An apparatus includes an inverse radar sensor model processor and a grid mapping processor. The inverse radar sensor model processor receives radar sensor data for a time k from a radar sensor, generates object data based on the radar sensor data, and calculates instantaneous masses at the time k for each cell in a field of view (FOV) of the radar sensor based on the object data and a sensor characteristic. The inverse radar sensor model processor outputs the calculated instantaneous masses to the grid mapping processor, which also receives accumulated masses for each cell in the FOV for a time period 0:k−1. An accumulated mass represents a combination of instantaneous masses for the cell at each time increment in the time period 0:k−1. The grid mapping processor generates updated accumulated masses for a time period 0:k.