Lorenzo Scala, Marine Mammal & Offshore Technical Lead at Seiche, authored this article, and all views expressed reflect Seiche’s professional expertise in offshore acoustic monitoring and mitigation. This publication supports the MMOAs 2026 strategy to Support Professional Development, helping practitioners strengthen their skills and industry knowledge.
What is PAM?
Passive Acoustic Monitoring (PAM) has become an essential tool in the suite of technologies and methods available for marine mammal mitigation and monitoring. PAM is a common means of detecting vocalising marine mammals, enabling continuous, autonomous data collection and providing an opportunity for detection of deep-diving and cryptic species. There is an increasing need to monitor and report marine mammal baseline information, particularly offshore. This is important for environmental impact assessment (EIA) and mitigation of disturbance from human activities.
Two broad aspects of PAM for marine mammals in the offshore industry are real-time mitigation and baseline monitoring. Real-time mitigation, uses arrays of hydrophones deployed from an offshore survey vessel or construction platform. The hydrophone array is typically cabled to a monitoring station housing PAM electronics, which process the incoming acoustic signals through a series of data acquisition units and output to real-time processing and monitoring software.
Baseline PAM monitoring provides information on temporal variation in species occurrence, distribution, and density. These data feed into population‑level impact assessments for offshore industry activities. Such information is requested as part of the EIA approvals process for consenting of offshore infrastructure construction activities, such as offshore wind farm development. For long-term monitoring programmes, fixed or static PAM devices are deployed on seafloor mounted moorings in carefully designed arrays or nodes across the area or region of study.
Static PAM moorings typically consist of single, or multi-channel autonomous recording units (ARUs) configured to record at an appropriate sample rate and duty cycle to enable monitoring of marine mammals on deployments of up to several months. ARUs process acoustic signals and archive the data as a series of timestamped sound files (.wav) to micro-SD cards which are extracted and replaced periodically during mooring service visits. ARU data is processed and analysed offline using a suite of acoustic analysis software. Baseline monitoring programmes for marine mammals can last for several years and may be designed to capture monitoring periods pre, during and post construction of offshore developments to enable assessment of behavioural impacts at population level in response to offshore construction.
There is a large scope for innovation within PAM technology, including variations in real-time and offline/autonomous data collection. Technologies may range from remotely monitored real-time PAM systems to automated or AI driven classifier enabled monitoring systems, multi-channel seabed mounted lander systems, portable light-weight PAM devices for small vessel offshore operations, or long-term continuous monitoring PAM buoys with satellite data transmission.
The role of the PAM Operator in industry primarily relates to mitigation activities, requiring the real-time detection, classification and localisation of marine mammals from their vocalisations within the context of an exclusion zone surrounding an industrial noise source, such as a seismic source array used in geophysical exploration, or impact pile driving during the installation of offshore wind turbine foundation monopiles. In the UK, MMOs are required to undergo formal mitigation training by a Joint Nature Conservation Committee (JNCC) approved provider. In addition, PAM training courses are designed to deliver the fundamentals of underwater sound theory, PAM requirements for mitigation activities, practical training on the setup, configuration and maintenance of PAM hardware and training on PAM software and its application for mitigation monitoring. Following completion of formal training, the PAM Operator is then deemed qualified to engage in PAM roles within industry and must apply their knowledge of PAM in the context of offshore operations to provide concise advice and reporting on compliance with mitigation protocols and guidelines. Newly trained PAM Operators are typically paired with more experienced colleagues with the aim of progressing their skills and experience in deployment/recovery of PAM equipment from various vessel and offshore installation types and honing their confidence and skills to improve competency in the role.
PAM Limitations
PAM, while highly effective for detecting vocalising marine mammals, has several inherent limitations that must be considered during mitigation and baseline monitoring. PAM can only detect animals that are actively vocalising, meaning silent or low‑vocalising species may go unnoticed, and high levels of environmental noise from vessels, weather or industrial activity can mask calls and reduce detection ranges. Acoustic propagation is also influenced by local oceanographic conditions, creating variability in how far signals travel and potentially resulting in shadow zones. Species identification can be challenging where vocalisations overlap, and localisation accuracy may be reduced in shallow or noisy environments or when using single‑element systems. Additionally, non‑vocal species remain undetectable, and equipment performance can be affected by deployment constraints such as cable noise, flow noise, hydrophone depth and vessel motion. These factors highlight the importance of integrating PAM with other monitoring methods and ensuring operators understand the system’s capabilities and limitations.
Seiche
Seiche is the world’s leading producer and supplier of PAM systems for offshore industry, with over 500,000 recorded days at sea. Seiche offers modular and portable PAM systems suitable for both towed and static deployments. Their systems are commonly used in offshore operations such as geophysical surveying, pile driving and unexploded ordnance (UXO) clearance operations.
TOWED PAM SYSTEM
Extensively used throughout the world, the Seiche Towed PAM System is robust, reliable and available at short notice with either 4 or 6 hydrophone arrays. The system is available in a number of configurations and is supported by PAMGuard software. Variations of the standard PAM systems include local remote monitored systems (LMS), and specialised modular array designs tailored to meet the requirements of regulators globally.
VERTICAL PAM
The Seiche vertically deployed PAM system provides a simple and flexible approach suited to static operations such as oil rig Vertical Seismic Profiling (VSP) and offshore wind farm construction works. It is designed to be lightweight and easy to transport, including by helicopter.
REMOTELY MONITORED PAM
Seiche has pioneered the use of satellite technology to transmit PAM signals from a vessel anywhere in the world to a shore base. PAM Operators listen to the live audio feed from Seiche headquarters (HQ) or dedicated centres. 24/7 flexibility allows mitigation support to on-board operators.
DIGITAL HYDROPHONE
This new generation of digital hydrophone improves signal to noise ratio and enables advanced array control through real-time configuration of gain and filters.
MICROPAM
A full PAM monitoring and mitigation system in a small, highly portable package. It is designed for use in tough marine environments and may be used as an autonomous sound recorder or linked to a laptop computer for real-time monitoring.
ARRAY FOR AUTONOMOUS VEHICLES
A high-performance, miniaturised underwater acoustic measurement device for static and low-speed towed monitoring applications. This array can be tailored to individual requirements and deployed as a cost-effective method of offshore monitoring.
PAM GO
A lightweight, portable and ruggedised PAM system for use on small vessels for mitigation monitoring. The system comprises pelicase mounted PAM electronics with a lightweight hydrophone array cable. The system connects over Wi-Fi to a rugged tablet display to enable real-time monitoring. The PAM Go is ideal for fast rescue craft (FRC) deployment during UXO clearance operations.
REAL-TIME SOUND MEASUREMENT (RT-SM) BUOY
The RT-SM buoy is designed and built for deployment on offshore sites to provide autonomous measurement of underwater noise from impulsive sources, such as pile driving. Noise measurements are processed on board the recording system and transmitted to a dedicated and secure web portal over iridium satellite, providing near real-time monitoring to facilitate underwater noise management for offshore operators.
SEICHE TRAINING & SUPPORT
Seiche offers PAM level 1 (fundamentals) and level 2 (advanced) training courses throughout the year at their facility in Devon, and other locations around the world by arrangement. Seiche prides itself on the reputation of its highly skilled PAM experts and is equipped with a support service for PAM Operators using Seiche technology in the field. All Seiche systems are accompanied by extensive help files, tutorials and customised standard PAMGuard configuration files, including test files to assist with system setup. Seiche also provides specialist offshore technicians at client request for complex installations to ensure standardised setup and operation of monitoring equipment. In addition, all Seiche PAM systems are supplied with 100% redundancy and undergo extensive in-house servicing and testing prior to project mobilisation.
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