Mini-Seismic for the 'Rosetta Stone'

Exploration Technology Goes to Mars

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 wrong.

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 seismic source.

"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 gas industry."

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 techniques.

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 professor?

Image Caption

Seismic technology: It works on earth, but will it work on Mars? Geoscientists tried to learn the answer by simulating Martian conditions as found in desolate, northern Canadian islands. Field work photos courtesy of University of Calgary

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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 wrong.

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 seismic source.

"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 gas industry."

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 techniques.

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 professor?

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 (VSPs).

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 drilling."

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 landscape.

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 exploration.

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 configurations.

  • 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 second.

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 levels.

The rationale for the reverse VSP, Stewart said, was that drilling operations on Mars will probably incorporate simultaneous seismic data acquisition.

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 geology.

Ground-Truthing

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 apart.

"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 solar system."

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