Abstract:
Knowing the reproductive status of an animal (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 that specific time. The aim of the project was to gain
knowledge for the development of an instrument that is affordable and with which
the farmer can do pregnancy determination himself and therefore enables him to
make the correct management decisions.
Experimental data were obtained from pregnant Dorper ewes with the aid of a
portable Doppler instrument.
In order to gain insight in the frequency spectrum of the Doppler signal,
simulations of Wavelet transforms (WT), Fourier transforms (FT) and short time
Fourier transforms (STFT) were done in MathCAD. By using real data as input,
simulations of correlation, autocorrelation and a specifically developed filter
method 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 autocorrelation and the filter method, which led to a DSP
implementation of the two methods.
In the DSP implementation of the autocorrelation method signals with a SNR of
-6.5 dB was successfully identified and with the filter method the fetal heartbeat
with a SNR of -8 dB was also identified successfully. It can thus be concluded
that both the filter and the autocorrelation method can be used successfully for
the detection of the fetal heartbeat in noisy ultrasonic Doppler signals.
