INTRODUCTION
Ever since the inception of the first radar systems, the concept of radar horizon has limited their effective detection range. Through examination of the interaction of radio waves with the Earth's atmosphere, various methods have been developed allowing for the creation of radar systems capable of limiting the radar horizon's effect on system performance. These radar systems are referred to as over the horizon (OTH) radar systems, capable of viewing targets beyond the point where the majority of modern radar systems are constrained by the radar horizon. While OTH radar systems were primarily employed for early warning purposes early in their development, current efforts have turned them into far more sinister systems.
SKY WAVE VS SURFACE WAVE
Modern OTH radar systems fall into one of two basic categories, defined by the method used to allow for detection of targets beyond the radar horizon. These categories are sky wave and surface wave radar systems. Sky wave radar systems are often more commonly referred to as OTH-B (backscatter) systems The primary drawback of an OTH-B radar is the presence of a large "blind zone", an area where the radar has no viewing capability. This is derived from the fact that the radars function by reflecting radar waves, usually in the 5 to 28 MHz frequency range, off of the Earths ionosphere. These reflected radar waves then reflect off of airborne or surface targets and travel back to the receiver. An alternative to the OTH-B method is to employ surface waves in an OTH-SW system. This eliminates the "blind zone" found in OTH-B systems. OTH-SW systems diffract radar waves around the Earth along the surface of the ocean, allowing them to travel beyond the traditional radar horizon. Both systems use advanced Doppler processing techniques to filter out surface clutter and allow for accurate target detection. By nature, OTH-SW systems must be deployed along the shoreline in order to properly operate. OTH-B systems may be deployed at any location and represent some of the largest radar structures in the world, dwarfing their surface wave counterparts and possessing greater range as a result of their increased size and power output.
COLD WAR SYSTEMS
A common use for OTH radar systems during the Cold War was for bomber and ballistic missile detection. Both the USA and the USSR fielded OTH-B radar systems used for these purposes. In the United States, the primary OTH radar was the AN/FPS-118, while the Soviet Union developed the Duga-3 (STEEL YARD) radar system. The AN/FPS-118 and Duga-3 were each deployed at two locations. Neither system remains operational.
The transmitter of the west coast AN/FPS-118 can be seen in the image below:
The receiver of the west coast AN/FPS-118 can be seen in the image below:
UNITED STATES
Present-day OTH radar development in the United States has resulted in the fielding of the AN/TPS-71 Relocatable OTH Radar. The AN/TPS-71 is an OTH-B system designed initially to support the United States Navy. It was trialled on Amchitka island in Alaska and used to monitor the eastern coast of Russia until the system was dismantled in 1993.
Currently, the AN/TPS-71 is deployed at three locations, seen in the image below, and is employed to support the counter narcotics mission.
The transmitter of the AN/TPS-71 located in Puerto Rico can be seen in the image below:
The receiver of the AN/TPS-71 located in Texas can be seen in the image below:
RUSSIA
Current Russian OTH development has tended towards radars of the OTH-SW type. Russia has been marketing the transportable IRIDA OTH-SW system since the turn of the century. This system is advertised as being a bistatic system with a range capability of 300 kilometers. A second, larger OTH-SW system has been identified near Nakhodka in the Russian Far East. While the transmitter has not yet been identified in available imagery, the linear receiver assembly can clearly be seen in the image below. This system is likely intended to monitor the Sea of Japan and may support the Russian Pacific Fleet, although open-source data regarding this system is scarce.
AUSTRALIA & FRANCE
Australia has developed and fielded a long range OTH-B system called Jindalee. Three Jindalee locations, each containing a separate transmitter and receiver station, allow coverage of the bulk of the surface and airspace surrounding northern and western Australia as part of the Jindalee Operational Radar Network, or JORN. Jindalee has a range of between 800 and 3,000 kilometers, and it has been claimed that the radar is accurate enough to show changes in an aircraft's flightpath when breaking for a landing at an airport. Australia is also actively pursuing an OTH-SW system to monitor the littoral areas along the northern coast.
The transmitter for the central Jindalee OTH-B system can be seen in the image below. The central system was used for development.
The receiver for the central Jindalee system can be seen in the image below:
France has developed the NOSTRADAMUS OTH-B system. NOSTRADAMUS has a range of between 700 and 2,000 kilometers and is unique in not featuring a bistatic layout thanks to an unorthodox star-pattern antenna layout. The trial system is currently fielded at Dreux AB.
CHINA
Sky Wave
According to a report in Jane's Defence Weekly, China has been developing an OTH-B system since 2001. The prototype system is described by the Chinese National Electronics Import & Export Corporation as having a range of between 800 and 3,000 kilometers, with azimuth coverage of 60 degrees. The system is bistatic, with separate transmitter and receiver stations separated by a distance of 100 kilometers. The former location of the prototype receiver, described by CNEIEC as being 60 meters by 1100 meters, can be seen below. The imagery, dated 7 September 2005, seems to indicate that the prototype array has been dismantled, with vegetation having taken over much of the former array's position. The prototype transmitter has not yet been identified in available imagery.
An operational version of this system has likely been fielded in the intervening years since the Jane's report first came to light. A much larger receiver has been identified in open-source imagery, located roughly 50 kilometers southwest of Xiangfan. While the corresponding transmitter has yet to be identified in available imagery, the presence of the receiver array is indicative of China's intent to proceed with an operational OTH-B system.
The Chinese OTH-B receiver array can be seen in the image below:
Performance data of the new Chinese OTH-B system is not currently available, but a very basic overview of the capability of the system can be considered by using the data from the prototype system. Considering a mimimum range of 800 kilometers and a maximum range of 3,000 kilometers, coupled with azimuth coverage of approximately 60 degrees, an operational OTH-B system would be able to scan much of the ocean from Japan to the Philippine islands.
Using the aforementioned data, a rough estimate of the viewing area of the OTH-B system can be seen in the graphic below:
Surface Wave
China has also developed an OTH-SW system. Situated along the coast 8 kilometers east of Shencheng, China's OTH-SW system is a bistatic radar employing separate transmitter and receiver elements separated by a distance of 2.65 kilometers. An overview of this facility was previously provided as the 24 October Image of the Week and is reproduced below:
Very little is known about China's OTH-SW development, so performance data is speculative at best. It is not even known whether the OTH-SW system is a prototype or an operational version. Operational status seems likely, given the placement along the Strait of Taiwan, in which case the prototype system has yet to be identified. By examining the transmitter array it appears that azimuth coverage of up to 90 degrees is possible. Russian input may have been sought in developing the OTH-SW system, given the receiver's similarity to that of the Nakhodka OTH-SW system. The Russian system is likely the more capable of the two systems, however, given that the transmitter is not located in close proximity to the receiver suggesting a system of greater power output and therefore greater range. The Russian IRIDA OTH-SW system has a quoted range of 300 kilometers. Coupling this range figure with the apparent azimuth coverage of the Chinese system, a basic picture of the minimum coverage area can be constructed and is depicted in the image below:
It should be noted that both the OTH-B and OTH-SW range estimates are likely very conservative. The operational systems are likely more powerful than either the prototype OTH-B or the Russian transportable IRIDA OTH-SW system and therefore are likely to have greater range capability than is depicted. Both operational Chinese systems should not, however, have range capabilities lesser than those which are depicted. From an analyst's perspective, the depicted figures could therefore be viewed as "best case" scenarios when planning to combat China's radar network.
THE ASBM THREAT
One potential application for China's OTH radar systems is to perform initial targeting for anti-ship ballistic missiles (ASBMs). China has developed an ASBM to counter US Navy aircraft carriers during a time of hostility. While current testing of the AEGIS system in an ABM capacity may limit the effectiveness of such a weapon in the long run, the potential for such an unorthodox method of attack does merit consideration in the minds of naval tacticians.
The DF-21C
China's weapon of choice for the ASBM role is a conventionally-armed variant of the DF-21 (CSS-5) MRBM, possibly armed with terminally-guided submunitions. The DF-21C is an 1,800 to 3,000 kilometer range weapon (depending on the source) launched from a mobile TEL, allowing the system to be field deployed to complicate preemptive targeting. The DF-21C is reported to employ terminal homing to achieve a CEP in the order of 10 meters, a level of accuracy sufficient to target a large surface vessel such as an aircraft carrier. China has been researching MaRV systems to counter foreign ABM endeavors; combining the DF-21C with a terminal-homing MaRV would provide the PLA with a weapon system possessing a reasonable chance of breaking through the AEGIS umbrella and posessing the accuracy needed to finish the job. DF-21 missiles of an unspecified variant were flight tested with decoys in 2002, a development which would further complicate an ABM engagement and lend survivability to the weapon and therefore credibility and seriousness to the threat.
Engaging a Carrier
Where do Chinese OTH systems factor into the engagement scenario for an ASBM system? A 2002 DoD report stated that China was developing OTH-B systems with the desire to employ them against aircraft carriers. The OTH-B system currently fielded certainly has the range to do so, the only problem is one of target recognition needed to place a terminally-guided DF-21C in close proximity within the MaRV's maneuver envelope. The OTH-B system as currently deployed would permit long-range acquisition of naval vessels. Target identification would be provided by Chinese-produced derivatives of Russia's Kornet EO and radar satellites, the first constellation of which is scheduled to be operational in 2009. This effectively solves the issue of OTH-B resolution, allowing the OTH-B to provide early warning while the space-based assets confirm target identification and provide positioning data for ASBM launch, being cued to potential targets by the OTH-B radar system. The advantage of a long-range ASBM system, cued by OTH-B and space-based assets is such that aircraft carriers could potentially be at risk well before their air wings are within range to strike at the Chinese mainland.
Current Chinese OTH-B and OTH-SW developments are clearly an important facet of any future conflict. Congressional officials and the Office of Naval Intelligence have described the ASBM threat in various open sources, and they are taking the threat seriously. As well they should; current developments in the field of ballistic missiles as well as increased surveillance capabilities clearly have the potential to create serious problems for a carrier strike group operating in the Western Pacific theater of operations.
CONCLUSION
Over the horizon radar systems, once a source of long range early warning for Cold War enemies, have evolved to the point that their presence on the battlefield poses a serious threat to friendly forces. While many nations have developed OTH systems for various surveillance purposes, Chinese developments in this and other fields have effectively transformed the OTH from a missile warning system to a missile targeting system.
ADDITIONAL DISCUSSION
Feel free to discuss this feature at the IMINT & Analysis Forum discussion thread found here.
GOOGLE EARTH PLACEMARK DATA
The locations and range graphics used to create this article can be downloaded as a Google Earth placemark file here; this file contains the locations of all OTH systems discussed above, including those sites not depicted.
SOURCES
-Satellite imagery provided courtesy of Google Earth
China to test air-defence radar, Jane's Defence Weekly, August 22, 2001
Over-the Horizon Radar in the HF Band, Proceedings of the IEEE, Vol. 62, No. 6, June 1974
Annual Report to Congress: Military Power of the People’s Republic of China 2008
Jane's Strategic Weapon Systems 2008
China develops anti-ship missile, Jane's Defence Weekly, January 25, 2006
NOSTRADAMUS
IRIDA OTH-SW Radar
The Market For Surface Radar Systems 2001
Nakhodka OTH Radar
OTH-SW For Australia
The AN/TPS-71
The AN/FPS-118
JORN assures early warning for Australia
NOAA OTH
China Naval Modernization: Implications for U.S. Navy Capabilities — Background and Issues for Congress
People’s Liberation Army Leverage of Foreign Technology To Achieve Advanced Military Capabilities
Ever since the inception of the first radar systems, the concept of radar horizon has limited their effective detection range. Through examination of the interaction of radio waves with the Earth's atmosphere, various methods have been developed allowing for the creation of radar systems capable of limiting the radar horizon's effect on system performance. These radar systems are referred to as over the horizon (OTH) radar systems, capable of viewing targets beyond the point where the majority of modern radar systems are constrained by the radar horizon. While OTH radar systems were primarily employed for early warning purposes early in their development, current efforts have turned them into far more sinister systems.
SKY WAVE VS SURFACE WAVE
Modern OTH radar systems fall into one of two basic categories, defined by the method used to allow for detection of targets beyond the radar horizon. These categories are sky wave and surface wave radar systems. Sky wave radar systems are often more commonly referred to as OTH-B (backscatter) systems The primary drawback of an OTH-B radar is the presence of a large "blind zone", an area where the radar has no viewing capability. This is derived from the fact that the radars function by reflecting radar waves, usually in the 5 to 28 MHz frequency range, off of the Earths ionosphere. These reflected radar waves then reflect off of airborne or surface targets and travel back to the receiver. An alternative to the OTH-B method is to employ surface waves in an OTH-SW system. This eliminates the "blind zone" found in OTH-B systems. OTH-SW systems diffract radar waves around the Earth along the surface of the ocean, allowing them to travel beyond the traditional radar horizon. Both systems use advanced Doppler processing techniques to filter out surface clutter and allow for accurate target detection. By nature, OTH-SW systems must be deployed along the shoreline in order to properly operate. OTH-B systems may be deployed at any location and represent some of the largest radar structures in the world, dwarfing their surface wave counterparts and possessing greater range as a result of their increased size and power output.
COLD WAR SYSTEMS
A common use for OTH radar systems during the Cold War was for bomber and ballistic missile detection. Both the USA and the USSR fielded OTH-B radar systems used for these purposes. In the United States, the primary OTH radar was the AN/FPS-118, while the Soviet Union developed the Duga-3 (STEEL YARD) radar system. The AN/FPS-118 and Duga-3 were each deployed at two locations. Neither system remains operational.
The transmitter of the west coast AN/FPS-118 can be seen in the image below:
The receiver of the west coast AN/FPS-118 can be seen in the image below:
UNITED STATES
Present-day OTH radar development in the United States has resulted in the fielding of the AN/TPS-71 Relocatable OTH Radar. The AN/TPS-71 is an OTH-B system designed initially to support the United States Navy. It was trialled on Amchitka island in Alaska and used to monitor the eastern coast of Russia until the system was dismantled in 1993.
Currently, the AN/TPS-71 is deployed at three locations, seen in the image below, and is employed to support the counter narcotics mission.
The transmitter of the AN/TPS-71 located in Puerto Rico can be seen in the image below:
The receiver of the AN/TPS-71 located in Texas can be seen in the image below:
RUSSIA
Current Russian OTH development has tended towards radars of the OTH-SW type. Russia has been marketing the transportable IRIDA OTH-SW system since the turn of the century. This system is advertised as being a bistatic system with a range capability of 300 kilometers. A second, larger OTH-SW system has been identified near Nakhodka in the Russian Far East. While the transmitter has not yet been identified in available imagery, the linear receiver assembly can clearly be seen in the image below. This system is likely intended to monitor the Sea of Japan and may support the Russian Pacific Fleet, although open-source data regarding this system is scarce.
AUSTRALIA & FRANCE
Australia has developed and fielded a long range OTH-B system called Jindalee. Three Jindalee locations, each containing a separate transmitter and receiver station, allow coverage of the bulk of the surface and airspace surrounding northern and western Australia as part of the Jindalee Operational Radar Network, or JORN. Jindalee has a range of between 800 and 3,000 kilometers, and it has been claimed that the radar is accurate enough to show changes in an aircraft's flightpath when breaking for a landing at an airport. Australia is also actively pursuing an OTH-SW system to monitor the littoral areas along the northern coast.
The transmitter for the central Jindalee OTH-B system can be seen in the image below. The central system was used for development.
The receiver for the central Jindalee system can be seen in the image below:
France has developed the NOSTRADAMUS OTH-B system. NOSTRADAMUS has a range of between 700 and 2,000 kilometers and is unique in not featuring a bistatic layout thanks to an unorthodox star-pattern antenna layout. The trial system is currently fielded at Dreux AB.
CHINA
Sky Wave
According to a report in Jane's Defence Weekly, China has been developing an OTH-B system since 2001. The prototype system is described by the Chinese National Electronics Import & Export Corporation as having a range of between 800 and 3,000 kilometers, with azimuth coverage of 60 degrees. The system is bistatic, with separate transmitter and receiver stations separated by a distance of 100 kilometers. The former location of the prototype receiver, described by CNEIEC as being 60 meters by 1100 meters, can be seen below. The imagery, dated 7 September 2005, seems to indicate that the prototype array has been dismantled, with vegetation having taken over much of the former array's position. The prototype transmitter has not yet been identified in available imagery.
An operational version of this system has likely been fielded in the intervening years since the Jane's report first came to light. A much larger receiver has been identified in open-source imagery, located roughly 50 kilometers southwest of Xiangfan. While the corresponding transmitter has yet to be identified in available imagery, the presence of the receiver array is indicative of China's intent to proceed with an operational OTH-B system.
The Chinese OTH-B receiver array can be seen in the image below:
Performance data of the new Chinese OTH-B system is not currently available, but a very basic overview of the capability of the system can be considered by using the data from the prototype system. Considering a mimimum range of 800 kilometers and a maximum range of 3,000 kilometers, coupled with azimuth coverage of approximately 60 degrees, an operational OTH-B system would be able to scan much of the ocean from Japan to the Philippine islands.
Using the aforementioned data, a rough estimate of the viewing area of the OTH-B system can be seen in the graphic below:
Surface Wave
China has also developed an OTH-SW system. Situated along the coast 8 kilometers east of Shencheng, China's OTH-SW system is a bistatic radar employing separate transmitter and receiver elements separated by a distance of 2.65 kilometers. An overview of this facility was previously provided as the 24 October Image of the Week and is reproduced below:
Very little is known about China's OTH-SW development, so performance data is speculative at best. It is not even known whether the OTH-SW system is a prototype or an operational version. Operational status seems likely, given the placement along the Strait of Taiwan, in which case the prototype system has yet to be identified. By examining the transmitter array it appears that azimuth coverage of up to 90 degrees is possible. Russian input may have been sought in developing the OTH-SW system, given the receiver's similarity to that of the Nakhodka OTH-SW system. The Russian system is likely the more capable of the two systems, however, given that the transmitter is not located in close proximity to the receiver suggesting a system of greater power output and therefore greater range. The Russian IRIDA OTH-SW system has a quoted range of 300 kilometers. Coupling this range figure with the apparent azimuth coverage of the Chinese system, a basic picture of the minimum coverage area can be constructed and is depicted in the image below:
It should be noted that both the OTH-B and OTH-SW range estimates are likely very conservative. The operational systems are likely more powerful than either the prototype OTH-B or the Russian transportable IRIDA OTH-SW system and therefore are likely to have greater range capability than is depicted. Both operational Chinese systems should not, however, have range capabilities lesser than those which are depicted. From an analyst's perspective, the depicted figures could therefore be viewed as "best case" scenarios when planning to combat China's radar network.
THE ASBM THREAT
One potential application for China's OTH radar systems is to perform initial targeting for anti-ship ballistic missiles (ASBMs). China has developed an ASBM to counter US Navy aircraft carriers during a time of hostility. While current testing of the AEGIS system in an ABM capacity may limit the effectiveness of such a weapon in the long run, the potential for such an unorthodox method of attack does merit consideration in the minds of naval tacticians.
The DF-21C
China's weapon of choice for the ASBM role is a conventionally-armed variant of the DF-21 (CSS-5) MRBM, possibly armed with terminally-guided submunitions. The DF-21C is an 1,800 to 3,000 kilometer range weapon (depending on the source) launched from a mobile TEL, allowing the system to be field deployed to complicate preemptive targeting. The DF-21C is reported to employ terminal homing to achieve a CEP in the order of 10 meters, a level of accuracy sufficient to target a large surface vessel such as an aircraft carrier. China has been researching MaRV systems to counter foreign ABM endeavors; combining the DF-21C with a terminal-homing MaRV would provide the PLA with a weapon system possessing a reasonable chance of breaking through the AEGIS umbrella and posessing the accuracy needed to finish the job. DF-21 missiles of an unspecified variant were flight tested with decoys in 2002, a development which would further complicate an ABM engagement and lend survivability to the weapon and therefore credibility and seriousness to the threat.
Engaging a Carrier
Where do Chinese OTH systems factor into the engagement scenario for an ASBM system? A 2002 DoD report stated that China was developing OTH-B systems with the desire to employ them against aircraft carriers. The OTH-B system currently fielded certainly has the range to do so, the only problem is one of target recognition needed to place a terminally-guided DF-21C in close proximity within the MaRV's maneuver envelope. The OTH-B system as currently deployed would permit long-range acquisition of naval vessels. Target identification would be provided by Chinese-produced derivatives of Russia's Kornet EO and radar satellites, the first constellation of which is scheduled to be operational in 2009. This effectively solves the issue of OTH-B resolution, allowing the OTH-B to provide early warning while the space-based assets confirm target identification and provide positioning data for ASBM launch, being cued to potential targets by the OTH-B radar system. The advantage of a long-range ASBM system, cued by OTH-B and space-based assets is such that aircraft carriers could potentially be at risk well before their air wings are within range to strike at the Chinese mainland.
Current Chinese OTH-B and OTH-SW developments are clearly an important facet of any future conflict. Congressional officials and the Office of Naval Intelligence have described the ASBM threat in various open sources, and they are taking the threat seriously. As well they should; current developments in the field of ballistic missiles as well as increased surveillance capabilities clearly have the potential to create serious problems for a carrier strike group operating in the Western Pacific theater of operations.
CONCLUSION
Over the horizon radar systems, once a source of long range early warning for Cold War enemies, have evolved to the point that their presence on the battlefield poses a serious threat to friendly forces. While many nations have developed OTH systems for various surveillance purposes, Chinese developments in this and other fields have effectively transformed the OTH from a missile warning system to a missile targeting system.
ADDITIONAL DISCUSSION
Feel free to discuss this feature at the IMINT & Analysis Forum discussion thread found here.
GOOGLE EARTH PLACEMARK DATA
The locations and range graphics used to create this article can be downloaded as a Google Earth placemark file here; this file contains the locations of all OTH systems discussed above, including those sites not depicted.
SOURCES
-Satellite imagery provided courtesy of Google Earth
China to test air-defence radar, Jane's Defence Weekly, August 22, 2001
Over-the Horizon Radar in the HF Band, Proceedings of the IEEE, Vol. 62, No. 6, June 1974
Annual Report to Congress: Military Power of the People’s Republic of China 2008
Jane's Strategic Weapon Systems 2008
China develops anti-ship missile, Jane's Defence Weekly, January 25, 2006
NOSTRADAMUS
IRIDA OTH-SW Radar
The Market For Surface Radar Systems 2001
Nakhodka OTH Radar
OTH-SW For Australia
The AN/TPS-71
The AN/FPS-118
JORN assures early warning for Australia
NOAA OTH
China Naval Modernization: Implications for U.S. Navy Capabilities — Background and Issues for Congress
People’s Liberation Army Leverage of Foreign Technology To Achieve Advanced Military Capabilities
4 comments:
great work Sean.
Thanks. I intended it to be an overview of worldwide OTH systems, but decided later to reduce the emphasis on most of the systems out there and severely cut back the Cold War bit to focus more on the Chinese ASBM aspect.
Hi Sean,
Congrats from Hungary!
You may add this as well:
http://maps.google.com/maps?t=h&hl=en&ie=UTF8&ll=34.619603,32.945509&spn=0.006348,0.009613&z=17
Gabor
Hi Sean,
Very interesting. However there is one Chinese facility not on your list. Check out these GE coords:
40°30'4.64"N 116° 1'46.59"E
Interestingly the snow covered ground image that really highlights the antenna field is not available in the History layer. I added a placemark last year that included an image. The image was removed from the place mark as well. However go to the thread associated with the placemark and download kmz file. Check out this GE community thread:
http://bbs.keyhole.com/ubb/ubbthreads.php?ubb=showflat&Number=1142078&site_id=1#import
Here is the the kmz file:
1142078-ChineseHFRadar.kmz
You make me wonder if my place mark may be a transmit only site abd it could be tied to the receive site you identified. That could be one of three since a linear array typically only has 60 degrees in azimuth coverage. I'd like to know the site coordinates.
In my kmz file I show two semicirclular antenna arrays with the same orientation though one is broken into pieces while the other is a complete semicircle. One could be for transmit and the other for receive (see the text). On the other hand they could both be transmit sites with different operating characteristics and tied to a distant receive site. Improving accuracy with better signal processing makes me wonder about a dual transmission antenna capability for frequency, polarization, and/or space diversity as a means to improve accuracy - thus the two arcs. Alternatively, maybe you identified a transmit site and the facility I've placemarked is the receive site. This assumes that the two facilities are connected of course.
Regardless, its clear the Chinese have an active interest in HF radar sytems. Oh, BTW check out this curiosity at:
23°19'36.81"N 113° 5'6.72"E
Looks like a CDAA HF DF Site. But its the only one like it I've found. And I have no idea if in fact its that or something completely different.
satcom15
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