Published in Naval Forces.
Electronic support measures systems have a vital role to play in detecting hostile ships and near-surface threats like sea-skimming anti-ship missiles as they can often discern such threats at longer ranges.
The Physics Bit
This is because electronic support measures (ESM) need only detect the relatively stronger power of the pulse of radiofrequency (RF) energy transmitted by the hostile radar. A radar on the other hand must detect the much lower power echo of the pulse as it is reflected by the target back to the antenna.
For targets at the outermost reaches of the radar's range, the returned echo will be so weak that it can disappear in the prevailing electromagnetic noise constant in Earth's atmosphere. ESM systems do not have this problem as all they need to detect is the incoming radar pulse which may retain its strength beyond the radar's instrumented range.
The instrumented range is the maximum distance at which a target with the minimum radar cross-section detectable by the radar can be detected and tracked at all altitudes and speeds.