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Showing papers by "National Ocean Service published in 1992"


Journal ArticleDOI
TL;DR: In this article, the authors compare along-track gravity and gridded gravity fields derived from ERS-1 fast delivery altimeter data to those computed from Geosat Geodetic Mission altimeter observations in the Southern Ocean.
Abstract: To estimate how well ERS-1 data from the 35-day repeat mission can resolve fine structure in the marine geoid or gravity field, we compare along-track gravity and gridded gravity fields derived from ERS-1 fast delivery altimeter data to those computed from Geosat Geodetic Mission altimeter observations in the Southern Ocean. We find that single passes of ERS-1 data can resolve along-track gravity anomalies with wavelengths as short as 28–30 km (i.e., comparable to Geosat). However, the ERS-1 gridded gravity field can only resolve anomalies as short as 66 km (versus ∼18 km for Geosat). This two-dimensional resolution is limited by the larger ground track spacing (∼35 km at 60° S) of ERS-1. To resolve fine structure in the marine gravity field it is essential to have altimeter data along more closely-spaced ground tracks, such as those planned for the ERS-1 176-day repeat mission in 1994.

15 citations


Journal Article
TL;DR: A prefiltering procedure designed to identify and remove erroneous or questionable soundings from multibeam sonar data collected in support of the United States Exclusive Economic Zone Bathymetric Mapping Programme is implemented.
Abstract: As part of its continuing efforts to improve data quality, the National Oceanic and Atmospheric Administration (NOAA) has recently implemented a "prefiltering" procedure designed to identify and remove erroneous or questionable soundings from multibeam sonar data collected in support of the United States Exclusive Economic Zone Bathymetric Mapping Programme. Since the start of the 1991 field season, a simple, yet effective, prefiltering algorithm has been incorporated into the standard post-processing software used aboard NOAA ships equipped with MicroVAX-based survey systems. In addition, the prefiltering routine is also being utilized as part of NOAA's current effort to convert its archive of older PDP-11 multibeam surveys to standard full-resolution "beam" format. The sounding verification criteria employed by the prefiltering algorithm is discussed in detail and statistical results from the first season of its implementation are presented.

13 citations


01 Jan 1992
TL;DR: For the 80-year period 1905-1985, 23 essentially complete tide gauge records in 10 geographic groups are available for analysis and yielded the apparent global acceleration -0.011 (+/- 0.012) mm/yr2 as mentioned in this paper.
Abstract: Published values for the long-term, global mean sea level rise determined from tide gauge records range from about one to three mm per year. The scatter of the estimates appears to arise largely from the use of data from gauges located at convergent tectonic plate boundaries where changes of land elevation give fictitious sea level trends, and the effects of large interdecadal and longer sea level variations on short (less than 50+ years) or sappy records. In addition, virtually all gauges undergo subsidence or uplift due to isostatic rebound from the last deglaciation at a rate comparable to or greater than the secular rise of sea level. Modeling rebound by the ICE-3G model of Tushingham and Peltier (1990) and avoiding tide gauge records in areas of converging tectonic plates produces a highly consistent set of long sea level records. A global set of 21 such stations in nine oceanic regions with an average record length of 76 years during the period 1880-1980 yields the global sea level rise value 1.8 mm/year +/- 0.1. Greenhouse warming scenarios commonly forecast an additional acceleration of global sea level in the next 5 or 6+ decades in the range 0.1-0.2 mm/yr2. Because of the large power at low frequencies in the sea level spectrum, very long tide gauge records (75 years minimum) have been examined for past apparent sea level acceleration. For the 80-year period 1905-1985, 23 essentially complete tide gauge records in 10 geographic groups are available for analysis. These yielded the apparent global acceleration -0.011 (+/- 0.012) mm/yr2. A larger, less uniform set of 37 records in the same 10 groups with 92 years average length covering the 141 years from 1850-1991 gave 0.001 (+/- 0.008) mm/yr2. Thus there is no evidence for an apparent acceleration in the past 100+ years that is significant either statistically, or in comparison to values associated with global warming. Unfortunately, the large interdecadal fluctuations of sea level severely affect estimates of global sea level acceleration for time spans of less than about 50 years. This means that tide gauges alone cannot serve as a reliable leading indicator of climate change in less than many decades. This time required can be significantly reduced if the interdecadal fluctuations of sea level can be understood in terms of their forcing mechanisms, and then removed from the tide gauge records.

1 citations


Proceedings ArticleDOI
26 Oct 1992
TL;DR: In this paper, the use of a towed acoustic Doppler current profiler (ADCP) for the purpose of evaluating in situ current meters is discussed, and the results show that bottom-mounted ADCP is measuring current speeds accurately and is in the optimal location to report maximum channel currents under the Sunshine Skyway Bridge (SSB).
Abstract: This paper discusses the use of a towed acoustic Doppler current profiler (ADCP) for the purpose of evaluating in situ current meters. Data are presented from comparison tests between a towed and bottom-mounted ADCP. Velocity contours parallel and transverse to the main navigation channel under the Sunshine Skyway Bridge (SSB) in Tampa, Florida from a 600 KHz towed ADCP are compared to bottom-mounted current profiles from a 1200 KHz ADCP placed under the SSB. Data are presented to show instrument differences which are a combiination of random and systematic error. The study finds that the bottom-mounted ADCP is measuring current speeds accurately and is in the optimal location to report maximum channel currents under the SSB. The present location of the bottom-mounted ADCP under the SSB in the middle of the main navigation channel reports velocities accurate to 5 cmls. This metho+ is considered a viable technique for evaluating the reliability of moored or bottom-mounted units.