EM Theory

Tactically signficant objects (TSMOs) such as ships generate EM emissions from various key systems, in particular their engines. This EM wake is used to detect TSMOs at considerable distances.

EM Detection

EMDAR arrays are mounted around the vessel, detecting any EM radiation that hits them. EMDAR is a passive detection system in that it can only analyse radiation that it directly encounters, unlike a scan which can direct EM radiation towards a target to stimulate an assessable response. 

An individual EMDAR array contains different kinds of instruments for detecting EM radiation at different frequencies. An array can provide data on the approximate range of an EM radiation source by analysing dissipation patterns.

EM Bands

The EM Spectrum is divided into four bands for EMDAR purposes:

EM Bands as designated on EMDAR systems
EM Band Manifestation Frequency Wavelength
Ionising Radiation Gamma Rays, X-Rays 30PHz - 300EHz 1nm - 1pm
Ultraviolet Ultraviolet, Visible Light 300THz - 3PHz 1µm - 10nm
Infrared Infrared Light 3THz - 30THz 100µm - 10µm
Radio Microwaves, Radio Waves 3KHz - 300GHz 100km - 1mm

There is an additional band used by EMDAR system - magnetism - which is not part of the electromagnetic spectrum but is relevant (as a key output of impulse engines, for example) and is detectable by instruments included in EMDAR arrays.

System Sources

EM bands represent different source systems such as generation, propulsion or communications systems.

Ionising Range

Thought likely to be emitted by exotic propulsion systems.

UV Range

Flare of plasma exhaust from magnetoplasma engines is usually detected in the UV range.

IR Range

The IR range is potentially the most useful as it detects thermal emissions, such as from engine exhaust and thermal radiators.

Radio Range

Emissions are most likely caused by a vessel’s communications or sensor systems.

Magnetic Range

This isn’t part of the EM spectrum but strong magnetic fields can be detected by the EMDAR system. Common sources include the output of magnetoplasma impulse engines and torpedo launchers

EM Profiles

The proportions of EM output across the different bands is typically consistent for a vessel class, given common operating conditions. This can be described as an EM profile, which can be used to assess the likely class of a TSMO well before active tactical scans have been made.

Unit of Measurement

EMDAR systems measure the intensity of EM radiation, the unit of measure for which is the standard EM scalar or SEM. This is a composite unit of measurement which provides equivalence between the different units used by the EM bands EMDAR detects. The intensity of most EM radiation (the first four bands) can be measured in joules, for example, but magnetic fields (the fifth band) cannot. The composite SEM unit provides a common presentation scale for both, along with any additional detection types that might be added to EMDAR in future.

One SEM is the equivalent of an EM source of 1eV, output at 1KW, which would be detected as 1 SEM at a distance of 5000GUs.