Other Terms in Passive SE Equation
LS – Source level of tonal radiated by the target.
Le – Self Noise: noise radiated by the search platform. A function of speed and frequency.
NDI – Directivity Index: processing enhancement in signal to noise in the presence of isotropic noise. A function of frequency and bearing of the source relative to the sensor.
NRD – Recognition Differential: signal to noise ratio at the processor input required for a specified probability of detection. Typically PD = 0.5. A function of frequency.