What Is a Passive Acoustic Survey?
A Passive Acoustic Survey, also known as Ambient Noise Tomography (ANT), is a listening study that uses small sensors to record naturally occurring background vibrations in the Earth, such as wind and distant natural activity. No energy is generated and nothing is transmitted into the ground.
How the Survey Works
- A land agent will contact you in advance to request permission and explain the survey process.
- You will have the opportunity to provide input on acceptable locations for the sensors.
- The recording sensor is small and low-profile, approximately the size of a soda can or small lunchbox.
- The sensor is placed on the ground with minimal disturbance.
- Sensors listen passively to natural background vibrations.
- Sensors remain in place for approximately 30 days.
- No daily visits, noise, or activity are required once installed.
- All equipment is removed and the site is restored.
What This Survey Does NOT Do
- No drilling
- No vibrations
- No electrical charge
- No heavy equipment
- No wildfire risk
- No noise
- No emissions
- No impact to animals
What Is a Magnetotelluric (MT) Survey?
A Magnetotelluric (MT) survey is a passive listening study that uses small, temporary sensors to record naturally occurring electromagnetic fields that constantly flow through the Earth. No energy is generated and nothing is transmitted into the ground. The survey does not test for, detect, or extract hydrogen or any subsurface resource. It collects data on subsurface rock formations to build digital geological models and is only the first step in a multi-stage evaluation process.
What Equipment Is Used?
An MT survey station uses simple, surface-based instruments to measure the Earth’s natural electromagnetic fields. Each setup includes:
- A data logger at the center that records signals over time.
- Electrodes (about the size of a soda can) placed in the ground to the north, south, east, and west and connected to the data logger via cables.
- Induction coils (about the size of a baseball bat) placed just below the surface, aligned in three directions and connected to the data logger via cables.
How Is the Equipment Installed?
- Site locations are accessed via existing roads or on foot where there are no roads.
- Pre-deployment photos are taken to document existing conditions.
- Electrodes and induction coils are buried using hand tools only.
- Sensors are present for approximately 48 hours.
- Equipment is then removed and the site is restored.
Environmental Protection
These surveys are non-invasive, surface-level measurements that pose no risk to property or water. The equipment is battery-powered and contains no chemicals, fuels, or hazardous materials. Sensors are small, temporary, and passive—they only record natural signals and do not emit anything. All work is coordinated with local, state, and federal agencies to ensure compliance with environmental protection standards.
What This Survey Does NOT Do
• No drilling
• No vibrations
• No electrical charge
• No heavy equipment
• No wildfire risk
• No noise
• No emissions
• No impact to animals