CESMO Steps Forward

CESMO Plotted Radar Bearings
This map depicts how bearings from disparate ESMs and RWRs can be used to plot where a hostile radar is located, with the emitter being at the point where these blue lines meet.

NATO’s Cooperative Electronic Support Measure electronic warfare datalink protocol, better known as CESMO, is being enhanced with new capabilities.

The North Atlantic Treaty Organisation’s (NATO’s) CESMO datalink protocol helps aircraft share hostile emitter location information so these can be avoided or engaged. Military aircraft are routinely equipped with Radar Warning Receivers (RWRs) and Electronic Support Measures (ESMs). These protect aircraft by detecting, identifying and locating hostile radars. Ostensibly, these are used at the tactical level as part of an aircraft’s integrated self-defence system. An RWR tends to give aircrew a relatively simple alert and warning function giving details of a radar’s bearing relative to the aircraft. An ESM will tend to supply more detailed information on the radar’s identity and location. The ESM will also furnish specifics on the waveforms the radar is using although, to an extent, RWR and ESM functions overlap.

Modus Operandi

RWRs and ESMs can use two mechanisms to detect and locate red force radars, chiefly Angle-Of-Arrival (AOA) and Time of Arrival (TOA). AOA determines the Line-of-Bearing (LOB) from on point to another, in this case an aircraft and a hostile radar. Consider three aircraft flying in the vicinity of a ground-based air surveillance radar. One aircraft is flying towards the radar on a north-south bearing, the second is flying on an east-west radial away from it and the third is flying on a south-north bearing towards it. Each aircraft is equipped with an RWR which determines the radar’s LOB relative to the aircraft. All three aircraft detect the same radar transmission. The RWR on the first aircraft determines a southern LOB to the radar. The RWR on the second determines a westerly LOB to the radar while the RWR on the third aircraft determines a northerly LOB. By using this information, one determines the radar’s position as the point where all three bearings meet.

TOA works slightly differently. We will stick with our three aircraft, all of which are continuing to fly the same courses in the vicinity of the hostile radar. One aircraft is 100 nautical miles/nm (185.2 kilometres/km) from the radar flying on north-south bearing towards it. The second is 150nm (277.8km) from the radar flying away on an east-west radial. The third is 50nm (92.6km) flying on a south-north bearing towards it. Triangulation relies on the fact that radar transmissions travel at the speed of light; 161,595 nautical miles-per-second (299,274 kilometres-per-second).

Radar transmissions will take a different amount of time to reach each aircraft’s RWR. For the first aircraft it will take the transmissions 0.6 milliseconds to reach the plane. For the second it will take 0.9 milliseconds and for the third 0.1 milliseconds. By calculating the difference in time it takes radar transmissions to reach each aircraft relative to their position computes the radar’s position.

This data is fused with the aircraft’s position as derived from its navigation equipment and sent from each aircraft across their standard communications links to a central computer housing the CESMO software. Once the data arrives, CESMO computes the point where the LOBs from each RWR meet based on the aircraft’s position which will be where the radar is located. The cool thing about CESMO is that it employs Electronic Intelligence (ELINT) from RWRs and ESMs already on the aircraft.

Once the CESMO software ascertains the radar’s location it will retransmit this to other friendly aircraft at risk of detection from that radar. The radar can then be avoided, or engaged with kinetic, electronic and/or cyberattack. CESMO information is sent back out across the same standard communications links. CESMO data is carried across standard very/ultra-high frequency (30 megahertz to three gigahertz) links and tactical datalinks like NATO’s Link-16. Traffic is carried in IP (Internet Protocol) format messages absorbing under 16 kilobits-per-second of bandwidth. Furthermore, CESMO is a node-less network as there is no single, central point of control. Should one platform sharing its ELINT be lost this will not cause the loss of the CESMO network or its data.

New Message Formats

New information regarding CESMO came to light during the 2023 Association of Old Crows’ Electronic Warfare Europe conference, held in Bonn, western Germany between 15th and 17th May. Delegates were told that new messaging standards were in development to expand CESMO’s functionality. Plans are afoot to widen the remit of the data shared across a CESMO network. This will include the adoption of new message formats covering electronic attack and Emission Control (EMCON) information. Tactical messages could be carried by the network with information on how an emitter is to be engaged. Similarly, EMCON messages could be shared on frequencies off limits for electronic attack. NATO sources close to CESMO told delegates that these messaging standards could be available in circa twelve months.

Making Space

These new message formats will expand CESMO’s capabilities yet further while alleviating the EW burden on other networks. Link-16 remains the standard track and tactical information TDL used by NATO and allied nations for air operations. It handles tactical EW traffic, typically the J14 and J14.0 series messages. These messages share emitter parametric information and EW control coordination respectively. Parametric information relates to the characteristics of radar emissions in the locale of the operation. However, Link-16 is not designed exclusively to handle EW information. CESMO, on the other hand, is. Offloading some of Link-16’s EW burden onto CESMO frees up space on the former which is always in high demand during air operations. Something which can only be good thing.

by Dr. Thomas Withington

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