Keywords: Caspian Sea, rise in sea level, seismic survey planning, shoreline, base map
Abstract
This study focuses on the limitations and benefits of satellite images when scouting a near-shore
area in the North Caspian Coastal Lowland of Kazakhstan for the practical purpose of seismic survey
planning. In order to generate a base map for a seismic survey, the locations of recent transgressive and
retrogressive shorelines were interpreted and extracted from multi-temporal LANDSAT MSS/TM, JERS-1
OVN/SAR and SPOT HRV images. The rise in sea level from 1977 to 1995 resulted in a northward
migration of shorelines and reed zones in the study area near the Ural River mouth. The previous locations
of these shorelines were examined in terms of the present depth of water using a published curve showing
changes in Caspian Sea level. Thus a 1998 bathymetric map was successfully prepared by an integrated
analysis. This bathymetric map was further interpreted and land cover units were also added as
supplementary information. Finally, four zones are highlighted on the seismic base map as those to be the
receiver and/or source lines for the seismic data acquisition of 1998 as well as at the time of the lowest
(1977) and highest (1995) sea levels.
Introduction
When conducting a seismic survey in a very shallow water area for petroleum exploration,
operational constraints are highly related to surface conditions. Therefore, during planning it is of crucial
importance to investigate and analyze conditions such as depth of water, communities of aquatic plants (reed
zone) and subsurface geology. However, those conditions are not classified or shown in detail on some
published topographic maps. For this reason, a map with the above logistic information using satellite data
should be of high value when selecting survey lines and methods. The final goal of this study is to create a
base map for a survey design. The significant role of the satellite image interpretation is to obtain the
present isobaths in the southern part of the study area.
Study Area and Satellite Data Used
The study area is situated in the western part of Kazakhstan and covers the North Caspian Coastal
Lowland (Caspian Depression) as well as the near-shore to very shallow water area, with water depths of
less than five meters (Figure 1). This area covers approximately 25,000 km 2 and is located in the southern
part of the Pre-Caspian Basin where oil and gas potential is very high. Giant oil and gas fields, such as
Tengiz oil field and Astrakhan gas field have been discovered and developed along the coastal lowland.
The following multi-temporal satellite images, on a scale of 1:300,000, were used for the study; LANDSAT
MSS/TM and SPOT HRV (Figure 2) as well as JERS-1 OVN/SAR.
Current State of Rise in Sea Level
From a long-term viewpoint, changes in sea level of several meters have repeatedly occurred since
the 1600s. From 1977 up to 1995 the sea level has been continuously rising by up to more than two meters
(Figure 3). Because of this recent rise in sea level, water has been gradually intruding into the coastal
lowland, and a serious influence is taking place on harbor, petroleum facilities, roads etc. around the study
area. On the other hand, in terms of seasonal changes, the sea level during summer rises by up to
approximately 20 centimeters from the annual mean sea level, and, in turn, falls by approximately 10
centimeters in the winter (Figure 4).
Study Contents
This study involved the following contents.(1) The definition and extraction of shorelines from
multi-temporal satellite images, (2) the interpretation of recent changes of shoreline, (3) a field verification
survey, (4) an estimation of depth of water in 1998 and (5) the generation of a base map for seismic survey
planning.
Definition and Extraction of Shorelines
During the period of annual mean sea level (in spring / autumn), the near-shore area is usually
submerged up to the landward limit of the perennial dense reed zone which occupies the near-shore to very
shallow water area (Figure 4). This phenomenon was confirmed during a field verification survey. It was
defined that the shoreline at the annual mean sea level coincides with the landward limit of the reed zone.
Thus, the shorelines in 1977, 1979 (equal to 1975), 1984, 1986, 1988, 1989 and 1998 (equal to 1993) were
extracted by means of identification of those limits from multi-temporal satellite images (Figure 5).
