Receiver Velocity Calculation

There are two types of velocity outputs from our receiver: Doppler computed velocity and differenced carrier phase based velocity. The BESTVEL log is based on logic inside the receiver deciding which is best. Doppler velocity is computed using instantaneous Doppler frequency measurement to estimate velocity. It is phase rate; therefore it contains the velocity information. Instantaneous Doppler measurement contains 0.0 second of latency; hence there is no time interval used in this velocity computation. The latency in the Doppler velocity output is based on an analysis of the tracking loops to determine the lag inherent in the Doppler output. The latency of 0.15 for instantaneous velocity is for the tracking loops to detect and report a change in velocity. The latency value is not related to the rate of log output user requested. Differenced phase based velocity shows low latency solution since it is computed from the latest local observations and extrapolated base station observations. It uses code or carrier measurements and estimate velocity using Kalman filter. This supplies a valid velocity with the lowest latency possible at the expense of some accuracy. The latency value is related to the rate of log output user requested.