Recursos de colección

Caltech Authors (171.365 recursos)

Repository of works by Caltech published authors.

Group = Keck Institute for Space Studies

Mostrando recursos 1 - 20 de 129

  1. PhotoSpec: A new instrument to measure spatially distributed red and far-red Solar-Induced Chlorophyll Fluorescence

    Grossmann, Katja; Frankenberg, Christian; Magney, Troy S.; Hurlock, Stephen C.; Seibt, Ulrike; Stutz, Jochen
    Solar-Induced Chlorophyll Fluorescence (SIF) is an emission of light in the 650–850 nm spectral range from the excited state of the chlorophyll-a pigment after absorption of photosynthetically active radiation (PAR). As this is directly linked to the electron transport chain in oxygenic photosynthesis, SIF is a powerful proxy for photosynthetic activity. SIF observations are relatively new and, while global scale measurements from satellites using high-resolution spectroscopy of Fraunhofer bands are becoming more available, observations at the intermediate canopy scale using these techniques are sparse. We present a novel ground-based spectrometer system - PhotoSpec - for measuring SIF in the red (670–732 nm) and...

  2. Failures in sand in reduced gravity environments

    Marshall, Jason P.; Hurley, Ryan C.; Arthur, Dan; Vlahinic, Ivan; Senatore, Carmine; Iagnemma, Karl; Trease, Brian; Andrade, José E.
    The strength of granular materials, specifically sand is important for understanding physical phenomena on other celestial bodies. However, relatively few experiments have been conducted to determine the dependence of strength properties on gravity. In this work, we experimentally investigated relative values of strength (the peak friction angle, the residual friction angle, the angle of repose, and the peak dilatancy angle) in Earth, Martian, Lunar, and near-zero gravity. The various angles were captured in a classical passive Earth pressure experiment conducted on board a reduced gravity flight and analyzed using digital image correlation. The data showed essentially no dependence of the...

  3. Strongly Anisotropic Magnesiowüstite in Earth's Lower Mantle

    Finkelstein, Gregory J.; Jackson, Jennifer M.; Said, Ayman; Alatas, Ahmet; Leu, Bogdan M.; Sturhahn, Wolfgang; Toellner, Thomas S.
    The juxtaposition of a liquid iron‐dominant alloy against a mixture of silicate and oxide minerals at Earth's core–mantle boundary is associated with a wide range of complex seismological features. One category of observed structures is ultralow‐velocity zones, which are thought to correspond to either aggregates of partially molten material or solid, iron‐enriched assemblages. We measured the phonon dispersion relations of (Mg,Fe) O magnesiowüstite containing 76 mol% FeO, a candidate ultralow‐velocity zone phase, at high pressures using high energy‐resolution inelastic x‐ray scattering. From these measurements, we find that magnesiowüstite becomes strongly elastically anisotropic with increasing pressure, potentially contributing to a significant...

  4. Optical communication on CubeSats — Enabling the next era in space science

    Carrasco-Casado, Alberto; Biswas, Abhijit; Fields, Renny; Grefenstette, Brian; Harrison, Fiona; Sburlan, Suzana; Toyoshima, Morio
    CubeSats are excellent platforms to rapidly perform simple space experiments. Several hundreds of CubeSats have already been successfully launched in the past few years and the number of announced launches grows every year. These platforms provide an easy access to space for universities and organizations which otherwise could not afford it. However, these spacecraft still rely on RF communications, where the spectrum is already crowded and cannot support the growing demand for data transmission to the ground. Lasercom holds the promise to be the solution to this problem, with a potential improvement of several orders of magnitude in the transmission...

  5. Equations of state and anisotropy of Fe-Ni-Si alloys

    Morrison, Rachel A.; Jackson, Jennifer M.; Sturhahn, Wolfgang; Zhang, Dongzhou; Greenberg, Eran
    We present powder X‐ray diffraction data on body centered cubic (bcc)‐ and hexagonal close packed (hcp)‐structured Fe_(0.91)Ni_(0.09) and Fe_(0.8)Ni_(0.1)Si_(0.1) at 300 K up to 167 and 175 GPa, respectively. The alloys were loaded with tungsten powder as a pressure calibrant and helium as a pressure transmitting medium into diamond anvil cells, and their equations of state and axial ratios were measured with high statistical quality. These equations of state are combined with thermal parameters from previous reports to improve the extrapolation of the density, adiabatic bulk modulus, and bulk sound speed to the pressures and temperatures of Earth's inner core....

  6. PhotoSpec - Comprehensive Ground-Based Studies of Solar-Induced Chlorophyll Fluorescence: From the New Methods for Measurements of Photosynthesis from Space Study

    Frankenberg, Christian; Drewry, Darren; Stutz, Jochen
    The major goal of the PhotoSpec program was to develop a set of robust ground-based spectrometers that meet the measurement requirements to retrieve solar-induced chlorophyll fluorescence by exploiting solar Fraunhofer lines.

  7. Legacy of the Asteroid Redirect Robotic Mission (ARRM)

    Brophy, John R.
    NASA’s proposed Asteroid Redirect Robotic Mission (ARRM) began with the recognition in a 2010 NASA study that emerging high-power solar electric propulsion technology could be used to rendezvous with, capture, and return an entire, very small (~10,000 kg), near Earth asteroid to the International Space Station. A 2011 workshop by the Keck Institute for Space Studies (KISS) extended this NASA study to asteroid masses of order 500,000 kg by returning them to cislunar space. Subsequent detailed NASA studies in 2013-2014 confirmed the feasibility of this concept. This led to the establishment of the Asteroid Redirect Mission program that consisted of...

  8. Methane on Mars and Habitability: Challenges and Responses

    Yung, Yuk L.; Chen, Pin; Nealson, Kenneth H.; Atreya, Sushil; Beckett, Patrick; Ehlmann, Bethany; Blank, Jennifer; Eiler, John; Etiope, Giuseppe; Ferry, James G.; Forget, Francois; Gao, Peter; Hu, Renyu; Kleinböhl, Armin; Klusman, Ronald; Lefèvre, Franck; Miller, Charles; Mischna, Michael; Mumma, Michael; Newman, Sally; Oehler, Dorothy; Okumura, Mitchio; Oremland, Ronald; Orphan, Victoria; Popa, Radu; Russell, Michael; Shen, Linhan; Sherwood Lollar, Barbara; Stamenković, Vlada; Staehle, Robert; Stolper, Daniel; Templeton, Alex; Vandaele, Ann C.; Viscardy, Sébastien; Webster, Chris; Wennberg, Paul O.; Wong, Michael; Worden, John
    Recent measurements of methane (CH_4) by the Mars Science Laboratory (MSL) now confront us with robust data that demand interpretation. The baseline level of CH_4 (~1 ppbv, parts per billion by volume) requires a minimum production source of 1.7 × 10^7 mol year^(-1), while the pulses of CH_4 (~10 ppbv) require a source orders of magnitude larger (~5 × 10^9 mol year^(-1) if originating from a point source). What does this CH_4 represent in terms of interior geochemical processes, or is Martian CH_4 a biosignature? Discerning how CH_4 generation occurs on Mars may shed light on the potential habitability of...

  9. A Foreground Masking Strategy for [C II] Intensity Mapping Experiments Using Galaxies Selected by Stellar Mass and Redshift

    Sun, G.; Moncelsi, L.; Viero, M. P.; Silva, M. B.; Bock, J.; Bradford, C. M.; Chang, T.-C.; Cheng, Y.-T.; Cooray, A. R.; Crites, A.; Hailey-Dunsheath, S.; Uzgil, B.; Hunacek, J. R.; Zemcov, M.
    Intensity mapping provides a unique means to probe the epoch of reionization (EoR), when the neutral intergalactic medium was ionized by energetic photons emitted from the first galaxies. The [C II] 158 μm fine-structure line is typically one of the brightest emission lines of star-forming galaxies and thus a promising tracer of the global EoR star formation activity. However, [C II] intensity maps at 6 ≾ z ≾ 8 are contaminated by interloping CO rotational line emission (3 ⩽ J_(upp) ⩽ 6) from lower-redshift galaxies. Here we present a strategy to remove the foreground contamination in upcoming [C II] intensity...

  10. MEMS IMU navigation with model based dead-reckoning and one-way-travel-time acoustic range measurements for autonomous underwater vehicles

    Kepper, James H., IV
    Recent advances in acoustic navigation methodologies are enabling the way for AUVs to extend their submerged mission time and maintain a bounded XY position error. Additionally, advances in inertial sensor technology have drastically lowered the size, power consumption, and cost of these sensors. Nonetheless, these sensors are still noisy and accrue error over time. This thesis builds on the research and recent developments in single beacon one-way travel-time (OWTT) acoustic navigation and investigates the degree of bounding position error for small AUVs with a minimal navigation strap-down sensor suite, relying mostly on a consumer grade microelectromechanical system (MEMS) inertial measurement...

  11. Science-driven Autonomous & Heterogeneous Robotic Networks: A Vision for Future Ocean Observations

    Thompson, Andrew F.; Chien, Steve; Chao, Yi; Kinsey, James
    The goal of this project was to develop the first algorithms that allow a heterogeneous group of oceanic robots to autonomously determine and implement sampling strategies with the help of numerical ocean forecasts and remotely-sensed observations. Two-way feedback with shore-based numerical models, tested in the field, had not previously been attempted. New planning algorithms were tested during two field programs in Monterey Bay during a 12-month period using three different types of autonomous vehicles.

  12. Closed-loop one-way-traveltime navigation using low-grade odometry for autonomous underwater vehicles

    Claus, Brian; Kepper, James H., IV; Suman, Stefano; Kinsey, James C.
    This paper extends the progress of single beacon one‐way‐travel‐time (OWTT) range measurements for constraining XY position for autonomous underwater vehicles (AUV). Traditional navigation algorithms have used OWTT measurements to constrain an inertial navigation system aided by a Doppler Velocity Log (DVL). These methodologies limit AUV applications to where DVL bottom‐lock is available as well as the necessity for expensive strap‐down sensors, such as the DVL. Thus, deep water, mid‐water column research has mostly been left untouched, and vehicles that need expensive strap‐down sensors restrict the possibility of using multiple AUVs to explore a certain area. This work presents a solution...

  13. Constraints on small-scale heterogeneity in the lowermost mantle from observations of near podal PcP precursors

    Zhang, Baolong; Ni, Sidao; Sun, Daoyuan; Shen, Zhichao; Jackson, Jennifer M.; Wu, Wenbo
    Volumetric heterogeneities on large (∼>1000 km) and intermediate scales (∼>100 km) in the lowermost mantle have been established with seismological approaches. However, there are controversies regarding the level of heterogeneity in the lowermost mantle at small scales (a few kilometers to tens of kilometers), with lower bound estimates ranging from 0.1% to a few percent. We take advantage of the small amplitude PcP waves at near podal distances (0–12°) to constrain the level of small-scale heterogeneity within 250 km above the CMB. First, we compute short period synthetic seismograms with a finite difference code for a series of volumetric heterogeneity...

  14. Addressing the Mars ISRU Challenge: Production of Oxygen and Fuel from CO_2 using Sunlight

    West, William; Atwater, Harry A.; Kubiak, Clifford P.
    Advanced exploration of Mars, particularly human missions, will require vast amounts of fuel and oxygen for extended campaigns and the return of samples or humans back to Earth. If fuel and oxygen can be prepared on Mars from in-situ resources, this would greatly reduce the launch mass of the mission from Earth. In this Keck Institute for Space Sciences (KISS) study, the viability of Mars near-ambient temperature photoelectrochemical (PEC) or electrochemical (EC) production of fuel and oxygen from atmospheric carbon dioxide—with or without available water—was examined. With PEC devices incorporated into lightweight, large-area structures operating near 25°C and collecting solar...

  15. Analysis of Shear Bands in Sand Under Reduced Gravity Conditions

    Marshall, Jason P.; Hurley, Ryan C.; Arthur, Dan; Vlahinić, Ivan; Senatore, Carmine; Iagnemma, Karl; Trease, Brian; Andrade, José E.
    The strength of granular material, specifically sand is of pivotal importance for understanding physical phenomena on other celestial bodies. However, relatively few experiments have been conducted to determine the dependence of strength properties on gravity. In this work, we experimentally investigated three measures of strength (peak, confined flow, and unconfined flow friction angle) in Earth, Martian, Lunar, and near-zero gravity. The angles were captured in a passive Earth pressure experiment conducted on a reduced gravity flight. The results showed no dependence of the peak friction angle on gravity, a weak dependence of the confined flow friction angle on gravity, and...

  16. Autonomous sampling of ocean submesoscale fronts with ocean gliders and numerical model forecasting

    Flexas, Mar M.; Troesch, Martina I.; Chien, Steve; Thompson, Andrew F.; Chu, Selina; Branch, Andrew; Farrara, John D.; Chao, Yi
    Submesoscale fronts arising from mesoscale stirring are ubiquitous in the ocean and have a strong impact on upper-ocean dynamics. This work presents a method for optimizing the sampling of ocean fronts with autonomous vehicles at meso- and submesoscales, based on a combination of numerical forecast and autonomous planning. This method uses a 48-h forecast from a real-time high-resolution data-assimilative primitive equation ocean model, feature detection techniques, and a planner that controls the observing platform. The method is tested in Monterey Bay, off the coast of California, during a 9-day experiment focused on sampling subsurface thermohaline-compensated structures using a Seaglider as...

  17. A New Standard for Assessing the Performance of High Contrast Imaging Systems

    Jensen-Clem, Rebecca; Mawet, Dimitri; Gomez Gonzalez, Carlos A.; Absil, Olivier; Belikov, Ruslan; Currie, Thayne; Kenworthy, Matthew A.; Marois, Christian; Mazoyer, Johan; Ruane, Garreth; Tanner, Angelle; Cantalloube, Faustine
    As planning for the next generation of high contrast imaging instruments (e.g., WFIRST, HabEx, and LUVOIR, TMT-PFI, EELT-EPICS) matures and second-generation ground-based extreme adaptive optics facilities (e.g., VLT-SPHERE, Gemini-GPI) finish their principal surveys, it is imperative that the performance of different designs, post-processing algorithms, observing strategies, and survey results be compared in a consistent, statistically robust framework. In this paper, we argue that the current industry standard for such comparisons—the contrast curve—falls short of this mandate. We propose a new figure of merit, the "performance map," that incorporates three fundamental concepts in signal detection theory: the true positive fraction, the...

  18. A model for decoding the life cycle of granular avalanches in a rotating drum

    Marteau, Eloïse; Andrade, José E.
    Granular materials can behave as harmless sand dunes or as devastating landslides. A granular avalanche marks the transition between these distinct solid-like and fluid-like states. The solid-like state is typically described using plasticity models from critical state theory. In the fluid regime, granular flow is commonly captured using a visco-plastic model. However, due to our limited understanding of the mechanism governing the solid–fluid-like transition, characterizing the material behavior throughout the life cycle of an avalanche remains an open challenge. Here, we employ laboratory experiments of transient avalanches spontaneously generated by a rotating drum. We report measurements of dilatancy and grain...

  19. Assessment of errors and biases in retrievals of X_(CO2), X_(CH4), X_(CO), and X_(N2O) from a 0.5 cm^(-1) resolution solar-viewing spectrometer

    Hedelius, Jacob K.; Viatte, Camille; Wunch, Debra; Roehl, Coleen M.; Toon, Geoffrey C.; Chen, Jia; Jones, Taylor; Wofsy, Steven C.; Franklin, Jonathan E.; Parker, Harrison; Dubey, Manvendra K.; Wennberg, Paul O.
    Bruker™ EM27/SUN instruments are commercial mobile solar-viewing near-IR spectrometers. They show promise for expanding the global density of atmospheric column measurements of greenhouse gases and are being marketed for such applications. They have been shown to measure the same variations of atmospheric gases within a day as the high-resolution spectrometers of the Total Carbon Column Observing Network (TCCON). However, there is little known about the long-term precision and uncertainty budgets of EM27/SUN measurements. In this study, which includes a comparison of 186 measurement days spanning 11 months, we note that atmospheric variations of X_(gas) within a single day are well...

  20. Methane: Fuel or Exhaust at the Emergence of Life?

    Russell, Michael J.; Nitschke, Wolfang
    As many of the methanogens first encountered at hydrothermal vents were thermophilic to hyperthermophilic and comprised one of the lower roots of the evolutionary tree, it has been assumed that methanogenesis was one of the earliest, if not the earliest, pathway to life. It being well known that hydrothermal springs associated with serpentinization also bore abiotic methane, it had been further assumed that emergent biochemistry merely adopted and quickened this supposed serpentinization reaction. Yet, recent hydrothermal experiments simulating serpentinization have failed to generate methane so far, thus casting doubt on this assumption. The idea that the inverse view is worthy...

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