6,273 research outputs found
A multi-sensor approach for volcanic ash cloud retrieval and eruption characterization: the 23 November 2013 Etna lava fountain
Volcanic activity is observed worldwide with a variety of ground and space-based
remote sensing instruments, each with advantages and drawbacks. No single system can give
a comprehensive description of eruptive activity, and so, a multi-sensor approach is required. This
work integrates infrared and microwave volcanic ash retrievals obtained from the geostationary
Meteosat Second Generation (MSG)-Spinning Enhanced Visible and Infrared Imager (SEVIRI),
the polar-orbiting Aqua-MODIS and ground-based weather radar. The expected outcomes are
improvements in satellite volcanic ash cloud retrieval (altitude, mass, aerosol optical depth and
effective radius), the generation of new satellite products (ash concentration and particle number
density in the thermal infrared) and better characterization of volcanic eruptions (plume altitude,
total ash mass erupted and particle number density from thermal infrared to microwave). This
approach is the core of the multi-platform volcanic ash cloud estimation procedure being developed
within the European FP7-APhoRISM project. The Mt. Etna (Sicily, Italy) volcano lava fountaining
event of 23 November 2013 was considered as a test case. The results of the integration show the
presence of two volcanic cloud layers at different altitudes. The improvement of the volcanic ash
cloud altitude leads to a mean difference between the SEVIRI ash mass estimations, before and after
the integration, of about the 30%. Moreover, the percentage of the airborne “fine” ash retrieved from
the satellite is estimated to be about 1%–2% of the total ash emitted during the eruption. Finally,
all of the estimated parameters (volcanic ash cloud altitude, thickness and total mass) were also
validated with ground-based visible camera measurements, HYSPLIT forward trajectories, Infrared
Atmospheric Sounding Interferometer (IASI) satellite data and tephra deposits
A novel satellite mission concept for upper air water vapour, aerosol and cloud observations using integrated path differential absorption LiDAR limb sounding
We propose a new satellite mission to deliver high quality measurements of upper air water vapour. The concept centres around a LiDAR in limb sounding by occultation geometry, designed to operate as a very long path system for differential absorption measurements. We present a preliminary performance analysis with a system sized to send 75 mJ pulses at 25 Hz at four wavelengths close to 935 nm, to up to 5 microsatellites in a counter-rotating orbit, carrying retroreflectors characterized by a reflected beam divergence of roughly twice the emitted laser beam divergence of 15 µrad. This provides water vapour profiles with a vertical sampling of 110 m; preliminary calculations suggest that the system could detect concentrations of less than 5 ppm. A secondary payload of a fairly conventional medium resolution multispectral radiometer allows wide-swath cloud and aerosol imaging. The total weight and power of the system are estimated at 3 tons and 2,700 W respectively. This novel concept presents significant challenges, including the performance of the lasers in space, the tracking between the main spacecraft and the retroreflectors, the refractive effects of turbulence, and the design of the telescopes to achieve a high signal-to-noise ratio for the high precision measurements. The mission concept was conceived at the Alpbach Summer School 2010
MODIS: Moderate-resolution imaging spectrometer. Earth observing system, volume 2B
The Moderate-Resolution Imaging Spectrometer (MODIS), as presently conceived, is a system of two imaging spectroradiometer components designed for the widest possible applicability to research tasks that require long-term (5 to 10 years), low-resolution (52 channels between 0.4 and 12.0 micrometers) data sets. The system described is preliminary and subject to scientific and technological review and modification, and it is anticipated that both will occur prior to selection of a final system configuration; however, the basic concept outlined is likely to remain unchanged
Orbital debris research at NASA Johnson Space Center, 1986-1988
Research on orbital debris has intensified in recent years as the number of debris objects in orbit has grown. The population of small debris has now reached the level that orbital debris has become an important design factor for the Space Station. The most active center of research in this field has been the NASA Lyndon B. Johnson Space Center. Work is being done on the measurement of orbital debris, development of models of the debris population, and development of improved shielding against hypervelocity impacts. Significant advances have been made in these areas. The purpose of this document is to summarize these results and provide references for further study
A new simplified approach for simultaneous retrieval of SO2 and ash content of tropospheric volcanic clouds: an application to the Mt Etna volcano
A new procedure is presented for simultaneous estimation
of SO2 and ash abundance in a volcanic plume, using
thermal infrared (TIR) MODIS data. Plume altitude and
temperature are the only two input parameters required to run
the procedure, while surface emissivity, temperature, atmospheric
profiles, ash optical properties, and radiative transfer
models are not necessary to perform the atmospheric corrections.
The procedure gives the most reliable results when the
surface under the plume is uniform, for example above the
ocean, but still produces fairly good estimates in more challenging
and not easily modelled conditions, such as above
land or meteorological cloud layers. The developed approach
was tested on the Etna volcano.
By linearly interpolating the radiances surrounding a detected
volcanic plume, the volcanic plume removal (VPR)
procedure described here computes the radiances that would
have been measured by the sensor in the absence of a plume,
and reconstructs a new image without plume. The new image
and the original data allow computation of plume transmittance
in the TIR-MODIS bands 29, 31, and 32 (8.6, 11.0
and 12.0 \u3bcm) by applying a simplified model consisting of a
uniform plume at a fixed altitude and temperature. The transmittances
are then refined with a polynomial relationship obtained
by means of MODTRAN simulations adapted for the
geographical region, ash type, and atmospheric profiles.
Bands 31 and 32 are SO2 transparent and, from their transmittances,
the effective ash particle radius (Re), and aerosol
optical depth at 550 nm (AOD550) are computed. A simple
relation between the ash transmittances of bands 31 and 29
is demonstrated and used for SO2 columnar content (cs) estimation.
Comparing the results of the VPR procedure with
MODTRAN simulations for more than 200 000 different
cases, the frequency distribution of the differences shows the
following: the Re error is less than \ub10.5 \u3bcm in more than
60% of cases; the AOD550 error is less than \ub10.125 in 80%
of cases; the cs error is less than \ub10.5 gm 122 in more than
60% of considered cases. The VPR procedure was applied in
two case studies of recent eruptions occurring at the Mt Etna
volcano, Italy, and successfully compared with the results obtained
from the established SO2 and ash assessments based
on look-up tables (LUTs). Assessment of the sensitivity to
the plume altitude uncertainty is also made.
The VPR procedure is simple, extremely fast, and can be
adapted to other ash types and different volcanoes
Observations of Saharan dust layer electrification
Electrification of atmospheric dust influences the coagulation, wet removal and fall speeds of dust particles. Alignment of dust particles can also occur in fair weather atmospheric electrical conditions if the particles are charged. However, very few electrical measurements made in elevated dust layers exist. Balloon-borne charge and particle instrumentation have been used to investigate the electrical properties of elevated Saharan dust layers. Soundings from the Cape Verde Islands, which experience frequent Saharan dust outbreaks, intercepted several dust layers. Two balloon soundings during summer 2009 detected dust particles in layers up to 4 km altitude. Simultaneous electrical measurements showed charge inside the dust layers, with a maximum measured charge density of 25 pC m − 3, sufficient to influence wet removal processes
Observations of the relationship between sprite morphology and in-cloud lightning processes
[1] During a thunderstorm on 23 July 2003, 15 sprites were captured by a LLTV camera mounted at the observatory on Pic du Midi in the French Pyrénées. Simultaneous observations of cloud-to-ground (CG) and intracloud (IC) lightning activity from two independent lightning detection systems and a broadband ELF/VLF receiver allow a detailed study of the relationship between electrical activity in a thunderstorm and the sprites generated in the mesosphere above. Results suggest that positive CG and IC lightning differ for the two types of sprites most frequently observed, the carrot- and column-shaped sprites. Column sprites occur after a short delay (<30 ms) from the causative +CG and are associated with little VHF activity, suggesting no direct IC action on the charge transfer process. On the other hand, carrot sprites are delayed up to about 200 ms relative to their causative +CG stroke and are accompanied by a burst of VHF activity starting 25–75 ms before the CG stroke. While column sprites associate with short-lasting (less than 30 ms) ELF/VLF sferics, carrot sprites associate with bursts of sferics initiating at the time of the causative +CG discharge and persisting for 50 to 250 ms, indicating extensive in-cloud activity. One carrot event was found to be preceded by vigorous IC activity and a strong, long-lived cluster of ELF/VLF sferics but lacking a +CG. The observations of ELF/VLF sferic clusters associated with lightning and sprites form the basis for a discussion of the reliability of lightning detection systems based on VHF interferometry.Peer ReviewedPostprint (published version
The noctilucent cloud (NLC) display during the ECOMA/MASS sounding rocket flights on 3 August 2007: morphology on global to local scales
During the ECOMA/MASS rocket campaign large scale NLC/PMC was observed by satellite, lidar and camera from polar to mid latitudes. We examine the observations from different instruments to investigate the morphology of the cloud. Satellite observations show a planetary wave 2 structure. Lidar observations from Kühlungsborn (54° N), Esrange (68° N) and ALOMAR (69° N) show a highly dynamic NLC layer. Under favorable solar illumination the cloud is also observable by ground-based cameras. The cloud was detected by cameras from Trondheim (63° N), Juliusruh (55° N) and Kühlungsborn. We investigate planetary scale morphology and local scale gravity wave structures, important for the interpretation of the small scale rocket soundings. We compare in detail the lidar observations with the NLC structure observed by the camera in Trondheim. The ALOMAR RMR-lidar observed only a faint NLC during the ECOMA launch window, while the camera in Trondheim showed a strong NLC display in the direction of ALOMAR. Using the high resolution camera observations (t~30 s, Δx\u3c5 \u3ekm) and the wind information from the meteor radar at ALOMAR we investigate the formation and destruction of NLC structures. We observe that the NLC brightness is reduced by a factor of 20–40 within 100 s which can be caused by a temperature about 15 K above the frostpoint temperature. A horizontal temperature gradient of more than 3 K/km is estimated
A new simplified approach for simultaneous retrieval of SO2 and ash content of tropospheric volcanic clouds: an application to the Mt Etna volcano
A new procedure is presented for simultaneous estimation of SO2 and ash abundance in a volcanic plume, using
thermal infrared (TIR) MODIS data. Plume altitude and temperature are the only two input parameters required to run
the procedure, while surface emissivity, temperature, atmospheric profiles, ash optical properties, and radiative transfer
models are not necessary to perform the atmospheric corrections. The procedure gives the most reliable results when the surface under the plume is uniform, for example above the ocean, but still produces fairly good estimates in more challenging and not easily modelled conditions, such as above
land or meteorological cloud layers. The developed approach was tested on the Etna volcano. By linearly interpolating the radiances surrounding a detected volcanic plume, the volcanic plume removal (VPR)
procedure described here computes the radiances that would have been measured by the sensor in the absence of a plume, and reconstructs a new image without plume. The new image and the original data allow computation of plume transmittance in the TIR-MODIS bands 29, 31, and 32 (8.6, 11.0
and 12.0 μm) by applying a simplified model consisting of a uniform plume at a fixed altitude and temperature. The transmittances
are then refined with a polynomial relationship obtained by means of MODTRAN simulations adapted for the geographical region, ash type, and atmospheric profiles.
Bands 31 and 32 are SO2 transparent and, from their transmittances, the effective ash particle radius (Re), and aerosol optical depth at 550 nm (AOD550) are computed. A simple relation between the ash transmittances of bands 31 and 29
is demonstrated and used for SO2 columnar content (cs) estimation. Comparing the results of the VPR procedure with
MODTRAN simulations for more than 200 000 different cases, the frequency distribution of the differences shows the following: the Re error is less than ±0.5 μm in more than
60% of cases; the AOD550 error is less than ±0.125 in 80% of cases; the cs error is less than ±0.5 gm−2 in more than 60% of considered cases. The VPR procedure was applied in two case studies of recent eruptions occurring at the Mt Etna volcano, Italy, and successfully compared with the results obtained from the established SO2 and ash assessments based on look-up tables (LUTs). Assessment of the sensitivity to
the plume altitude uncertainty is also made.
The VPR procedure is simple, extremely fast, and can be adapted to other ash types and different volcanoes
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