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The spectral reflectance of ship wakes between 400 and 900 nanometers

by cfynanon 9 June 2015in Earth Science and Remote Sensing No comment

This technical note describes the use of an airborne hyperspectral imaging sensor (HICO – Hyperspectral Imager of the Coastal Ocean) to record the spectral reflectance characteristics of centerline ship wakes in the 400 to 900 nm wavelength region. Data were collected for a target of known provenance (the United States Coast Guard Cutter Kittiwake) off the Wai'anae coast of O'ahu, Hawai'i, on 8 April 2010. HICO acquired data in 60 spectral bands by flying along the long axis of the wake while the vessel travelled at three speeds (~3.6 m s<sup>-1</sup> or 7 knots; ~7.2 m s<sup>-1</sup> or 14 knots; and ~11.2 m s<sup>-1</sup> or 21 knots). A flying altitude of ~1500 m yielded a spatial resolution of ~1.5 m. Spectral profiles along and across the wake axes are presented which show how the spectral reflectance of the centerline wake varies spatially and temporally as a function of vessel speed. Length (and to a lesser extent, width) vary in proportion to speed. In common with previous studies and model predictions, the wakes show a pronounced greening of the wake (i.e. enhanced reflectance at ~550 nm), with evidence for elevated reflectance at 750-800 nm. Resampling the data from its raw 1.5 m spatial resolution yields insights into how the turbulent wake becomes spectrally inseparable from the background water as spatial resolution decreases (i.e. becomes increasingly coarse). Using a simple statistical test, the wake becomes spectrally similar to the background ocean as the resolution approaches 60 m.

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Gas Slit Camera (GSC) onboard MAXI on ISS

by cfynanon 9 June 2015in Earth Science and Remote Sensing No comment

The Gas Slit Camera (GSC) is an X-ray instrument on the MAXI (Monitor of All-sky X-ray Image) mission on the International Space Station. It is designed to scan the entire sky every 92-minute orbital period in the 2–30 keV band and to achieve the highest sensitivity among the X-ray all-sky monitors ever flown so far. The GSC employs large-area position-sensitive proportional counters with the total detector area of 5350 cm$^2$. The on-board data processor has functions to format telemetry data as well as to control the high voltage of the proportional counters to protect them from the particle irradiation. The paper describes the instruments, on-board data processing, telemetry data formats, and performance specifications expected from the ground calibration tests.

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Discovery of a Cyclotron Resonance Feature in the X-ray Spectrum of GX 304-1 with RXTE and Suzaku during Outbursts Detected by MAXI in 2010

by cfynanon 9 June 2015in Earth Science and Remote Sensing No comment

We report the discovery of a cyclotron resonance scattering feature (CRSF) in the X-ray spectrum of GX 304-1, obtained by RXTE and Suzaku during major outbursts detected by MAXI in 2010. The peak intensity in August reached 600 mCrab in the 2-20 keV band, which is the highest ever observed from this source. The RXTE observations on more than twenty occasions and one Suzaku observation revealed a spectral absorption feature at around 54 keV, which is the first CRSF detection from this source. The estimated strength of surface magnetic field, 4.7×1012 G, is one of the highest among binary X-ray pulsars from which CRSFs have ever been detected. The RXTE spectra taken during the August outburst also suggest that the CRSF energy changed over 50-54 keV, possibly in a positive correlation with the X-ray flux. The behavior is qualitatively similar to that observed from Her X-1 on long time scales, or from A 0535+26, but different from the negative correlation observed from 4U 0115+63 and X 0331+53.

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Calving and ice-shelf break-up processes investigated by proxy: Antarctic tabular iceberg evolution during northward drift

by cfynanon 9 June 2015in Earth Science and Remote Sensing No comment

Using a combination of satellite sensors, field measurements and satellite-uplinked in situ observing stations, we examine the evolution of several large icebergs drifting east of the Antarctic Peninsula towards South Georgia Island. Three styles of calving are observed during drift: 'rift calvings', 'edge wasting' and 'rapid disintegration'. Rift calvings exploit large pre-existing fractures generated in the shelf environment and can occur at any stage of drift. Edge wasting is calving of the iceberg perimeter by numerous small edge-parallel, sliver-shaped icebergs, preserving the general shape of the main iceberg as it shrinks. This process is observed only in areas north of the sea-ice edge. Rapid disintegration, where numerous small calvings occur in rapid succession, is consistently associated with indications of surface melt saturation (surface lakes, firn-pit ponding). Freeboard measurements by ICESat indicate substantial increases in ice-thinning rates north of the sea-ice edge (from <10ma−1 to >30ma−1), but surface densification is shown to be an important correction (>2m freeboard loss before the firn saturates). Edge wasting of icebergs in 'warm' surface water (sea-ice-free, >−1.8 °C) implies a mechanism based on waterline erosion. Rapid disintegration ('Larsen B-style' break-up) is likely due to the effects of surface or saturated-firn water acting on pre-existing crevasses, or on wave- or tidally induced fractures. Changes in microwave backscatter of iceberg firn as icebergs drift into warmer climate and experience increased surface melt suggest a means of predicting when floating ice plates are evolving towards disintegration.

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Operational retrieval algorithms for JEM/SMILES level 2 data processing system

by cfynanon 9 June 2015in Earth Science and Remote Sensing No comment

To measure the thermal emission from stratospheric minor species with high sensitivity, the Superconducting Submillimeter-wave Limb-Emission Sounder (SMILES) aboard the Japanese Experiment Module (JEM) of the International Space Station (ISS) carries 4 K cooled Superconductor–Insulator–Superconductor (SIS) mixers. The major feature of the SMILES is its high-sensitive measurement ability with low system noise temperature less than 700 K. As a part of the ground system for the SMILES, a level 2 data processing system (DPS-L2) has been developed. It retrieves the density distributions of the target species from calibrated spectra in near-real-time. The retrieval process consists of two parts: the forward model, which computes radiative transfer, and the inverse model, which deduces atmospheric states. Since the forward model must provide the most accurate basis for results and be implemented under limited computing resources, the forward model algorithm for an operational system has to be accurate and fast. Hence, the algorithm is improved (1) by designing accurate instrument functions such as the instrumental field of view (FOV), sideband rejection ratio of sideband separator, and spectral responses of acousto-optic spectrometer (AOS) and (2) by optimizing radiative transfer calculation. This paper presents the development of the DPS-L2 along with the details on its algorithm and the algorithm performance. The accuracy of this algorithm is better than 1%, and the processing time for single-scan spectra is less than 1 min with eight parallel processings using a 3.16-GHz Quad-Core Intel Xeon processor. Thus, this algorithm is suitable for the SMILES measurement.

Related URLs:
http://www.sciencedirect.com/science/article/pii/S0022407309002167

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Six-Channel Spectrophotometers (PH) Onboard JEM-GLIMS

by cfynanon 9 June 2015in Earth Science and Remote Sensing No comment

Six-channel spectrophotometers (PH) are the science instruments of JEM-GLIMS to measure absolute intensity of the emission originated from lightning discharges and upper atmospheric transient luminous events (TLEs). PH unit-1 (PH-U1) consists of four spectrophotometer channels named from PH1 to PH4, while PH unit-2 (PH-U2) two spectrophotometer channels named PH5 and PH6. Optical filters of these spectrophotometers are selected to detect TLE emission lines of N2 1PG, N2 2PG, N2+ 1NG, and N2 LBH. Since the bandwidth of the optical filter of PH2, 3, 5, and 6 is 10 nm and since PH1 measures NUV emission, photomultiplier tubes with high-voltage converters are used as a photon detector. To the contrary, PH4 uses a photodiode as a photon detector because the pass-band of the optical filter is enough wide to detect transient optical emission. Though PH does not equip spatial resolution, it can acquire light curve data with a high time resolution of 50 μs with a 12-bit resolution. Thus, the combinational analysis of PH data and Lightning and Sprite Imager (LSI) data, it is possible to clarify the relationship between TLEs and their parent lightning discharges, the occurrence condition of TLEs, and the energy of the electrons which excite TLE emission.

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Measurement of the pressure broadening coefficient of the 625 GHz transition of H2O2H2O2 in the sub-millimeter-wave region

by cfynanon 9 June 2015in Earth Science and Remote Sensing No comment

The hydrogen peroxide ( H 2 O 2 ) molecule plays an important role in stratospheric ozone chemistry as a reservoir molecule in the HO X cycle. The Superconducting Sub-Millimeter-Wave Limb Emission Sounder (SMILES) instrument in the Japanese Experiment Module (JEM) on the International Space Station monitors H 2 O 2 using the pure rotational J Ka , Kc = 20 1 , 19 – 19 2 , 17 transition at 625.044 GHz in the ground vibronic state. Accurate retrievals of H 2 O 2 abundances rely on a knowledge of pressure broadening effects for this transition, and the required nitrogen ( N 2 ) and oxygen ( O 2 ) broadening coefficients are measured here for the first time. Values of the pressure broadening coefficients, γ ( N 2 ) = 4.03 ± 0.06 MHz / Torr and γ ( O 2 ) = 2.49 ± 0.04 MHz / Torr are obtained at room temperature, with statistical 3 σ uncertainties given. The value for air broadening is then derived to be γ ( air ) = 3.71 ± 0.09 MHz / Torr , where the uncertainty includes possible systematic errors.

Related URLs:
http://www.sciencedirect.com/science/article/pii/S0022407309003653

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Vertical profile of δ18OOO from the middle stratosphere to lower mesosphere from SMILES spectra

by cfynanon 9 June 2015in Earth Science and Remote Sensing No comment

Ozone is known to have large oxygen isotopic enrichments of about 10% in the middle stratosphere; however, there have been no reports of ozone isotopic enrichments above the middle stratosphere. We derived an enrichment δ18OOO in the stratosphere and the lower mesosphere from observations of the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) onboard the International Space Station (ISS) using a retrieval algorithm optimized for the isotopic ratio. The retrieval algorithm includes (i) an a priori covariance matrix constrained by oxygen isotopic ratios in ozone, (ii) an optimization of spectral windows for ozone isotopomers and isotopologues, and (iii) common tangent height information for all windows. The δ18OOO by averaging the SMILES measurements at the latitude range of 20 to 40° N from February to March in 2010 with solar zenith angle < 80° was 13% (at 32 km) with the systematic error of about 5%. SMILES and past measurements were in good agreement, with δ18OOO increasing with altitude between 30 and 40 km. The vertical profile of δ18OOO obtained in this study showed an increase and a decrease with altitude in the stratosphere and mesosphere, respectively. The δ18OOO peak, 18%, is found at the stratopause. The δ18OOO has a positive correlation with temperature in the range of 220–255 K, indicating that temperature can be a dominant factor to control the vertical profile of δ18OOO in the stratosphere and mesosphere. This is the first report of the observation of δ18OOO over a wide altitude range extending from the stratosphere to the mesosphere (28–57 km).

Related URLs:
http://www.atmos-meas-tech.net/7/941/2014/
http://www.atmos-meas-tech.net/7/941/2014/amt-7-941-2014.pdf

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ICESat profiles of tabular iceberg margins and iceberg breakup at low latitudes

by cfynanon 9 June 2015in Earth Science and Remote Sensing No comment

ICESat elevation profiles of tabular iceberg margins and the Ronne Ice Shelf edge reveal shapes indicative of two types of bending forces. Icebergs and shelf fronts in sea-ice-covered areas have broad (∼1000 m wide), rounded, ∼0.6 m high ‘berms’ and outer edges that slope down several meters toward the water. Bergs in warmer water have 2 to 5m ‘ramparts’ with ∼1500 m wide edge-parallel ‘moats’ inboard of the edge. This latter pattern was first revealed in images from International Space Station (ISS) showing edge-parallel melt ponds on one iceberg just prior to its disintegration. Model results indicate the patterns are caused by hydrostatic and lithostatic forces acting on the ice face. ‘Berm’ profiles arise from differences between ice and water pressure along the face. ‘Rampart-moat’ profiles result from waterline erosion, creating a submerged bench of ice that lifts the ice edge. We use the results to discuss iceberg breakup at low latitudes.

Related URLs:
http://dx.doi.org/10.1029/2005GL023802

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ISS-SOLAR: Total (TSI) and spectral (SSI) irradiance measurements

by cfynanon 9 June 2015in Earth Science and Remote Sensing No comment

The primary objective of the ISS-SOLAR mission on Columbus (to be launched in 2006) is the quasi-continuous measurement of the solar irradiance variability with highest possible accuracy. For this reason the total spectral range will be recorded simultaneously from 3000 to 17 nm by three sets of instruments: SOVIM is combining two types of absolute radiometers and three-channel filter radiometers. SOLSPEC is composed of three double monochromators using concave gratings, covering the wavelength range from 3000 to 180 nm. SOL-ACES has four grazing incidence planar grating spectrometers plus two three-signal ionization chambers (two signals from a two stage chamber plus a third signal from a silicon diode at the end of the chamber) with exchangeable band pass filters to determine the absolute fluxes from 220 to 17 nm repeatedly during the mission. For the TSI the relative standard uncertainty (RSU) to be achieved is of the order of 0.15% and for the SSI from 1% in the IR/Vis, 2% in the UV, 5% in the FUV up to 10% in the XUV spectral regions. The general requirements for the TSI and SSI measurements and their conceptual realization within this payload will be discussed with emphasis on instrumental realization and calibration aspects.

Related URLs:
http://www.sciencedirect.com/science/article/pii/S0273117705000670

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