247,357 research outputs found
Airborne tracking sunphotometer apparatus and system
An airborne tracking Sun photometer apparatus has a rotatable dome. An azimuth drive motor is connected to rotate the dome. The dome has an equatorial slot. A cylindrical housing is pivotally mounted inside the dome at the equatorial slot. A photometer is mounted in the housing to move in the equatorial slot as the housing pivots. The photometer has an end facing from the slot with an optical flat transparent window. An elevation drive motor is connected to pivot the cylindrical housing. The rotatable dome is mounted in the bulkhead of an aircraft to extend from the interior of the aircraft. A Sun sensor causes the photometer to track the Sun automatically. Alternatively, the photometer may be oriented manually or by computer
A thermodynamical model for rainfall-triggered volcanic dome collapse
Dome-forming volcanic eruptions typically involve the slow extrusion of viscous lava onto a steep-sided volcano punctuated by collapse and the generation of hazardous pyroclastic flows. We show an unequivocal link between the onset of intense rainfall and lava dome collapse on short time scales (within a few hours) and develop a simple thermodynamical model to explain this behavior. The model is forced with rainfall observations from the Soufriere Hills Volcano, Montserrat, and suggests that when the dome is in a critical state, a minimum rainfall rate of approximately 15 mm hr-1 for 2-3 hr could trigger a dome collapse
Identification of structural controls in an active lava dome with high resolution DEMs:Volcán de Colima, Mexico
Monitoring the topography of active lava domes is critical for detecting changes that may trigger or influence collapse or explosive activity. Internal dome structure and conditions are more difficult to elucidate, but also play vital roles. Here, we describe the exposure (following an explosion) of significant scarps in the active dome at Volcán de Colima, Mexico, that are interpreted as evidence of brittle failure planes and a complex internal dome morphology. In the first use of automated 3D computer vision reconstruction techniques (structure-from-motion and multi-view stereo, SfM-MVS) on an active volcanic dome, we derive high resolution surface models from oblique and archive photographs taken with a consumer camera. The resulting 3D models were geo-referenced using features identified in a web-sourced orthoimage; no ground-based measurements were required. In December 2010, the dome (2.14×106 m3) had a flat upper surface, reflecting an overall ductile emplacement regime. Between then and May 2011, a period of low explosivity was accompanied by a small volume loss (0.4×105 m3) and arcuate steps appeared in the dome surface, suggesting the presence of localized planes of weakness. The complex array of summit scarps was exposed following a significant explosion in June 2011, and is interpreted to be the surface expression of fault planes in the dome. The 1-m resolution DEMs indicated that the region of greatest volume loss was not coincident with the assumed location of the conduit, and that heterogeneity within the dome may have been important during the June explosion
The Nature of Cima Dome
In the Mojave Desert of southeasternmost California is a remarkably
smooth, symmetrical rock-alluvial dome which takes its name
from Cima on the Union Pacific Railroad. Lawson (1915, pp. 26, 33)
cited Cima Dome as a prime example of a panfan, but Thompson
(1929, p. 550) later showed that its upper part is bare rock. Davis
(1933, pp. 240-243) considered it a fine example of a convex desert
dome evolved from back-wearing of a fault block, but this concept
is contradicted by the geological relations (Hewett, 1954), which
throw more light on the nature and origin of Cima Dome than do
geomorphological theories
Excellent daytime seeing at Dome Fuji on the Antarctic plateau
Context. Dome Fuji, the second highest region on the Antarctic plateau, is
expected to have some of the best astronomical seeing on Earth. However, site
testing at Dome Fuji is still in its very early stages.
Aims. To investigate the astronomical seeing in the free atmosphere above
Dome Fuji, and to determine the height of the surface boundary layer.
Methods. A Differential Image Motion Monitor was used to measure the seeing
in the visible (472 nm) at a height of 11 m above the snow surface at Dome Fuji
during the austral summer of 2012/2013.
Results. Seeing below 0.2'' has been observed. The seeing often has a local
minimum of ~0.3'' near 18 h local time. Some periods of excellent seeing, 0.3''
or smaller, were also observed, sometimes extending for several hours at local
midnight. The median seeing is higher, at 0.52''---this large value is believed
to be caused by periods when the telescope was within the turbulent boundary
layer.
Conclusions. The diurnal variation of the daytime seeing at Dome Fuji is
similar to that reported for Dome C, and the height of the surface boundary
layer is consistent with previous simulations for Dome Fuji. The free
atmosphere seeing is ~0.2'', and the height of the surface boundary layer can
be as low as ~11 m.Comment: 4 pages, 6 figures, Submitted to Astronomy & Astrophysics (letter
Prospects of long-time-series observations from Dome C for transit search
The detection of transiting extrasolar planets requires high-photometric
quality and long-duration photometric stellar time-series. In this paper, we
investigate the advantages provided by the Antarctic observing platform Dome C
for planet transit detections during its long winter period, which allows for
relatively long, uninterrupted time-series. Our calculations include limiting
effects due to the Sun and Moon, cloud coverage and the effect of reduced
photometric quality for high extinction of target fields. We compare the
potential for long time-series from Dome C with a single site in Chile, a
three-site low-latitude network as well as combinations of Dome C with Chile
and the network, respectively. Dome C is one of the prime astronomical sites on
Earth for obtaining uninterrupted long-duration observations in terms of
prospects for a high observational duty cycle. The duty cycle of a project can,
however, be significantly improved by integrating Dome C into a network of
sites.Comment: 10 pages, 9 figures, accepted by PAS
Wind tunnel study of an observatory dome with a circular aperture
Results of a wind tunnel test of a new concept in observatory dome design, the Fixed Shutter Dome are presented. From an aerodynamic standpoint, the new dome configuration is similar in overall shape to conventional observatory domes, with the exception of the telescope viewing aperture. The new design consists of a circular aperture of reduced area in contrast to conventional domes with rectangular or slotted openings. Wind tunnel results of a side-by-side comparison of the new dome with a conventional dome demonstrate that the mean and fluctuating velocity through the aperture and in the center of the new dome configuration are lower than those of conventional domes, thus reducing the likelihood of telescope flow-induced vibration
Dome craters on Ganymede
Voyager observations reveal impact craters on Ganymede that are characterized by the presence of broad, high albedo, topographic domes situated within a central pit. Fifty-seven craters with central domes were identified in images covering approx. 50% of the surface. Owing to limitations in resolution, and viewing and illumination angles, the features identified are most likely a subset of dome craters. The sample appears to be sufficiently large to infer statistically meaningful trends. Dome craters appear to fall into two distinct populations on plots of the ratio of dome diameter to crater rim diameter, large-dome craters and small-dome craters. The two classes are morphologically distinct from one another. In general, large dome craters show little relief and their constituent landforms appear subdued with respect to fresh craters. The physical attributes of small-dome craters are more sharply defined, a characteristic they share with young impact craters of comparable size observed elsewhere in the solar system. Both types of dome craters exhibit central pits in which the dome is located. As it is difficult to produce domes by impact and/or erosional processes, an endogenic origin for the domes is reasonably inferred. Several hypotheses for their origin are proposed. These hypotheses are briefly reviewed
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