LIDAR / iPhone 12 underwater

[Rick Brant]

Just wondering if anyone has tried using the iPhone 12 underwater with the LIDAR sensor. Using the iPhone and an app called PolyCAM it is possible to create 3D models very easily. I'd like to do this with reef structures rather than using the photogrammetry approach. LIDAR does work underwater but I want to know about the iPhone in particular. BTW if you have an IPhone with LIDAR and want to try this I'll pay for your PolyCAM copy to do so. PolyCAM can be licensed for short-term use, which is what this would be.

 

[Michael Perdue]

LiDAR only work well underwater if the instrument in question uses visible wavelengths. Most LiDAR sensors use an infrared wavelength (most topographic sensors are 1064nm) which have very poor penetrative performance in water. The wavelength used for bathymetric LiDAR is typically 532nm (green) but shorter wavelengths in the blue range would be better if they could make them with high enough output power.

I’m not really familiar with the iPhone’s sensor, but suspect it is in the near infrared range. Even if it is in the visible range, you would have to work out the optics to get an undistorted model.

 

[Miyaru]

In crystal clear water (eg. Cave) you'll get a reading within 2m distance. Any further and the water absorbs the IR light (theoretically 6m but in real life it's not detectable beyond 4m).
Since the speed is roughly 2.25/3.00 (water/air), you'd have to recalculate distances.

I'm working on this for an underwater project, IR laser diodes are easy to get, but there is no commercial chip yet that uses 532nm (green) like NOAA does. The automotive industry is exploring 532nm for use in rain and fog, so it's wait-and-see.....

 

[Rick Brant]

I did some tests today, finally. The viz was not great, maybe 25' with lots of particulates. I could not get any scanning from my iPhone, even at very close distances. I will have better visibility over the next week or so and will give it another try then.

 

[Joel Thomas]

I've tried using iphone LiDAR. iPhone 15. It doesn't work even a few millimeters through water. The objects have to be pretty much touching the screen for it to work, even then it was hit and miss. I assume it is using infrared, or something that doesn't penetrate the water. Probably some light wavelength that travels well through water would have a chance which rules out the iPhones. I had great viability, about 50ft. The particles in the water seem not to be the issue.

 

[Rick Brant]

I ended up not using LiDAR. Instead I created two apps that do simple photogrammetry using images that have depth maps. The iPhone creates depth maps on the fly so it is fairly easy to create 3D models based on 2D images.
ReefScan for iOS
ReefBuild for MacOS