REPORTER 39

The total station constantly
determines the horizontal
and vertical angle to the
prism as well as its current
distance from continually
running measuring sequences,
from electro-optical
angle measuring and
electronic infra red laser
distance measuring. This
data is immediately computed
by the Leica TCA 1800
into position and height
coordinates of the prism or
of the georadar centre
point, exact to the centimetre.
At the same time,
where the terrain has an
inclination, the vertical
variations of the prism at
the point of the measuring
carriage are also mathematically
compensated by
the SAGAS software. The
georadar equipment and
measuring station are
directly connected to the
geophysicist’s laptop
computer by thin glass fibre
cables and he draws the
measuring carriage along
the desired profiled lines
with the help of the realtime
position data.
3-D evaluation directly in
the field
The SAGAS software
continuously integrates all
reflection and coordinate
data and presents it to the
In this interlocking georadar
picture sections and the equal
time section, the geophysicist
recognises on location at once
the water table (green line) and
reflections from objects transmitted
from above the surface of
the ground (yellow lines) thanks
to the 3-D presentation. SP1 and
SP2 mark the lower boundary
between two erosion troughs.
© Frank Lehmann/ETH.
geophysicist in the desired
form directly in the field.
Special features of the
territory investigated and its
surroundings, such as, for
example, the ground water
table and reflections from
buildings above ground
level which are also represented
in the georadar data,
can in this way be explained
more quickly and if required,
filtered out. Naturally, these
comprehensive and threedimensionallyhigh-resolution
data sets can be used in
the office later for various
purposes including further
and more detailed study.
In comparison with the static
methods, appreciably finer
analyses are possible in a
distinctly shorter period of
time.
At least ten times quicker
than previously
Frank Lehmann together
with Alan G Green has
described this system in
detail in a paper entitled
”Semi-automated georadar
data acquisition in three
dimensions”.
It is accessible by e-mail
(frankl@augias.ig.erdw.ethz
.ch) to anyone who is
interested. As Frank
Lehmann says: ”With this
method a variety of
problems affecting the
subsoil and of concern in
geology, engineering
science and archaeology
can be solved more simply
and more exactly than
previously. During our
study we pulled our measu-
Six equal time sections of the scour pool. Its boundaries are
shown here marked with green lines.
© Frank Lehmann/ETH
The Leica TCA 1800 total station
tracked the measuring carriage
continuously and provided the
geophysicist with his actual
position by way of a graphic
display in real-time on the
laptop screen. Thus he can also
always keep to the ideal line for
his current project and the
system trigger the radar measurements
at the correct intervals.
The geophysicist is carrying the
georadar control unit on his
back.
ring carriage at the rate of
only 0.3 m/s although as far
as the measuring system
itself was concerned, even
3 m/s would have been
possible for providing
sufficient accuracy. Even
with our gentle speed, we
obtained our results ten
times more quickly when
compared with the methods
available up till now. The
data processing was also
carried out so quickly that
we could easily display, on
our laptop screen, threedimensional
profile sections
in various directions and
also sections covering periods
from the past, while still
in the gravel pit ”.
- Stf -
Here SAGAS presents a section of the scour pool
of the two water courses from the complete picture
in raised, three-dimensional volume presentation.
© Frank Lehmann/ETH
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