Velocity

Velocity Determined from GNSS Measurements:

Instantaneous Doppler Velocity

Velocity estimated from instantaneous Doppler frequency measurements. As a Doppler frequency measurement is phase rate, no averaging time interval is used in this type of velocity estimation. The latency in the Doppler velocity output is based on an analysis of the receiver's tracking loops to determine the lag inherent in the Doppler measurement.

Instantaneous Doppler velocity has low latency associated with the measurement and is suited for high dynamic applications where the velocity of an object changes quickly but is noisier than other velocity determination methods.

Successive Position Averaged Velocity (available in RTK or L-Band enabled models only)

Average velocities are computed from the average change in position over a set time interval or extracted from a low latency positioning filter. As such, it is an average velocity based on the time difference between successive position computations and not an instantaneous velocity tagged at a particular time.

The velocity latency to be subtracted from the time tag is normally half the time between filter updates. For example, a logging rate of 10 Hz would translate into a velocity latency of 0.05 seconds. The latency value is related to the output rate of a velocity log request.

Velocity Determined from GNSS/INS Measurements:

An Inertial Navigation System (INS) is a self-contained navigation technique used to track an object's position and orientation relative to a known starting point, orientation and velocity. It consists of an Inertial Measurement Unit (IMU) that has three accelerometers and three gyroscopes to measure linear acceleration and angular velocity respectively.

High accuracy velocity, position and orientation of an object can be determined when combining GNSS and INS measurements. GNSS/INS solutions can be output up to 200 Hz (based the IMU data rate).

Post-Processed Velocity Measurements:

GrafNav and Inertial Explorer® post-processing software take advantage of both forward and backward data computations to generate the most accurate combined solution. This is especially useful to increase solution accuracy and availability and to provide quality assessment of data collected under challenging environments. Both GNSS only velocity and GNSS/INS velocity measurements can be computed in post mission processing software.

When choosing a velocity solution, consider the following needs of your application:

• Solution accuracy
• Signal availability
• Solution rate
• Latency of solution
• Type of motion
• Continuity of solution updates
• System exportability
• System price
• System installation constraints
• Real time versus post-processed solution