"GO FAST" Footage from Tom DeLonge's To The Stars Academy. Bird? Balloon?

[gtoffo]

Again, I think a balloon is more likely, mostly because of the radar return.

What do you mean? Birds should have a radar return (source: https://www.smithsonianmag.com/smart-news/how-doppler-radar-can-track-bird-migrations-180952834/)

If this was a bird shouldn't its shape be more discernible at such a range (around 5400 meters at the low point in the video)?

 

[Mick West]

Birds should have a radar return

Flocks of birds can fool weather radar, but I don't think an individual bird is going to give a strong return on a radar designed to detect larger metal objects. But I'm not sure.

If this was a bird shouldn't its shape be more discernible at such a range

Well, it's only a few pixels across, and would likely be mostly gliding at that altitude. But the general "blob" shape does seem to resemble a balloon more than a bird. Very hard to say though. At a distance planes and birds also look like blobs.

 

[gtoffo]

Flocks of birds can fool weather radar, but I don't think an individual bird is going to give a strong return on a radar designed to detect larger metal objects. But I'm not sure.


Well, it's only a few pixels across, and would likely be mostly gliding at that altitude. But the general "blob" shape does seem to resemble a balloon more than a bird. Very hard to say though. At a distance planes and birds also look like blobs.

Remember those are military grade radars. They are the best sensors in the world. Their mission is to track stealth planes at extreme range.

The radar cross section of a stealth fighter isn't different from a bird according to some sources (it's all classified of course). An F-22 is supposedly "comparable to the radar cross sections of birds and bees" (source: https://www.globalsecurity.org/military/systems/aircraft/f-22-stealth.htm)

So of course those radars can distinguish birds but they probably filter them out normally (remember F-18 radars are so sophisticated they can recognise the exact aircraft type based on the radar return of their turbine blades which are characteristic for each model https://www.princeton.edu/~ota/disk1/1993/9351/935106.PDF so it's safe to assume they can distinguish the radar return of a bird). But if you ask them to calculate the range to a large bird you are tracking with ATFLIR they won't have any problem at all.

Also, 4 miles is not a lot in terms of the capabilities of those sensors. You are around 10% of the total range of ATFLIR (40 nm). A big bird should be pretty clear and distinguishable.

And just how big is the "bird"?
Not sure if someone did this already but to calculate approximate size:
Pixels of object / total pixels of the video on my screen: 13/644=0.020
ATFLIR NFOV Zoom level 1 field of view 0.70 deg https://www.explorescu.org/post/nimitz_strike_group_2004
So apparent size is 0.020*0.70=0.014126° which at a distance of 3.4 nautical miles=6296 meters means the object is around 1.55 meters wide.

No problem tracking anything that big with an F-18. And its shape should be distinguishable as this is a very normal range for those sensors.

 

[Buraje]

The radar could probably detect a bird, but there is no indication radar was used in the Go Fast video. Someone speculated that radar was used to determine range, but that has not been confirmed. Which brings up a potential problem with the (impressive) analyses contributed on this thread: Unlike radar which can measure distance to a target by the timed echo, visual and infrared tracking do not provide direct range information. How does real-time range information appear on the display? I suspect that Raytheon engineers generated an algorithm to calculate the apparent range to a visual- or infrared-tracked target by assuming a stationary target and basing the calculation on the aircraft/ATFLIR motion data (translations and rotations), angular direction to the target, and instantaneous slew rates of the camera positioner required to maintain tracking lock. If that’s correct, and if we now use those calculated range values in frame-by-frame trigonometric motion analysis, it’s not surprising that the results indicate the target is nearly stationary. It’s indeed possible that the tracked target in the video is near the indicated distance, at around 13,000 feet altitude, moving relatively slowly. But if the target is actually in motion, the fixed target assumption is false and the indicated range values are wrong. We can’t exclude the possibility that the target is much further away, near the water surface, going fast.

 

[Mick West]

I suspect that Raytheon engineers generated an algorithm to calculate the apparent range to a visual- or infrared-tracked target by assuming a stationary target and basing the calculation on the aircraft/ATFLIR motion data (translations and rotations), angular direction to the target, and instantaneous slew rates of the camera positioner required to maintain tracking lock.

That doesn't make any sense. Why would they assume a stationary target? The vast majority of flying targets are moving, even a balloon. To find the distance from the angle change you'd need the relative velocity. Why would they program a system that invariably gives the wrong answer?

Also the Gimbal video was shot by the same plane at around the same time, and no range indication appeared.

And if you assume the range is wrong, then all that tells you is that the object is somewhere along the line of sight - it could even be close and fast.

 

[Buraje]

The visual and infrared mode are typically used instead of radar for ground targets. So the ATFLIR provides the apparent range to fixed ground targets when the track lock is established. How else could it be measured?

The technique of using the instantaneous slew rates of the camera positioner to calculate range would not work well if the angle to the target is close the to the aircraft's direction of travel. That's probably why a range solution was not obtained in the Gimbal video.

 

[Mick West]

The visual and infrared mode are typically used instead of radar for ground targets. So the ATFLIR provides the apparent range to fixed ground targets when the track lock is established. How else could it be measured?

With the terrain maps, and intersecting that with the line of sight.

The technique of using the instantaneous slew rates of the camera positioner to calculate range would not work well if the angle to the target is close the to the aircraft's direction of travel. That's probably why a range solution was not obtained in the Gimbal video.

It seems like a highly inaccurate method of judging distance, which will not work at all in many situations, and relies on assumptions for other situations.

Everyone seems to think that there was a radar lock, or at least some accurate range determination. So it seems like pointless speculation to entertain this non-working method.