where formula_13 is a space-time snap-shot of the input data. The main difficulty of STAP is solving for and inverting the typically unknown interference covariance matrix, formula_9. Other difficulties arise when the interference covariance matrix is ill-conditioned, making the inversion numerically unstable. In general, this adaptive filtering must be performed for each of the unambiguous range bins in the system, for each target of interest (angle-Doppler coordinates), making for a massive computational burden. Steering losses can occur when true target returns do not fall exactly on one of the points in our 2-D angle-Doppler plane that we've sampled with our steering vector formula_5.