An Exploration of an Analog for Icy Ocean Worlds

---

In our previous newsletters, we explored the icy depths of Interior Alaska to learn about the successes and learning opportunities of the Gulkana glacier deployment. We travel once again to another polar region to continue the research of the Seismometer to Investigate Ice and Ocean Structure (SIIOS) funded by NASA. After troubleshooting the experimental design used during the Gulkana mission, the SIIOS team treks to Greenland - where the workspace is vaster, and the ice layer is thicker - to further investigate the potential to rapidly deploy a seismic station on the Europa lander.

Getting to the actual location of deployment in Greenland was no easy task. The SIIOS team was comprised of scientists from all over the country who traveled through many layovers before arriving at the Thule airbase (now named Pituffik airbase). This was the closest accessible base before traveling via helicopter to get to the analog field site. The team was staggered in their arrival over the span of two days due to inclement weather, one of the major challenges of this experiment. After 6 helicopter loads, all the necessary equipment finally arrived at the field site and work could finally begin. 

The overall experimental design consisted of the lander in the center and 4 independent stations positioned 1 km out from all cardinal directions. The purpose of this was to compare data from the sensors of the lander versus a small baseline array - i.e., can a single sensor perform as well as an array? A deep hole was dug at the independent stations to mitigate ice from melting and moving the sensors. In addition, the lander was also placed in a deep hole underneath a windshield to replicate the absence of wind on Europa. Many sensors were placed inside the windshield creating a data mine for any future research. Similar to the Gulkana deployment, active and passive source experiments were performed on the Greenland ice sheet.  

The picture below illustrates the field site right before the team returned to Thule airbase. The orange boxes are the data acquisition systems comprising of batteries and digitizers powered by solar panels. Data was to be collected throughout the summer but only 2 weeks were captured as the snow piled on top of the equipment burying the solar panels and leaving the batteries to die. Despite this, our sensors performed comparably to traditional equipment. The following year, another experiment in Greenland was planned after the discovery of a crater nearby in satellite imagery, however, COVID-19 delayed this project.

---

This write-up is a continuation of the last newsletter where we used our sensors to measure seismic activity at the Gulkana glacier. The Silicon Audio team ventured out to the interiors of Alaska as an analog for Europa; there, we tested the viability of the experimental design of the proposed Europa lander. Although the team of scientists faced a few challenges, the mission was an overall success.  

Our sensors were put to the test in low temperatures and functioned well. The ability to withstand the low temperatures of Europa is a necessary attribute for the sensors that will be placed on the lander. During the experiment, the glacier would slowly move causing the sensors to move along with it. This normally would be a problem, but due to the high tilt tolerance of our sensors it was able to overcome these conditions.

Of course, we know we can use seismic to measure the thickness of the ice, but the main purpose of this project was to determine if a seismic station could be rapidly deployed in icy conditions. The team discovered that the small table that was used needed to be stiffer in construction so the vibrations coming from the table were minimized. This caused an inability to differentiate the vibrations coming from the table versus the passive seismic. Changing the experimental design was a key lesson learned as well as the minimum amount of gear that was needed for future experiments.  

The next steps of this project were to improve the lander design and continue testing in icy conditions such as Greenland. Stay tuned for the next newsletter where we dive deeper into the Greenland deployment. 

A Study of Earth's Artic Domains

---

In the fall of 2017, Silicon Audio embarked on a journey to the icy terrains of the Gulkana Glacier in the interior of Alaska. This project was sponsored by NASA’s Planetary Science and Technology Through Analog Research (PSTAR) program. The mission: use seismology to determine the thickness of the ice on Gulkana as a stand-in for Europa’s icy crust.  

Europa is highly remarked in the solar system for its potential for extraterrestrial life, boasting necessary elements for the creation of life. So why Gulkana? For starters, its topography poses as an excellent candidate to replicate Europa with its icy layer atop bedrock. But most importantly, it’s on planet Earth and accessible to scientists to trial the lander before its final launch to Europa.  

Partnering with the University of Alaska, the team loaded up all the equipment into a sling and had a helicopter transport everything to the location. The team, however, did not get the same treatment and drove as far as they could before hiking the rest of the way to the site.  

We had 16 of our 3-axis sensors deployed during this test. The sensors were laid out on top and below a small table that represented the test lander. Passive seismic was measured including the noises of the water trickling, ice cracking and other natural events while active seismic was created with a hammer. These were the basic parameters of the experiment and the logistics that went behind the test lander.  

Silicon Audio has sensors all over the world.

---

We’re even shooting for our sensors to be all over the solar system, but we’ll touch more on that on a later day. Today, we are going to explore a sensor whose story dates back to 1985 in the city of Arequipa, Peru.

In 1985, El Misti erupted and caused disastrous effects that rippled through the nation. Scientists in the area began aggressively monitoring and studying this volcano to properly prepare for the next eruption. 

Fast forward to 2019 and Silicon Audio was contacted by the government of Peru about using our sensors to expand the volcano monitoring network.

In 2022, we were invited to a conference in Arequipa, Peru to demonstrate our sensors and their functionalities. 

During this visit, we hiked up to El Misti to visit one of the sites that was built to house our seismometers. The sensor was placed in a steel frame box near a GNSS pier and a gas meter pointed up at the volcano to detect trace gases. These three components combined work together to collect data that is monitored at the observatory back in Arequipa. 

---

Peru is one of many places around the globe where our sensors reside. Tune into the next newsletter to follow along for more of Silicon Audio's adventures! 

Silicon Audio is starting a newsletter to keep customers up to date on the latest engineering challenges we face as well as getting further insight into the brains of the company. To kick things off, let’s explore a commonly received question: Why the name Silicon "Audio" Seismic? 

Silicon Audio began operations in 2009 making high-SNR MEMS microphones for consumer electronics while using a compact embodiment of the optical interferometer used in Silicon Audio’s seismic sensor today. By 2012, Silicon Audio had partnered with a market-leading smartphone OEM and MEMS microphone chip maker.  In a 2013 pilot manufacture, the best-in-class SNR was successfully created  The microphone, however, had an Achille's heel. Operating in open-loop, the intrinsic dynamic range was limited to 100 dB, and the product was difficult to manufacture. 

While working on the microphone, The Department of Energy asked Silicon Audio if the low-noise optical read-out technology could be used to measure seismic signals to listen for nuclear explosions anywhere in the world. Around the same time, the oil and gas industry asked if the sensor could be used for seafloor seismic exploration and beat the low-frequency performance of common geophones. This led to an evolution of products to address hi-fi seismic. Silicon Audio's engineers borrowed tried-and-true design features of the workhorse geophone and added low-noise optical readout. The moving element of the seismometer was now equipped with a strong, linear coil-magnet actuator.  When combined with interferometric detection and low noise electronics, a closed-loop, force-balanced sensor was born.  

Fast forward and Silicon Audio has built high-fidelity seismometers for dam monitoring, volcano monitoring, and deep bore-hole deployments over 1 km beneath the surface. A recent project has been building space-ready sensors to survive shuttle launch and land on the moon. As the genesis seismic application was oil and gas, the product was designed from the very beginning for high shock tolerance and rough handling.  The sky’s the limit with what these sensors can do and Silicon Audio is glad to have you on this journey.

___________________________________________________________________________________

Cheers from the Silicon Audio team!