How to get rid of clutter from a Radar data? - Page 1
Forum section: electronics / general

author: MrOmnos
author_rank: Frequent Contributor
timestamp: January 03, 2017, 09:42:11 am
content: So, I having a bit of problem. I have finally started getting data from a FMCW radar that I built. I can see the frequencies that is clearly being reflected from the target on scope after a quick FFT. But it seems a single target is reflecting multiple data which is quite obvious actually. For example if it's car, the headlights will reflect different data and rear tires will reflect different. Similar is for an aircraft. So, how do you radar engineers determine that it's a single target not 2 different or 3 different targets. Also, in case of an air traffic radar (not transponders radar), there are several houses, skyscrapers, bridges, power lines, radio towers and what not. How do you prevent all that from ruining your data? Similar for the cars. Tesla has long range radars in it's sensors, how do they remove the clutter? Where can I learn about all this stuff? Anyone here worked on radars then please guide me. Thank you!!

author: BrianHG
author_rank: Super Contributor
timestamp: January 03, 2017, 12:37:22 pm
content: My guess would be that you have to plot your received signal over time, giving you a Z axis. You then would need to judge over time the depth size of the object and determine if it's a single object with Z-sized depth, or, if its too large of at the wrong time for that portion of your returned data to be considered a single object.

author: Bud
author_rank: Super Contributor
timestamp: January 03, 2017, 03:32:38 pm
content: Do your reading on SVD based methods. But not being a radar engineer i do not know if this is what is actually used out there in real production applications.

author: coppice
author_rank: Super Contributor
timestamp: January 03, 2017, 07:38:01 pm
content: There are a lot of questions there about a big topic. Primary air traffic radars are relatively free of clutter because they look up. A radar in a military aircraft is technically much more interesting because it looks down, is hit by a flood of ground clutter, and needs to apply a number of techniques to tame it.Is your present test setup a fixed boresight, or are you scanning? What is your FM pattern like? Do you sweep up, then down, then hold a constant frequency (i.e are you trying to extract dopler), or a simple sweep that can be confused by anything moving? What convinces you that you are seeing different parts of a vehicle, and is this a moving vehicle?

author: MrOmnos
author_rank: Frequent Contributor
timestamp: January 03, 2017, 08:15:03 pm
content: Quote from: coppice on January 03, 2017, 07:38:01 pmHi, It's fixed setup with 2 tx and rx horns. I am FMing with a ramp signal, which basically generates an up chirp from 2.3 to 2.4ghz roughly. (I don't know the exact value). Yes, I can extract Doppler if I hold the frequency but I am not doing it currently. No the vehicle is not moving. I am getting two frequencies which correlates to about the length of the car, if I average the difference over some time, also I spike is bigger at the near frequency which makes me think, the headlights are acting as a corner reflector.

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: January 04, 2017, 05:16:10 am
content: Raw sensor data from a surveillance radar goes through several pre-processing steps prior to being discriminated into targets. Most of this stuff has been around long enough that you can get plenty of information by searching for the right keywords. The specific step you're asking about is calledcentroiding- looking for the 'center of mass' of the echo. Modern radars do this in two dimensions (range and azimuth; can add height if it's a 3D radar). Prior to this step, one can apply aconstant false alarm rate(CFAR) filter, effectively AGC to normalize the detection threshold based on surrounding range bins. Detection itself can be done with a number of different methods, and is often combined with the centroiding step. What's often referred to as clutter filtering is done prior to any of this, this is done on the doppler spectrum of the echo to filter out echos close to zero (for stationary radar) or some constant frequency (for radars on a mobile platform). That's how ATC radar filters out echos from ground targets.For a track-while-scan radar, post centroiding and detection 'hits' go through the radar tracking algorithms. These maintain a history of tracks, and correlate incoming detections against existing tracks. If none are found, new tracks are created. Tracks that haven't seen detections for a number of sweeps are aged off. The tracker output is what's displayed to the end user.Greg Charvat's book has plenty of info on these topics, and introduced in a gradual manner. Another introductory source is Merril Skolnik's Radar Handbook.

author: vealmike
author_rank: Regular Contributor
timestamp: January 05, 2017, 02:48:37 pm
content: Google the Nimrod project. Canned after numerous problems with clutter, cooling, not being able to tell the difference between a tree and a tank...