News Article | August 22, 2016
A team of small, shoebox-sized satellites, flying in formation around the Earth, could estimate the planet’s reflected energy with twice the accuracy of traditional monolith satellites, according to an MIT-led study published online in Acta Astronautica. If done right, such satellite swarms could also be cheaper to build, launch, and maintain. The researchers, led by Sreeja Nag, a former graduate student in MIT’s Department of Aeronautics and Astronautics (AeroAstro), simulated the performance of a single large, orbiting satellite with nine sensors, compared with a cluster of three to eight small, single-sensor satellites flying together around the Earth. In particular, the team looked at how each satellite formation measures albedo, or the amount of light reflected from the Earth — an indication of how much heat the planet reflects. The team found that clusters of four or more small satellites were able to look at a single location on Earth from multiple angles, and measure that location’s total reflectance with an error that is half that of single satellites in operation today. Nag says such a correction in estimation error could significantly improve scientists’ climate projections. “Total outgoing radiation is actually one of the biggest uncertainties in climate change, because it is a complex function of where on Earth you are, what season it is, what time of day it is, and it’s very difficult to ascertain how much heat leaves the Earth,” Nag says. “If we can estimate the reflectance of different surface types, globally, frequently, and more accurately, which a cluster of satellites would let you do, then at least you’ve solved one part of the climate puzzle.” Nag, who is now a research engineer at the Bay Area Environmental Research Institute, NASA Ames Research Center, and NASA Goddard Space Flight Center, has co-authored the paper with Oli de Weck, an AeroAstro professor at MIT; Charles Gatebe of NASA Goddard Space Flight Center; and David Miller, NASA Chief Technologist and the Jerome C. Hunsaker Professor in AeroAstro. Nag says that to accurately estimate the reflectance of any ground spot on Earth requires measurements taken of that spot from multiple angles at the same time. “The Earth does not reflect equally in all directions,” Nag says. “If you don’t get these multiple angles, you might under- or overestimate how much it’s reflecting, if you have to extrapolate from just one direction.” Today, satellites that measure the Earth’s albedo typically do so with multiple cameras, arranged on a single satellite. For example, NASA’s Multi-angle Imaging SpectroRadiometer (MISR) instrument on the Terra satellite houses nine cameras that take images of the Earth from a fan-like arrangement of angles. Nag says the drawback of this design is that the cameras have a limited view, as they are not designed to change angles and can only observe within a single plane. Instead, the team proposes a cluster of small satellites that travel around the Earth in a loose formation, close enough to each other to be able to image the same spot on the ground from their various vantage points. Each satellite can move within the formation, taking pictures of the same spot at the same time from different angles. “Over time, the cluster would cover the whole Earth, and you’d have a multiangular, 3-D view of the entire planet from space, which has not been done before with multiple satellites,” Nag says. “Moreover, we can use multiple clusters for more frequent coverage of the Earth.” Nag and her colleagues simulated formations of three to eight small, orbiting satellites, and developed an algorithm to direct each satellite to point to the same ground spot simultaneously, regardless of its position in space. They programmed each formation to measure a theoretical quantity known as bidirectional reflectance distribution function, or BRDF, that is used to calculate albedo and total outgoing radiation, based on the angles at which measurements are taken and the angle of the sun’s incoming rays. For each formation, Nag calculated the satellites’ error in measuring BRDF and compared these errors with those of the MISR instrument on the Terra satellite. She validated all errors against data from the NASA Goddard’s Cloud Absorption Radiometer, an airborne instrument that obtains tens of thousands of angular measurements of a ground spot. She found that every formation with seven or more single-sensor satellites performed better than the nine-sensor monolith satellite, with lower estimation errors. The best three-satellite clusters generated half the error of MISR’s estimates of albedo. The accuracy of overall estimates improved with the number of satellites in the cluster. “We found that even if you can’t maintain your satellites perfectly, the worst-case error is less than what the single satellite is able to do,” Nag says. “For the best-case scenario, if you are more than halving the error that you currently get, you’re halving the amount of error you would get in reflected heat leaving the Earth. That’s really important for climate change.” Expanding on this point, Volker Gass, director of the Swiss Space Center at the Swiss Federal Institute of Technology, says better estimates of Earth’s reflectance can help scientists predict long-term environmental trends. “Halving the error, or increasing the precision, has a direct impact on the climate model used,” says Gass, who was not involved in the study. “As an example, the reflection of a snow covered surface (or the absence thereof) at a certain time of the year can predict flooding or drought in later months. Better and more accurate predictions may lead to cost savings, or even the prevention of loss of life.” "This work is significant not only for demonstrating the capability for instantaneous multiangular BRDF measurements from space for different land surface types and biomes, but also for establishing a strong methodological bridge between the systems engineering of future small satellite clusters and high fidelity Earth science simulations,” de Weck says. “Our team fully expects that a demonstration mission of this type could be flown within the next decade." While multisatellite formation flights have been deemed expensive endeavors, Nag says this assumption mostly pertains to satellites that need to maintain very strict formations, with centimeter-level accuracy — a precision that requires expensive control systems. The satellites she proposes would not have to keep to any single formation as long as they all point to the same location. There’s another big advantage to monitoring the Earth with small satellites: less risk. “You can launch three of these guys and start operating, and then put three more up in space later — your performance would improve with more satellites,” Nag says. “If you lose one or two satellites, you don’t lose the whole measurement system — you have graceful degradation. If you lose the monolith, you lose everything.”
Contreras C.S.,NASA |
Contreras C.S.,Bay Area Environmental Research Institute |
Astrophysical Journal, Supplement Series | Year: 2013
The formation and destruction mechanisms of interstellar dust analogs formed from a variety of polycyclic aromatic hydrocarbon (PAH) and hydrocarbon molecular precursors are studied in the laboratory. We used the newly developed facility COSmIC, which simulates interstellar and circumstellar environments, to investigate both PAHs and species that include the cosmically abundant atoms O, N, and S. The species generated in a discharge plasma are detected, monitored, and characterized in situ using highly sensitive techniques that provide both spectral and ion mass information. We report here the first series of measurements obtained in these experiments which focus on the characterization of the most efficient molecular precursors in the chemical pathways that eventually lead to the formation of carbonaceous grains in the stellar envelopes of carbon stars. We compare and discuss the relative efficiencies of the various molecular precursors that lead to the formation of the building blocks of carbon grains. We discuss the most probable molecular precursors in terms of size and structure and the implications for the expected growth and destruction processes of interstellar carbonaceous dust. © 2013. The American Astronomical Society. All rights reserved.
Influence of stellar multiplicity on planet formation. I. evidence of suppressed planet formation due to stellar companions within 20 AU and validation of four planets from the kepler multiple planet candidates
Wang J.,Yale University |
Xie J.-W.,University of Toronto |
Xie J.-W.,Nanjing University |
Barclay T.,NASA |
And 2 more authors.
Astrophysical Journal | Year: 2014
The planet occurrence rate for multiple stars is important in two aspects. First, almost half of stellar systems in the solar neighborhood are multiple systems. Second, the comparison of the planet occurrence rate for multiple stars to that for single stars sheds light on the influence of stellar multiplicity on planet formation and evolution. We developed a method of distinguishing planet occurrence rates for single and multiple stars. From a sample of 138 bright (KP < 13.5) Kepler multi-planet candidate systems, we compared the stellar multiplicity rate of these planet host stars to that of field stars. Using dynamical stability analyses and archival Doppler measurements, we find that the stellar multiplicity rate of planet host stars is significantly lower than field stars for semimajor axes less than 20 AU, suggesting that planet formation and evolution are suppressed by the presence of a close-in companion star at these separations. The influence of stellar multiplicity at larger separations is uncertain because of search incompleteness due to a limited Doppler observation time baseline and a lack of high-resolution imaging observation. We calculated the planet confidence for the sample of multi-planet candidates and find that the planet confidences for KOI 82.01, KOI 115.01, KOI 282.01, and KOI 1781.02 are higher than 99.7% and thus validate the planetary nature of these four planet candidates. This sample of bright Kepler multi-planet candidates with refined stellar and orbital parameters, planet confidence estimation, and nearby stellar companion identification offers a well-characterized sample for future theoretical and observational study. © 2014. The American Astronomical Society. All rights reserved..
Ganguly S.,Bay Area Environmental Research Institute |
Friedl M.A.,Boston University |
Tan B.,Earth Resources Technology Inc. |
Zhang X.,Earth Resources Technology Inc. |
Verma M.,Boston University
Remote Sensing of Environment | Year: 2010
Information related to land surface phenology is important for a variety of applications. For example, phenology is widely used as a diagnostic of ecosystem response to global change. In addition, phenology influences seasonal scale fluxes of water, energy, and carbon between the land surface and atmosphere. Increasingly, the importance of phenology for studies of habitat and biodiversity is also being recognized. While many data sets related to plant phenology have been collected at specific sites or in networks focused on individual plants or plant species, remote sensing provides the only way to observe and monitor phenology over large scales and at regular intervals. The MODIS Global Land Cover Dynamics Product was developed to support investigations that require regional to global scale information related to spatio-temporal dynamics in land surface phenology. Here we describe the Collection 5 version of this product, which represents a substantial refinement relative to the Collection 4 product. This new version provides information related to land surface phenology at higher spatial resolution than Collection 4 (500-m vs. 1-km), and is based on 8-day instead of 16-day input data. The paper presents a brief overview of the algorithm, followed by an assessment of the product. To this end, we present (1) a comparison of results from Collection 5 versus Collection 4 for selected MODIS tiles that span a range of climate and ecological conditions, (2) a characterization of interannual variation in Collections 4 and 5 data for North America from 2001 to 2006, and (3) a comparison of Collection 5 results against ground observations for two forest sites in the northeastern United States. Results show that the Collection 5 product is qualitatively similar to Collection 4. However, Collection 5 has fewer missing values outside of regions with persistent cloud cover and atmospheric aerosols. Interannual variability in Collection 5 is consistent with expected ranges of variance suggesting that the algorithm is reliable and robust, except in the tropics where some systematic differences are observed. Finally, comparisons with ground data suggest that the algorithm is performing well, but that end of season metrics associated with vegetation senescence and dormancy have higher uncertainties than start of season metrics. © 2010 Elsevier Inc.
Carballido A.,National Autonomous University of Mexico |
Cuzzi J.N.,NASA |
Hogan R.C.,Bay Area Environmental Research Institute
Monthly Notices of the Royal Astronomical Society | Year: 2010
We use magnetohydrodynamic simulations to measure relative speeds of solids in a protoplanetary disc with turbulence generated by the magnetorotational instability. Relative velocities are calculated as functions of particle Stokes number St, which measures the aerodynamic coupling to the gas. When relative velocities Vrel are calculated between two particles i and j such that Sti ≫Stj and Stj ≪ 1, the data matches the analytical model of Ormel and Cuzzi. However, if Vrel corresponds to two particles with the same St, only the data for the more loosely coupled solids (i.e. those with large St) follow the model. The discrepancy at the low- St end can be attributed to: (i) the numerical disc model's coarse resolution, which is unable to probe smaller turbulent eddies and, therefore, the dominant contribution to the particle relative velocities is given by the interpolation of the gas velocity inside the grid cells; (ii) the sparse particle sampling, which prevents the measurement of relative velocities between two particles in the same place at the same time. The distribution of turbulence-induced relative speeds can have a wide spread of values, which may lead to particle shattering, subject to the turbulent gas velocity. Codes such as the one used in this work, in general, underestimate relative velocities in turbulence for particles with because they lack energy on short time-scales (relative to a Kolmogorov spectrum). In making comparisons with theory, it is important to use the exact numerical energy spectrum instead of assuming a Kolmogorov inertial range. © 2010 The Authors. Journal compilation © 2010 RAS.
Sears D.W.G.,Bay Area Environmental Research Institute
Geochimica et Cosmochimica Acta | Year: 2016
Thermoluminescence (TL) properties of 29 CO chondrites from the Miller Range (MIL) and five chondrites from the Dominion Range (DOM) have been measured. MIL has a relatively strong natural TL signal (19.6 ± 14.7 krad), while some of the DOM samples have a very weak natural TL signal (<1 krad) whereas others resemble the MIL meteorites. I argue that MIL and some of the DOM samples had a normal perihelion (~1.0 AU) and terrestrial age of ~450-700 ka, while some of the DOM samples have a terrestrial age of ~100 ka but a perihelion of ~0.8 AU. The DOM meteorites also show considerable heterogeneity in their induced TL properties, also suggesting that the DOM fragments represent more than one fall. The induced TL data for the MIL samples studied here are consistent with them all being from a single fragmented meteorite. Small (50 mg) chips have TL properties similar to 500 mg chips, so that the smaller chips are representative, although samples taken from original masses less than ~2 g have low natural TL suggesting that they were heated during atmospheric fall. The properties of CO chondrites are reviewed in terms of their petrologic types. Correlations between TL sensitivity, the most quantitative technique for evaluating metamorphic alteration in CO chondrites, and data for olivine composition and heterogeneity, matrix composition, inert gas content, metal composition (Ni, Co, and Cr in the kamacite), bulk carbon, C and O isotopes, graphite ordering, spectral reflectance at 0.8 μm, and textural characteristics of the ameboid olivine and Ca-rich inclusions are examined. The petrographic types appear to be largely metamorphic in origin with perhaps a minor role for metasomatism. Contrary to recent proposals it is here argued that petrologic type definitions should (1) be specific enough to be meaningful, but broad enough to be simple in application and robust to new developments, (2) be descriptive and not interpretative, (3) should not oversimplify and obscure important class-to-class differences, and (4) take account of all the available information, while avoiding reliance on any one technique or single observation whose application is based on interpretation. With these considerations in mind the petrographic type definitions for CO chondrites are restated and the petrologic type of 3.2 assigned to both the MIL and DOM CO chondrites. © 2016 Elsevier Ltd.
Shinozuka Y.,Bay Area Environmental Research Institute |
Redemann J.,Bay Area Environmental Research Institute
Atmospheric Chemistry and Physics | Year: 2011
We present statistics on the horizontal variability of aerosol optical depth (AOD) directly measured from the NASA P-3 aircraft. Our measurements during two contrasting phases (in Alaska and Canada) of the ARCTAS mission arguably constrain the variability in most aerosol environments common over the globe. In the Canada phase, which features local emissions, 499 nm AOD has a median relative standard deviation (stdrel, med) of 19 % and 9 % and an autocorrelation (r) of 0.37 and 0.71 over 20 km and 6 km horizontal segments, respectively. In the Alaska phase, which features long-range transport, the variability is considerably lower (stdrel, med Combining double low line 3 %, r Combining double low line 0.92 even over 35.2 km). Compared to the magnitude of AOD, its wavelength dependence varies less in the Canada phase, more in the Alaska phase. We translate these findings from straight-line flight tracks into grid boxes and points, to help interpretation and design of satellite remote sensing, suborbital observations and transport modeling. © 2011 Author(s).
Sears D.W.G.,Bay Area Environmental Research Institute
Meteoritics and Planetary Science | Year: 2014
Vagn Buchwald (Fig. ) was born in Copenhagen where he attended school and college. Then after 18 months of military service, he assumed a position at the Technical University of Copenhagen. A few years later, he was presented with a piece of the Cape York meteorite, which led to an interest in iron meteorites. Through a campaign of informed searching, Vagn found the 20 ton Agpalilik meteorite (part of the Cape York shower) on 31st July 1963 and by September 1967 had arranged its transport to Copenhagen. After sorting and describing the Danish collection, which included application of the Fe-Ni-P phase diagram to iron meteorite mineralogy, Vagn was invited to sort and describe other iron meteorite collections. This led to a 7 yr project to write his monumental Handbook of Iron Meteorites. Vagn spent 3 yr in the United States and visited most of the world's museums, the visit to Berlin being especially important since the war had left their iron meteorites in bad condition and without labels. During a further decade or more of iron meteorite research, he documented natural and anthropomorphic alterations experienced by iron meteorites, discovered five new minerals (roaldite, carlsbergite, akaganeite, hibbingite, and arupite); had a mineral (buchwaldite, NaCaPO4) and asteroid (3209 Buchwald 1982 BL1) named after him; and led expeditions to Chile, Namibia, and South Africa in search of iron meteorites and information on them. Vagn then turned his attention to archeological metal artifacts. This work resulted in many papers and culminated in two major books on the subject published in 2005 and 2008, after his retirement in 1998. Vagn Buchwald has received numerous Scandinavian awards and honors, and served as president of the Meteoritical Society in 1981-1982. © The Meteoritical Society, 2014.
Kahre M.A.,Bay Area Environmental Research Institute |
Kahre M.A.,NASA |
Icarus | Year: 2010
Mars General Circulation Model (GCM) simulations are presented to illustrate the importance of the ice emissivity of the seasonal CO2 polar caps in regulating the effects of airborne dust on the martian CO2 cycle. Simulated results show that atmospheric dust suppresses CO2 condensation when the CO2 ice emissivity is high but enhances it when the CO2 ice emissivity is low. This raises the possibility that the reason for the repeatable nature of the CO2 cycle in the presence of a highly variable dust cycle is that the CO2 ice emissivity is " neutral" - the value that leads to no change in CO2 condensation with changing atmospheric dust. For this GCM, the " neutral" emissivity is approximately 0.55, which is low compared to observed cap emissivities. This inconsistency poses a problem for this hypothesis. However, it is clear that the CO2 ice emissivity is a critical physical parameter in determining how atmospheric dust affects the CO2 cycle on Mars. © 2009 Elsevier Inc.
Agency: NSF | Branch: Continuing grant | Program: | Phase: SOLAR-TERRESTRIAL | Award Amount: 109.25K | Year: 2016
This 3-year SHINE project is aimed at developing data assimilation techniques for physics-based predictions of the solar activity on the scale of the solar cycle. The project is expected to improve our modeling capabilities to predict the solar cycle, and to advance our knowledge about the solar dynamo and the nature of the solar cycle. The data assimilation techniques applied to the sophisticated dynamo models would benefit the broad solar physics community. The scientific outcome of this project would be important for the studies in the heliosphere, the Earths upper atmosphere, and possibly climate in the long-term, and it would be beneficial for current and future space missions and society.
The research plan of this 3-year SHINE project includes the following tasks: (i) investigate the sensitivity of model predictions to uncertainties in observational data for various data assimilation methods and various reduced dynamo models in a dynamical system formulation; (ii) develop procedures to estimate the model parameters, system state, and their uncertainties; verify and test data assimilation procedures by applying them to simulated data and previous solar cycle observations; (iii) using current observational data, calculate predictions of the sunspot number and total poloidal and toroidal magnetic field components for Cycle 25, and provide uncertainties and confidence intervals; and (iv) develop a data assimilation procedure for long-term synoptic forecasts of solar activity by using 2D dynamo models, synoptic magnetograms, and meridional flow measurements from the Solar Dynamics Observatory and ground-based synoptic networks such as GONG and SOLIS. The project is directly relevant to the NSFs SHINE program, because it will provide important knowledge about the global solar activity, which is the major source of high-energy disturbances in the solar, heliospheric, and interplanetary environment. Such knowledge is critical for accurate modeling and prediction of space weather conditions from the solar surface to the Earth and beyond. The research and EPO agenda of this project supports the Strategic Goals of the AGS Division in discovery, learning, diversity, and interdisciplinary research.