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1.
The Texaco Harvest Oil Platform Experiment took place August 22–28, 1990, off Point Conception, California. This platform has been designated as the NASA/JPL verification site for the TOPEX radar altimeter, which is to be launched in mid‐1992. The purpose of the experiment was to obtain measurements from GPS and other instrumentation that will be used at the site for the verification activities, and to determine the potential effects of the platform environment on the quality of the measurements. In conjunction with this experiment, a buoy equipped with a GPS receiver was floated in the vicinity of the platform for the purpose of measuring sea‐level change and waves relative to a reference receiver located on the platform. A pressure transducer installed at the site also provided sea‐level change and wave measurements relative to the platform. We present the data collection, processing, and analysis results comparing the GPS‐buoy and pressure transducer data. The GPS‐determined sea‐surface height measurements show 1.3‐cm agreement when compared with transducer‐determined heights taken over the same period of time. Low‐rate (15‐s) data were used to measure the change in sea‐level height due to tides, while high‐rate (1‐s) measurements provided temporal resolution sufficient for determining wave spectra.  相似文献   

2.
Wanshan area has been chosen to be the specified field to calibrate and validate(Cal/Val) the HY-2 altimeter and its follow-on satellites. In March 2018, an experiment has been conducted to determine the sea surface height(SSH) under the HY-2 A ground track(Pass No. 203). A GPS towing-body(GPS-TB) was designed to measure the SSH covering an area of about 6 km×28 km wide centered on the HY-2 A altimeter satellite ground track. Three GPS reference stations, one tide gauge and a GPS buoy were placed in the research area, in order to process and resolve the kinematic solution and check the precision of the GPS-TB respectively. All the GPS data were calculated by the GAMIT/GLOBK software and TRACK module. The sea surface was determined by the GPS-TB solution and the tide gauge placed on Zhiwan Island. Then the sea surface of this area was interpolated by Arc GIS10.2 with ordinary Kriging method. The results showed that the precision of the GPS-TB is about 1.10 cm compared with the tide gauge placed nearby, which has an equivalent precision with the GPS buoy. The interpolated sea surface has a bias of –1.5–4.0 cm with standard deviation of 0.2–2.4 cm compared with the checking line. The gradient of the measured sea surface is about 1.62 cm/km along the HY-2 orbit which shows a good agreement compared with the CLS11 mean sea surface(MSS). In the Cal/Val of satellites, the sea surface between the tide gauge/GPS buoy and the footprint of altimeter can be improved by this work.  相似文献   

3.
Abstract

This article describes the design and initial tests of the GPS portion of a system for making seafloor geodesy measurements. In the planned system, GPS antennas on a floating platform will be used to measure the location of an acoustic transducer, attached below the platform, which interrogates an array of transponders on the seafloor. Since the GPS antennas are necessarily some distance above the transducer, a short‐baseline GPS interferometer consisting of three antennas is used to measure the platform's orientation.

A preliminary test of several crucial elements of the system was performed at the Scripps Institution of Oceanography (SIO) in December 1989. The test involved a fixed antenna on the pier and a second antenna floating on a buoy about 80 m away. GPS measurements of the vertical component of this baseline, analyzed independently by two groups using different software, agree with each other and with an independent measurement within a centimeter.

The first test of an integrated GPS/acoustic system took place in the Santa Cruz Basin off the coast of southern California in May 1990. In this test a much larger buoy, designed and built at SIO, was equipped with three GPS antennas and an acoustic transducer that interrogated a transponder on the ocean floor. Preliminary analysis indicates that the horizontal position of the transponder can be determined with a precision of about a centimeter. Further analysis will be required to investigate the magnitude of systematic errors.  相似文献   

4.
Abstract

Using GPS phase observations in the kinematic mode, we are able to achieve centimeter accuracy in relative three‐dimensional coordinates. This could be verified even for fast‐moving sensors in aircraft, such as airborne photogrammetric cameras, at the time of exposure. Sophisticated kinematic software has been developed resolving cycle slips and carrier‐phase ambiguities during motion. To determine the instantaneous sea surface, the GPS receiver is placed in a free‐drifting buoy with the antenna on top. Differencing the 1‐Hz observations, wave heights can be determined as well as velocity and direction of ocean (tidal) currents.

This article deals with the experiences from a test for the practical realization of this proposal. Hardware installation, software, and data analysis are described. Plans to use such an observational scenario of a GPS buoy array in the North Sea for the calibration of the radar altimeter of the European satellite ERS‐1 are presented.  相似文献   

5.
Abstract

It is desired to track the location of an underwater data collecting platform using acoustic range data. A long‐range and high‐resolution acoustic system for underwater locating has been investigated. The system provides continuous and highly accurate tracking of a platform referenced to bottom‐mounted buoys. Each reference buoy contains an acoustic transponder, which is used to obtain ranging data from the transponder to the platform. The transponder has a signal source that is phase‐modulated by a maximal‐length binary sequence and a correlation processing unit to be capable of detecting received acoustic signals with high SNR in a noisy environment or in attenuation due to long‐range propagation, and to identify multipath acoustic signals. The acoustic system has been designed and sea tests tried. The results of that experiment have yielded capability of a submeter underwater acoustic positioning system.  相似文献   

6.
An improved absolute calibration technology based on indirect measurements was developed through two probative experiments, the performance of which was evaluated by applying the approach to in situ sea surface height(SSH) at the Tianheng Island(tidal gauge) and the satellite nadir(GPS buoy). Using Geoid/MSS(mean sea surface) data, which accounted for a constant offset between nadir and onshore tidal gauge water levels, and TMD(tidal model driver), which canceled out the time-varying offsets, nadir SSH(sea surface height) could be indirectly acquired at an onshore tidal gauge instead of from direct offshore observation. The approach extrapolated the onshore SSH out to the offshore nadir with an accuracy of(1.88±0.20) cm and a standard deviation of 3.3 cm, which suggested that the approach presented was feasible in absolute altimeter calibration/validation(Cal/Val), and the approach enormously facilitated the obtaining SSH from the offshore nadir.  相似文献   

7.
Ten-day mean surface level air-temperature from SSMI precipitable water (SSMI-T a ) has been derived and compared with the temperature from two ocean data buoys (Buoy-T a ) of Japan Meteorological Agency (JMA) for a period of six months (July–December, 1988). Statistical relations between air-temperature and mixing ratio, using data from ocean data buoys are used to derive air-temperature from mixing ratio, obtained from SSMI precipitable water. For getting the mixing ratio from precipitable water, regional mixing ratio-precipitable water relations have been used, instead of global relation proposed by Liu (1986). The rms errors (standard deviation of the difference between SSMI-T a and Buoy-T a ) for two buoy locations are found to be 1.15 and 1.12°C, respectively. Surface level temperature for the two buoy locations are also derived using direct regression relation between Buoy-T a and precipitable water. The rms errors of the SSMI-T a , in this case are found to be reduced to 1.0°C.  相似文献   

8.
为了更好地利用卫星测高数据分析黄海和东海的潮汐特性 ,对 1 993— 1 999年期间的TOPEX/Poseidon测高数据进行了质量控制和共线平差处理。在此基础上 ,在黄海、东海选取了 1 738个测高点 ,用最小二乘拟合法计算出 1 2个分潮的调和常数。计算得出的M2 和m1分潮的调和常数 ,在交叉点评估的内符精度振幅分别为 2 4cm和 0 8cm ,迟角分别为 2 3°和2 5°。测高点与附近验潮站的这两个分潮结果相比 ,振幅的均方根误差小于 4cm ,而迟角相差较大。这可能与验潮站的地理环境因素有关。用卫星测高数据算得的调和常数绘制的主要分潮特性图与现有常规观测得到的相应图进行了比较 ,在外海深水区两者符合较好 ;近岸由于卫星测高误差较大 ,所以两者符合差。  相似文献   

9.
Surface velocities determined from trajectory of a drifting buoy from March through November 1987 are compared with surface geostrophic velocities determined from sea surface dynamic topography (SSDT) obtained from altimetry data with the aid of long-term hydrographic observation data. In general, these velocities show similar temporal variations in both zonal and meridional components, except in a period when obvious error is found in the altimetric SSDT field. When the buoy was trapped by several mid-ocean meso-scale eddies, the comparison is especially good. Systematic discrepancy is found, however, when the buoy was in the Kuroshio region, because of using both temporally and spatially smoothed mean SSDT estimated from hydrographic data; instead, surface geostrophic velocities determined from the altimetric SSDT referred to the improved geoid model result in better comparison.  相似文献   

10.
《Marine Geodesy》2013,36(3-4):319-334
In the framework of the TOPEX/Poseidon and Jason-1 CNES-NASA missions, two probative experiments have been conducted at the Corsica absolute calibration site in order to determine the local marine geoid slope under the ascending TOPEX/Poseidon and Jason-1 ground track (No. 85). An improved determination of the geoid slope was needed to better extrapolate the offshore (open-ocean) altimetric data to on-shore tide-gauge locations. This in turn improves the overall precision of the calibration process. The first experiment, in 1998, used GPS buoys. Because the time required to cover the extended area with GPS buoys was thought to be prohibitive, we decided to build a catamaran with two GPS systems onboard. Tracked by a boat at a constant speed, this innovative system permitted us to cover an area of about 20 km long and 5.4 km wide centered on the satellites' ground track. Results from an experiment in 1999 show very good consistency between GPS receivers: filtered sea-surface height differences have a mean bias of ?0.2 cm and a standard deviation of 1.2 cm. No systematic error or distortions have been observed and crossover differences have a mean value of 0.2 cm with a standard deviation of 2.7 cm. Comparisons with tide gauges data show a bias of 1.9 cm with a standard deviation of less than 0.5 cm. However, this bias, attributable in large part to the effect of the catamaran speed on the waterline, does not affect the geoid slope determination which is used in the altimeter calibration process. The GPS-deduced geoid slope was then incorporated in the altimeter calibration process, yielding a significant improvement (from 4.9 to 3.3 cm RMS) in the agreement of altimeter bias determinations from repeated overflight measurements.  相似文献   

11.
In the framework of the TOPEX/Poseidon and Jason-1 CNES-NASA missions, two probative experiments have been conducted at the Corsica absolute calibration site in order to determine the local marine geoid slope under the ascending TOPEX/Poseidon and Jason-1 ground track (No. 85). An improved determination of the geoid slope was needed to better extrapolate the offshore (open-ocean) altimetric data to on-shore tide-gauge locations. This in turn improves the overall precision of the calibration process. The first experiment, in 1998, used GPS buoys. Because the time required to cover the extended area with GPS buoys was thought to be prohibitive, we decided to build a catamaran with two GPS systems onboard. Tracked by a boat at a constant speed, this innovative system permitted us to cover an area of about 20 km long and 5.4 km wide centered on the satellites' ground track. Results from an experiment in 1999 show very good consistency between GPS receivers: filtered sea-surface height differences have a mean bias of -0.2 cm and a standard deviation of 1.2 cm. No systematic error or distortions have been observed and crossover differences have a mean value of 0.2 cm with a standard deviation of 2.7 cm. Comparisons with tide gauges data show a bias of 1.9 cm with a standard deviation of less than 0.5 cm. However, this bias, attributable in large part to the effect of the catamaran speed on the waterline, does not affect the geoid slope determination which is used in the altimeter calibration process. The GPS-deduced geoid slope was then incorporated in the altimeter calibration process, yielding a significant improvement (from 4.9 to 3.3 cm RMS) in the agreement of altimeter bias determinations from repeated overflight measurements.  相似文献   

12.
An absolute calibration of the TOPEX/Poseidon (T/P) and Jason-1 altimeters has been undertaken during the dedicated calibration phase of the Jason-1 mission, in Bass Strait, Australia. The present study incorporates several improvements to the earlier calibration methodology used for Bass Strait, namely the use of GPS buoys and the determination of absolute bias in a purely geometrical sense, without the necessity of estimating a marine geoid. This article focuses on technical issues surrounding the GPS buoy methodology for use in altimeter calibration studies. We present absolute bias estimates computed solely from the GPS buoy deployments and derive formal uncertainty estimates for bias calculation from a single overflight at the 40-45 mm level. Estimates of the absolute bias derived from the GPS buoys is -10 ± 19 mm for T/P and +147 ± 21 mm for Jason-1 (MOE orbit) and +131 ± 21 mm for Jason-1 (GPS orbit). Considering the estimated error budget, our bias values are equivalent to other determinations from the dedicated NASA and CNES calibration sites.  相似文献   

13.
Guoqi Han 《Marine Geodesy》2004,27(3):577-595
Sea level observations from the tandem TOPEX/Poseidon (T/P) and Jason-1 altimetry missions (2002-2003) are used to study characteristics of sea level and surface currents over the Scotian Shelf and Slope off Nova Scotia. The consistency and error characteristics of T/P and Jason-1 measurements are examined not only in terms of sea level and cross-track current anomalies but also with respect to current anomalies at crossovers, kinematic properties associated with Gulf Stream warm core rings (WCR), and the shelf-edge current transport. Nominal absolute currents are constructed by adding the altimetric geostrophic current anomalies to an annual-mean model circulation field. The concurrent frontal analysis data are analyzed for occurrence of the WCRs and associated kinematic properties are derived from altimetric current anomalies. The comparison of the sea level and cross-track current anomalies from January to July 2002 shows overall good agreement between T/P and Jason, with correlation coefficients different from zero at the 5% significance level at essentially all locations for sea level and at most locations for currents. The cross-track geostrophic current anomalies from January to July 2002 and from September 2002 to December 2003 are further used to calculate the root-mean-square (rms) current magnitude, and the normalized relative vorticity associated with WCRs. The altimetric currents are consistent with each other and complementary to frontal analysis data in deriving the properties of the WCRs. The rms current magnitude is ∼55 cm/s and the normalized relative vorticity is ∼0.15. The model-altimetry combined absolute currents are used to estimate near-surface transport associated with the shelf-edge current, showing good correlation between T/P and Jason estimates and strong seasonal changes. The current anomalies derived from altimetry and moored measurements are significantly (at the 5% significance level) correlated and comparable in the rms magnitude.  相似文献   

14.
The ocean is an important sink for carbon and heat, yet high-resolution measurements of biogeochemical properties relevant to global climate change are being made only sporadically in the ocean at present. There is a growing need for automated, real-time, long-term measurements of CO2 in the ocean using a network of sensors, strategically placed on ships, moorings, free-drifting buoys and autonomous remotely operated vehicles. The ground-truthing of new sensor technologies is a vital component of present and future efforts to monitor changes in the ocean carbon cycle and air–sea exchange of CO2.A comparison of a moored Carbon Interface Ocean Atmosphere (CARIOCA) buoy and shipboard fugacity of CO2 (fCO2) measurements was conducted in the western North Atlantic during two extended periods (>1 month) in 1997. The CARIOCA buoy was deployed on the Bermuda Testbed Mooring (BTM), which is located 5 km north of the site of the US Joint Global Ocean Flux Study (JGOFS) Bermuda Atlantic Time-series Study (BATS). The high frequency of sampling revealed that temperature and fCO2 responded to physical forcing by the atmosphere on timescales from diurnal to 4–8 days. Concurrent with the deployments of the CARIOCA buoy, frequent measurements of surface fCO2 were made from the R/V Weatherbird II during opportunistic visits to the BTM and BATS sites, providing a direct calibration of the CARIOCA buoy fCO2 data. Although, the in situ ground-truthing of the CARIOCA buoy was complicated by diurnal processes, sub-mesoscale and fine-scale variability, the CARIOCA buoy fCO2 data was accurate within 3±6 μatm of shipboard fCO2 data for periods up to 50 days. Longer-term assessments were not possible due to the CARIOCA buoy breaking free of the BTM and drifting into waters with different fCO2-temperature properties. Strategies are put forward for future calibration of other in situ sensors.  相似文献   

15.
为实现多频多模GNSS浮标在远距离海洋潮汐测量中的应用,基于精密单点定位(precision pointing positioning,PPP)数据处理策略获取潮位信息,以压力验潮仪为参考,对GNSS浮标测量海面高进行经验模态分解(empirical mode decomposition,EMD),滤去高频波浪和噪声,获取潮位进行精度分析。结果表明:多系统可以提高PPP解算潮位精度。GPS/GLONASS双系统和GPS/GLONASS/Bei Dou三系统PPP提取潮位与验潮仪潮位差值的最大误差均小于18cm,RMSE小于6. 5cm。因此,多系统PPP解算GNSS浮标海面高可以实现远离海岸的潮位获取与监测,能够提高海上潮位测量的效率。  相似文献   

16.
Satellite-measured along-track and gridded sea surface height (SSH) anomaly products from AVISO are compared with in situ SSH anomaly measurements from an array of 43 pressure-recording inverted echo sounders (PIESs) in the Kuroshio Extension. PIESs measure bottom pressure (P bot) and round-trip acoustic travel time from the sea floor to the sea surface (τ). The P bot and τ measurements are used to estimate, respectively, the mass-loading and steric height variations in SSH anomaly. All comparisons are made after accurate removal of tidal components from all data. Overall good correlations are found between along-track and PIES-derived SSH anomalies with mean correlation coefficient of 0.97. Comparisons between the two measurements reveal that the mass-loading component estimated from P bot is relatively small in this geographical region. It improves regression coefficients about 5?% and decreases mean root-mean-squared (rms) differences from 7.8 to 6.4?cm. The AVISO up-to-date gridded product, which merges all available satellite measurements of Jason-1, Envisat, Geosat Follow-On, and TOPEX/Poseidon interlaced, shows better correlations and smaller rms differences than the AVISO reference gridded product, which merges only Jason-1 and Envisat. Especially, the up-to-date gridded product reveals 6.8?cm rms improvement on average at sites away from Jason-1 ground tracks. Gridded products exhibit low correlation (0.75–0.9) with PIES-derived SSH in a subregion where the SSH fluctuations have relatively high energy at periods shorter than 20?days.  相似文献   

17.
基于GNSS浮标和验潮资料的HY-2A卫星高度计绝对定标   总被引：1，自引：0，他引：1  
为探测我国HY-2A卫星高度计海面高测量绝对偏差及其在轨运行状态,本文利用GNSS浮标星下点同步测量和验潮资料海面高传递方法在山东千里岩和珠海担杆岛海域开展定标研究。为验证GNSS浮标定标方法的准确性,还对国外卫星Jason-2和Saral进行了定标实验。实验表明GNSS浮标绝对海面高测量精度达2 cm,对Jason-2和Saral高度计多个周期定标得到的海面高偏差均值分别为5.7 cm和-2.3 cm,与国际专门定标场的结果符合较好。2014年9月和2015年5月HY-2A卫星高度计浮标定标结果分别是-65 cm和-91 cm,因两次结果差异显著,故又利用千里岩验潮站资料对HY-2A卫星高度计第56至73周期进行了定标分析,结果证明HY-2A卫星海面高存在约-51 cm/a的漂移,置信度为95%的回归分析表明浮标和验潮定标结果符合。本文研究结果表明在我国尚无专门定标场的情况下,可利用GNSS浮标对我国高度计实施灵活、精准的在轨绝对定标,在有高度计轨迹经过验潮站的情况下可使用验潮资料结合精密大地水准面模型进行绝对定标。  相似文献   

18.
Absolute Calibration of the Jason-1 Altimeter Using UK Tide Gauges   总被引：1，自引：0，他引：1  
This article describes an “absolute” calibration of Jason-1 (J-1) altimeter sea surface height bias using a method developed for TOPEX/Poseidon (T/P) bias determination reported previously. The method makes use of U.K. tide gauges equipped with Global Positioning System (GPS) receivers to measure sea surface heights at the same time, and in the same geocentric reference frame, as Jason-1 altimetric heights recorded in the nearby ocean. The main time-dependent components of the observed altimeter-minus-gauge height-difference time series are due to the slightly different ocean tides at the gauge and in the ocean. The main harmonic coefficients of the tide differences are calculated from analysis of the copious TOPEX data set and then applied to the determination of T, P, and J-1 bias in turn. Datum connections between the tide gauge and altimetric sea surface heights are made by means of precise, local geoid differences from the EGG97 model. By these means, we have estimated Jason-1 altimeter bias determined from Geophysical Data Record (GDR) data for cycles 1-61 to be 12.9 cm, with an accuracy estimated to be approximately 3 cm on the basis of our earlier work. This J-1 bias value is in close agreement with those determined by other groups, which provides a further confirmation of the validity of our method and of its potential for application in other parts of the world where suitable tide gauge, GPS, and geoid information exist.  相似文献   

19.
GUOQI HAN 《Marine Geodesy》2013,36(3-4):577-595
Sea level observations from the tandem TOPEX/Poseidon (T/P) and Jason-1 altimetry missions (2002–2003) are used to study characteristics of sea level and surface currents over the Scotian Shelf and Slope off Nova Scotia. The consistency and error characteristics of T/P and Jason-1 measurements are examined not only in terms of sea level and cross-track current anomalies but also with respect to current anomalies at crossovers, kinematic properties associated with Gulf Stream warm core rings (WCR), and the shelf-edge current transport. Nominal absolute currents are constructed by adding the altimetric geostrophic current anomalies to an annual-mean model circulation field. The concurrent frontal analysis data are analyzed for occurrence of the WCRs and associated kinematic properties are derived from altimetric current anomalies. The comparison of the sea level and cross-track current anomalies from January to July 2002 shows overall good agreement between T/P and Jason, with correlation coefficients different from zero at the 5% significance level at essentially all locations for sea level and at most locations for currents. The cross-track geostrophic current anomalies from January to July 2002 and from September 2002 to December 2003 are further used to calculate the root-mean-square (rms) current magnitude, and the normalized relative vorticity associated with WCRs. The altimetric currents are consistent with each other and complementary to frontal analysis data in deriving the properties of the WCRs. The rms current magnitude is ～55 cm/s and the normalized relative vorticity is ～0.15. The model-altimetry combined absolute currents are used to estimate near-surface transport associated with the shelf-edge current, showing good correlation between T/P and Jason estimates and strong seasonal changes. The current anomalies derived from altimetry and moored measurements are significantly (at the 5% significance level) correlated and comparable in the rms magnitude.  相似文献   

20.
This article describes an “absolute” calibration of Jason-1 (J-1) altimeter sea surface height bias using a method developed for TOPEX/Poseidon (T/P) bias determination reported previously. The method makes use of U.K. tide gauges equipped with Global Positioning System (GPS) receivers to measure sea surface heights at the same time, and in the same geocentric reference frame, as Jason-1 altimetric heights recorded in the nearby ocean. The main time-dependent components of the observed altimeter-minus-gauge height-difference time series are due to the slightly different ocean tides at the gauge and in the ocean. The main harmonic coefficients of the tide differences are calculated from analysis of the copious TOPEX data set and then applied to the determination of T, P, and J-1 bias in turn. Datum connections between the tide gauge and altimetric sea surface heights are made by means of precise, local geoid differences from the EGG97 model. By these means, we have estimated Jason-1 altimeter bias determined from Geophysical Data Record (GDR) data for cycles 1–61 to be 12.9 cm, with an accuracy estimated to be approximately 3 cm on the basis of our earlier work. This J-1 bias value is in close agreement with those determined by other groups, which provides a further confirmation of the validity of our method and of its potential for application in other parts of the world where suitable tide gauge, GPS, and geoid information exist.  相似文献   

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