Doppler Principles

Question 1

Doppler shift

Answer 1

change in frequency caused by motion

Question 2

doppler shift is positive when

Answer 2

the object is moving closer

Question 3

the doppler shift is negative when

Answer 3

the object is moving away

Question 4

Doppler shift formula and units (simple)

Answer 4

KHz

Fd= F (received) - F (operating)

Question 5

Doppler shift formula including speed

Answer 5

Fd = 2 x Fo x V(cm/s) / c (cm/s)

Question 6

Doppler shift is directly related to

Answer 6

operating/source frequency

scatterer velocity

Question 7

velocity/doppler shift formula

Answer 7

V = 77 (cm/ms) x Fd (kHz) / Fo (MHz)

Question 8

if you incorporate an angle correction what happens to the doppler shift

Answer 8

Fd will be smaller

This is why we incorporate cos to compensate for the lesser shift

Question 9

if you increase the angle of interrogation what happens to the velocity?

Answer 9

velocity increases!

Question 10

true or false - if you hit a vessel perpendicular you will reach the maximum doppler shift

Answer 10

false. perpendicular is 90 degrees = 0 shift

parallel is the max doppler shift

Question 11

which doppler shift will be the greatest, if you hit a vessel at 30 degrees vs 60 degrees?

Answer 11

at 30 degrees there will be a greater doppler shift

Remember: as you increase angle from 0, cos decreases, shift decreases, and speed increases

Greatest Doppler shift at zero angle (parallel)

Question 12

what will a 90 degree angle show as?

Answer 12

no flow

Question 13

what are some techniques to get closer to a zero angle? (3)

Answer 13

heel-toe
steering
angle correct (tell the machine and it compensates)

Question 14

what is the optimal angle range

Answer 14

30-60

Question 15

steering the colour window changes (2)

Answer 15

• doppler angle

- doppler shift

Question 16

lack of colour in a vessel may mean (3)

Answer 16

• low colour gain
• high wall filter
• low priority setting