Callahan M.P.,National Aeronautics and Space Administration Goddard Space Flight Center |
Callahan M.P.,Goddard Center for Astrobiology |
Gerakines P.A.,National Aeronautics and Space Administration Goddard Space Flight Center |
Gerakines P.A.,Goddard Center for Astrobiology |
And 6 more authors.
Icarus | Year: 2013
Aromatic hydrocarbons account for a significant portion of the organic matter in carbonaceous chondrite meteorites, as a component of both the low molecular weight, solvent-extractable compounds and the insoluble organic macromolecular material. Previous work has suggested that the aromatic compounds in carbonaceous chondrites may have originated in the radiation-processed icy mantles of interstellar dust grains. Here we report new studies of the organic residue made from benzene irradiated at 19. K by 0.8. MeV protons. Polyphenyls with up to four rings were unambiguously identified in the residue by gas chromatography-mass spectrometry. Atmospheric pressure photoionization Fourier transform mass spectrometry was used to determine molecular composition, and accurate mass measurements suggested the presence of polyphenyls, partially hydrogenated polyphenyls, and other complex aromatic compounds. The profile of low molecular weight compounds in the residue compared well with extracts from the Murchison and Orgueil meteorites. These results are consistent with the possibility that solid phase radiation chemistry of benzene produced some of the complex aromatics found in meteorites. © 2013.
Meier W.N.,National Aeronautics and Space Administration Goddard Space Flight Center |
Peng G.,North Carolina State University |
Peng G.,National Oceanic and Atmospheric Administration |
Scott D.J.,University of Colorado at Boulder |
Savoie M.H.,University of Colorado at Boulder
Polar Research | Year: 2014
A new satellite-based passive microwave sea-ice concentration product developed for the National Oceanic and Atmospheric Administration (NOAA) Climate Data Record (CDR) programme is evaluated via comparison with other passive microwave-derived estimates. The new product leverages two well-established concentration algorithms, known as the NASA Team and Bootstrap, both developed at and produced by the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC). The seaice estimates compare well with similar GSFC products while also fulfilling all NOAA CDR initial operation capability (IOC) requirements, including (1) selfdescribing file format, (2) ISO 19115-2 compliant collection-level metadata, (3) Climate and Forecast (CF) compliant file-level metadata, (4) grid-cell level metadata (data quality fields), (5) fully automated and reproducible processing and (6) open online access to full documentation with version control, including source code and an algorithm theoretical basic document. The primary limitations of the GSFC products are lack of metadata and use of untracked manual corrections to the output fields. Smaller differences occur from minor variations in processing methods by the National Snow and Ice Data Center (for the CDR fields) and NASA (for the GSFC fields). The CDR concentrations do have some differences from the constituent GSFC concentrations, but trends and variability are not substantially different. © 2014 W.N. Meier et al.
Garry W.B.,Smithsonian Institution |
Bleacher J.E.,National Aeronautics and Space Administration Goddard Space Flight Center
Special Paper of the Geological Society of America | Year: 2011
The volcanic processes that formed Vallis Schröteri are not well understood. Vallis Schröteri, located on the Aristarchus Plateau, is the largest rille on the Moon, and it displays three key morphologic components: the Cobra Head, the 155-km-long primary rille, and the 240-km-long inner rille. Observations of terrestrial eruptions are applied here to help explain the morphologic relationships observed for Vallis Schröteri. The Cobra Head, a 10-km-wide source vent surrounded by a 35-kmdiameter and 900-m-high low shield, might have been constructed from flows, spatter, and pyroclastic deposits erupted during lava fountain events, similar to the early stages of the vent at Pu'u 'Ō'ō in Hawaii and the fi nal morphology of Bandera crater, a cinder cone in New Mexico. The vent fed an initial sheet flow controlled by preeruption topography. A channel formed within this sheet flow was the foundation for the primary rille, which deepened through construction and thermomechanical erosion by lava. The inner rille is confi ned to the fl at fl oor of the primary rille and is characterized by tight gooseneck meanders. This rille crosscuts the distal scarp of the primary rille and extends toward Oceanus Procellarum. This enigmatic relationship can be explained through backup, overflow, and diversion of the lava into a new rille that eroded into the margin of the primary rille. Similar backup, overflow, and redirection of the lava flow were observed during the 1984 Mauna Loa eruption in Hawaii. Analysis of the fi nal morphology of lunar rilles provides key information about lunar volcanic processes and insight into the local stratigraphy. © 2011 The Geological Society of America. All rights reserved.
Zhang Q.,Unversities Space Research Association |
Zhang Q.,National Aeronautics and Space Administration Goddard Space Flight Center |
Cheng Y.-B.,National Aeronautics and Space Administration Goddard Space Flight Center |
Cheng Y.-B.,Earth Resources Technology Inc. |
And 8 more authors.
Agricultural and Forest Meteorology | Year: 2014
Accurate estimation of gross primary production (GPP) is essential for carbon cycle and climate change studies. Three AmeriFlux crop sites of maize and soybean were selected for this study. Two of the sites were irrigated and the other one was rainfed. The normalized difference vegetation index (NDVI), the enhanced vegetation index (EVI), the green band chlorophyll index (CIgreen), and the green band wide dynamic range vegetation index (WDRVIgreen) were computed from the moderate resolution imaging spectroradiometer (MODIS) surface reflectance data. We examined the impacts of the MODIS observation footprint and the vegetation bidirectional reflectance distribution function (BRDF) on crop daily GPP estimation with the four spectral vegetation indices (VIs - NDVI, EVI, WDRVIgreen and CIgreen) where GPP was predicted with two linear models, with and without offset: GPP=a×VI×PAR and GPP=a×VI×PAR+b. Model performance was evaluated with coefficient of determination (R2), root mean square error (RMSE), and coefficient of variation (CV). The MODIS data were filtered into four categories and four experiments were conducted to assess the impacts. The first experiment included all observations. The second experiment only included observations with view zenith angle (VZA)≤35° to constrain growth of the footprint size, which achieved a better grid cell match with the agricultural fields. The third experiment included only forward scatter observations with VZA≤35°. The fourth experiment included only backscatter observations with VZA≤35°. Overall, the EVI yielded the most consistently strong relationships to daily GPP under all examined conditions. The model GPP=a×VI×PAR+b had better performance than the model GPP=a×VI×PAR, and the offset was significant for most cases. Better performance was obtained for the irrigated field than its counterpart rainfed field. Comparison of experiment 2 vs. experiment 1 was used to examine the observation footprint impact whereas comparison of experiment 4 vs. experiment 3 was used to examine the BRDF impact. Changes in R2, RMSE, CV and changes in model coefficients "a" and "b" (experiment 2 vs. experiment 1; and experiment 4 vs. experiment 3) were indicators of the impacts. The second experiment produced better performance than the first experiment, increasing R2 (↑0.13) and reducing RMSE (↓0.68gCm-2d-1) and CV (↓9%). For each VI, the slope of GPP=a×VI×PAR in the second experiment for each crop type changed little while the slope and intercept of GPP=a×VI×PAR+b varied field by field. The CIgreen was least affected by the MODIS observation footprint in estimating crop daily GPP (R2, ↑0.08; RMSE, ↓0.42gCm-2d-1; and CV, ↓7%). Footprint most affected the NDVI (R2, ↑0.15; CV, ↓10%) and the EVI (RMSE, ↓0.84gCm-2d-1). The vegetation BRDF impact also caused variation of model performance and change of model coefficients. Significantly different slopes were obtained for forward vs. backscatter observations, especially for the CIgreen and the NDVI. Both the footprint impact and the BRDF impact varied with crop types, irrigation options, model options and VI options. © 2014 Elsevier B.V.
Petro N.E.,NASA |
Mest S.C.,Planetary Science Institute |
Mest S.C.,National Aeronautics and Space Administration Goddard Space Flight Center |
Teich Y.,Walter Johnson High School
Special Paper of the Geological Society of America | Year: 2011
The interior of the enigmatic South Pole-Aitken basin has long been recognized as being compositionally distinct from its exterior. However, the source of the compositional anomaly has been subject to some debate. Is the source of the ironenhancement due to lower-crustal/upper-mantle material being exposed at the surface, or was there some volume of ancient volcanism that covered portions of the basin interior? While several obvious mare basalt units are found within the basin and regions that appear to represent the original basin interior, there are several regions that appear to have an uncertain origin. Using a combination of Clementine and Lunar Orbiter images, several morphologic units are defi ned based on albedo, crater density, and surface roughness. An extensive unit of ancient mare basalt (cryptomare) is defined and, based on the number of superimposed craters, potentially represents the oldest volcanic materials within the basin. Thus, the overall iron-rich interior of the basin is not solely due to deeply derived crustal material, but is, in part due to the presence of ancient volcanic units. © 2011 The Geological Society of America. All rights reserved.