HD-GNSS FOR LAND
SEISMIC SURVEYS
WHITE PAPER
HD-GNSS FOR LAND SEISMIC SURVEYS
TRIMBLE GEOSPATIAL DIVISION
WESTMINSTER, CO, USA
ABSTRACT
Recent advancements in technology have made it possible to conduct GNSS surveys in areas that were once the
exclusive realm of optical and inertial instruments. Applied correctly, this technology can provide considerable cost
savings and improved quality in seismic stakeout operations. This paper discusses these technological advancements
and why they are so important to the seismic industry.
Geospatial Division, 10368 Westmoor Drive, Suite #100, Westminster, CO 80021, USA
© 2013, Trimble Navigation Limited. All rights reserved. Trimble and the Globe & Triangle logo are trademarks of Trimble Navigation Limited, registered in the United
States and in other countries. Microsoft and Windows are either registered trademarks or trademarks of Microsoft Corporation in the United States and/or other countries.
All other trademarks are the property of their respective owners. PN 022543-575 (09/13)
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INTRODUCTION
SURVEY TOOLS FOR SEISMIC STAKEOUT
A recent study of seismic survey positioning
specifications shows that most seismic projects require
the coordinates of all sources and receivers to be better
than one meter in three dimensions at the 95%
confidence level. This specification is oblivious to
collection technology, whether GNSS, optical, or
inertial, as long as the measurement quality is achieved.
However, traditional GNSS systems have often been
unable to meet the desired precisions under canopy,
resulting in the addition of GNSS technology-specific
details to the pure seismic specification. Including these
additional requirements, such as the minimum number
of satellites in the RTK solution is common practice. It is
important to remember that a simple survey
specification detailing only positioning requirements
has therefore always been the truest specification of
the needs of the seismic analyst.
The seismic industry is very competitive and all aspects
of the industry are being revolutionized by new
technologies. Survey operations are no exception and it
is important to minimize the cost to produce every
staked location. The cost per point has three major
components: the purchase cost of survey equipment;
the costs associated with skilled equipment operators;
the speed with which the survey equipment and crew
can produce results in the field.
The three common positioning technologies used in
seismic surveys are optical, inertial, and GNSS. Each of
these has advantages and disadvantages in certain
operating environments.
The high-end RTK systems of the last decade tend to
compute solutions at two distinct levels of precision.
The “float” solution offers precisions which are unable
to meet the required tolerances for seismic, while the
“fixed” solution has precisions which are an order of
magnitude better than needed. As such, in addition to
stating the required tolerances, many seismic survey
specifications either explicitly prohibit “float” solutions
or adjust the tolerances to levels which can only be met
by “fixed” solutions.
With the release of the Trimble® R10 GNSS receiver,
Trimble has introduced a revolutionary concept called
HD-GNSS. The implications for the Trimble R10 with HDGNSS in land seismic surveying are profound: the
receiver is capable of obtaining seismic level precisions
in tree-covered areas in real time, which previously
could be achieved only with optical or inertial
instruments. Together, the Trimble R10 and survey
specifications appropriate for seismic objectives will
deliver dramatic productivity improvements and cost
savings compared to other GNSS systems in
compromised sky-view environments.
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Figure 1 - Optical instruments work well under canopy
Optical technology is reliable and has been applied to
survey activities for more than a century. There is no
question that optical technology allows precise
positioning under trees. This comes at the price of at
least a two-person crew and a requirement to clear
vegetation to ensure line-of-sight between the
instrument and surveyed points. The particular optical
survey instruments required for seismic stakeout are
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relatively low cost but they require more skilled, more
expensive operators. Cutting lines require additional
labor that also comes at a cost. In heavily-wooded areas
including jungle, conventional instrument use is
common for seismic stakeout.
Inertial measurement systems were introduced into
land seismic in the mid-1970s. These navigation systems
are able to position seismic elements under tree canopy
with good precision and without the need to clear
vegetation for line-of-sight. However, these capabilities
come with very high initial equipment and maintenance
costs. Inertial systems also require skilled, relatively
expensive operators. In spite of the expense, when
operating in the jungle and cutting lines is not practical,
inertial technology is used for land seismic stakeout.
Most seismic stakeout crews rely on RTK GNSS first, and
use conventional and/or inertial instruments when
required. GNSS positioning technology has continued to
evolve since its introduction and there is now reason to
rely on GNSS for a significantly greater portion of
seismic stakeout work.
Figure 3 - GNSS offers many cost-saving advantages
MAJOR EPOCHS OF RTK INNOVATION
Figure 2 - Inertial systems do not require line-of-sight
GNSS survey solutions have a modest initial equipment
cost and are relatively easy to use. With GNSS, one
highly-qualified surveyor can often support the
productive operations of several less-experienced
survey technicians. GNSS also offers very rapid point
placement without cutting lines. GNSS technology’s
normal limitation is that it requires reasonably clear
line-of-sight to satellites orbiting the Earth. Tree canopy
obstructs this clear path between satellites and the
surveyor.
The operational benefits of GNSS technology have
made this the dominant technology for seismic survey
operations in clear and lightly-wooded prospect areas.
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To better understand why it is worth reevaluating the
use of GNSS technology for a greater portion of seismic
surveys, it is valuable to review the evolution of survey
grade GNSS systems. Positioning a GNSS rover with
centimeter-level precision using signals broadcast from
satellites that are orbiting approximately 20,000
kilometers above the Earth and moving at 14,000
kilometers per hour is quite a formidable task. The basic
theory can be easily understood. If we know where the
satellites are, and we can measure how far the rover is
from each satellite, we can calculate the rover’s
location by trilateration. The use of at least four
satellites, as shown in Figure 4, eliminates the necessity
for the clock within the receiver equipment to be
synchronized with the GNSS system time. This time3
offset, together with the three coordinates of the rover
position, become the unknowns solved for by the
positioning algorithms.
In 1988 Trimble introduced the 4000SLD receiver that
achieved survey-grade accuracies. This was a kinematic
packable receiver that weighed about 44 pounds,
excluding the car battery used for power. This receiver
was capable of tracking the limited constellation of GPS
satellites that were in operation at the time and used
differential techniques to obtain accurate positions. To
provide a better view of the technology of the day, a
quality personal computer at this time used an Intel
80286 processor, had 640KB of RAM, used a 5.25”
floppy disk, and supported a 16 color video display.
Figure 4 - Trilateration of satellite ranges to estimate rover position
GNSS satellites broadcast their locations to the rover in
the form of ephemerides that describe the orbit and
atomic clock offset from GNSS time for each satellite,
but only with accuracy at the meter level. Ranges from
the rover to each satellite can be measured using
broadcast Pseudorandom Noise (PRN) codes –
providing the fundamental ranging signal – together
with the phase of the received signals. However,
because of atmospheric effects on signal propagation
and the accuracy of the satellite orbit estimation, the
position of a single autonomous rover can be estimated
only to approximately 5 to 15 meters. To overcome
these fundamental error sources and achieve
centimeter-level positioning, a GNSS reference station
is required. Some error correction methods even rely
on a network of GNSS reference stations.
Figure 6 - 1988 Trimble 4000SD and computer of the same era
Figure 5 - Rover positioning with a reference station
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A GNSS processing engine like the one in the Trimble
4000 SLD uses the combined data from a rover and
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reference receiver to differentially reduce the effects of
orbit and atmospheric errors as these errors are
common to both receivers in real time. A software
processing engine in an office computer was able to
produce postprocessed kinematic solutions using
observations logged on the rover receiver combined
with data from a base receiver. This processing
technique uses the carrier phase of each satellite signal
to measure the range from rover to satellite with a
precision of millimeters. This is possible using carrier
phase because it has a much smaller wavelength than
the PRN code signal. The latter has an effective
wavelength given by the code bit (or chip) length. For
the GPS C/A-code, this is 300 meters, while the carrier
wavelength on the L1 frequency is 19 centimeters. Like
a measuring tape with a finer graduation, carrier phase
can be used more precisely to measure the range to a
satellite. Making precise carrier phase measurements
requires more processing power and improved signal
tracking. Portable receivers in this era were not capable
of making these measurements in real time.
In 1994 Trimble introduced the 4000SSE receiver with
Real Time Kinematic (RTK) positioning, featuring on-thefly initialization. This truly portable receiver weighed
only 15.4 pounds including batteries, and was able to
resolve ambiguities in the field. The breakthroughs in
performance were made possible by major increases in
processing power and component miniaturization. The
very best positional computations were available only
through postprocessing, while real-time positioning was
possible primarily with a clear sky view. In the PC world,
we had moved on to the 3.5” diskette. Microsoft
released Windows® 95 the following year. This was the
first instance of the mainstream Windows operating
system that was not overlaid on the original Disk
Operating System (DOS). Computers were becoming
quite capable – Windows 95 even had built-in support
for dial-up networking! 1995 was also the year that
Amazon.com went online.
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Figure 7 - 1994 Trimble 4000SSE with Windows-equipped PC of the
same era
What was happening in the Trimble 4000SSE that was
not possible with previous technologies? Unambiguous
carrier phase measurements could be made in real
time, and this was no simple task. In the following
discussion, the satellite signal can be simply considered
as a sine wave, as shown in Figure 8. The carrier phase
measurement is actually the difference in the phase of
the received signal and the phase of an equivalent
signal generated from the receiver’s oscillator (clock) at
the nominal transmitted frequency. As the phase of the
receiver’s clock (starting at zero when powered up) is
arbitrary relative to the satellite’s clock, for the first
measurement after acquiring the satellite signal only
the fractional part of the phase can be used. The
distance between the transmitting and receiving
antennas comprises this fraction and an unknown
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integer number of whole cycles (wavelengths). This
famous ‘integer ambiguity’ remains constant for
subsequent measurements unless there is a cycle-slip or
loss of signal tracking, and has to be resolved by the
processing engine. Note that the Doppler on the
received signal corresponds to the rate of change of the
phase measurement as the satellite moves relative to
the user, with subsequent phase measurements
reflecting this motion.
Figure 8 - Integer ambiguity is the unknown number of whole carrier
phase wavelengths between the rover and each satellite
Traditional GNSS processing engines use the
combination of the reference station and rover data to
attempt to “fix” the number of whole wavelengths
between the rover and the satellites. The process would
occur in two distinct steps – first the generation of a
“float” solution using both PRN code and carrier phase
observables in which the ambiguities were not integers,
but in fact were “real numbers” containing fractional
parts, followed by a search process to resolve the
integer portion, after which the solution was “fixed”.
The precision of the float solution is primarily driven by
the PRN code noise, which is much larger than for the
carrier phase due to the respective wavelengths. Typical
float precisions are several decimeters and of limited
value for survey applications. The convergence from
float to fixed is highly polarized, with the float solution
maintained for perhaps a considerable time when
working in a difficult environment or with a long
baseline, followed by an instantaneous switch to a fixed
solution with significantly improved precisions.
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Over the next few years, the quality of embedded
processors continued to improve and electronics shrank
rapidly. In 1997 Trimble introduced the 4800 receiver.
This was an integrated survey solution offering full RTK
capability in a package that weighed only 8.5 pounds.
This innovative receiver offered up to 20 channels and
could simultaneously track 9 GPS satellites. The
integrated design held the GPS receiver and RTK radio
modem in a single package with the GPS antenna at the
top. This rover worked with the Trimble TSC1 field
controller, which offered some of the capabilities of a
personal computer in a rugged portable package.
Having a more sophisticated microprocessor in the
Trimble 4800, coupled with a powerful field controller,
created new possibilities for more advanced GPS signal
processing. While these advancements provided
improved performance, there were not any major
changes in the available GPS signals and, therefore, no
push to significantly change the signal handling
algorithms. The field controller could undertake the
survey and workflow provision capabilities while the
receiver’s processing remained focused on precise
positioning. In the world of personal computers,
Windows 98 was about to be introduced and a capable
computer included a 233MHz Intel Pentium 2 processor
and possibly a graphics card with a separate dedicated
processor. Computer games were advancing rapidly as
was the use of the Internet.
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In 2005, Trimble introduced the Trimble® R8 GNSS
receiver. This receiver offered RTK solutions using both
GPS and GLONASS satellites. The integrated 48-channel
receiver also supported the GPS L5 signal and could be
equipped with an internal GSM/GPRS cellular modem
for data communications. This receiver offered 11 MB
of internal memory for data logging. Trimble offered
the TSCe™ controller at the same time. This controller
offered 512 MB of compact flash memory, a 206 MHz
processor, and a touchscreen. There were more
satellite signals available and more portable processing
power to make use of them. RTK performance
increased greatly and it was possible to conduct RTK
operations in more locations with compromised sky
views than ever before. Surveyors began operating
deeper in mine pits and further under tree canopy. At
this time in personal computing, many systems began
to be equipped with 64-bit processors and laptop sales
exceeded those of desktop computers. Sunnyvale, CA
became the first city in the US to offer free city-wide
Wi-Fi and YouTube.com was launched. We began
expecting ubiquitous Internet access and relying on
online services everywhere for every purpose.
Figure 9 - 1997 Trimble 4800 and Pentium 2-equipped PC
The GLONASS satellite navigation system was deemed
fully operational in 1995. This system was operated for
several years without any major improvements. In
2003, modernized GLONASS satellite design was
introduced and system improvement gained renewed
focus. Having an additional, reliable, GNSS satellite
constellation created new possibilities for GNSS
positioning. Using both constellations, positioning
availability increased and it became possible to
undertake even more complex signal processing
methods.
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of a simplified ambiguity resolution method were
encountered more frequently. The most obvious
disadvantage to a fixed/float approach is the inability to
extract position solutions of good precision while in the
float mode. Beyond this, the most troublesome
behavior was the possibility of a ‘bad init’ in which an
incorrect set of integer ambiguities is selected. Put
another way, the correct set was discarded and could
not be selected until the search was repeated. This
resulted in a position outlier being reported with
unrealistically low precisions for many seconds until
detected by automated integrity checking processes.
For many years, GNSS scientists improved the
automated integrity checking process and even
implemented multiple parallel GNSS processing engines
in order to reduce instances of incorrect fixing. These
various conditions are depicted in Figure 11 where the
precisions are given by the magnitude of the ellipses.
Note that the precision ellipse for an incorrectly fixed
solution is deceptively similar to the one for a correctly
fixed solution.
Figure 10 - 2005 Trimble R8 with laptop computer from 2005
As the number of available satellite signals increased
rapidly along with portable computing power, it
became obvious to GNSS scientists that faster and more
accurate position determination techniques could be
implemented. Work on GNSS reference networks and
modeled corrections led to additional significant
advancements in error modeling and positioning
improvements on server class computers. It was no
longer necessary to use so many approximations and
simplifications in the determination of signal distortion
effects and for ambiguity resolution.
The original less rigorous approaches to ambiguity
resolution gained favor because they could be
implemented on available embedded processors and
effectively cope with the relatively few satellites
providing contributing signals at any given time. As
surveyors began to rely on GNSS sensors in more
difficult observation environments, the disadvantages
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Figure 11 - In challenging GNSS environments, a traditional GNSS
processor is susceptible to imprecise float solutions and incorrectly
fixed integer ambiguity solutions
In 2012 Trimble introduced the Trimble R10 receiver.
This 7.9 pound integrated receiver supports 440 GNSS
channels and can track all GNSS signals that are
currently available and even those that are proposed to
be available in the current decade. The Trimble R10 has
two application-specific integrated circuits (ASIC)
dedicated to GNSS signal tracking and processing. In
addition, the receiver integrates non-GNSS sensors to
increase productivity. Teamed with a powerful external
field controller such as the Trimble® TSC3, it is now
possible to undertake previously unimaginable
computations in the field.
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The Trimble R10 offers new levels of productivity and
includes many of the technologies that are
revolutionizing mobile computing. In 2012, Wi-Fienabled tablet computers and smart phones changed
the public’s expectations for a mobile computing
device. The Trimble R10 offers a similar, profound
change to the way that seismic surveys are conducted.
Many of the world’s leading GNSS scientists have
recently implemented fundamental changes to the
ambiguity resolution process. This innovative, advanced
technology is called HD-GNSS. The specific algorithms
developed by Trimble to realize HD-GNSS capability are
patented and not freely available. Although many
papers have been written on the topic of instantaneous
ambiguity resolution, HD-GNSS represents an
unprecedented and significant leap forward in this field.
The HD-GNSS processing engine performs very detailed
calculations accounting for many more of the elements
that can affect the determination of precise GNSS
positions. With this technique, available computing
power is applied to accurately resolving integer
ambiguities using advanced statistical methods. The
traditional float state of RTK positioning does not occur
and the need for continual monitoring to detect
incorrect fixes is eliminated. HD-GNSS techniques are
an excellent match for the performance and accuracy
requirements of a survey sensor for land seismic
stakeout. In combination with ever-expanding satellite
constellations, HD-GNSS can provide accuracies of
better than one meter at the 95% confidence level in
challenging GNSS environments where other processing
engines would never fix. This means rapid and accurate
stakeout operations.
SEISMIC SURVEY REQUIREMENTS
Figure 12 - 2012 Trimble R10 with Tablet computer
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So far, this paper has discussed the need to undertake
seismic surveys with speed and appropriate accuracy in
order to be competitive. GNSS is the survey sensor of
choice when it provides acceptable results. This section
discusses the tolerances associated with seismic
surveying. This is the final element in analyzing the
application of the latest GNSS technology to seismic
work in obstructed sky view environments. HD-GNSS
technology replaces the float stage of solution
determination with other methods and does not report
solutions as “float” or “fixed” which makes it essential
to examine seismic survey specifications and the
traditional use of these labels in them.
In January of 2013, a letter was sent to nine major
geophysical contractors, most of whom have global
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operations. This letter requested examples of seismic
survey specifications for RTK operations that these
contractors received from oil companies for recent
projects. The letter also requested they check with their
staff geophysicists on the appropriate required
positional accuracy for sources and receivers. After
evaluating more than a dozen replies, it was clear that
current RTK survey specifications for seismic include
one of three sets of requirements. These are:
•
The required positional accuracy for the staking
of all sources and receivers is one meter in both
horizontal and vertical axes at the 95%
confidence level.
•
The required positional accuracy for the staking
of all sources and receivers is one meter in both
horizontal and vertical axes at the 95%
confidence level. In addition, integer
ambiguities shall be “Fixed”. RTK “Float”
solutions are not acceptable.
•
The required positional accuracy for the staking
of all sources and receivers is 5 centimeters in
both horizontal and vertical axes at the 95%
confidence level.
Additional criteria specified often include minor
variations of a maximum PDOP of 6, a minimum
number of satellites of 5, maximum baseline lengths of
10 kilometers, and limits for the layout tolerance (how
close the survey evidence must be to the theoretical
preplot location). The second two bullets are clearly
defensive in nature to prevent the use of RTK float
solutions which are unable to meet the tolerance of one
meter in three dimensions at the 95% confidence level.
Note that all geophysicists who replied confirmed that
this level of survey accuracy is all that is needed for
modern oil and gas seismic exploration projects.
The one meter accuracy requirement can be easily
derived by an analysis of the expected ranges of seismic
frequencies and P-wave velocities along with wavelet
sampling criteria. Using an extreme case of a near
surface weathering layer with an exceptionally low
acoustic velocity of 200 m/s, a peak frequency of 100
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Hz, and the Nyquist criteria of two samples per
wavelength, we compute from v = f*λ where Δz = λ/2:
∆𝑧 (min) =
200𝑚/𝑠
= 1 𝑚𝑒𝑡𝑒𝑟
2 ∗ 100 𝐻𝑧
We express this 1 meter level at the 95% confidence
level (roughly 2 standard deviations) for consistency
with SEG and UKOOA standards.
THE IDEAL SURVEY SENSOR FOR SEISMIC
The perfect survey sensor for seismic stakeout would
have a combination of the best features of
conventional, inertial, and GNSS instruments. It would
achieve the required one meter precision requirements
at the 95% confidence level. This system would be easy
to operate, allowing a single surveyor to stake
productively. The solution would not require the
maintenance of line-of-sight with the burden of line
cutting. The solution would be robust to endure rough
handling and use in seismic operations, and not require
extensive routine maintenance and calibration. The
perfect system would provide all of this at a reasonable
initial cost.
Basically, the ideal system would be a GNSS sensor that
provides the necessary accuracy even under tree
canopy and reports positioning precisions which
accurately reflect the true uncertainty in position. This
seems to be an unlikely combination of capabilities but
the purposeful evolution of RTK technology and the
increase in available GNSS signals has been favorable
for seismic survey operations.
HD-GNSS APPROACHES THIS IDEAL
To better understand the significance of HD-GNSS to
seismic stakeout, let’s look again at the “traditional”
RTK solution found in most modern GNSS receivers.
Here, the process of ambiguity determination involves a
series of sequential and deliberate steps which initially
calculate floating point (not integer) estimates of the
carrier wavelength ambiguities via a least squares
process. This float solution carries precisions on the
order of many decimeters which are not suitable for
seismic surveying. These initial estimates are then
evaluated to determine an optimal set of integer
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ambiguities which minimize the residuals of the
position solution. All other combinations of integer
ambiguities are ignored until the next search process is
initiated. Once “fixed”, the reported precisions then
drop to a few centimeters as only carrier phase
measurements are considered. Unfortunately, this
technique can produce incorrect ambiguities which
result in large position errors (meters) yet carry
inherently low reported precisions. In addition, the
transition from “float” to “fixed” requires favorable
tracking conditions with good DOPs and low multipath.
When poor tracking environments prevent obtaining
the desired precision levels in real time, some users opt
to postprocess the data despite the burden it carries.
HD-GNSS technology offers greatly improved
performance. HD-GNSS in the Trimble R10 receiver uses
a highly optimized and extremely fast microprocessor
which supports new statistical techniques for
processing GNSS carrier phase data including a
generalized method for dealing with biases. Using all
available GNSS observables and state-of-the-art
proprietary estimation theory, information within the
ambiguity search space is used to provide a statistically
optimal position. All combinations of integers are
constantly evaluated. This rapid ambiguity resolution
process is continuous and never enters a traditional
float stage. The possibility of false initializations with
their misleadingly low reported precisions is eliminated.
The realistic precision estimates of the reported
positions are a function of satellite geometry (PDOP)
and the local signal environment (primarily multipath).
The HD-GNSS solution always uses ambiguity-resolved
carrier phase-derived ranges where the estimated
precisions seamlessly converge from high to low
without the polarizing switch from float to fixed. The
process is so fast that it may only be obvious on longer
baselines or in difficult environments such as under
canopy, but even here, acceptable precision values can
often be obtained with appropriate field procedures.
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RECOMMENDED SEISMIC SURVEY SPECIFICATIONS
There are two general philosophies when writing
specifications. The first is to simply define your
acceptance criteria and then have the
contractor/bidder detail their approach to obtaining
these. The second is to define your acceptance criteria
and then dictate specific methodologies and/or
equipment the contractor will use in their work.
Consider the case where you hire a carpenter to build a
storage shed. You must provide him with plans, a list of
acceptable building materials, and tolerances within
which he is allowed to deviate. If you adhere to the
second philosophy, you will also dictate what tools he
uses and even how he should use them.
For land seismic surveying, there are numerous
technologies in use today. Three of these have already
been mentioned in this paper; optical, inertial, and RTK.
In addition to these are many hybrids where height
determination is aided with the use of LiDAR,
barometers, and various GNSS postprocessing
techniques. For specifications which dictate equipment
and procedures, staying current without eliminating
new cost-saving technologies is a challenging task.
Just as in the fields of personal computing and seismic
acquisition, survey technologies continually evolve.
Specifications which reflect systems and methodologies
that are no longer current result in a disservice to both
client and contractor as new beneficial technologies are
either dismissed or forced to work within the
parameters of older systems. HD-GNSS represents a
significant leap forward which can greatly enhance
productivity, minimize line clearing, and reduce cost in
land seismic stakeout operations. With HD-GNSS, just as
with other survey systems, there are specific
procedures to follow and quality indicators to monitor
to ensure that the reported positions are within
tolerance. For the writer of specifications, one could
append this information to an already lengthy set of
guidelines covering other technologies, or take a
simpler approach and rely on the expertise of their
survey contractors to determine the best way to
achieve these requirements.
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We suggest the following for oil and gas exploration
land seismic survey operations:
•
The layout tolerance, defined as how close the
survey evidence must be to the theoretical
preplot location, shall be two meters in the
horizontal axis.
•
The accuracy tolerance, defined as the accuracy
of the coordinates associated with the survey
evidence, shall be one meter in both the
horizontal and vertical axes at the 95%
confidence level.
There are many alternative systems and associated
procedures which can be used to obtain these. It is the
responsibility of the contractor/bidder to demonstrate
to the client details of their equipment and field
procedures they are proposing to ensure these
specifications are met.
CONCLUSIONS
To most fully benefit from new technologies in seismic
surveying, survey specifications should be written to
define the true accuracy and precision requirements of
the survey. These specifications should not dictate the
sensor type or unrealistic constraints to control
operational aspects of the survey that do not affect the
outcome of the geophysical analysis. HD-GNSS
processing technology offers exceptional positioning
performance that supersedes the traditional float/fix
solution type. With HD-GNSS it is possible to address
the real positioning requirements of land seismic and to
meet these goals with speed and efficiency in the field.
All of this can be accomplished using the system of
choice for land seismic survey - RTK GNSS. Even under
canopy, the cost per staked point can be reduced
significantly without compromising the survey results.
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Figure 13 – Trimble R10 in a challenging GNSS environment
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