ISSN:0149-0419    

DOI:10.1080/01490417809387966

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

For centuries the nautical chart has been an important part of activities related to the ocean. Today the nature of ocean operations is changing and placing increasing demand for navigational accuracy at sea; however, the nautical chart has not significantly changed. This article briefly examines some aspects of the nautical chart which could limit its usefulness and suggests, in the opinion of the author, the need for additional investigations into the proper role of the nautical chart.

ISSN:0149-0419    

DOI:10.1080/01490417809387967

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

An adequate conceptual definition of the geoid is essential for the unambiguous combination of satellite tracking data, satellite al‐timetry, and surface gravity measurements to obtain sea surface topography. The factors influencing the selection of a particular level surface of the earth's gravity field include the purpose(s) for which the geoid is to be used at the 5‐cm level, and the types of data to be used in achieving these objectives. The principal reasons for high precision determinations of the shape of the geoid are: the determination of sea surface topography for applications in oceanography; and the unification of leveling datums with a resolution equivalent to that of first order geodetic leveling. A conceptual definition of the geoid acceptable to oceanographers would be: The geoid for a selected epoch of measurement is that level surface of the earth's gravity field in relation to which the average non‐tidal (or quasi‐stationary) sea surface topography is zero as sampled globally in ocean regions. In the geodetic context, it would be convenient, though not essential, to modify this definition in such a way that the global sea surface topography had zero mean as sampled for evaluations of the geodetic boundary value problem. In either case, a basis exists for unifying all leveling datums serving areas in excess of 106km2, using either gravity anomaly data for the regions or precise determinations of position at first order bench marks. Unfavorable signal‐to‐noise ratios can pose problems when dealing with datums serving smaller areas. Elevation and gravity data banks must be correctly referenced to leveling datums prior to use in sea surface topography determinations. A recent attempt to upgrade the Australian gravity anomaly data bank indicates that all current data banks of this type are inadequate for the task. It is unlikely that time variations in the radial position of the geoid as conceptually defined above, will exceed ±5 cm per century, provided the rate of earth expansion was less than 1 part in 1010yr‐land there is no dramatic change in the present rate of secular change in Mean Sea Level.

ISSN:0149-0419    

DOI:10.1080/01490417809387968

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

A 5’ detailed gravimetric geoid has been computed for the northwest Atlantic Ocean as ground truth for the GEOS‐3 satellite altimeter experiment. Comparisons of this geoid with satellite derived geoceiver station heights show an r.m.s. difference of 1.2 m. Initial comparisons with GEOS‐III altimeter derived geoid profiles have indicated a relative agreement of generally better than 2 m.

ISSN:0149-0419    

DOI:10.1080/01490417809387969

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The current accuracy of sea‐going and airborne gravity measurements is not bounded by the precision of the gravimeter but by the precision with which external parameters such as vehicle velocity (speed), azimuthal heading, and geographic position can be determined. Uncertainties in these parameters are summed up in the Eötvös correction in the reduction of the measured data. This work investigates the suitability of baseline navigation systems, in particular Loran‐C and Omega, to further reduce the uncertainty of the Eötvös correction. Emphasis is placed on the velocity measurement error. A new algorithm is developed which derives velocity based upon the change in hyperbolic (or circular) grid readings, as opposed to the standard change in geographic position technique. A comparative analysis shows the new algorithm to be as precise as the currently used conventional calculation. Further, this simplified technique is accompanied with a 20‐fold reduction in computational complexity. Application of the results presented in this paper to the Loran‐C and Omega systems shows a velocity determination capability of 0.1 knot over a six minute integration time, and 0.05 knot for a 15 minute integration time for Loran‐C. The minimum error attainable in Omega is 0.1 knot when determined over a 17 minute measurement time. Further precision can be gleaned by applying the calculated error as a correction to subsequent velocity calculations.

ISSN:0149-0419    

DOI:10.1080/01490417809387970

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Classical hydrographic mapping in shallow waters with surface craft is slow, hazardous, and expensive. The remarkable water penetration capability of several currently used film emulsions and their dramatic presentation of submerged detail provides an alternative tool and supplement for mapping the seabed in shoals and waters of moderate depth. Photogrammetric bathymetric surveys preceding hydrography can show many of the rocks, reefs, shallow areas, photogrammetrically observed depth measurements and depth curves, and other features and thereby assist the hydrographers whose work is more difficult because they do not have the overall view of the bottom to guide their operations in developing important details. The objective of this paper is to advance the comprehension of the potential of photogrammetric bathymetry to provide the following benefits: (1) improve the accuracy and completeness of the hydrographie survey; (2) reduce the cost and time of the field hydrographie survey; and, (3) reduce ship requirements for a particular hydrographic survey, thereby releasing some of the craft for other assignments and/or enlarging the size of the coastal water areas that can be surveyed within a given time frame. The investigation of the potential for accomplishing photogrammetric bathymetry was restricted to ten regions of high priority along the East Coast and the Gulf of Mexico. A five‐year photobathymetry program is envisaged that will require a maximum of 10,765 man‐days of work and cost $1,154,750. These figures can be substantially reduced by employing digitized stereoscopic plotting instruments and developing advanced, sophisticated photogrammetric analytic aerotriangulation procedures.

ISSN:0149-0419    

DOI:10.1080/01490417809387971

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

ISSN:0149-0419    

DOI:10.1080/01490417809387972

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

ISSN:0149-0419    

DOI:10.1080/01490417809387973

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Proceedings of the Symposium on Tide Recording, edited by R. Britton. (The Hydrographic Society Special Publication No. 4, The Hydrographic Society at North East London Polytechnic, Dept. of Land Surveying, London, U.K.) 203 pp., paper cover.

ISSN:0149-0419    

DOI:10.1080/01490417809387974

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

ISSN:0149-0419    

DOI:10.1080/01490417809387975

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor