  In many advanced control strategies the wave excitation force is key to
determining the control input. However, it is often difficult to measure the
excitation force on a Wave Energy Converter (WEC). The use of Kalman filters to
estimate the wave excitation force based on readily available measurement data
can potentially fill the gap between the development of WEC control strategies
and the data that is available. Two different estimation methods using an
nonlinear Extended Kalman Filter are tested on experimental wave tank data for
a heaving semi-submerged float. The first method relies on directly including
the excitation force as a state in the first order dynamics---which allows the
"random walk" of the Kalman filter to identify an estimate of the excitation
force. The second method of estimation involves modeling the wave excitation
force as a harmonic oscillator comprised of sinusoidal components. Both methods
are evaluated for a variety of incident waves and additional sensitivity
analyses are performed to investigate the susceptibility of these estimation
methods to changes in the model, measurement noise, and sampling rate.
