Electromagnetic signal propagation

The outcome should contribute to:

• providing a vital tactical advantage to the military performance of EU Member States and EDF associated countries (Norway) by improving the joint enhanced monitoring and situation awareness capability including with respect to stealth and hypersonic targets, the capability for stealth operations, the usage of Unmanned Aerial Vehicles and the performance of self-defence systems;
• the reduction of resources duplication and creation of collaborative long-term tactical advantages for the armed forces of EU Member States and EDF associated countries (Norway) by a reduction of the fragmentation of current methodologies;
• the overall improvement of resilience of communication methods for military and civil applications;
• supporting mission planning and strengthening hypersonic defence capabilities, amongst other through hypersonic system performance forecasting;
• the strengthening of the competitiveness of European radar and military communication industrial and technological base.

Situational awareness is one of the key elements affecting military field actions and planning. Most of the military detection and control methods are based on the use of electromagnetic (EM) radiation, either for detection and ranging, or data transfer. In the recent years, military activity has significantly increased, especially in the northern and eastern Europe and Arctic areas, where specific environment parameters prevail.

The performance of radar and communication systems depends on the characteristics of the electromagnetic signal propagation in the atmosphere. Properties of the atmosphere and the Earth’s surface may lead to situations where propagation deviates drastically from normal, leading to situations where the radars and radio communications do not function as expected, including degradation of signal quality or even loss of signal. Under anomalous propagation conditions, radars and radio communications may have unusually long range or may be unable to reach and monitor certain locations. The latter may result in targets being invisible to radars and a loss of radio communications with any object traveling into, or operated from, an area.

The reflection and ducting in the troposphere can affect a large range of frequencies from VHF (50-100MHz) to EHF (40GHz) that are relevant for radar and communication applications. Due to its relatively frequent occurrence and intermittent nature, this phenomenon can have a heavy impact on the operations of defence systems.

Therefore, there is a need for forecasts of future environmental conditions that can be used to assess and predict the propagation conditions of electromagnetic signal in different relevant wavelengths with limit estimates for expected variability. The resulting anticipation and forecasting capability of system performance would increase the situational awareness of military planners on both operational and tactical levels. It would also allow advance identification of locations and occurrences when alternative means of monitoring might be necessary.

The current openly or commercially available propagation models have limited functionality and/or accuracy, leading some nations to develop their own national propagation models tailored to national needs. The challenges are however common for all EU Member States and EDF associated countries (Norway) and require joint cross-border research as the current knowledge is fragmented, and many nations lack partly or fully the capability to address the problem. The relevant area of interest in e.g. radar surveillance for all nations stretches hundreds - or thousands of kilometres - behind the actual borders of a country, above the neighbouring countries and sea areas, thus requiring knowledge not only over a particular state, but over the whole region.

Simultaneously, new stealth capabilities, electronic counter measures or specific characteristics of new threats such as hypersonic threats, have compromised the detection capabilities of existing radars and radar networks used by all military branches. The performance of such systems must be known accurately and improved to ensure the capability to plan and conduct tactical military operations including monitoring, detecting, concealing, counter-measuring, and electronic counter-counter measuring of such threats.

Endo-atmospheric hypersonic weapons pose an entirely different challenge. Hypersonic weapons such as Hypersonic Glide Vehicles and Hypersonic Cruise Missiles are surrounded by a plasma sheath causing signal reflections to behave differently, including a distortion of radar signatures. The electromagnetic interaction with the plasma sheath, accurate models and experimental validation are not fully available up to now.

Specific objective

The main objective is to develop and test an efficient model of electromagnetic wave propagation capable of assessing and predicting EM signal propagation conditions to contribute to the creation of a tactical decision-making aid (TDA).

It is challenging to forecast and assess the prevailing environmental conditions affecting electromagnetic signal propagation, due to limited vertical resolution in the current meso-scale numerical weather prediction (NWP) models and accuracy of surface boundary condition fields. Another challenge is validating the model results. Above the ocean, where anomalous propagation conditions like ducting frequently occur, and in the Arctic areas, this is particularly challenging due to a limited number of meteorological and sea surface in-situ observations. Even more challenging is the Baltic Sea and its heterogeneous coastal environment, with low salinity creating unique reflection conditions for electromagnetic signal propagation. Current forecasting tools available to the military planners and operators are insufficient and often outdated with respect to the forecast of tropospheric ducting. In particular naval assets could benefit from a performant tool.

The rise of new, remotely controlled autonomous platforms is another rapidly developing field with strict requirements for electromagnetic data transfer. Awareness of data transfer performance will contribute to the optimisation of the usage of drone and other unmanned assets.

Additionally, another challenge arises for the detection and tracking of threats in endo-atmospheric hypersonic flight conditions. The study of plasma effects requires the definition of an aerothermodynamic model, an EM plasma model, and a radiation and scattering model. To date, this overall set of models does not possess an established validation with experiments reproducing the actual flight conditions. Such investigations can only constitute a first step to the longer-term objective to develop specific tools that ensure the best detection and tracking performance during each phase of the hypersonic flight path (i.e. long range detection for Over-the-Horizon radar, short range detection and tracking ground radar, on-board radio-frequency missile seeker) and to identify innovative sensor architectures and techniques appropriate for hypersonic threat defence.

The proposals must provide the first steps towards a joint European capability to estimate and address the impacts of anomalous atmospheric electromagnetic signal propagation on radar performance and RF communication over the ocean and ice-covered areas in and around Europe. The proposals should also address anomalous atmospheric electromagnetic signal propagation over land, over and around Europe. The proposals must consider atmospheric conditions up to 30km in height and may consider atmospheric conditions at other heights.

The proposals must aim at quantifying the frequency of occurrence and geographical extent of anomalous propagation conditions. They must address the key processes causing anomalous propagation and their occurrence.

They must also include research into a joint modular propagation model. They should improve understanding of the needs and quality requirements for in-situ instrumentation and observations of key environmental variables to support anomalous propagation forecasting.

The proposals should address the functional requirements and suggest a design for nowcasting and forecasting tools for signal propagation conditions and radar and communication performance.

The proposals must also address and aim to partially validate physical assumptions and electromagnetic signal interaction properties related to hypersonic threats, in particular related to the plasma sheath induced by hypersonic flight regime.

Types of activities

The following table lists the types of activities which are eligible for this topic, and whether they are mandatory or optional (see Article 10(3) EDF Regulation):

The proposals must cover at least the following tasks as part of the mandatory activities:

• Generating knowledge:
  • provide the state of the art on and determine the frequency and occurrence of sea (including the Baltic Sea and its heterogeneous coastal environment) and land surface ducting and anomalous signal propagation conditions in Europe;
  • provide in-situ observations and accurate information on Earth’s surface characteristics (e.g. topography, land cover and vegetation, temperature, waves, currents, evaporation, ice and snow cover), whether above the sea or land and identify and define the most efficient modelling approach(es) suited for nowcasting and forecasting electromagnetic signal propagation;
  • define a Hypersonic Glide Vehicle and Hypersonic Cruise Missile radiation and scattering model of electromagnetic signals based on an aero-thermodynamic and an electromagnetic plasma model for those threats;
  • aim at partial validation of the computational models and the underlying physical assumption (e.g. by reproducing hypersonic flight conditions in a test environment);
• Studies:
  • assess the impact on radar performance (e.g. detection performance, classification of threats, tracking…) linked to anomalous atmospheric propagation conditions, including for new threats;
• Design:
  • design the models required for nowcasting and forecasting radar and electromagnetic signal propagation;
  • conduct tests of the designed electromagnetic propagation model.

In addition, the proposals should cover the following tasks:

• Generating knowledge:
  • assess necessary requirements to establish an accurate signal propagation model over different areas, including marine environments, such as vertical and horizontal resolution requirements of NWP models, refractivity conditions and surface heterogeneity (e.g. for archipelagos, mountains, sea ice) and sea surface properties (e.g. sea surface temperature, waves, sea-ice cover);
  • investigate plasma sheath specifications for the models by estimating hypersonic threat trajectories, e.g. using Artificial Intelligence techniques or others;
  • examine the signal frequency dispersion induced by the plasma sheath;
• Integrating knowledge:
  • investigate a joint observation approach and protocols for supporting and validating the forecasting;
  • assess different options for the transfer of information on anomalous propagation condition forecast to users to adapt it to the available bandwidth;
  • examine and suggest methodologies for using multiple assets to map anomalous signal propagation, e.g. by integrated multi-type radar mapping;
  • investigate signal modulation, such as scale effect and intra-pulse Doppler signal modulation, in presence of objects with hypersonic flight trajectories;
• Design:
  • design requirements for a future joint European electromagnetic signal propagation now- and forecasting tool;
  • design requirements for an interoperable European reference observation network providing in-situ data to support electromagnetic signal propagation forecasting.

The proposals may also cover the following tasks:

• Generating knowledge:
  • identify necessary modifications and/or improvements of existing operational weather and ocean models to provide possible variable and boundary fields for assessment of electromagnetic signal propagation;
• Studies:
  • elaborate guidelines to enhance cost-efficiently the performance of existing radar networks used by all military branches in the context of anomalous atmospheric propagation conditions, including for hypersonic scenarios;
  • address the benefits of cooperative and multi-static radar architectures to enhance target detection and tracking in the context of anomalous atmospheric propagation conditions, including for hypersonic scenarios;
• Design:
  • identify the requirements for a European ducting and anomalous propagation forecast message format;
  • based on the defined models, provide recommendations on signal waveforms;
  • provide recommendations on detection, classification and tracking approaches for hypersonic threats and propose innovative solutions.

Functional requirements

The proposed technologies should meet the following functional requirements:

• be based on a solid open-source strategy, for EU Member States and EDF associated countries (Norway), that ensures the possibility to share source code, documentation and executables in accordance with the provisions and the objectives of the EDF regulation and with a licence scheme compatible with further development and commercial exploitation of the results;
• the determination of the frequency and occurrence of sea and land surface ducting and anomalous signal propagation should be based on existing military, marine and weather radars, and suitable sources of signal, e.g. AIS and radio transmitters;
• the meteorological and signal propagation observations should cover all seasons and include the following types of areas: sea surface, land surfaces with different vegetation cover types, and ice- and snow-covered areas;
• the modelling system should be applicable in varying specific circumstances, especially terrain, e.g. environment conditions like topography, surface roughness, vegetation (height and nature), urban structures, open sea or coastal conditions with varying electric conductivities, waves (height and direction), snow, ice surface conditions;
• the model should be compatible with inputs and outputs of radar performance modules and tactical decision aid (TDA) modules;
• the signal propagation modelling and in-situ observation approach(es) should be wavelength dependent and suitable for the frequency range used by the military radars and for radio communication, covering VHF to EHF (up to at least 20GHz);
• the electromagnetic signal propagation model should take into account realistic conditions, such as land, sea and hydrometeors clutter as well as thermal noise and compute signal-to-thermal noise ratio and signal-to-clutter ratios;
• the signal propagation modelling approach should make optimal use of existing operational weather and ocean models and should be compatible with operational weather and ocean models used by the national (civil / military) operational weather and ocean model service providers, if useful for efficiency gains;
• the electromagnetic signal propagation model should cover a height of at least up to 30km;
• the electromagnetic propagation model should take into account refractive conditions (i.e. modified refractivity profiles including evaporation layer), diffraction (above land and sea), multipath (above land and sea) and hydrometeor attenuation (rain, snow...);
• the electromagnetic signal propagation model should be able to support estimates of the confidence interval of detection and communication ranges, based on uncertainty of atmospheric propagation characteristics;
• should be able to ensure some level of anomalous signal propagation forecasts and nowcasts under conditions where in-situ observations are not available or are unreliable, e.g. by extrapolation of suitable data;
• accuracy, resolutions of the nowcasting and forecasting should meet or outperform the state of the art;
• execution time of the electromagnetic propagation model should be compatible with modern multi-mode radars (e.g. less than few seconds for 400x400 altitude distance spatial grid for one radar mode), even without implementation on a GPU;
• the forecasting of ducting should cover time ranges at least up to 36h;
• the nowcasting and forecasting should include estimates of the generic communication distances, surveillance radar detection ranges and confidence interval of detection and communication ranges;
• the forecasting should give predictions of changes of propagating conditions.