Auto correlation on ultrasonic Doppler signals for pregnancy determination in sheep

Knowing the reproductive status of his animals (sheep in the case of this project) is of utmost importance to the modern farmer. Decisions concerning the management of the flock are influenced by knowledge of the percentage of animals that are pregnant at any specific time. The aim of the project was to gain knowledge for the development of an instrument that is affordable and with which a farmer can do pregnancy determination himself, thereby enabling him to make the correct management decisions. Experimental data were obtained from pregnant Dorper ewes with the aid of a portable Doppler instrument. By using real data as input, simulations of correlation and auto correlation were done in MathCAD. In the simulations, known levels of noise were added to the Doppler signals. Satisfactory results were obtained from the simulations of auto correlation, which led to a DSP implementation of the method. In the DSP implementation of the auto correlation method, signals with an SNR of -6.5 dB were successfully identified. It can thus be concluded that the auto correlation method can be used successfully for the detection of the fetal heartbeat in noisy ultrasonic Doppler signals