Jet Propulsion Laboratory

About: Jet Propulsion Laboratory is a facility organization based out in La Cañada Flintridge, California, United States. It is known for research contribution in the topics: Mars Exploration Program & Telescope. The organization has 8801 authors who have published 14333 publications receiving 548163 citations. The organization is also known as: JPL & NASA JPL.

High performance lyot and piaa coronagraphy for arbitrarily shaped telescope apertures

Abstract: Two high-performance coronagraphic approaches compatible with segmented and obstructed telescope pupils are described Both concepts use entrance pupil amplitude apodization and a combined phase and amplitude focal plane mask to achieve full coronagraphic extinction of an on-axis point source While the first concept, called Apodized Pupil Complex Mask Lyot Coronagraph (APCMLC), relies on a transmission mask to perform the pupil apodization, the second concept, called Phase-Induced Amplitude Apodization complex mask coronagraph (PIAACMC), uses beam remapping for lossless apodization Both concepts theoretically offer complete coronagraphic extinction (infinite contrast) of a point source in monochromatic light, with high throughput and sub-λ/D inner working angle, regardless of aperture shape The PIAACMC offers nearly 100% throughput and approaches the fundamental coronagraph performance limit imposed by first principles The steps toward designing the coronagraphs for arbitrary apertures are described for monochromatic light Designs for the APCMLC and the higher performance PIAACMC are shown for several monolith and segmented apertures, such as the apertures of the Subaru Telescope, Giant Magellan Telescope, Thirty Meter Telescope, the European Extremely Large Telescope, and the Large Binocular Telescope Performance in broadband light is also quantified, suggesting that the monochromatic designs are suitable for use in up to 20% wide spectral bands for ground-based telescopes

The Apollo lunar sounder radar system

Abstract: The objectives of the Apollo 17 Lunar Sounder Experiment (ALSE) were to detect subsurface geologic structures, to generate a continuous lunar profile, and to image the moon a radar wavelengths. The first objective is generally impossible on Earth, but is possible on the moon because of the very low EM attenuation found in lunar rocks. A three-wavelength synthetic-aperture radar (SAR) operating at 60 m, 20 m, and 2 m (5, 15, and 150 MHz) was designed to attain these objectives. The design choices reflected a balance of scientific requirements versus Apollo mission and hard-ware constraints. The most difficult choice was that of wavelength, since longer wavelengths have the potential for deeper subsurface penetration at the expense of depth resolution. Shorter wavelengths enhance the ability to generate surface images and accurate profiles. The sounding requirement led to a system requirement for large dynamic range and precise sidelobe control. The radar data from the lunar mission were recorded on photographic film in a conventional SAR format, and were returned to Earth for processing. A combination of optical and digital processing and exploitation techniques was applied to the scientific interpretation of the data. Some preliminary results from the lunar mission have been obtained. The system design and data exploitation techniques developed in support of the ALSE experiment show considerable promise for eventual application to earth-resource survey radar systems.

The Evolution of the Number Density of Large Disk Galaxies in COSMOS

Abstract: We study a sample of approximately 16,500 galaxies with I_(ACS,AB) ≤ 22.5 in the central 38% of the COSMOS field, which are extracted from a catalog constructed from the Cycle 12 ACS F814W COSMOS data set. Structural information on the galaxies is derived by fitting single Sersic models to their two-dimensional surface brightness distributions. In this paper we focus on the disk galaxy population (as classified by the Zurich Estimator of Structural Types), and investigate the evolution of the number density of disk galaxies larger than approximately 5 kpc between redshift z ~ 1 and the present epoch. Specifically, we use the measurements of the half-light radii derived from the Sersic fits to construct, as a function of redshift, the size function Φ(r_(1/2), z) of both the total disk galaxy population and of disk galaxies split in four bins of bulge-to-disk ratio. In each redshift bin, the size function specifies the number of galaxies per unit comoving volume and per unit half-light radius r_(1/2). Furthermore, we use a selected sample of roughly 1800 SDSS galaxies to calibrate our results with respect to the local universe. We find the following: (1) The number density of disk galaxies with intermediate sizes (r_(1/2) ~ 5-7 kpc) remains nearly constant from z ~ 1 to today. Unless the growth and destruction of such systems exactly balanced in the last eight billion years, they must have neither grown nor been destroyed over this period. (2) The number density of the largest disks (r_(1/2) > 7 kpc) decreases by a factor of about 2 out to z ~ 1. (3) There is a constancy—or even slight increase—in the number density of large bulgeless disks out to z ~ 1; the deficit of large disks at early epochs seems to arise from a smaller number of bulged disks. Our results indicate that the bulk of the large disk galaxy population has completed its growth by z ~ 1 and support the theory that secular evolution processes produce—or at least add stellar mass to—the bulge components of disk galaxies.

Trends in Global Tropospheric Ozone Inferred from a Composite Record of TOMS/OMI/MLS/OMPS Satellite Measurements and the MERRA-2 GMI Simulation

Abstract: . Past studies have suggested that ozone in the troposphere has increased globally throughout much of the 20th century due to increases in anthropogenic emissions and transport. We show, by combining satellite measurements with a chemical transport model, that during the last four decades tropospheric ozone does indeed indicate increases that are global in nature, yet still highly regional. Satellite ozone measurements from Nimbus-7 and Earth Probe Total Ozone Mapping Spectrometer (TOMS) are merged with ozone measurements from the Aura Ozone Monitoring Instrument/Microwave Limb Sounder (OMI/MLS) to determine trends in tropospheric ozone for 1979–2016. Both TOMS (1979–2005) and OMI/MLS (2005–2016) depict large increases in tropospheric ozone from the Near East to India and East Asia and further eastward over the Pacific Ocean. The 38-year merged satellite record shows total net change over this region of about +6 to +7 Dobson units (DU) (i.e., ∼15 %–20 % of average background ozone), with the largest increase ( ∼4 DU) occurring during the 2005–2016 Aura period. The Global Modeling Initiative (GMI) chemical transport model with time-varying emissions is used to aid in the interpretation of tropospheric ozone trends for 1980–2016. The GMI simulation for the combined record also depicts the greatest increases of +6 to +7 DU over India and East Asia, very similar to the satellite measurements. In regions of significant increases in tropospheric column ozone (TCO) the trends are a factor of 2–2.5 larger for the Aura record when compared to the earlier TOMS record; for India and East Asia the trends in TCO for both GMI and satellite measurements are ∼ + 3 DU decade −1 or greater during 2005–2016 compared to about +1.2 to +1.4 DU decade −1 for 1979–2005. The GMI simulation and satellite data also reveal a tropospheric ozone increases in ∼ + 4 to +5 DU for the 38-year record over central Africa and the tropical Atlantic Ocean. Both the GMI simulation and satellite-measured tropospheric ozone during the latter Aura time period show increases of ∼ + 3 DU decade −1 over the N Atlantic and NE Pacific.

Geochemical diversity in first rocks examined by the Curiosity Rover in Gale Crater: Evidence for and significance of an alkali and volatile‐rich igneous source

Abstract: The first four rocks examined by the Mars Science Laboratory Alpha Particle X-ray Spectrometer indicate that Curiosity landed in a lithologically diverse region of Mars. These rocks, collectively dubbed the Bradbury assemblage, were studied along an eastward traverse (sols 46–102). Compositions range from Na- and Al-rich mugearite Jake_Matijevic to Fe-, Mg-, and Zn-rich alkali-rich basalt/hawaiite Bathurst_Inlet and span nearly the entire range in FeO* and MnO of the data sets from previous Martian missions and Martian meteorites. The Bradbury assemblage is also enriched in K and moderately volatile metals (Zn and Ge). These elements do not correlate with Cl or S, suggesting that they are associated with the rocks themselves and not with salt-rich coatings. Three out of the four Bradbury rocks plot along a line in elemental variation diagrams, suggesting mixing between Al-rich and Fe-rich components. ChemCam analyses give insight to their degree of chemical heterogeneity and grain size. Variations in trace elements detected by ChemCam suggest chemical weathering (Li) and concentration in mineral phases (e.g., Rb and Sr in feldspars). We interpret the Bradbury assemblage to be broadly volcanic and/or volcaniclastic, derived either from near the Gale crater rim and transported by the Peace Vallis fan network, or from a local volcanic source within Gale Crater. High Fe and Fe/Mn in Et_Then likely reflect secondary precipitation of Fe^(3+) oxides as a cement or rind. The K-rich signature of the Bradbury assemblage, if igneous in origin, may have formed by small degrees of partial melting of metasomatized mantle.