On Mars, NASA’s Perseverance Rover’s Playlist Like No Other

Microphones on the rover capture, characterize sounds from red planet’s atmosphere

Media Contact:
Larry Frum
AIP Media
301-209-3090
media@aip.org

DENVER, May 25, 2022 – Since NASA’s Perseverance rover landed on Mars, its two microphones have recorded hours of audio that provide valuable information about the Martian atmosphere.

Baptiste Chide, of Los Alamos National Lab, will discuss the importance of this acoustical information in the presentation, “Mars soundscape: Review of the first sounds recorded by the Perseverance microphones,” at the 182nd Meeting of the Acoustical Society of America on May 25 at 3:45 p.m. Eastern U.S.at the Sheraton Denver Downtown Hotel.

After more than a year of recording on the surface, the team reduced the data to a Martian playlist that features about five hours of sounds. Most of the time, Mars is very quiet. Sounds are 20 decibels lower than on Earth for the same source, and there are few natural noises except for the wind.

“It is so quiet that, at some point, we thought the microphone was broken!” said Chide.

However, after listening carefully to the data, the group uncovered fascinating phenomena. There was a lot of variability in the wind, and the atmosphere could abruptly change from calm to intense with rapid gusts. By listening to well-characterized and intentional laser sparks, Perseverance calculated the dispersion of the sound speed, confirming a theory that high-frequency sounds travel faster than those at low frequencies.

“Mars is the only place in the solar system where that happens in the audible bandwidth because of the unique properties of the carbon dioxide molecule that composes the atmosphere,” said Chide.

The red planet’s seasons impact its soundscape. As carbon dioxide freezes in the polar caps during winter, the density of the atmosphere changes and the environment loudness varies by about 20%. That molecule also attenuates high-pitched sounds with distance.

Perseverance continues to collect audio recordings as it moves across different regions of Mars. Chide believes this technique will be even more informative on planets and moons with denser atmospheres, such as Venus and Titan, where sound waves interact more strongly and propagate farther.

———————– MORE MEETING INFORMATION ———————–
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Main meeting website: https://acousticalsociety.org/asa-meetings/
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WORLDWIDE PRESS ROOM
In the coming weeks, ASA’s Worldwide Press Room will be updated with additional tips on dozens of newsworthy stories and with lay language papers, which are 300 to 500 word summaries of presentations written by scientists for a general audience and accompanied by photos, audio and video. You can visit the site during the meeting at https://acoustics.org/world-wide-press-room/.

PRESS REGISTRATION
We will grant free registration to credentialed journalists and professional freelance journalists. If you are a reporter and would like to attend, contact AIP Media Services at media@aip.org. For urgent requests, staff at media@aip.org can also help with setting up interviews and obtaining images, sound clips, or background information.

ABOUT THE ACOUSTICAL SOCIETY OF AMERICA
The Acoustical Society of America (ASA) is the premier international scientific society in acoustics devoted to the science and technology of sound. Its 7,000 members worldwide represent a broad spectrum of the study of acoustics. ASA publications include The Journal of the Acoustical Society of America (the world’s leading journal on acoustics), JASA Express Letters, Proceedings of Meetings on Acoustics, Acoustics Today magazine, books, and standards on acoustics. The society also holds two major scientific meetings each year. See https://acousticalsociety.org/.

Acoustic Sensors Pinpoint Shooters in Urban Setting

Modeling and optimizing sensor networks for a specific environment will help missions narrow in on shooter locations

Media Contact:
Larry Frum
AIP Media
301-209-3090
media@aip.org

DENVER, May 23, 2022 – During a gunshot, two sound events occur: the muzzle blast and the supersonic shock wave. Acoustic sensors, such as single or arrays of microphones, can capture these sounds and use them to approximate the location of a shooter.

As part of the 182nd Meeting of the Acoustical Society of America at the Sheraton Denver Downtown Hotel, Luisa Still, of Sensor Data and Information Fusion, will discuss the important factors in determining shooter localization accuracy. Her presentation, “Prediction of shooter localization accuracy in an urban environment,” will take place May 23 at 12:45 p.m. Eastern U.S.

In an urban setting, buildings or other obstacles can reflect, refract, and absorb sound waves. The combination of these effects can severely impact the accuracy of shooter localization. Preemptively predicting this accuracy is crucial for mission planning in urban environments, because it can inform the necessary number of sensors and their requirements and positions.

Still and her team used geometric considerations to model acoustic sensor measurements. This modeling, combined with information on sensor characteristics, the sensor-to-shooter geometry, and the urban environment, allowed them to calculate a prediction of localization accuracy.

“In our approach, the prediction can be interpreted as an ellipse-shaped area around the true shooter location,” said Still. “The smaller the ellipse-shaped area, the higher the expected localization accuracy.”

The group compared their accuracy prediction to experimental performance under various geometries, weapons, and sensor types. The localization accuracy depended significantly on the sensor-to-shooter geometry and the shooting direction with respect to the sensor network. The smaller the distance between the shooting line and a sensor, the more accurate they could be with their prediction of the source. Adding more sensors increased the accuracy but had diminishing returns after a certain point.

“Each urban environment is too individual (e.g., in terms of layout, building types, vegetation) to make a general recommendation for a sensor set up,” said Still. “This is where our research comes in. We can use our approach to recommend the best possible setup with the highest accuracy for a given location or area.”

———————– MORE MEETING INFORMATION ———————–
USEFUL LINKS
Main meeting website: https://acousticalsociety.org/asa-meetings/
Technical program: https://eventpilotadmin.com/web/planner.php?id=ASASPRING22
Press Room: https://acoustics.org/world-wide-press-room/

WORLDWIDE PRESS ROOM
In the coming weeks, ASA’s Worldwide Press Room will be updated with additional tips on dozens of newsworthy stories and with lay language papers, which are 300 to 500 word summaries of presentations written by scientists for a general audience and accompanied by photos, audio and video. You can visit the site during the meeting at https://acoustics.org/world-wide-press-room/.

PRESS REGISTRATION
We will grant free registration to credentialed journalists and professional freelance journalists. If you are a reporter and would like to attend, contact AIP Media Services at media@aip.org. For urgent requests, staff at media@aip.org can also help with setting up interviews and obtaining images, sound clips, or background information.

ABOUT THE ACOUSTICAL SOCIETY OF AMERICA
The Acoustical Society of America (ASA) is the premier international scientific society in acoustics devoted to the science and technology of sound. Its 7,000 members worldwide represent a broad spectrum of the study of acoustics. ASA publications include The Journal of the Acoustical Society of America (the world’s leading journal on acoustics), JASA Express Letters, Proceedings of Meetings on Acoustics, Acoustics Today magazine, books, and standards on acoustics. The society also holds two major scientific meetings each year. See https://acousticalsociety.org/.

LEGO Down! Focused Vibrations Knock Over Minifigures

Time reversal technique focuses wave energy to knock over minifigure targets in museum demonstration

Media Contact:
Larry Frum
AIP Media
301-209-3090
media@aip.org

SEATTLE, December 2, 2021 — A tabletop covered in miniature LEGO minifigures. There is a whooshing sound, a pause, and then a single minifigure in the center of the table topples over, leaving the remaining minifigures standing.

Brian Anderson, of Brigham Young University, will discuss how this is achieved in his presentation at the 181st Meeting of the Acoustical Society of America, “Knocking over LEGO minifigures with time reversal focused vibrations: Understanding the physics and developing a museum demonstration.” The session will take place on Dec. 2 at 5:15 p.m. Eastern U.S. in the Elwha B Room, as part of the conference running from Nov. 29 to Dec. 3 at the Hyatt Regency Seattle.

Anderson and his team use speaker shakers to generate vibrations in a plate. They place LEGO minifigures on the plate, choose a target, and measure the impulse response between each shaker and the target location. Playing that very response from the shakers, but reversed in time, creates sound waves that constructively interfere at the target minifigure. The focused energy knocks over the single LEGO minifig without disrupting the surrounding minifigs.

This demonstration was transformed into a two-player game for a museum exhibit in a wave propagation museum hosted by ETH Zurich in Switzerland. Two visitors take turns focusing vibrations and attempting to knock over the LEGO minifigures on the other team.

The technique also has numerous applications beyond LEGO, and Anderson said it shows the power of focused vibrations.

“Time reversal has been used to focus sound in the body that is intense enough to destroy kidney stones or brain tumors without requiring surgery,” Anderson said. “I have used time reversal to locate cracks or defects with ultrasound in metal structures, such as storage canisters for spent nuclear fuel. Time reversal can also be used to locate and characterize earthquakes or locate gun shots within an urban city environment.”

———————– MORE MEETING INFORMATION ———————–
USEFUL LINKS
Main meeting website: https://acousticalsociety.org/asa-meetings/
Technical program: https://eventpilotadmin.com/web/planner.php?id=ASAFALL21
Press Room: https://acoustics.org/world-wide-press-room/

WORLDWIDE PRESS ROOM
In the coming weeks, ASA’s Worldwide Press Room will be updated with additional tips on dozens of newsworthy stories and with lay language papers, which are 300 to 500 word summaries of presentations written by scientists for a general audience and accompanied by photos, audio and video. You can visit the site during the meeting at https://acoustics.org/world-wide-press-room/.

PRESS REGISTRATION
We will grant free registration to credentialed journalists and professional freelance journalists. If you are a reporter and would like to attend, contact AIP Media Services at media@aip.org. For urgent requests, staff at media@aip.org can also help with setting up interviews and obtaining images, sound clips, or background information.

ABOUT THE ACOUSTICAL SOCIETY OF AMERICA
The Acoustical Society of America (ASA) is the premier international scientific society in acoustics devoted to the science and technology of sound. Its 7,000 members worldwide represent a broad spectrum of the study of acoustics. ASA publications include The Journal of the Acoustical Society of America (the world’s leading journal on acoustics), JASA Express Letters, Proceedings of Meetings on Acoustics, Acoustics Today magazine, books, and standards on acoustics. The society also holds two major scientific meetings each year. See https://acousticalsociety.org/.

2aPAa – Three-dimensional wavefront modeling of secondary sonic booms

Dr. Joe Salamone – joe.salamone@boom.aero
Boom Supersonic
12876 East Adam Circle
Centennial, CO 80112

Popular version of 2aPAan- Three-dimensional wavefront modeling of secondary sonic booms
Presented Tuesday morning, May 24, 2022
182^nd ASA Meeting, Denver, Colorado
Click here to read the abstract

A sonic boom is the impulsive sound heard resulting from a vehicle flying faster than the speed of sound. The origin of this impulsive sound is the localized shock structure close to the vehicle due to regions of compression and expansion of the air (Figure 1) which manifest as pressure disturbances. The leading shock at the vehicle typically forms a cone that circumferentially spreads around its nose. A commonly used formula that relates the interior cone angle to the supersonic vehicle’s Mach number is: cone angle = asin(1/Mach). Thus, the cone angle gets larger with decreasing supersonic Mach number and vice versa.

The sonic boom propagates along acoustic ray paths, and these paths can refract based on temperature gradients and wind speed gradients. A fundamental premise is the ray path will always bend towards the slower speed of sound. The initial ray direction is normal to the Mach cone, with some additional influence for its initial direction due to the presence of wind at the vehicle’s flight altitude. A depiction of the Mach cone compared to the ray cone was presented by Plotkin (2008) shown in Figure 2. The Mach cone exists at an instance in time, travelling with the supersonic vehicle, while the specific locations that comprise the Mach cone surface represent the pressure disturbances that propagate along ray paths.

Figure 2 – Notional comparison between the supersonic Mach cone and its corresponding ray cone

Work presented here examines the shape of the Mach cone when propagated significantly large distances away from the vehicle in three-dimensional, realistic atmospheric conditions. Also recognize the work here only depicts where the sonic boom could travel and not what its amplitude could be at the Earth’s surface. Figure 3 shows that as the vehicle travels it is constantly generating new portions of the Mach cone, while the existing portions of the Mach cone all propagate at the local (effective) speed of sound.

Figure 3 – Mach cone construction from ray paths that originate from vehicle positions along its trajectory

A computational example of an extended Mach cone is shown in Figure 4 where the vehicle is flying at Mach 1.15. Note the atmospheric refraction of the ray paths result in the lower portions of the Mach cone not reaching the Earth’s surface. And likewise, the upper portions of Mach cone warp back towards the Earth’s surface. Thus, the Mach cone no longer resembles a cone but is a more complicated shape.

Figure 4 – Computational example of a Mach cone for a vehicle traveling at Mach 1.15

Another computational example is presented in Figure 5, where the vehicle is flying at Mach 1.7. Note the increase in Mach number creates a shallower initial Mach cone and portions of the Mach cone reach the Earth’s surface. Additionally, the outer fringes of the Mach cone above and below the vehicle that do reach the Earth’s surface result in primary, direct secondary and indirect secondary sonic booms as indicated in Figure 5. However, some portions of the Mach cone centered above and below the vehicle eventually refract at an extremely high altitude in the thermosphere. Thus, those portions of the Mach cone, when they reach the Earth’s surface, would be inaudible due to their significantly longer propagation distances.

Figure 5 – Computational example of a Mach cone for a vehicle traveling at Mach 1.7

2aPAb – Ultrasound technology to remove kidney stones

Mohamed A. Ghanem – mghanem@uw.edu
Adam D. Maxwell – amax38@uw.edu
Oleg A. Sapozhnikov – olegs@uw.edu
Michael R. Bailey – mbailey@uw.edu

University of Washington
1013 NE 40th St.
Seattle WA 98105

Popular version of 2aPAb – Designing an array for acoustic manipulation of kidney stones
Presented Tuesday morning, May 24, 2022
182^ndASA Meeting
Click here to read the abstract

Ultrasound technology is becoming an important treatment tool. For instance, sound waves can apply a radiation pressure that can displace an object. Multi-element arrays are complex ultrasound sources that consist of several small transducers that can be driven in sync or a specific order to output pressure waves with different shapes. Pressure wave shapes that have a doughnut shape or a long tube are useful as they can trap an object in the center and as we control the location of the doughnut the object follows. This technology can be used to trap small kidney stones or stone fragments and move them from the kidney collection areas toward the kidney exit without surgery. We have demonstrated the ability to move kidney stone models in the bladders transcutaneously in live pigs under anesthesia. We are currently designing a new multi-element array that will enable us to adapt this technology to move stones in the complex structure of the kidney over larger distances. This technology will reduce the surgery associated with kidney stone treatments by removing small stones or fragments before they become larger, which will lead to surgery, and eliminating emergency room visits by relieving blockages from these stones or fragments.

Controlled steering of kidney stones toward the kidney exit with an ultrasound array.

2aPAa6 – Boom Buh-Boom! A brief analysis of a Falcon-9 booster landing

J. Taggart Durrant – taggart.durrant@gmail.com
Kent L. Gee – kentgee@byu.edu
Mark C. Anderson – anderson.mark.az@gmail.com
Logan T. Mathews – loganmathews103@gmail.com
Grant W. Hart – grant_hart@byu.edu

Department of Physics and Astronomy
Brigham Young University
N283 ESC
Provo, UT 84602

Popular version of 2aPAa6 – Analysis of sonic booms from Falcon 9 booster landings
Presented Tuesday morning, May 24, 2022
182^nd ASA Meeting
Read the article in Proceedings of Meetings on Acoustics

It’s an understatement to say that rockets are loud. The high-speed exhaust rushing out of the nozzles mixes with the surrounding air, creating sound waves that can be heard over great distances. Even several miles away the sound waves can vibrate your whole body as the rocket lifts off and rides its pillar of fire into the cosmos.

If you watch a SpaceX Falcon 9 launch, you may be treated to another impressive experience: watching the rocket’s first-stage booster return to Earth in a “flyback” maneuver and land (see Figure 1). During flyback, the booster falls through the atmosphere at supersonic speeds, with increasing drag from an ever-thickening atmosphere gradually slowing its descent. Seconds before a would-be impact, a single rocket engine fires up again, landing legs deploy, and the rocket lands safely. Depending on your location, not only will you hear the engine firing during the landing, but it may also be preceded by a startling, rapid sequence of loud bangs. No, the rocket hasn’t exploded; this is the Falcon 9’s unique “triple sonic boom” caused by its unique geometry and flight profile while it was still high above you and falling at supersonic speeds.

“Figure 1. Left: Photo of a Falcon 9 launch. Photo from NASA/Joel Kowsky, public domain. Right: Photo of a Falcon 9 booster landing. Photo from SpaceX Photos, public domain.”

Want to hear a Falcon 9 sonic boom created during flyback? Here are some examples on YouTube.

Considering how loud this “triple boom” is, let’s take a look at its pressure waveform in relation to the other launch and landing noise. Figure 2 shows a microphone recording of an entire Falcon 9 launch and landing at Vandenberg Space Force Base over a period of 10 minutes at a distance of 5 miles from the launch and landing pads. Also shown are half-second snippets of the waveform during each of three main phases. The launch noise, indicated in red, is littered with shocks (nearly instantaneous changes in pressure) while the landing noise, indicated in green, contains many shocks of smaller amplitude and lesser steepness. All three phases of noise contain shock-like content, but the sonic boom, indicated in blue, is much larger in amplitude.

“Figure 2. A Falcon 9 launch recording, around 5 miles away from the launch and landing sites.”

In order to determine the “sound exposure” of ground observers, we can use the Sound Exposure Level (SEL) metric over each section of the recording, as it accounts for both the amplitude and duration of the recording. The launch phase, calculated over 150 seconds, has an SEL of 127 dB (re 400 pPa² s). However, the sonic boom – less than 1 second long – has an SEL of 124 dB. Although the boom’s duration is shorter than the launch, the amplitude is much greater, resulting in a total SEL similar to that of the entire launch noise. Lastly, the landing noise after the sonic boom (19 seconds) has an SEL of 112 dB.

This brief analysis shows that the landing noise (including the sonic boom) contributes a large amount of noise, similar to that of the launch phase, and needs to be considered when studying the effects of rocket launches on communities and environments.