8. Moving Target Indication Flashcards
Overview: What is MTI?
Motion Target Indication
Differentiating moving targets from stationary clutter using Doppler analysis. It compares successive returns for Doppler shift.
Analyzes frequency shift for each CPI… I think.
It filters out zero Dopper shift frequencies.
Only tells you there are one or more moving targets.
What are blind speeds?
Due to aliasing, you have blind spots at integer multiples of the PRF.
Explain this diagram
MTI filter is used to eliminate zero Doppler shift range.
Pulse Cancellers
Used to subtract the incoming pulse from the outgoing pulse so that you are left witht the Doppler shift.
This is how you actually determine if the frequency has shifted.
What is the Blind Frequency (formula)
Range-velocity coverage (with formula)
Combination of the maximum unambiguous range and the unamiguous Doppler
What is a limitation of MTI? Where do the limitations come from?
If the received echo from a stationary target varies.
PRI jitter, PW Jitter, amplitude instability, phase drift.
Moving weather systems, radar platform motion (fast platforms such as aircraft or space based radars)
Explain Pulse-Doppler
Spectral analysis is performed on each range bin (row) for a set of CPI’s.
Each range bin is assigned a doppler shift.
We obtain a spectral distribution unique to each range bin.
In this way, the signal competes only with the noise within the target’s Doppler bin.
Straddle Loss
When the sampling rate is low, you may not get accurate representation f the frequency distribution. You may sample at points “Straddling” the peak.
Straddle Loss represents the dB of loss between the actual peak and the peak you get due to your sampling rate.
Sampling rate of 1.92m (m is pulses) limits Straddle Loss to 1dB.
How do Staggered PRFs affect the unambiguous range
Staggered PRFs raises the first blind speed without significantly degrading unambiguous range. How does it raise blind speed???
Moving Target Detector (MTD)
A method of detection for targets with zero or low Doppler shift. These targets would be discarded by MTI.
Pulse Doppler separates Doppler returns into bins. The zero-Doppler bin returns create a map of clutter power.
Will not try to detect if the return passes threshold. Instead, it checks each doppler resolution bin for change. It is making a map of clutter and determining if any clutter is moving.
Difference between MTI and Doppler Pulse?
MTI: No PRF. Has MTI Filter which removes everything at zero doppler shift. Only tells you that something is moving but no other information.
Pulse Doppler: FFT CPIs, then perform threshold testing on shifted frequencies.
