Hallo Abhishek,

your methode sounds very interesting. But there are some details which makes measurement with continuos wave, either with constant frequency or sweeping, very difficult, if not impossible. Think about reflections at additional surfaces: After emitting your wave, there will be a reflection at your object. But that's not all! Reflected wave is again reflected, and again and again. This results in some reverberation signal, no more showing any sharp edge, which could be used for triggering in order to measure frequency.
There is another point: If shape of object, where wave is reflected, is not homogenous, wave is not only reflected but also refracted, also resulting in many partial reflections, with same consequences.

I would use a methode emitting only ONE pulse, and waiting for the FIRST reflection, so, whole measurement is done BEFORE reverberation takes place.

May be, that's what Steve meant with his 'Polaroid methode'?

Regards,
Kai