In urban areas with obstacles such as trees and buildings, like public roads, multipath interference causes significant noise in the Doppler-based velocity output, as shown in the diagram. Furthermore, when passing through areas where satellites cannot be observed, such as elevated bridges, it becomes impossible to measure velocity using GPS alone.
By combining speed information from GPS with speed data obtained from the IMU's 3-axis accelerometer/3-axis gyroscope in an appropriate ratio, we achieve extremely smooth and highly accurate speed output, even in multipath environments, compared to using GPS alone, as shown in the figure below.
Furthermore, even in locations where GPS alone cannot measure speed, such as when passing over an elevated bridge, the use of an IMU enables speed interpolation processing, ensuring continuity of speed output and providing highly accurate speed output even in the event of short-term loss of GPS satellites.
