Honey, I shrunk the … vibroseis truck?
Robert Stewart, a professor of geophysics at the University of
Calgary (Canada), is the alter ego of the fictional movie scientist
who accidentally shrinks his kids in an experiment that goes terribly
Except there’s no accident about this downsizing.
Involved in a 21st century "space" race to be the first
geophysicist to acquire seismic data on Mars, Stewart is experimenting
with shrinking a 40,000 pound vibroseis truck — designed to shake
the ground with massive force — down to a size of cellular phone
vibrator that is capable of generating sufficient force to send
sound waves into the Martian subsurface.
Unlike his alter ego, Stewart’s experiments are on the right track
— and have moved beyond the realm of science fiction.
Stewart envisions, further, embedding these miniature vibrators
into the tires of the next generation of Mars Exploration Rovers,
ensuring a good coupling with the ground as the vibrators shake.
A geophone, or receiver, located on another wheel of the Rover
would record the arrival times of the sound waves as they return
to the surface.
Things Are Looking Up
As the "space" race heats up to explore the Red Planet
— as widely reported in January, two NASA Exploration Rovers landed
on Mars and the European Space Agency’s Mars Express started
orbiting the planet — Stewart’s team is modifying geophysical
technologies currently used in the oil and gas industry to image
the Martian subsurface.
Using the Canadian Arctic for a field laboratory, Stewart is testing
his innovative technologies in a harsh environment that features
desert-like conditions, permafrost and geological structures analogous
to those on Mars.
Stewart’s miniature, cellular phone vibrators are innovative
— the insertion of three spinning discs enables them to shake in
three directions (two horizontal and one vertical), creating a multi-component
"It’s very cool," Stewart said. "You have high
power output (shaking) from low power input."
As the geophysical industry strives to reduce its environmental
footprint during field operations, advances for applications in
space exploration are expected to reap earthly benefits.
"Almost everything we’re doing for Mars, we want to be
useful on Earth," Stewart said.
"We want to develop the most sensitive, lightweight, lowest
power-consuming, robust geophysical sensor (geophone) in the world,"
he continued. "In fact, it’s critical for the oil and
He described his concept, a work-in-progress, as the "spacephone"
or the "Marsphone."
"Space" seems to be a recurring theme: The size, weight
and volume and of an instrument — and its power source — will
become critical factors in determining which competing technologies
are carried on Mars Exploration Rovers during the next decade.
In 2003, Stewart’s applied geophysics group, the Consortium
for Research in Elastic Wave Exploration Seismology at the University
of Calgary, won the Society of Exploration Geophysicists’ Distinguished
Achievement Award for its earthly pursuits in multi-component seismic
Stewart has a very personal connection with space travel: In the
mid-1990s he was selected by the Canadian Space Agency to represent
Canada in NASA’s space shuttle program.
It was a difficult decision for Stewart — astronaut, or university
After a lot of soul searching he chose to remain in academia, where
he delights in turning students onto geophysics and space-physics.
The Rosetta Stone
Mars is viewed by scientists as the Rosetta Stone of the universe:
Stewart and other investigators are trying to unlock its mysteries,
and to determine whether there is water buried at the middle latitudes
of the Red Planet.
The existence of subsurface water is fundamental in determining
whether life is unique to Earth, or common to the universe.
During the past two field seasons, Stewart and his team have tested
their space-bound technologies on Devon Island, high in the Canadian
Arctic, where they have acquired 2-D and 3-D surveys using ground
penetrating radar (GPR) and high-resolution, multi-component seismic
methods. They also have acquired borehole vertical seismic profiles
GPR measures the dielectrical properties of the subsurface, while
the seismic method measures the ground’s acoustical properties.
GPR data are acquired at much higher frequencies than seismic
data; during seismic data acquisition, higher frequencies are frequently
attenuated in the shallow subsurface.
"We’re adapting or reinventing the seismic method for
a completely different target (permafrost and shallow stratigraphy),"
Stewart explained. "There’s a lot of expertise in Calgary’s
oil and gas industry for northern studies — it’s second to
none in the world. The industry has the software and knowledge base
to develop the whole exploration process for Mars — from reconnaissance
surveys, detailed surveys, sample collection and all the way to
Stewart duplicated field experiments to cross-correlate results
and to determine which technology — GPR or the seismic method —
was most appropriate for permafrost investigations. His experiments
focused on mapping the interface between the active, or "thaw,"
layer of sediments and the underlying permafrost buried at a depth
of 60 to 70 centimeters on Devon Island.
Devon Island is the largest uninhabited island on earth — it’s
also home to a unique geological structure called the Haughton Crater,
the second most northerly meteorite impact feature known on the
planet’s surface. Twenty-three million years ago, an extraterrestrial
body hit the Earth’s surface with a force so catastrophic that
it destroyed the area’s lush green forests, gouging out a crater
24 kilometers in diameter and several hundred meters deep.
The scars from the impact remain today and, for an intrepid group
of modern-day explorers, represent a terrestrial analog to the Martian
Since 1997, the Haughton Crater has been the focus of a ground
breaking science and technology R&D project — studies have
focused on understanding the evolution of the crater and its geology,
biology and similarity to the extraterrestrial landscape of Mars.
Pascal Lee, a planetary scientist, heads the NASA Haughton-Mars
Project (HMP), an international consortium of interdisciplinary
scientists led by the NASA Ames Research Centre, the SETI (Search
for Extraterrestrial Intelligence) Institute and the Mars Institute.
A geophysicist by training, Lee is the HMP’s principal
investigator and is also affiliated with the SETI and Mars Institutes.
Canadian participants in the HMP have included the Canadian Space
Agency, the Geological Survey of Canada and several Canadian universities.
Lee views the Canadian Arctic as a "world treasure" for
investigations leading to the exploration of Mars. He describes
Devon Island and the Haughton Crater as "Mars Wonderland."
The canyons, gullies and hills observed on the surface of Mars
closely resemble geological features that have been shaped by water
on Earth. By inference, Lee said, "we find clues that liquid
water was readily available on Mars in the past. Mars should have
had an endowment of water that was much bigger than meets the eye."
Lee uses a thermal definition to identify permafrost: It’s
ground that has been frozen for two or more consecutive years.
"Mars, by definition, is a planet that is completely covered
with permafrost," Lee said.
Scientific knowledge of water on Mars, he continued, is limited
to the distribution of permanent and seasonal ice caps at the Martian
North and South Poles, which are comprised of frozen water and frozen
carbon dioxide. Lee also points to the existence of water vapor
recently detected in the Martian atmosphere — but, he said of the
middle latitudes, "we don’t really know if there’s
ice in the ground."
Mars Express, the European Space Agency’s Orbiter, established
its orbiting pattern in February and is now searching the planet
for signs of water and life. It carries seven instruments, including
a subsurface sounding radar altimeter equipped with a 40-meter-long
antenna designed to direct high-frequency radio waves at Mars, enabling
it to probe several hundreds of meters into the subsurface.
Now Playing Mars … Canada!
Characterizing the Mars Express Orbiter’s level of investigation
as a "reconnaissance fly-by," Lee eventually wants to
gather high-resolution, GPR data from the Martian surface. He described
Stewart’s geophysical research on Arctic permafrost as "world
class," and suggested it will be critical in unlocking the
secrets of the Red Planet.
The summer field season is short in the Canadian Arctic — it spans
about four weeks in July. Lee kicked off the field season last May
by driving a Humvee from the eastern shore of Cornwallis Island,
across 37 kilometers of thinning, ocean pack ice, to Cape McBain
on Devon Island’s western shore.
It was a daring, three-hour-long crossing — the four participants
wore survival suits, and the 8,000-pound tracked vehicle was stripped
of its doors in the unfortunate event that it broke through the
ice. Lee, the Humvee’s only occupant, was escorted by three
people (including two Innuit) on skidoos, arranged one in front
and two behind. They encountered polar bear tracks during the crossing.
Equipped with interchangeable wheels and tracks, the Mars-1 Humvee
Rover will provide the HMP’s scientists with a terrestrial
simulation of the laboratories carried on the Mars Exploration Rovers.
Lee described the Mars-1 Humvee Rover as "one of a kind."
AM General leased the refurbished Humvee to the Mars Institute for
three years at $1 per year. The vehicle was shipped to Cornwallis
Island by the U.S. Marine Corps in a C-130 transport plane.
Stewart and Carlos Nieto, a graduate student of geophysics at the
University of Calgary, spent 10 days on Devon during the 2003 field
season. Despite the Arctic weather — rain, snow, sleet and high
winds — they managed to acquire significant amounts of geophysical
data. The fact that the sun never set certainly helped.
"In 10 days, you don’t really get used to the fact that
there’s 24 hours-a-day sunlight," Nieto said.
Originally from Caracas, Venezuela, Nieto was overwhelmed by Canada’s
Arctic, its landscapes and the culture of the Innuit People.
"It was amazing, like a new world," he said. Carlos’
world continues to expand, far beyond the realm of Earth — his
doctorate studies at the University of Calgary will focus on developing
extraterrestrial seismic data acquisition methods for future Mars
To acquire the seismic data, Stewart and Nieto used:
A Geometrics Strataview, 60-channel recorder with 28 Hz Omni-phones
(multi-component) that were planted in vertical and horizontal
A small sledgehammer as the seismic source, striking a base
plate in either a vertical or horizontal direction.
Hitting the hammer at 30 degrees off vertical creates a shear
wave seismic source (S-wave); a vertical blow to the base plate,
in contrast, generates a primary wave seismic source (P-wave).
- A "microsource" used to produce very high frequency
seismic sound waves — in other words, they used air pistols to
fire pellets into the ground. The data were recorded at a receiver
spacing of 10 centimeters with 40 Hz Oyo-Geospace, three-component
geophones and the Geometrics Strataview 60-channel system.
A 3-D, three-component seismic survey was acquired over an area
that measured 25 meters by 25 meters. The shallow, high-resolution
seismic data were recorded using 20 geophones and a record length
of 250 milliseconds.
The 3-D’s primary objective, according to Nieto, was to image
the interface between the thaw layer and the permafrost; the secondary
objective was to image any inter-bedded ice lenses and variations
in the permafrost.
"The velocity of the thaw layer depends a lot on the fluid
level or saturation," Nieto said. "Modeling tells you
that there’s a change in velocity due to fluid saturation."
Processing of the seismic data indicates two velocities in the
thaw layer: a P-wave velocity of 260 meters per second and a S-wave
velocity of 168 meters per second. Velocities in the permafrost
layer vary dramatically from the thaw layer: a P-wave velocity of
3,100 meters per second and a S-wave velocity of 2,060 meters per
Stewart and Nieto also acquired a three-component VSP and a three-component,
reverse VSP. The oil and gas industry generally conducts VSPs by
placing a string of geophones down the borehole, once drilling has
concluded. The seismic source — usually a vibroseis truck — is
situated at the surface on the lease site. At Devon Island, Stewart
drilled through the thaw layer and into the top of the permafrost
— he conducted a conventional VSP, and then flipped the configuration
around, laying the geophones on the surface and running an impact
seismic source (coring tool) downhole, hitting progressively deeper
The rationale for the reverse VSP, Stewart said, was that drilling
operations on Mars will probably incorporate simultaneous seismic
Nieto acquired 2-D and 3-D GPR surveys while on Devon Island, using
the NOGGIN SmartCart, which resembles a small lawn mower and is
rolled over the surface, providing real-time displays of radar arrivals.
It contains a 250 MHz PulseEKKO device, and a 50 MHz and
a100 MHz antennae. GPR has many terrestrial applications, including
archaeology, civil engineering, construction, bedrock mapping, ice
profiling and oil and gas remediation.
Peter Annan, president of Sensors & Software Inc., who, as
a graduate student in the late 1960s and early 1970s worked on NASA’s
Apollo 17 Mission, donated the SmartCart to the University of Calgary
for its investigations on Devon Island.
"There isn’t a huge demand for these things in space,"
Annan said. "We do this out of scientific curiosity and love
— not business."
According to Annan, research is under way in Canada to incorporate
the tool into the next generation of Mars Exploration Rovers. The
Canadian Space Agency and the Canadian scientific community are
conducting feasibility studies for a 2011 robotic mission to Mars
that would investigate the planet’s surface and subsurface
In order to ground-truth the GPR experiments, Stewart and Nieto
dug a trench down to the permafrost and pounded a one-meter length
of rebar into the end of the trench, along the top of the permafrost.
They then ran a GPR survey orthogonally across the undisturbed ground
above the rebar.
The rebar generated a very good diffraction signature, enabling
a time to depth correlation between the signature from the rebar
and the top of the permafrost.
Stewart turned to Laurie Ross, a processing geophysicist with Geo-X
Systems of Calgary, to enhance the Devon GPR images.
Used to handling seismic data acquired in milliseconds, Ross had
to fudge her signal processing software to deal with GPR data acquired
in nanoseconds. Seismic traces are traditionally spaced at 10 to
20 meters apart — the GPR traces were spaced at five centimeters
"It’s all possible if you do your book-keeping,"
Ross said of the manipulations required to process the data.
She experimented with a processing flow used for conventional seismic
data — deconvolution, noise attenuation and migration tests.
In an attempt to simulate a "manned" mission to Mars,
segments of the fieldwork were conducted in NASA-concept spacesuits,
which Stewart described as "cumbersome yet manageable."
The suits, according to Nieto, were tough to get into.
"You feel constrained," Nieto said. "And hot."
The suits are designed to protect astronauts from the hostile climate
and deadly gases that comprise the thin Martian atmosphere — made
up predominantly of carbon dioxide, the atmosphere has a pressure
that’s less than 1/100th of Earth’s atmosphere.
According to Lee, the suits will be pressurized next summer.
Seeking the ‘Sweet Spot’
What inspires these modern-day explorers to pursue extraterrestrial
studies in such a hostile climate on Earth?
Stewart is looking for a "Martian" first — his stripped
down, modified versions of conventional oil patch seismic equipment
may enable the next generation of Mars Exploration Rovers to conduct
geophysical imaging of the subsurface. Equipped with panoramic cameras
and scientific instrumentation, the Rovers’ current capabilities
are limited to using robotic arms to scoop up, abrade and analyze
surface soils and rocks.
"I can imagine a mission to Mars that finds the sweet spot,
geophysically," Stewart said. "Clearly, you want to have
the best drill site possible."
"What’s at stake, scientifically, at Mars is very profound
— the search for life and the search for our origins," Lee
explained, who described the importance of teamwork in getting to
Mars by saying, "It calls upon excellence in the widest possible
areas of space exploration."
"If you master Mars," he added, "you master the