DEPTH REFERENCE TO THE DATUM OF THE OB BAY SOUTHERN AREA| Depth reference to the datum of the Ob bay southern area |
 |
 |
|
KOROTKOV S.V. In accounting materials of carrying out of sea engineering researches as synonyms concepts "isobath" (the characteristic of depth) and "horizontal" (the characteristic of marks of a bottom) quite often act. Such understanding has developed owing to transferring practice of the hydrographic works, carried out long time for good safety navigation, to topographical shooting water areas of the seas for problems{tasks} of sea engineering researches.According to the Statute book 11-104-97, topographical plans of a sea-bottom are represented in isobaths when they are intended for designing actions of water areas directly connected to operation, and on them depths should be shown. Topographical plans of a sea-bottom are represented in horizontals when they are intended for designing objects of the construction connected to coast. In communication stated above, it is frequent in programs of prospecting works, for example, on statement of chisel platforms on points of prospecting drilling the choice of conditional surfaces from which depths or marks of a bottom - so-called " zero of depths " (chart datum) are counted is not always proved. As zero of depths in the Russian Federation are accepted ? by the tidal seas or their sites with average size of inflow equal or exceeding 0,5m - the Least Astronomical Tide (LAT); ? by not tidal seas – the Mean Sea Level (MSL); ? zero of the Kronstadt tide-gauge, describing a zero high-altitude mark of the main high-altitude basis of the Russian Federation - the Baltic system of the absolute heights resulted by an epoch 1977г (BS, 1977) Average levels of northern seas are below zero BS on 0,3-0,7m, that correspondens to an allowable error of measurements on depths more 30m. But as marks of a bottom in BS are shown on plans with the minus the concept " depth of the sea " can be attributed to such data conditionally is familiar. Except for the basic zero of depths named above, to this concept it is possible to attribute various used in hydraulic engineering construction reading surfaces, for example, the settlement levels of different security calculated on the long-term data of measurements on stationary level stations of Federal Hydrometeorology and Environmental Monitoring Service, uniform zero of a post for northern seas, zero of Pacific system of heights, etc. Transfer of chart datum (high-altitude marks) to areas of carrying out of sea engineering researches is carried out by a method of water leveling. The method is based on property level surfaces of the sea to occupy by gravity horizontal position.Communication is carried out between pairs level station (LS), one of which is the basic, and another additional. The basic LS should have a high-altitude mark in system state leveling networks, and LS should settle down in identical hydro meteorological and morphological conditions. The basic document where procedure of calculations is described, are "Rules of hydrographic service №35. Depth reference to the datum ". Connection of a LS is with the help of the linear equation, and mean-square errors (MSE) of factors included in it are estimated. As criteria of reliability of communication are considered excess of factor of correlation of value 0,85 and not output MSE of the equation of communication for 10sm. The requirement in area of water area of researches is resulted in an error of transfer of zero BS in the SB 11-114-2004 which unites errors echo-sounder measurements, a error of transfer of zero BS, that in a result makes as much as possible allowable MSE in 1 % on depths from 30m and is deeper. The basic discrepancy of the methodical literature concerning to 40-90 years of the last century, to modern practice of carrying out of engineering researches in water areas of the seas, the condition of long hydro meteorological measurements, not the account of opportunities of varying instrument park, the equipment, development of software of processing of measurements is necessary. Now researches, it is especial at a stage of "The Feasibility report on investments" in various sites of a shelf of northern seas are carried out in deadlines. These terms are defined as volume of works required by the concrete project, and hydro meteorological area and the period of carrying out of researches. The purpose of the report - to show the decision of a question in Open Society " AMIGE " where annually it is necessary to operate with short numbers of the oceanographic data during carrying out of complex researches. Some increase in numbers of measurements is reached due to preliminary arrangement in the planned areas of researches of-line buoy-based station with the recorders admitting long measurements and record of oceanographic parameters. In the report two questions are considered. The first - transfer of high-altitude marks by traditional way on communications of corresponding levels with temporarily organized coastal level stations in areas of statements of-line buoy-based station. The second - by the example of a southern part of gulf of Ob of Kara sea to show an opportunity of reduction of results of measurements to zero of depths without use coastal level stations, but under condition of observance of requirements to MSE measurements for various depths in its water area. For transfer of high-altitude marks on communications of posts by the author the algorithm of calculations (programmer A.V.Smirnov) where the traditional method [RHS №35] is expanded with statistical estimations of compared numbers is developed. Also additions to a method are calculations allowable MSE bindings of a level for depth of installation of-line buoy-based station (area of researches) [The Management …, 1991] and the equations describing position LAT and MSL in area of-line buoy-based station in relation to coastal (basic) level stations [V.I.Peresypkin, 1982]. Results of calculations are displayed the monitor of a computer in a tabulated and graphic kind that allows to leadtheir visual estimation and to execute, necessarily, recalculations. Let's notice, that errors of the linear equation of communication and its factors concern only to the characteristic of communication of two numbers limited by sample of the general time lines of measurements of a level on two compared level stations. The designed errors of this communication do not take into account an error of definition of height of a working reference point coastal level stations, metrological characteristics of the used measuring instruments and conditions of an environment during carrying out of measurements. The general (total) error , the author suggests to estimate transfers of high-altitude marks by water leveling by the sum of dispersions: ?S Errors S2 and S4 are estimated on a level of a dispersion allocated of total tides acyclic components. Reduction of results of measurements a level without use coastal level stations can be considered, as an emergency measure in case of impossibility for any reasons to organize such supervision with a binding to reference points leveling networks, absence of the reliable data on marks LAT and area MSL of researches, etc. The high-altitude mark of a bottom concerning zero BS (В) represents the sum of high-altitude marks MSL, LAT and some size n (2). Values of first two composed are considered as constants and get out of cards - circuits of distributions of their value on considered{examined} area [S.V.Korotkov, 2004]: Size n a variable. Its variability is defined by variability of depth in a place of statement of-line buoy-based station owing to dynamic factors of the water environment for the period of measurements of a tides on of-line buoy-based station (tides, set-down-pileup fluctuations, fluctuations due to change of a drain of water). The size of variability is characterized by average value of a tides for the period of measurements on of-line buoy-based station (ML) and a dispersion (Ss): The problem is reduced to a presence of conformity of an average level (ML), calculated on of-line buoy-based station for the period of measurements (and accepted for zero), to value of an average long-term level (MSL) concerning zero BS for the area of-line buoy-based station received from the data of the circuit of its distribution to water areas of gulf of Ob. For reduction of size n to conditions of construction of circuits of MSL and LAT it is necessary to correct value ML (4) amendment ML' (3-4) which characterizes variability of border of a dynamic part of a level in relation to conditions of internal variability (Sm) numbers of the measurements used for calculations and construction of cards - circuits of MSL and LAT. The error of calculation B can be estimated from the equation: wdLATMSLBSSSSS+++= (5) Where first two equations composed in the right part characterize errors of construction and removal of the data from cards - circuits accordingly MSL and LAT, and others two composed (Sd-errors of the device and Sw - an error of conditions of environment) pay off similarly to errors S1 and S2 in the equation (1). Results of calculations and comparisons are resulted by the example of measurements in considered area 2007-2008гг. The literature Oil and gas of Arctic shelf 2008
Set as favorite
Bookmark
Email This
Hits: 3643 |
