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101.
Airborne laser altimetry survey of Glaciar Tyndall, Patagonia 总被引:1,自引:1,他引:0
Kristian Keller Gino Casassa Andrs Rivera Rene Forsberg Niels Gundestrup 《Global and Planetary Change》2007,59(1-4):101
The first airborne laser altimetry measurements of a glacier in South America are presented. Data were collected in November of 2001 over Glaciar Tyndall, Torres del Paine National Park, Chilean Patagonia, onboard a Twin Otter airplane of the Chilean Air Force. A laser scanner with a rotating polygon-mirror system together with an Inertial Navigation System (INS) were fixed to the floor of the aircraft, and used in combination with two dual-frequency GPS receivers. Together, the laser–INS–GPS system had a nominal accuracy of 30 cm after data processing. On November 23rd, a total of 235 km were flown over the ablation area of Glaciar Tyndall, with 5 longitudinal tracks with a mean swath width of 300 m, which results in a point spacing of approximately 2 m both along and across track. A digital elevation model (DEM) generated using the laser altimetry data was compared with a DEM produced from a 1975 map (1:50,000 scale — Instituto Geográfico Militar (IGM), Chile). A mean thinning of − 3.1 ± 1.0 m a− 1 was calculated for the ablation area of Glaciar Tyndall, with a maximum value of − 7.7 ± 1.0 m a− 1 at the calving front at 50 m a.s.l. and minimum values of between − 1.0 and − 2.0 ± 1.0 m a− 1 at altitudes close to the equilibrium line altitude (900 m a.s.l.). The thinning rates derived from the airborne survey were similar to the results obtained by means of ground survey carried out at 600 m of altitude on Glaciar Tyndall between 1975 and 2002, yielding a mean thinning of − 3.2 m a− 1 [Raymond, C., Neumann, T.A., Rignot, E., Echelmeyer, K.A., Rivera, A., Casassa, G., 2005. Retreat of Tyndall Glacier, Patagonia, over the last half century. Journal of Glaciology 173 (51), 239–247.]. A good agreement was also found between ice elevation changes measured with laser data and previous results obtained with Shuttle Radar Topography Mission (SRTM) data. We conclude that airborne laser altimetry is an effective means for accurately detecting glacier elevation changes in Patagonia, where an ice thinning acceleration trend has been observed during recent years, presumably in response to warming and possibly also drier conditions. 相似文献
102.
The paper considers morphology of craters, smooth surfaces, and flows as well as signatures of layering observed on nuclei of Borrelly, Wild 2, and Tempel 1. In our analysis, we emphasize the role of the so-called planation process, which involves avalanche-type flows and can be responsible for the formation of flow-like features, smooth terrains, terraces, and flat floors of some craters observed on cometary nuclei. In agreement with some other researchers (e.g., Belton, 2006), we suggest that in the thicker layers on Tempel 1 and in some features on Borrelly and Wild 2, we may see elements of the comet primordial structure. We also see more and less degraded impact craters formed early in the comet history in distant parts of the Solar System and landforms formed very recently during comet visits to the inner part of the Solar System. The recent resurfacing processes certainly changed the nucleus surface materials, possibly enhancing the sublimation of volatile species, so it should be taken into account in interpretations of the Deep Impact results and in selecting study areas when the Rosetta spacecraft will approach its target comet. 相似文献
103.
龙门山断裂带位于四川盆地西缘;青藏高原东部;为四川盆地与松潘-甘孜地块的接触构造边界。龙门山地区海拔从东侧100 km外四川盆地的500 m突升至3 000 m高度;明显地标注了青藏高原的东部边界;其隆升机制也引起了国内外地质工作者的广泛兴趣;并且提出了多种隆升机制模型。在本次研究中;我们利用SinoProbe-02深反射地震剖面数据对龙门山地区的隆升机制进行研究;从而进一步探讨龙门山地区隆起造山的独特性;并讨论其与传统意义中的造山带的区别;认为龙门山断裂造山带为板块内部构造活动引起岩石圈隆起所形成的。本文的研究结果将使我们更深刻地了解龙门山地区的构造活动特点;并且有助于了解青藏高原东缘对印度-欧亚板块碰撞的构造响应。 相似文献
104.
The dynamics of learning about a climate threshold 总被引:1,自引:0,他引:1
Anthropogenic greenhouse gas emissions may trigger threshold responses of the climate system. One relevant example of such
a potential threshold response is a shutdown of the North Atlantic meridional overturning circulation (MOC). Numerous studies
have analyzed the problem of early MOC change detection (i.e., detection before the forcing has committed the system to a
threshold response). Here we analyze the early MOC prediction problem. To this end, we virtually deploy an MOC observation
system into a simple model that mimics potential future MOC responses and analyze the timing of confident detection and prediction.
Our analysis suggests that a confident prediction of a potential threshold response can require century time scales, considerably
longer that the time required for confident detection. The signal enabling early prediction of an approaching MOC threshold
in our model study is associated with the rate at which the MOC intensity decreases for a given forcing. A faster MOC weakening
implies a higher MOC sensitivity to forcing. An MOC sensitivity exceeding a critical level results in a threshold response.
Determining whether an observed MOC trend in our model differs in a statistically significant way from an unforced scenario
(the detection problem) imposes lower requirements on an observation system than the determination whether the MOC will shut
down in the future (the prediction problem). As a result, the virtual observation systems designed in our model for early
detection of MOC changes might well fail at the task of early and confident prediction. Transferring this conclusion to the
real world requires a considerably refined MOC model, as well as a more complete consideration of relevant observational constraints. 相似文献
105.
N. Malarkodi G. Keller P. J. Fayazudeen U. B. Mallikarjuna 《Journal of the Geological Society of India》2010,75(6):851-863
Intertrappean beds exposed between upper and lower traps of the Government and Sunnamrayalu quarries of Rajahmundry were analyzed
based on benthic and planktic foraminifera, ostracodes and algae observed in thin sections. Planktic foraminifera indicate
deposition occurred in the early Danian Parvularugoglobigerina eugubina (P1a) zone shortly after deposition of the lower trap flows. The most diverse planktic assemblages were deposited in limestones
of the middle intertrappean interval and indicate an upper P1a age, or subzone P1a(2), as marked by the co-occurrence of P. eugubina, Globoconusa daubjergensis, Parasubbotina pseudobulloides and Subbotina triloculinoides. Reworked late Maastrichtian planktic foraminifera are common in a limestone interval and suggest erosion of uplifted Cretaceous
sediments. Benthic foraminiferal assemblages indicate deposition occurred predominantly in shallow inner shelf to brackish
environments. Similarly, ostracodes indicate variable environments ranging from inner neritic to brackish with fresh water
influx, as also indicated by the presence of fresh water algae. These data confirm an overall deepening from restricted shallow
marine to estuarine, lagoonal and finally open marine conditions followed by abrupt emersion and paleosoil deposition prior
to the arrival of the upper trap flows at or near the base of C29n. 相似文献
106.
S. Marchi C. Barbieri F. Marzari H.U. Keller P. Lamy M. Massironi 《Planetary and Space Science》2010,58(9):1116-490
The cratering history of main belt asteroid (2867) Steins has been investigated using OSIRIS imagery acquired during the Rosetta flyby that took place on the 5th of September 2008. For this purpose, we applied current models describing the formation and evolution of main belt asteroids, that provide the rate and velocity distributions of impactors. These models coupled with appropriate crater scaling laws, allow the cratering history to be estimated. Hence, we derive Steins’ cratering retention age, namely the time lapsed since its formation or global surface reset. We also investigate the influence of various factors—like bulk structure and crater erasing—on the estimated age, which spans from a few hundred Myrs to more than 1 Gyr, depending on the adopted scaling law and asteroid physical parameters. Moreover, a marked lack of craters smaller than about 0.6 km has been found and interpreted as a result of a peculiar evolution of Steins cratering record, possibly related either to the formation of the 2.1 km wide impact crater near the south pole or to YORP reshaping. 相似文献
107.
The idea of transforming the geodetic boundary value problem into a boundary value problem with a fixed boundary dates back
to the 1970s of the last century. This transformation was found by F. Sanso and was named as gravity-space transformation. Unfortunately, the advantage of having a fixed boundary for the transformed problem was counterbalanced by
the theoretical as well as practical disadvantage of a singularity at the origin. In the present paper two more versions of
a gravity-space transformation are investigated, where none of them has a singularity. In both cases the transformed differential
equations are nonlinear. Therefore, a special emphasis is laid on the linearized problems and their relationships to the simple
Hotine-problem and to the symmetries between both formulations. Finally, in numerical simulation study the accuracy of the
solutions of both linearized problems is studied and factors limiting this accuracy are identified. 相似文献
108.
Abundant and regionally unique dolostone lithoclast breccias occur throughout the shallow-marine, Lower to Middle Ordovician Pogonip Group in the Nopah Range and adjacent ranges in eastern California and southern Nevada. Breccia bodies display sharply cross-cutting relationships with host dolostone bedrock stratigraphy. They also show stratigraphic variability in size, shape and dolostone clast composition, but similarity in breccia matrix composition and framework texture and fabric. These characteristics are consistent with a palaeokarst origin. Upsection changes in breccia clast lithology as well as multiple occurrences of associated quartz sand-filled grikes (solution-widened fissures) indicate multiple episodes of carbonate platform exposure and karstification. Repeated karstification is also indicated by stratiform bodies of quartz sand and thin terra rossa palaeosols that locally truncate breccias and grike systems, thus bracketing karstified exposure surfaces. Facies successions and stacking patterns between recognized exposure surfaces are developed as transgressive–regressive cycles and thus show depositional sequence architecture. Hence, these breccias and other associated palaeokarst features are related to a succession of disconformities that provide a sequence-stratigraphic framework for assessing Ordovician relative sea-level history of the south-western Cordilleran margin of Laurentia. 相似文献
109.
W. I. Rose Jr. S. Bonis R. E. Stoiber M. Keller T. Bickford 《Bulletin of Volcanology》1973,37(3):338-364
The 1971 eruptions of Cerro Negro volcano in Nicaragua and Fuego volcano in Guatemala produced ash blankets with minimum volumes of 7 × 107 m3 and 6 × 107 m3, respectively. Seven new chemical analyses show that ash produced by both eruptions was basaltic and similar to previously — erupted lavas of both volcanoes. Both ash blankets were sampled areally and stratigraphically before they were affected by rain. Chemical analyses of soluble materials leached from these ashes show that near the end of both eruptions the concentrations of soluble materials increased by about an order of magnitude. These changes are believed to reflect changes in the composition of eruptive gases. 相似文献
110.
Analysis of State and Provincial Atlas Reviews* 总被引:1,自引:0,他引:1
Ninety-eight reviews of state and provincial atlases are examined in order to address several questions. Reviews are subjected to content analysis to identify the judgement criteria that experts use in evaluating a provincial or state atlas, and the aspects of each criterion that reviewers praise or condemn. An attempt is made to search for expert consensus and to identify a provincial or state atlas review recipe. The research reported here is part of a larger study undertaken to assist those in the process of planning a new provincial or state atlas initiative. This paper also assists individuals who are searching for rules and guidelines when undertaking an atlas review. 相似文献