Sensors 8 Flashcards
Doppler Definition?
Frequency shift observed due to relative motion of source and/or receiver.
What is the real shift?
Source is moving
What is the apparent shift?
Observer is moving
What are the Factors affecting Doppler Shift?
- (F)Frequency: Higher freq. = greater frequency shift
- Angle: between direction of travel and line of propagation from Tx and Rx.
- (V)Relative velocity
- (C)Speed of propagation. Sound or light
Why do we use 4 Beam JANUS?
To compensate for changes in A/C attitude
What does the conical pattern does?
Helps eliminate roll errors and ensure reception of adequate returns/signal overlap
What does it do to account for vertical velocity?
it compares front and rear beams during climb or descent; errors will cancel each other out.
Why is it not nessary to precisely control Tx freq.
• Uses an average freq; it’s not necessary to precisely control Tx freq because system uses an average freq; Allows higher tolerance + lower cost for Transmitter.
It compares diagonal returns, and average the result.
Smoot sea returns is affected by 2 things..what?
- Reduction in energy level of signal
- Altered depression angle of return signal
Echo is from the trailing edge, therefore there’s a changed depression angle
Does Land, rough ice and rough sea gives good returns?
YES.
Why is there a Latitude error?
Because earth is an oblate spheroid, thus 1nm = different number of feet at different altitude.
@ Equator = 1’ lat = 1 nm = 6108ft
@ Poles = 1’ lat = 1 nm = 6046ft
Altitude error?
1’ Arc doesn’t = 6080ft at higher altitude
What is Sea movement?
movement of reflecting surface; small errors in G/S + Drift
What is Spray errors?
Caused by wind; small error in G/S
What are the DOPPLER errors?
Sea movement Altitude Latitude Terrain Spray
