Ultrasonic anemometer

Hello Good Friends

I am using four ultrasonic sensors and PIC 18F462 to measure wind speed and direction. For each sensor pair (North-South and East-west) I want to send one 40kHz signal and wait until the signal is received by the opposite sensor and then calculate the time of flight. Then again the signal is sent to the opposite sensor. The same thing happens to the other sensor pair.
My problem is that I do not know how to connect the sensors such that measuring back and forth is possible.
I am trying to do the programming in C but I cannot calculate the time of flight so far.

May you please help me with any possible circuits and codes that may help me complete this task successfully.

Thanks Good Friends

Mehlo

I have a problem with measuring the time of flights accurately. I am using Timer0 in 16-bit mode, PIC 18F462 with ext 10MHz oscillator configured in HS+PLL mode(4xFosc). The time delay is 8.4 microseconds as seen on the oscilloscope. The time of flights that I obtain are in the range of 19.2 to 22.4 microseconds by using timer 0.

Please help me get the accurate measurements.

Thanks