摘要:

This study deals with the assimilation of TOPEX altimeter-derived sea level variability in a reduced-gravity model of the northwestern Indian Ocean. The assimilation has been done using variational assimilation method with adjoint technique. A cost function representing the misfit between the model and the data is minimized with the model equations acting as constraints. The initial conditions of the model are used as control parameters and the best-fit initial conditions are determined as a result of minimization carried out using a variable-storage quasi-Newton method. Experiment has been done with 10 days' cycle-averaged data of TOPEX. Assimilation for 10 days and 20 days has been performed and it has been seen that 20 days' assimilation of satellite data provides better results.

ISSN:0149-0419    

DOI:10.1080/014904199273425

出版商:Informa UK Ltd    

年代:1999

数据来源: Taylor

摘要:

The maximum error in ocean depth measurement as specified by the International Hydrographic Organization is 1% for depth greater than 30m. Current acoustic multibeam bathymetric systems used for depth measurement are subject to errors from various sources which may significantly exceed this limit. The lack of sound speed profiles may be one significant source of error. Because of the limited ability of sound speed profile measurement, depth values are usually estimated using an assumed profile. If actual sound speed profiles are known, depth estimate errors can be corrected using ray-tracing methods. For depth measurements, the calculation of the location at which a sound pulse impinges on the sea bottom varies with the variation of the sound speed profile. We demonstrate that this location is almost unchanged for a family of sound speed profiles with the same surface value and the same area under them. Based on this observation, we can construct a simple constant-gradient equivalent sound speed profile to correct errors. Compared with ray-tracing methods, the equivalent sound speed profile method is more efficient. If a vertical depth is known (or independently measured), then depth correction for a multibeam system can be accomplished without knowledge of the actual sound speed profile. This leads to a new type of precise acoustic multibeam bathymetric system.

ISSN:0149-0419    

DOI:10.1080/014904199273434

出版商:Informa UK Ltd    

年代:1999

数据来源: Taylor

摘要:

This article investigates the problem of cycle slip detection and ambiguity resolution using dual-frequency GPS data. Several algorithms are proposed and described. F or cycle slip detection, three L1/L2 observable combinations have been integrated to formulate a new algorithm for cycle slip detection. For ambiguity resolution, both widelane and narrowlane ambiguity resolution algorithms are presented, but the focus is on the narrowlane ambiguity resolution. Numerical results are included to evaluate the performance of the proposed algorithms, which have shown that cycle slips can be effectively detected and the narrowlane ambiguities can be resolved almost instantaneously after successful determination of the widelane ambiguities.

ISSN:0149-0419    

DOI:10.1080/014904199273443

出版商:Informa UK Ltd    

年代:1999

数据来源: Taylor

摘要:

Based on an analysis of the source of errors in marine gravity measurements, an error model, firstly, is constructed mathematically which can characterize the change of systematic errors and with which a new crossover adjustment model is presented in this paper. Then, two methods of compensating the systematic errors are proposed, i.e., the self-calibrating adjustment and the a-posteriori compensation. Some questions involved in solving the adjustment problem, such as the rank deficiency, the choice of error model, the weighting of model parameters and the significance test of compensation efficiency, etc., are discussed in detail. Finally, a practical survey network is used as a case study to test the efficiency and reliability of the two compensation methods.

ISSN:0149-0419    

DOI:10.1080/014904199273452

出版商:Informa UK Ltd    

年代:1999

数据来源: Taylor

摘要:

Precise long-range kinematic GPS positioning requires the use of carrier phase measurements, the data processing of which suffers from the technical challenges of ambiguity resolution and cycle slip repair. In this paper, the combination of an ambiguity recovery technique and a linear bias correction method has been used to overcome such problems. An experiment was conducted to test the utility of this technique to determine aircraft height to high accuracy, over very long baselines (of the order of one thousand kilometres), in support of the Laser Airborne Depth Sounder (LADS). From a comparison of four independently derived trajectories, this airborne GPS kinematic positioning experiment has confirmed that the sea surface can be determined to centimetre accuracy. The sea surface profiles thus obtained can be used to correct the errors introduced by long period ocean swells.

ISSN:0149-0419    

DOI:10.1080/014904199273461

出版商:Informa UK Ltd    

年代:1999

数据来源: Taylor

ISSN:0149-0419    

DOI:10.1080/014904199273470

出版商:Informa UK Ltd    

年代:1999

数据来源: Taylor

ISSN:0149-0419    

DOI:10.1080/014904199273489

出版商:Informa UK Ltd    

年代:1999

数据来源: Taylor