China's SeaWeb Undersea Surveillance Network

The HQ of each of the Chinese Peoples Liberation Army - Navy (PLAN's) Fleets are indicated, along with ship and submarine numbers in each. The undersea surveillance network particularly protects major ports - with (perhaps top) priority for China's 4 Yulin-Sanya (Hainan Island) based SSBNs (South Sea Fleet).  (Map courtesy US Department of Defense, Annual Report to Congress - Chinese Military Power 2016 on page 29)
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The following description of China's SeaWeb undersea sensor network is based on Prasun K. Sengupta's TRISHUL website article of April 15, 2016 which reported on DEFEXPO INDIA 2016 (March 28 -31, 2016). It indicates that China has developed/deployed its SeaWeb sensors relatively late compared to other major powers (eg. noting the UK's successful use of sensors, at Scapa Flow naval base in 1918).

China may give priority to sensor protection of naval bases and then seas in the following order: Bohai Sea, Yellow Sea, East China Sea and then South China Sea. Proximity of seas to Beijing may be one criterion. Officials and politicians in Beijing would be concerned about sub launched missile range to Beijing - this includes SSK launched cruise missiles. Also the smaller the sea (smaller in the north) the faster that sea can be "sown" with sensors by Chinese forces.

"China’s Undersea Trip-Wire

The PLAN’s seabed-based surveillance network, developed jointly by Ukraine [some current Russian, some ex-Russian Ukrainian interests] and China since 1996, has been under installation along China's territorial waters since 2012, with work expected to be completed later this [in 2016].

The seabed-based component of this network comprises arrays of hydrophones and magnetic anomaly detectors spaced along undersea cables laid at the axis of deep sound-channels roughly [“normal” orientated] to the direction that the arrays are to listen. This capability is next paired with maritime reconnaissance/ASW aircraft assets to establish a multi-tier ASW network. The first naval bases to be covered by this network were the PLAN’s submarine bases in four sites:

1.  the Bohai shipyard at Huludao on the Bohai Sea [Huludao is about 400 km east of Beijing] where all nuclear-powered submarines are built;

2.  the North Sea Fleet’s Xiaopingdao naval refit base near Dalian [see Dalian in map at bottom]  where the SSBNs are fitted out for SLBM test-firings from the Bohai Sea across China into Delingha in the Qinghai desert and the desert of Lop Nor in Xinjiang;

3.  the North Sea Fleet’s base at Jianggezhuang (Laoshan) approximately 18km east of Qingdao in Shandong Province;

4.  and the South Sea Fleet’s bases at Longpo and Yulin at Yalong Bay near Sanya on the southern tip of Hainan Island.

Elements of PLAN's undersea sensor network. The sensors can be tethered or sit on the seafloor to track a submarine, a UUV's or Diver Delivery Vehicle's presence, direction and speed. The sensors can then surface or remain submerged when alerting other submerged or onshore communications nodes including (in wartime) missile batteries. (see more readable large image)

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As far back as 2001, a researcher at the PLAN’s Institute 715 had published a survey of ocean surveillance technologies that included a detailed discussion of the US SOSUS programme....Another analysis by several PLAN researchers in late 2012 discussed this station and military applications for its seabed-based sensors, alongside civilian uses, including environmental protection, navigation, and disaster prevention.

The analysis compared different configurations for seabed-based sensor networks, including linear, circular, and tree-type designs, and also evaluating their respective cost, security and reliability implications. It also mentioned the Xiaoqushan Station as the basis for a larger ‘East Sea Ocean Floor Sensor Network’ that will be completed by 2016. The analysis also mentioned undersea mobile sensor stations, as well as fixed seabed sensors.

China is not only deploying sensors for surveillance but, in wartime, as triggers for explosive  destruction of unwelcome submarines. Once definitely detected China could send warheads small torpedos carried by cruise missiles, subrocs, aircraft or charges from mines (tethered, seafloor or mobile). More see Submaine Matters March 2016 article. 

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In early 2013, China Science Daily’s March 26 edition opted to go public with the system by publishing a feature with the banner headline: “Here They Are Quietly Listening to the Ocean: The Whole Story of the Building of Our Country’s First Deep Sea Ocean Floor Sensor Network Base”. According to this article, R & D efforts had commenced in 1996 and an initial prototype of the seabed-based sensor system was tested back in 2005 in the waters surrounding the PLAN’s base at Qingdao in Shandong Province. 

An additional site was selected for the Longpo naval base, and work formally commenced there in April 2009. Initial set-up was completed in 2010. The undersea-sensor system has since been integrated with a larger surveillance network that also has airborne and space-based components. Two articles appearing in mid-2013 in the technical journal Ship Electronic Engineering, confirmed that this network was now at an active deployment stage. One article discussed the technical challenge of energy supply by proposing a low-power ‘sleep-wake mode’, and mentioned the interesting additional problem that a country’s undersea sensors are subject to being captured by an adversary. Another article discussed the importance of advances in ‘burst communications’ for enhancing the military value of the seabed-based sensor network. A mid-2012 analysis in the naval magazine Modern Ships unequivocally confirmed the existence of PLAN’s network of seabed-based sensors.

The cover-story of a second quasi-official naval journal, Naval & Merchant Ships from mid-2013, similarly showed an acute PLAN sensitivity to its perceived vulnerability to Western and Japanese submarines. The central concern shown there was protecting the PLAN’s SSBNs, while the main threat vector mentioned was the USN.

(Map courtesy photos4travel)
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Pete