We describe results obtained with a two-channel fiber optic grating sensor system using interferometric determination of strain-induced Bragg-wavelength shifts. The system provides high resolution to quasi-static and dynamic strain perturbations of the gratings in the system. Results demonstrating the detection of low frequency (about 1 Hz) strain levels of about 6 nanostrain/sq rt Hz in a 3-point bending flexural beam experiment are presented.
Abstract Coastal regions have historically represented a significant challenge for air quality investigations because of water–land boundary transition characteristics and a paucity of measurements available over water. Prior studies have identified the formation of high levels of ozone over water bodies, such as the Chesapeake Bay, that can potentially recirculate back over land to significantly impact populated areas. Earth-observing satellites and forecast models face challenges in capturing the coastal transition zone where small-scale meteorological dynamics are complex and large changes in pollutants can occur on very short spatial and temporal scales. An observation strategy is presented to synchronously measure pollutants “over land” and “over water” to provide a more complete picture of chemical gradients across coastal boundaries for both the needs of state and local environmental management and new remote sensing platforms. Intensive vertical profile information from ozone lidar systems and ozonesondes, obtained at two main sites, one over land and the other over water, are complemented by remote sensing and in situ observations of air quality from ground-based, airborne (both personned and unpersonned), and shipborne platforms. These observations, coupled with reliable chemical transport simulations, such as the National Oceanic and Atmospheric Administration (NOAA) National Air Quality Forecast Capability (NAQFC), are expected to lead to a more fully characterized and complete land–water interaction observing system that can be used to assess future geostationary air quality instruments, such as the National Aeronautics and Space Administration (NASA) Tropospheric Emissions: Monitoring of Pollution (TEMPO), and current low-Earth-orbiting satellites, such as the European Space Agency’s Sentinel-5 Precursor ( S5-P ) with its Tropospheric Monitoring Instrument (TROPOMI).
This paper describes an optical fiber interferometer that uses a short segment of silica hollow- core fiber spliced between two sections of single-mode fiber to form a mechanically robust in- line optical cavity. The hollow-core fiber is specifically manufactured to have an outer diameter that is equal to the outer diameter of the single mode lead fibers, thereby combining the best qualities of existing intrinsic and extrinsic Fabry-Perot sensors. Uniaxial tension and pure bending strength tests are used to show that the new configuration does not diminish the axial strength of bare fiber and reduces the bending strength by 17% at most. Similar tests confirm that the fiber sensor has 1.96% strain to failure. Axisymmetric finite element analysis is used to investigate the reliability of the in-line etalon during typical thermoset composite cure conditions, and parametric studies are performed to determine the mechanically optimal cavity length. The sensor strain response tests demonstrate a dynamic strain resolution of 21 n(epsilon) /(root)Hz at frequencies > 5 Hz with a sensor gauge length of 137 micrometers .
Nabro volcano (13.37°N, 41.70°E) in Eritrea erupted on 13 June 2011 generating a layer of sulfate aerosols that persisted in the stratosphere for months. For the first time we report on ground-based lidar observations of the same event from every continent in the Northern Hemisphere, taking advantage of the synergy between global lidar networks such as EARLINET, MPLNET and NDACC with independent lidar groups and satellite CALIPSO to track the evolution of the stratospheric aerosol layer in various parts of the globe. The globally averaged aerosol optical depth (AOD) due to the stratospheric volcanic aerosol layers was of the order of 0.018 ± 0.009 at 532 nm, ranging from 0.003 to 0.04. Compared to the total column AOD from the available collocated AERONET stations, the stratospheric contribution varied from 2% to 23% at 532 nm.
The spatiotemporal sampling differences between ground-based and satellite lidar data can contribute to significant errors for direct measurement comparisons. Improvement in sample correspondence is examined by the use of radiosonde wind velocity to vary the time average in ground-based lidar data to spatially match coincident satellite lidar measurements. Results are shown for the 26 February 2004 GLAS/ICESat overflight of a ground-based lidar stationed at NASA GSFC. Statistical analysis indicates that improvement in signal correlation is expected under certain conditions, even when a ground-based observation is mismatched in directional orientation to the satellite track.
Figure S1: (a) The HALO aerosol extinction curtain plot on August 28 afternoon and (b) the LMOL O3 measurement on August 28.The black vertical line shows the coincidence measurement when HALO overpass LMOL at 13.17 EDT.
This paper describes an ongoing effort to develop techniques capable of locating the position of space debris impacts and to quantify the strain energy absorbed by the space structure as a result of these impacts. The techniques under development use optical fiber sensors and neural networks as the primary sensor and decision making components. To date, this project has resulted in the development of (1) a mathematical model of plate impact dynamics for use in sensor and neural network paradigm development, (2) a sensor demodulation system specifically designed for moderate impact energies, (3) several neural network paradigms with the potential to locate impacts, and (4) a test configuration to experimentally confirm the proposed paradigms.
