritic composition. In metamorphosed chondrites, matrix olivines are coarse-grained (up to 10 μm) and enriched in FeO. Due to small grain sizes, oxygen isotopic compositions of matrix olivines are poorly known. Mapping of matrices of Vigarano and Kakangari using isotope microscopes (secondary ion mass-spectrometer (SIMS) plus SCAPS detector) revealed the presence of 16O-rich olivine grains. While most matrix olivines in Vigarano have 16O-poor compositions, nearly half of olivines measured in Kakangari matrix are16O-rich.Here, we present for the first time new lithologies largely composed of 16O-and Fe-rich olivine. We attempt to address the question of whether these 16O-richolivine grains were formed by condensation in the solar nebula or by a secondary process during the evolution of the parent body. Mineralogical characteristics of these unusual olivines, as well as in-situ measured oxygen-isotope compositions of different phases are reported in detail.

I. Kerraouch↗
DOE OSTI2021

Triple-frequency radar retrieval of microphysical properties of snow

Abstract. An algorithm based on triple-frequency (X, Ka, W) radar measurements that retrieves the size, water content and degree of riming of ice clouds is presented. This study exploits the potential of multi-frequency radar measurements to provide information on bulk snow density that should underpin better estimates of the snow characteristic size and content within the radar volume. The algorithm is based on Bayes' rule with riming parameterised by the “fill-in” model. The radar reflectivities are simulated with a range of scattering models corresponding to realistic snowflake shapes. The algorithm is tested on multi-frequency radar data collected during the ESA-funded Radar Snow Experiment For Future Precipitation Mission. During this campaign, in situ microphysical probes were mounted on the same aeroplane as the radars. This nearly perfectly co-located dataset of the remote and in situ measurements gives an opportunity to derive a combined multi-instrument estimate of snow microphysical properties that is used for a rigorous validation of the radar retrieval. Results suggest that the triple-frequency retrieval performs well in estimating ice water content (IWC) and mean mass-weighted diameters obtaining root-mean-square errors of 0.13 and 0.15, respectively, for log 10IWC and log 10Dm. The retrieval of the degree of riming is more challenging, and only the algorithm that uses Doppler information obtains results that are highly correlated with the in situ data.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1982

MSG-7: Atmospheric Penetration of Solar Radiation in the Range of Schumann-runge Bands

There have been major efforts in measuring extraterrestrial solar irradiance for use in atmospheric studies. The quantity of immediate relevance to theoretical studies is the number of photons which reach a given altitude in the middle atmosphere. Current models compute the attenuated radiation field but the cross sections available for the major absorbers, O2 and O3, often come from experiments that are now quite old. Balloon measurements show some significant differences between the predicted and observed ultraviolet radiation field between 30 and 40 km. The wavelength region to be studied includes Lyman alpha plus the range 175 nm to the visible. Specific topics to be addressed are as follows: (1) the cross sections of the major absorbers, O2 and O3 including the Schumann-Runge bands as a subset; (2) comparison of the in situ measurements of the attenuated radiation field with calculations; and (3) the relevance of the scattered and reflected radiation fields for middle atmospheric processes.

Frederick, J. E.↗
NASA NTRS1991

Determination of the optical thickness and effective particle radius of clouds from reflected solar radiation measurements. II - Marine stratocumulus observations

A multispectral scanning radiometer has been used to obtain measurements of the reflection function of marine stratocumulus clouds at 0.75 micron and at 1.65 and 2.16 microns. These observations were obtained from the NASA ER-2 aircraft as part of the FIRE, conducted off the coast of southern California during July 1987. Multispectral images of the reflection function were used to derive the optical thickness and the effective particle radius of stratiform cloud layers on four days. In addition to the radiation measurements, in situ microphysical measurements were obtained from an aircraft. In this paper, the remote sensing results are compared with in situ observations, which show a good spatial correlation for both optical thickness and effective radius. These comparisons further show systematic differences between remote sensing and in situ values, with a tendency for remote sensing to overestimate the effective radius by about 2-3 microns, independent of particle radius. The optical thickness, in contrast, is somewhat overestimated for small optical thicknesses and underestimated for large optical thicknesses. An introduction of enhanced gaseous absorption at a wavelength of 2.16 microns successfully explains some of these observed discrepancies.

Nakajima, Teruyuki↗
NASA NTRS2006

CO Signatures in Subtropical Convective Clouds and Anvils during CRYSTAL-FACE: An Analysis of Convective Transport and Entrainment using Observations and a Cloud-Resolving Model

Convective systems are an important mechanism in the transport of boundary layer air into the upper troposphere. The Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE) campaign, in July 2002, was developed as a comprehensive atmospheric mission to improve knowledge of subtropical cirrus systems and their roles in regional and global climate. In situ measurements of carbon monoxide (CO), water vapor (H2Ov), and total water (H2Ot) aboard NASA's WB-57F aircraft and CO aboard the U.S. Navy's Twin Otter aircraft were obtained to study the role of convective transport. Three flights sampled convective outflow on 11, 16 and 29 July found varying degrees of CO enhancement relative to the free troposphere. A cloud-resolving model used the in situ observations and meteorological fields to study these three systems. Several methods of filtering the observations were devised here using ice water content, relative humidity with respect to ice, and particle number concentration as a means to statistically sample the model results to represent the flight tracks. A weighted histogram based on ice water content observations was then used to sample the simulations for the three flights. In addition, because the observations occurred in the convective outflow cirrus and not in the storm cores, the model was used to estimate the maximum CO within the convective systems. In general, anvil-level air parcels contained an estimated 20-40% boundary layer air in the analyzed storms.

Lopez, Jimena P.↗
NASA NTRS2006

CO Signatures in Subtropical Convective Clouds and Anvils During CRYSTAL-FACE: An Analysis of Convective Transport and Entertainment Using Observations and a Cloud-Resolving Model

Convective systems are an important mechanism in the transport of boundary layer air into the upper troposphere. The Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE) campaign, in July 2002, was developed as a comprehensive atmospheric mission to improve knowledge of subtropical cirrus systems and their roles in regional and global climate. In situ measurements of carbon monoxide (CO), water vapor (H20v), and total water (H20t) aboard NASA's . WB-57F aircraft and CO aboard the U.S. Navy's Twin Otter aircraft were obtained to study the role of convective transport. Three flights sampled convective outflow on 11, 16 and 29 July found varying degrees of CO enhancement relative to the fiee troposphere. A cloud-resolving model used the in situ observations and meteorological fields to study these three systems. Several methods of filtering the observations were devised here using ice water content, relative humidity with respect to ice, and particle number concentration as a means to statistically sample the model results to represent the flight tracks. A weighted histogram based on ice water content observations was then used to sample the simulations for the three flights. In addition, because the observations occurred in the convective outflow cirrus and not in the storm cores, the model was used to estimate the maximum CO within the convective systems. In general, anvil-level air parcels contained an estimated 20-40% boundary layer air in the analyzed storms.

Lopez, Jimena P.↗
NASA NTRS2021

Measuring Atmospheric CO2 Enhancements from the 2017 British Columbia 1 Wildfires Using a Lidar

During the summer 2017 ASCENDS/ABoVE airborne science campaign, the NASA Goddard CO2 Sounder lidar overflew smoke plumes from wildfires in the British Columbia, Canada. In the flight path over Vancouver Island on 8 August 2017, the column XCO2 retrievals from the lidar measurements at flight altitudes around 9 km showed an average enhancement of 4 ppm from the wildfires. A comparison of these enhancements with those from the Goddard Global Chemistry Transport model suggested that the modeled CO2 emissions from wildfires were underestimated by more than a factor of 2. A spiral-down validation performed at Moses Lake airport, Washington showed a bias of 0.1 ppm relative to in situ measurements and a standard deviation of 1 ppm in lidar XCO2 retrievals. The results show that future airborne campaigns and spaceborne missions with this type of lidar can improve estimates of CO2 emissions from wildfires and estimates of carbon fluxes globally.

Jianping Mao↗
NASA NTRSDate not supplied

Wide Band Gap Radiation Detectors for Deep Space Science

Understanding how the Sun, Earth, and other objects in the solar system interact with the space radiation environment is crucial for improving activities of humans on Earth and in space. Low-power, low-noise, multidirectional robust detectors for detecting ions with a wide range of mass and energies will provide a more complete understanding of space environment physics. To meet these challenges, new ion detectors based on wide band gap (WBG) semiconductors are being developed for integration on a variety of deep space platforms. NASA Glenn Research Center (GRC) is applying its expertise and facilities in harsh environment instrumentation to develop supporting technologies to enable improved instruments for space science missions. New detector technologies being developed at GRC include SiC solid-state devices as practical robust, thermally stable large area detectors for LET measurements in compact, stacked charged particle telescope. The low-noise, thermally stable nature of the WBG detectors allows a small multidirectional array of charged particle telescopes to be packed in a 6U CubeSat without active cooling for operation in lunar orbit or deep space. Using a full variety of different WBG detectors, an extremely compact instrument to provide multi-directional, comprehensive (composition, velocity, and direction) in-situ measurements of heavy ions in space plasma environments can be realized.

ion detectors↗