f\ PRAKlA-SEISMDS

PRAKLA-SEISMOS GMBH V V

Shallow Water Surveys

DECADES OF EXPERIENCE

IN SHALLOW WATER SEISMICS

IN EUROPE AS WELL AS

ALL OVER THE WORLD

VERSATILITY AND

FLEXIBILITY

IN EQUIPMENT

AND METHODS

TOGETHER WITH A HIGH

LEVEL OF EXPERIENCE

IN THE

OPERATING PERSONNEL

Shallow Water Surveys

Shallow water surveys were integrated into our ser­

vice program in 1938.

Since then numerous shallow wate r surveys under

various conditions have been carried out in several

parts of the world ; in the North and Baltic Seas: in

Danish, British, German, Dutch and Norwegian waters;

in South-East Asia: Brunei , Sarawak, Saba; and in

Africa: Tunisia.

The aim of these special investigations is to link land

and marine surveys. However, the range of variation in

local conditions - i. e. the presence of mud flats,

estuaries with heavy traffic or strong currents, reefs,

or other critical coastal features, and the dependence

on tides - does not permit a prearranged scheme to

be adhered to.

Flexibility in the equipment used and in the execution

of the program, together with a willingness in the

highly experienced operating personnel to accept

responsibility, are necessary prerequisites for the

economic accomplishment of the program.

Shallow Water Surveys

Research Vessels and Equipment

Investigations in shallow wate r areas basically require

research vessels and boats of shallow draught and

suitable displacement, as weil as other special vehic­

les.

The prevalent conditions determ ine which kind of

equipment has to be used:

Recording pontoons fo r extremely shallow areas ,

draught 0.7 m, each fully equipped with streamer

drum, seismic recording instruments, electronic navi­

gation-positioning systems, gyrocompass, radar,

echograph, echosounder, sextants, range finders and

radio communication.

Coasters with shallow draught between 1.2-1.4 m and

flat bottoms for beaching at low t ide, used as house

boats as weil as for storage of explosives.

Catamarans for amphibious operations, e. g. in tropi­

cal areas where combined Swamp/Land/Shallow

water surveys have been applied very successfully.

Here the flexibility of our methods has always been

highly appreciated by our clients.

Cabin speed boats for communication and security,

and to reconnoitre critical waters for navigable passa­

ges. Each boat is equipped with echosounder, com­

pass and walkie-talkie.

Hovercraft are ideal for connections between onshore

and offshore surveys ; allowing uninterrupted straight

lines over difficult mixed terrain such as sand, mud,

waterweed, ice and snow, obstacles up to 1 m high,

and both shallow and deep water.

Shallow Water Surveys

Special vehicles and accessories like amphicats, out­

boards, rubber dinghies and mud sledges are available

as weil as locally hired launches, longboats and fishing

vessels.

Drilling

Versatile drilling equipment is in use according to

existing extreme and different working conditions,

e. g. drilling in mud areas at low tide and shooting

later at high or low tide.

Energy Sources

Common dynamite water shooting and shooting in

boreholes.

Cortex shooting in coastal and deep water operations

up to 12-fold coverage. The high multiplicity and off­

set in line shooting require a two or three ship method.

Airpulser shooting can be applied in areas with water­

depths of over 1.5 m up to 24-fold coverage.

Recording Equipment and Office Outfit

Seismic digital field systems, type TI DFS 111 or

DFS IV, recording on 21 track 1" tapes, monitor elec­

trostatic oscillographs and other modern accessories

such as trace switching devices for land- and bay

cables, radio transmission of the time break, are in

use.

The ships ' office is equipped with receivers for inter­

ship communication and a radio-telephone unit for

contact with land stations.

SOSIE* technique is available.

• Source Sism ique Echant i llonnee, Sampled Seismic Source, Trademark of SNPA

Shallow Water Surveys

ann, •• ~ - ,r===~~~------------------~

R D s E

Recording Pontoon 100 m or 500 m

Trace 12 Trace 1 Trace 12 Trace 1 Trace 24 Trace 1

.... 550m---~ 14-- --550 m .. 14--- - - ----- 1150 m ---------~ .. Land Cable Bay Cable S treame r

Continuous Recording from Land to Sea with Land Cable, Bay Cable and Fixed Streamer

UNINTERRUPTED STRAIGHT

LlNES FROM SEA TO LAND

SPECIAL SHALLOW WATER

CREWS FOR

EXTENSIVE SURVEYS

IN COASTAL WATERS

FLEXIBLE LAND CREWS

FOR EXTENSION OF

LAND AND/OR

OFFSHORE SURVEYS

Shallow Water Surveys

Sea Type Operation

Streamer length 1200 m, 50 m group spacing and

multiplicity up to 12-fold using dynamite or cortex.

Multiplicity up to 24-fold using airpulser where water­

depth is more than 1.5 m;

Each method is employed as necessary in stop-start

operation.

Application of in line offset up to 1000 m is possible

by using a second electronic navigation unit on board

the shooting boat.

Bay Cable Technique

Recording is carried out with a bay cable and

PRAKLA-SEISMOS self-orientating geophones HGL,

which are independent of water coverage. Several

lengths of 600 m with 12 traces are simultaneously in

use and switched by the trace switching device unit.

Operation at Low Tide

Special surveys on banks at low tide are carried out

by crews with many years' experience.

Shallow Water Surveys

ACCURATE SURVEYING

IS A BASIC REQUIREMENT

FOR SHALLOW WATER

DATA GATHERING

MODERN ELECTRONIC

NAVIGATION METHODS

. AS WELL AS

COMMON OPTICAL

SURVEYING METHODS

HA VE TO BE APPLI ED

BY SURVEYING PERSONNEL

WITH MANY YEARS '

EXPERIENCE

Navigation and Positioning

The reliability of positioning is a basic requirement

for an accurate evalution of shallow water data.

The most modern electronic navigation is installed on

board the vessels:

DECCA Main Chain or

DECCA Hi Fix or

DECCA Sea Fix or

other systems are in use depending on the area.

The desired lines are surveyed by following track

plots. Deviations from straight lines are avoided.

Accuracy of the chains is checked daily at certain

fixed points.

Additionally bearings to land marks are taken when­

ever possible, to control and correct the chain data.

Land connections and surveys on banks are carried

out by triangulat ion with coincident range finders and

rods.

Postplotting of base maps is included in the contracts

without additional charge .

PRECISE POSITIONING

USING TRACK PLOTTER

ELECTRONIC NAVIGATION

AND ECHOGRAPH

RADAR EQUIPMENT FOR

FEATHERING ANGLE

CONTROL

IN CONNECTION WITH

TAl LEND REFLECTOR BUOY

Shallow Water Surveys

Streamer feathering is controlled and measured by

gyrocompass and radar in connection with a tailend

reflector buoy.

Waterdepth is recorded by echograph, and carefully

measured by rods when less than 2 m.

Shallow Water Surveys

More Than Five Decades of Worldwide Geophysical Activity

Onshore · Offshore · Airborne

PRAKLA-SEISMOS GMBH · 3000 HANNOVER· HAARSTRASSE 5 . P.O.B. 4767 . PH: 80721 . TELEX: 922847· CABLE: PRAKLA . GERMAN

Amsterdam . A nkara . Brisbane . Jakarta . Lima . London . Madrid · Milan· Rangoon . Rio de Janeiro . Singapore . Teheran . Tri po li . Vienn

@ 25001172