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  • 1
    Publication Date: 2019-07-16
    Description: Intended for long-term monitoring of the vertical structure and optical properties of clouds and aerosol in bi-polar regions, we are operating Micro-Pulse Lidars (MPLs) at Ny-Aalesund (79N, 12E), Svalbard in the Arctic and at Syowa Station (69S, 40E), Antarctica. These sites are part of the NASA Micro-Pulse Lidar Network (MPLNET). The Arctic MPL measurement started in 1998, and the Antarctic MPL measurement started in 2001. The Geoscience Laser Altimeter System (GLAS) on board the Ice, Cloud and Land Elevation Satellite (ICESat) was successfully launched in January 2003. The lidar observation in a near-polar orbit with an inclination of 94 degrees provides a global coverage of vertical profiles of clouds and aerosol including both polar regions. Data products include thin cloud and aerosol optical depth. GLAS data validation issues include the sensitivity of cloud detection and optical depth accuracy. The polar MPL measurements include GLAS overpasses in 2003 and 2004. ICESat pointed directly to the Ny-Aalesund and Syowa sites when within five degrees off nadir. In this paper, preliminary results from the Arctic and Antarctic MPL measurements will be shown and discussed as ground truth of cloud and aerosol measurements by ICESat/GLAS.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 2
    Publication Date: 2019-07-16
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Global change biology 9 (2003), S. 0 
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Forest development following stand-replacing disturbance influences a variety of ecosystem processes including carbon exchange with the atmosphere. On a series of ponderosa pine (Pinius ponderosa var. Laws.) stands ranging from 9 to〉 300 years in central Oregon, USA, we used biological measurements to estimate carbon storage in vegetation and soil pools, net primary productivity (NPP) and net ecosystem productivity (NEP) to examine variation with stand age. Measurements were made on plots representing four age classes with three replications: initiation (I, 9–23 years), young (Y, 56–89 years), mature (M, 95–106 years), and old (O, 190–316 years) stands typical of the forest type in the region. Net ecosystem productivity was lowest in the I stands (−124 g C m−2 yr−1), moderate in Y stands (118 g C m−2 yr−1), highest in M stands (170 g C m−2 yr−1), and low in the O stands (35 g C m−2 yr−1). Net primary productivity followed similar trends, but did not decline as much in the O stands. The ratio of fine root to foliage carbon was highest in the I stands, which is likely necessary for establishment in the semiarid environment, where forests are subject to drought during the growing season (300–800 mm precipitation per year). Carbon storage in live mass was the highest in the O stands (mean 17.6 kg C m−2). Total ecosystem carbon storage and the fraction of ecosystem carbon in aboveground wood mass increased rapidly until 150–200 years, and did not decline in older stands. Forest inventory data on 950 ponderosa pine plots in Oregon show that the greatest proportion of plots exist in stands ∼ 100 years old, indicating that a majority of stands are approaching maximum carbon storage and net carbon uptake. Our data suggests that NEP averages ∼ 70 g C m−2 year−1 for ponderosa pine forests in Oregon. About 85% of the total carbon storage in biomass on the survey plots exists in stands greater than 100 years, which has implications for managing forests for carbon sequestration. To investigate variation in carbon storage and fluxes with disturbance, simulation with process models requires a dynamic parameterization for biomass allocation that depends on stand age, and should include a representation of competition between multiple plant functional types for space, water, and nutrients.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Global change biology 10 (2004), S. 0 
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: We used a spatially nested hierarchy of field and remote-sensing observations and a process model, Biome-BGC, to produce a carbon budget for the forested region of Oregon, and to determine the relative influence of differences in climate and disturbance among the ecoregions on carbon stocks and fluxes. The simulations suggest that annual net uptake (net ecosystem production (NEP)) for the whole forested region (8.2 million hectares) was 13.8 Tg C (168 g C m−2 yr−1), with the highest mean uptake in the Coast Range ecoregion (226 g C m−2 yr−1), and the lowest mean NEP in the East Cascades (EC) ecoregion (88 g C m−2 yr−1). Carbon stocks totaled 2765 Tg C (33 700 g C m−2), with wide variability among ecoregions in the mean stock and in the partitioning above- and belowground. The flux of carbon from the land to the atmosphere that is driven by wildfire was relatively low during the late 1990s (∼0.1 Tg C yr−1), however, wildfires in 2002 generated a much larger C source (∼4.1 Tg C). Annual harvest removals from the study area over the period 1995–2000 were ∼5.5 Tg C yr−1. The removals were disproportionately from the Coast Range, which is heavily managed for timber production (approximately 50% of all of Oregon's forest land has been managed for timber in the past 5 years). The estimate for the annual increase in C stored in long-lived forest products and land fills was 1.4 Tg C yr−1. Net biome production (NBP) on the land, the net effect of NEP, harvest removals, and wildfire emissions indicates that the study area was a sink (8.2 Tg C yr−1). NBP of the study area, which is the more heavily forested half of the state, compensated for ∼52% of Oregon's fossil carbon dioxide emissions of 15.6 Tg C yr−1 in 2000. The Biscuit Fire in 2002 reduced NBP dramatically, exacerbating net emissions that year. The regional total reflects the strong east–west gradient in potential productivity associated with the climatic gradient, and a disturbance regime that has been dominated in recent decades by commercial forestry.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Global change biology 10 (2004), S. 0 
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: To test the hypothesis that variation in soil respiration is related to plant production across a diverse forested landscape, we compared annual soil respiration rates with net primary production and the subsequent allocation of carbon to various ecosystem pools, including leaves, fine roots, forests floor, and mineral soil for 36 independent plots arranged as three replicates of four age classes in three climatically distinct forest types.Across all plots, annual soil respiration was not correlated with aboveground net primary production (R2=0.06, P〉0.1) but it was moderately correlated with belowground net primary production (R2=0.46, P〈0.001). Despite the wide range in temperature and precipitation regimes experienced by these forests, all exhibited similar soil respiration per unit live fine root biomass, with about 5 g of carbon respired each year per 1 g of fine root carbon (R2=0.45, P〈0.001). Annual soil respiration was only weakly correlated with dead carbon pools such as forest floor and mineral soil carbon (R2=0.14 and 0.12, respectively). Trends between soil respiration, production, and root mass among age classes within forest type were inconsistent and do not always reflect cross-site trends.These results are consistent with a growing appreciation that soil respiration is strongly influenced by the supply of carbohydrates to roots and the rhizosphere, and that some regional patterns of soil respiration may depend more on belowground carbon allocation than the abiotic constraints imposed on subsequent metabolism.
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 1543-1544 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A resonant-cavity avalanche photodiode using a GaNAs absorption region grown on GaAs has been demonstrated. The peak quantum efficiency was 59% at 1.064 μm with a full width at half maximum of 11 nm. The absorption coefficient was determined to be α=9×103/cm at this wavelength. The devices exhibited gain up to 100 at a low breakdown voltage of 13 V. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 2810-2812 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the device performance of selective-area regrown Al0.30Ga0.70N p–i–n photodiodes. Tensile strain, induced by the lattice mismatch between AlxGa1−xN and GaN, leads to cracking above the critical thickness in layers with high aluminum concentration. Selective-area regrown devices with ≤70 μm diameters were fabricated without signs of cracking. These devices show low dark current densities with flat photoresponse and a forward turn-on current of ∼25 A/cm2 at 7 V. A quantum efficiency greater than 20% was achieved at zero bias with a peak wavelength of λ=315 nm. A differential resistance of R0=3.46×1014 Ω and a detectivity of D*=4.85×1013 cm Hz1/2 W−1 was demonstrated. © 2000 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 2824-2825 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A p-i-n avalanche photodiode (APD) using GaNAs grown on GaAs has been demonstrated. Characterization of the excess noise in the material was used to determine that the ratio of ionization coefficients (k=β/α) is k=0.4. The quantum efficiency was above 25% at 0.94 μm for 0.75% nitrogen incorporation. The APDs exhibited low dark currents (〈60 nA/mm2 at 90% of breakdown) and a gain-bandwidth product of 42 GHz. GaNAs therefore shows promise for extending the operation of GaAs-based APDs to longer wavelengths. © 2000 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 1945-1947 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electronic properties of the (100) Si/SiO2 interfacial defect called Pb1 are quite controversial. We present electron spin resonance measurements that demonstrate: (1) that the Pb1 defects have levels in the silicon band gap, (2) that the Pb1 correlation energy is significantly smaller than that of the Pb1 defect, and (3) that the Pb1 levels are skewed toward the lower part of the silicon band gap. © 2002 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 1900-1902 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the growth, fabrication, and characterization of AlxGa1−xN (0≤x≤0.60) heteroepitaxial back-illuminated solar-blind p-i-n photodiodes on (0001) sapphire substrates. The group III-nitride heteroepitaxial layers are grown by low-pressure metalorganic chemical vapor deposition on double polished sapphire substrates using various growth conditions. The back-illuminated devices exhibit very low dark current densities. Furthermore, they exhibit external quantum efficiencies up to 35% at the peak of the photoresponse (λ∼280 nm). Improvements were made to the growth technique in order to achieve crack-free Al0.4Ga0.6N active regions on a thick Al0.6Ga0.4N window layer and to obtain activated p-type Al0.4Ga0.6N layers. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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