Serious efforts are needed to manage underwater noise

By on October 8, 2022 0

Any alteration to the acoustic environment will have a significant impact on the long-term life of marine mammals. welfare. This is called acoustic habitat degradation.

The global community recently celebrated World Maritime Day on September 29. The purpose of World Maritime Day is to appreciate the importance of the maritime industry and to highlight the importance of maritime safety, maritime environment, security and shipping. This day also marks the day of the adaptation of the convention of the International Maritime Organization (IMO) in 1958 within the framework of the United Nations. The importance of the maritime industry and more particularly maritime transport, does not need to be underlined. The shipping industry is so intertwined with the growth engines of the global economy that any reform becomes a political issue.
The term “Noiseonomics” was coined by GV Frisk to describe the relationship between ambient noise levels in the sea and global economic trends. The growing awareness among stakeholders of marine eco-concerns has drawn significant attention to the subject of noise in the oceans and its impact on marine mammals from the scientific community and the general public. The two main concerns raised by Frisk are:
A: What are the historical changes in ambient noise levels on decadal time scales, and can reliable predictions be made of future changes in noise levels for decades to come?
B: What is the impact of a changing acoustic environment on the behavior of marine mammals, since they rely heavily on acoustics as their primary means of communication, navigation and foraging in the marine environment?
Marine mammals are known to depend on acoustic cues to perceive the environment around them and therefore any change in the acoustic environment will have a significant impact on their long-term well-being. This is called acoustic habitat degradation. Low-frequency ambient noise levels in the open sea are estimated to have increased by 3.3 dB per decade over the period 1950-2007. Frisk’s work attributes this increase in ambient noise levels in the ocean primarily to commercial shipping activity which is seen as the primary driver of global economic growth. As a corollary, they conclude that ambient noise levels are directly related to global economic conditions and offer models to predict future ambient noise levels based on global economic trends. Figure 1 presents the results of extensive research undertaken by GV Frisk. The trends shown in Figure 1 are alarming and serious efforts are needed to manage low frequency underwater noise from shipping.
Although belatedly, the IMO has now taken the issue of underwater noise very seriously in recent times and several countries and their researchers are pushing their noise mitigation strategies and products at an aggressive pace. As usual, crisis is also an opportunity and therefore there is intense activity to seize such an unimaginable opportunity. However, a critical appreciation of the broader dimension of the crisis has not yet been achieved. The Western-led world order always misses the demands of the rest of the world and always tries to advance its agenda. The new world order now demands a much more inclusive approach.
The question of underwater noise must be considered from a source-path-receiver model. The source is ship radiated noise which is the only pervasive source of noise in the low frequency band. Another concern from a sustainability perspective is the distribution of maritime traffic around the world with the least attenuated low-frequency noise in the underwater environment. The impact of low frequency shipping noise is observed thousands of kilometers from the source. The lack of regulatory provisions for noise control measures at source is a serious limitation. Although acoustic stealth aboard naval platforms was an important requirement and significant investments were made to manage the problem, it remained classified with the developed west as a military secret. Thus the cost of noise control has been prohibitive to the rest of the world community and there is now an attempt by the developed west to recoup its investment.

Figure 2: Map of shipping noise in the Indian Ocean Region (IOR)

The path is the modification of the noise radiated at the source, while propagating in the underwater environment. Tropical waters are known to have the greatest impact when it comes to the underwater environment and the research community globally has the least understanding of tropical conditions. Underwater research that was largely undertaken during the Cold War period focused on the temperate/polar waters of the area between Greenland, Iceland and the United Kingdom (GIUK). Distortions of radiated noise at the source in tropical waters are of the order of 60% and therefore the impact analysis at the receiver cannot ignore propagation distortions linked to the path. The space of the Indo-Pacific region is today experiencing a maximum of strategic interactions and more and more global players are maintaining their maritime assets in the region. All of the world’s maritime traffic passes through this region. The Indo-Pacific strategic space is defined as the tropical waters of the Indian Ocean and the Pacific Ocean. So how can we ignore the impact of tropical waters, simply because the West does not understand the unique characteristics of tropical waters? Put simply, it is not economically viable for the West to invest in local site-specific R&D that is unavoidable in tropical waters. The most important requirement here is that nations in the tropical region do not need to adhere to the formalized standards for the temperate/polar region and can ask for concessions. The developing world in the Indo-Pacific region, depending on its socio-economic conditions, will need more time to reach the standards set by the West.
The receiver translates vulnerable species that will ultimately be impacted by underwater noise. The impact of the acoustic degradation of the habitat must be assessed quantitatively and qualitatively, before any attempt to regulate the entire space. The entire spectrum of species, given the rich biodiversity of tropical waters, should be analyzed for their unique perception of the acoustic signal. A generic extrapolation of noise impact based on studies by Western researchers will have less relevance in tropical waters.
The Maritime Research Center (MRC), Pune has developed a digital tool to provide a real-time low-frequency ambient noise spatio-temporal map based on maritime traffic Automatic Identification System (AIS) data. Figure 2 depicts ambient low frequency noise in the Indian Ocean Region (IOR), but the tool can generate similar maps across the globe, if AIS and underwater environment parameters are provided in real time. The tool provides qualitative and quantitative analysis of acoustic habitat degradation, with a comprehensive source-path-receiver appreciation in tropical waters. Such an assessment will go a long way towards providing well-informed policy and technological intervention to manage the Sustainable Development Goals (SDG-14). As the United Nations (UN) has declared the Decade of Ocean Science for Sustainable Development, such a digital transformation will be a fundamental shift in the new world order.

Figure 3: Underwater Radiated Noise (URN) Management Framework

The proposed digital tool received worldwide recognition in 2019, for its innovative contribution to the Narwhal Challenge organized by the city of Brest in France. Subsequently, the work was presented to IMO by the Government of India, as a document at the Marine Environment Protection Committee (MEPC-76) meeting in 2021. Now IMO has come back and has requested the Indian government to be the lead country for underwater noise in the IOR.
The Undersea Domain Awareness (UDA) framework proposed by the MRC has significant relevance to ongoing geopolitical and geostrategic development globally. The UDA framework encourages pooling of resources and synergy of efforts among stakeholders. A typical example of the broader UDA framework is the management of underwater radiated noise (URN). Figure 3 shows the equivalent UDA framework for managing URNs. The prohibitive cost of acoustic capacity and capacity building can be easily offset by this approach. Multiple stakeholders can come together, particularly in developing countries, to support local experimental R&D on the ground in nearshore tropical waters. India, with its stated vision of Security and Growth for All in the Region (SAGAR), can take the lead and drive the UDA framework across the IOR. The digital transformation supported by the UDA framework can bring good maritime governance to tropical waters across the Indo-Pacific region. It will be a useful model for managing the challenges and opportunities of the tropical region.
The UDA framework is well equipped to drive the safe, secure and sustainable growth model for the entire world, given the current economic and sustainable development concerns we face. The strengthened maritime governance structure supported by the UDA framework should be a strong reason to make it an integral part of all regional and global strategic forums such as G20, Quad, IORA, etc.

Dr (Cdr) Arnab Das is the founder and director of the Maritime Research Center (MRC), Pune.