Timeofarrival

Timeofarrival, often written "time of arrival" and abbreviated TOA, refers to the recorded or computed instant at which a signal, particle, object, or wavefront reaches a detector, receiver, or target location. In practice it is the difference between an emission or event time and the observed reception time, and it is commonly used to infer distance, speed, or location when the propagation speed is known.

Measurement of timeofarrival is central to fields such as telecommunications, radar and sonar, global navigation satellite systems (GNSS), seismology, medical imaging (ultrasound), and particle physics. Techniques include direct timestamping with synchronized clocks, time-difference-of-arrival (TDOA) methods that use relative measurements among multiple sensors, and time-of-flight (TOF) measurements that infer travel time between known points.

Accuracy of timeofarrival estimates depends on clock synchronization, signal bandwidth, signal-to-noise ratio, multipath propagation, and sampling resolution. Systematic biases and random errors can degrade position or timing solutions; mitigation strategies include calibration, filtering, and use of redundant measurements. Units are typically seconds or submultiples thereof, with precision requirements ranging from microseconds or nanoseconds in communications and navigation to milliseconds in some acoustic applications.

The concept is closely related to, but distinct from, arrival time distributions in statistics and from event timing in time-series analysis; terminology and methods vary by discipline.