Passive Hemispherical Sensing

ComNavOps has long called for greatly enhanced emphasis on passive detection, tracking, and fire control for ships.  The benefits of passive sensing are blindingly obvious (the enemy can’t detect you from your emissions because there aren’t any and homing weapons have nothing to home on), however, there are equally obvious drawbacks to the system such as weather effects and difficulty automating the real time image analysis.
 
Radar provides 360 degree hemispherical sensing so, to be useful, a passive sensing system should be capable of the same.  For passive sensors, this would, currently, consist of several sensors distributed around the ship to provide complete coverage (and, one would hope, redundancy in the event of battle damage!).
 
The need for a hemispherical passive sensing system has been obvious for a couple of decades, at least.  The F-14 Tomcat, among other aircraft, had long range passive sensors so it’s not as if the need and the technology haven’t existed for many, many years.  Despite this, the Navy has made no real effort to develop full passive systems.
 
Finally, however, it now appears that the Navy has opted to move forward with a hemispherical EO/IR system, the L3 SPEIR/SPATIAL system.
 
From a Navy contract award announcement,
 

L3 Technologies Inc., Systems Company, Camden, New Jersey, is awarded a $205,899,580 cost-plus-incentive-fee, cost-reimbursement, firm-fixed-price, cost-plus-fixed-fee, and fixed-price incentive (firm target) contract for engineering, manufacturing, and development; engineering support labor; low rate initial production systems, and spares for the Shipboard Panoramic Electro-Optic/Infrared (SPEIR) program.

A Naval News website offers a brief description of the SPATIAL system which meets the SPEIR system requirements:
 

Above decks, the SPATIAL system has been designed around two separate camera systems and associated mountings. The ‘staring’ WFOV [Wide Field of View] system uses three mid-wave infrared cameras and three colour visible cameras mounted on a single three-axis stabilised [sic] pedestal. Each ship fit will comprise a minimum of two WFOV pedestals, the exact number being dependent on the vessel size and ship fitting constraints.
 
The NFOV [Narrow Field of View] camera system, which will slew to cues, has three different payloads – a mid-wave imager, a colour visible camera and a laser rangefinder. Again, there will be a number of NFOV systems on each ship.[1]

WFOV on the left and NFOV on the right

 
It is unknown to what degree the passive system will be integrated into the ship’s combat suite software, if at all.  For example, EO/IR detectors have been fairly standard equipment on Navy ships for some time but have been limited to isolated, limited tasks (for example, optical fire control for a single gun) rather than main ship’s sensing responsibilities.  Hopefully, this signals the attempt to establish complete hemispherical passive sensing capability.
 
In addition to the previously mentioned, obvious benefits, there are others:
 
Cost.  Passive sensors are hugely cheaper than radar systems.
 
Complexity.  Passive sensors are infinitely simpler than radar systems which makes them easier to maintain and repair/replace in the event of battle damage.
 
Weight/Volume.  Passive systems are far smaller and lighter than radar systems which helps with ship’s topweight, stability, internal volume, and so forth.
 
Power.  Being passive, very little power is required relative to radars which have enormous electrical requirements to power their emissions.
 
Stealth.  Passive systems are unaffected by radar stealth with consistent reports that optical systems can detect stealth aircraft at great distances.
 
 
 
Issues:
 
Range.  Radars, depending on type and power can provide detection from several miles out to a hundred miles or more, depending on target size and type.  It is unknown what effective range a passive sensor can reliably achieve.  As one interesting data point, F-14 Tomcat electro-optical camera systems were claimed to be able to detect bomber size aircraft out to 70-100 miles.
 
Automation.  Radars offer largely automated detection of targets which is a great benefit to the operator. In contrast, a small boat or drone appearing and disappearing in waves is a very difficult target to detect by eye and even harder to detect via real time, automated image analysis.  Without reliable automated detection, passive systems will be reliant on operator alertness and, therefore, much less reliable.  This is a software development effort whose status is unknown.  Manufacturer claims are, as always, unreliable and nearly worthless.
 
Protection.  Current passive systems on ships are mounted in the open, unprotected from even simple shrapnel.  If passive sensors are to be utilized in combat, they must be armored and highly redundant.
 
Integration.  Ship combat systems integrate sensors and weapons.  To the best of my knowledge, there is no comprehensive, passive sensor based, ship combat system.  One would need to be developed and, as we have repeatedly seen, large, complex software development efforts are problematic in the extreme.
 
 
 
The potential benefits of a passive, main sensing system are enormous, however, the drawbacks and challenges are equally enormous.  Still, given the role of stealth and the difficulty in countering radar stealth makes the effort to develop a full passive system well worth the effort.
 

 
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[1]Naval News website, “SPEIR To Improve Passive Situational Awareness And Ship Self-Defense”, Richard Scott, 11-Jan-2023,
https://www.navalnews.com/event-news/sna-2023/2023/01/speir-to-improve-passive-situational-awareness-and-ship-self-defense/