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PETER JENNISKENS PAUL WERCINSKI JOE OLEJNICZAK GARY ALLEN PRASUN N. DESAI GEORGE RAICHE DEAN KONTINOS DOUG REVELLE JASON HATTON RICHARD L. BAKER RAY W. RUSSELL MIKE TAYLOR FRANS RIETMEIJER 《Earth, Moon, and Planets》2004,95(1-4):339-360
The imminent return of the Genesis Sample Return Capsule (SRC) from the Earth’s L1 point on September 8, 2004, represents
the first opportunity since the Apollo era to study the atmospheric entry of a meter-sized body at or above the Earth’s escape
speed. Until now, reentry heating models are based on only one successful reentry with an instrumented vehicle at higher than
escape speed, the 22 May 1965 NASA “FIRE 2” experiment. In preparation of an instrumented airborne and ground-based observing
campaign, we examined the expected bolide radiation for the reentry of the Genesis SRC. We find that the expected emission
spectrum consists mostly of blackbody emission from the SRC surface (T∼
∼2630 K@peak heating), slightly skewed in shape because of a range of surface temperatures. At high enough spectral resolution,
shock emission from nitrogen and oxygen atoms, as well as the first positive and first negative bands of N2+, will stand out above this continuum. Carbon atom lines and the 389-nm CN band emission may also be detected, as well as
the mid-IR 4.6-μm CO band. The ablation rate can be studied from the signature of trace sodium in the heat shield material,
calibrated by the total amount of matter lost from the recovered shield. A pristine collection of the heat shield would also
permit the sampling of products of ablation. 相似文献
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BRUCE HAINES YOAZ BAR-SEVER WILLY BERTIGER SHAILEN DESAI PASCAL WILLIS 《Marine Geodesy》2013,36(1-2):299-318
The U.S./French Jason-1 satellite is carrying a state-of-the-art GPS receiver to support precise orbit determination (POD) requirements. The performance of the Jason-1 “BlackJack” GPS receiver was strongly reflected in early POD results from the mission, enabling radial accuracies of 1–2 cm soon after the satellite's 2001 launch. We have made further advances in the GPS-based POD for Jason-1, most notably in describing the phase center variations of the on-board GPS antenna. We have also adopted new geopotential models from the Gravity Recovery and Climate Experiment (GRACE). The new strategies have enabled us to better exploit the unique contributions of the BlackJack GPS tracking data in the POD process. Results of both internal and external (e.g., laser ranging) comparisons indicate that orbit accuracies of 1 cm (radial RMS) are being achieved for Jason-1 using GPS data alone. 相似文献
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H.B. DESAI S.R. KAYASTH C.G. UDAS M. SANKAR DAS 《Geostandards and Geoanalytical Research》1983,7(2):325-329
The reported values for the chromium contents of standard acidic rocks show a large spread, making it difficult to assign firm recommended values. A radiochemical neutron activation analysis procedure was developed and its reliability examined critically. The method involves separation of chromium as chromyl chloride by distillation followed by precipitation as barium chromate. The chromium content of a number of international standard rocks has been determined and results obtained are critically reviewed in relation to the available data. 相似文献
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The Okha Shell Limestone Member of Chaya Formation is the coarse grained, shell rich deposit commonly recognized as the beach
rocks. It has been age bracketed between Late Pleistocene and Holocene. Late Quaternary sea level changes have been studied
with beach rocks along the Saurashtra coastal region. The present study has been carried out in the Okhamandal area of the
Saurashtra peninsula especially on the Okha Shell Limestone Member as exposed at various locations along the coast from north
to south. Temporal and spatial correlations of the observations have revealed three events in the Okha Shell Limestone Member
of Chaya Formation that are correlated laterally. The events show depositional breaks represented by discontinuity surfaces,
the taphofacies varieties and ichnological variations. The present study in the context of available geochrnological data
of the region suggests a prominent depositional break representing low sea level stand (regression) during an Early Holocene
during the deposition of Okha Shell Limestone Member. 相似文献
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Monitoring Measurements from the Jason-1 Microwave Radiometer and Independent Validation with GPS 总被引：1，自引：1，他引：0
The Jason-1 Microwave Radiometer (JMR) provides measurements of the wet troposphere content to correct the altimetric range measurement for the associated path delay. Various techniques are used to monitor the JMR wet troposphere path delays, with measurements of zenith troposphere content from terrestrial GPS sites used as an independent verification technique. Results indicate that an unexpected offset of approximately +4.1 ± 1.2 mm (drier) emerged in the JMR measurements of wet path delay between cycles 28–32 of the Jason-1 mission, and that the measurements may be drifting at a rate of approximately ?0.5 mm/year. These anomalies are shown to be caused by a ?0.7 K offset in 23.8 GHz brightness temperatures between cycles 28–32, and a 0.16 ± 0.04 and ?0.45 ± 0.08 K/year drift in the 18.7 and 34.0 GHz brightness temperatures, respectively. Intercomparison of the 3-Hz JMR brightness temperature measurements show that they have been drifting with respect to each other, and that a dependence on yaw-steering regime is present in these measurements. An offset of 0.5 m/s between cycles 28–32 and a drift of approximately 0.5 m/s/year in the JMR wind speed measurements is also associated with these anomalies in the 1-Hz brightness temperatures. These errors in JMR wind speeds presently have a negligible impact on the retrieved JMR path delays. 相似文献
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The paper discusses the low contrast of the Fabry-Perot (FP) fringes observed in the interferograms of the solar corona. The various factors which affect the interfringe intensity of Fabry-Pérot line profiles are considered. The effect of continuum radiation on the interfringe intensity of Fabry-Pérot line profiles is calculated by assuming a coronal model. For the given FP, it was found that unless the ratio of line to continuum intensity (integrated line intensity to continuum per angström) is less than 10, continuum contribution has no significant effect on the fringe contrast. The analysis may be pertinent in the design aspects of a FP interferometer for astronomical observations. The excess interfringe intensity found in the coronal line profiles is interpreted as due to the presence of fast moving plasma components in corona along the line of sight. A detailed analysis qualitatively shows that the line excitation conditions existing in ambient corona and coronal loops are different in active regions while they are more similar in polar regions. 相似文献
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The Jason microwave radiometer (JMR) provides a crucial correction due to water vapor in the troposphere, and a much smaller correction due to liquid water, to the travel time of the Jason-1 altimeter radar pulse. An error of any size in the radiometer's measurement of wet path delay translates as an error of equal size in the measurement of sea surface height, the ultimate quantity that the altimetric system should yield. The estimate of globally-averaged sea surface height change associated with climate change, requires that uncertainties in the trends in such a global average be accurate to much better than the signal of 1–2 mm/yr. We first compare the JMR observations to those from the TOPEX/Poseidon radiometer (TMR) over approximately six months, since the intent of Jason is to continue the 10-year time series of precision ocean surface topography initiated by T/P. We then assess the stability of the JMR measurement by comparing its wet path delay to those of other orbiting radiometers over 22 months, specifically the Special Sensor Microwave Imager aboard the Defense Meteorological Satellite Program (DMSP-SSM/I) series of satellites, and the Tropical Rainfall Mapping Mission's Microwave Imager (TMI), as well as the European Center for Medium Range Weather Forecasting's (ECMWF) atmospheric numerical model estimate of water vapor. From the combined set, we obtain a robust assessment of the stability of JMR measurements. We find, that JMR is in remarkable agreement with TMR, only 2.5 mm longer, and 6–7 mm standard deviation on their difference in 0.5 degree averages; that JMR has experienced a globally-averaged step-function change, yielding an apparent shortening in wet path delay estimates of 4–5 mm around October 2002 (Jason cycles 28–32); that this step-function is visible only in the 23.8 GHz channel; and that the 34 GHz channel appears to drift at a rate of ?0.4K/year. In addition, we find that, while in 2002 there was no evidence of sensitivity to the Jason satellite's attitude (a correlation of the wet path delay with yaw state), in 2003 there are strong (2–3 mm, up to 7 mm globally averaged) changes associated with such yaw state. These JMR issues were all found in the first 22 months of Jason's geophysical data records (GDR) data, and thus they apply to any investigations that use such data without further corrections. 相似文献
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