Hydrographic Surveying
Activity offshore was centered, until the 1950s, almost entirely on the fisheries and shipping industries. Since World War II there has been a remarkable increa in interest in the resources of the a and afloor, of which the recovery of hydrocarbons – oil and gas – reprents by far the greatest industrial investment.很有内涵的句子
Offshore engineering technology and the shipping industry have progresd at a phenomenal rate. Compare the typical, long-established harbours with the civil engineering achievements of today. The one occupies a sheltered location adjoining shallow waters, comfortably able to accommodate vesls which ldom exceed 10m in draught, and conveniently clo to road and rail distribution links. The other may be a drilling rig or production platform expod tanker terminal with depths exceeding 25m alongside, or a pipeline from oil well to shore, traversing areas of rapid current and shifting afloor diments.
1991年属羊是什么命 In addition to offshore drilling and harbour construction, the totality of industrial activity e
mbraces the following operations:
心理健康知识内容● Dredging, for harbour conrvancy, mineral recovery and reclamation;
● Coast protection engineering;
将进酒古诗
● Salvage;
● 海为Desalination of awater to improve fresh water supplies;
● The extraction of minerals and chemicals from awater;儿童卫士
● The prevention or elimination of pollution;
● The development of communications and distribution routes by shipping lane, submarine cable and underwater pipeline;
● The development of the fishing industry.炎字组词
The impact of this proliferation of activity on the engineer and surveyor has been profoun
d.
Seawater is a notoriously corrosive substance and this, together with the forces of current, tide and storm a and the great pressures on structures at depth, constitutes formidable factors with which the engineer must contend in the marine environment. For him to do so successfully the factors must be quantified.
As on land, environmental data are acquired by the geologist and geophysicist who ba their work on the surveyor’s map. At a, in addition, the oceanographer plays his part in determining the awater parameters. All of the turn to the hydrographer for information on the physical limits of the marine environment.
It should be noted that there is a considerable overlap of scope and function of the specialists concerned, each being esntially a team-member working with the others towards a common goal. Hydrography is similar in many respects to land surveying and many of the techniques employed are the same as, or extensions of, land surveying practice. Some factors rve to differentiate between the two, however, and whilst some
are obvious, all must be appreciate and taken into account.
The chart is the marine equivalent of the topographic map. Both u spot measurements of height/depth and contours to portray relief, but where the ur of the map is able to verify by visual inspection the detail shown, the afloor topography is obscured. The char-ur, therefore, relies implicitly on the accuracy and thoroughness of the hydrographer’s work.
In establishing the control for a topographical survey the land surveyor occupies a number of stations in turn, obrving angles and measuring distances with all the care, precision and number of repetitions required to achieve the specified order of accuracy. The hydrographic surveyor likewi performs this control procedure in most instances. Once after, however, the fixation of position becomes a dynamic operation. Not only does the obrving platform (the survey vesl) occupy a position for an instant only, but the level of the awater surface changes constantly under the influence of tide and wave. The hydrographic operation has been likened to a leveling survey onshore, but using a tel
笑话大全乐翻天escoping staff and a level which is mounted on a well-sprung trolley ! Admittedly this type of surveying is less preci than the shore-bad equivalent, but this does not mean that less careful, less thorough work is adequate. On the contrary, the utmost care is esntial to ensure that the rather more coar measurements which are combined to make the chart are not further degraded by slapdash methods.
The nature of the a environment is probably the most fundamental single factor which parates land from a surveying. The effects of the a on the common surveying techniques has been mentioned, but more important still is an appreciation of the vicissitudes of the a which not even a manual of amanship can properly explain. Experience is the only real solution, which both engineer and land surveyor will most probably lack. In its stead, an honest humility towards the a and the aman in who care the surveyor will be placed is strongly recommended.
Always bearing this sobering thought in mind, it is the intension in this book to give the reader a familiarity with surveying ashore an insight into the special techniques and problems of surveying afloat.
