One of the most important problems in radar systems is to transmit signal to target and receive echo signal with high SNR. We know from the communication concepts that if we integrate multiple noisy signals, increment in the power of desired signal is more than the increment in noise power. Thus, with a greater number of integrated signals, higher SNR can be obtained. A possible way to increase the number of received signals is extension in integration time. In airborne passive radars with long integration time, moving targets do not have unique range and velocity in range-Doppler surface. Indeed, the bistatic range and velocity of moving target vary during an extended integration time. In this paper we demonstrate that even targets without acceleration have variations in bistatic velocity. Further, we propose an algorithm to mitigate the impact of aforementioned variations.