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Murky water and video quality


(Wayne Holtzclaw) #1

Good evening all;

After much support (thank-you everyone), we pulled off our first successful real-world dive this past weekend. My daughter built an ROV for her science project with the goal of “Inland Water Conservation and Observation”. Inland water refers to coastal rivers (less than a mile from the ocean), not lakes / etc.

Part of the project was to build a water collection tube that could collect water samples at depth (successful), the water samples are to be sent to a lab for analysis.

The other part of the project (observation) we weren’t as successful. Out of the water, the image quality is awesome, but underwater you really can’t see anything. Part of the problem is the turbidity of the water; visibility is only about 5’ at the surface, so it’s really hard to pilot when you can’t get a point of reference, and by the time you see something in the camera it is gone.

Is there another type of camera (perhaps infrared) that we can use to get better imagine (even with the loss of fine detail)? Lighting is not an issue as at even only 5’ in full sunlight, image is still garbage. Any suggestions would be greatly appreciated.


(Harold Scadden) #2

Turbidity is always going to be an issue in shallow water … more so with soft bottom areas. If the water is already murky you are pretty much stuck. Considering the particle count in the water it is going to absorb light, acoustics you name it.

I don’t know how much holding the unit in a quasi hover state would do for you. The water is just going to have to settle out for you to see anything. Bright lights won’t help any better than you slapping your high beams on in a dense fog … you just blind yourself.


(Rusty) #3

Hi Wayne,

Glad to hear the ROV came together well and the first dive was successful!

Murky water is very troublesome and there’s not too much that can be done about it as far as we know. In the commercial ROV world, where work is often done in these conditions, sonars are frequently used to aid with navigation. Unfortunately, they’re quite expensive.

My best tips right now are to keep the lights off to avoid backscatter on the particles in the water and try to follow reference features whenever possible, such as a post on a dock or an anchor line.

There are a few companies that specialize in various solutions to help cameras see further through the murkiness, but they are all quite expensive and specialized.

I’m sorry I can’t be more helpful than that!

-Rusty


(Eric) #4

Which camera are you using?

I used to “fly” with the Raspberry Pi v2 Camera, which was hard in my native Dutch waters.
Since i switched to the Low-Light HD USB Camera, things have gone much better.


(Wayne Holtzclaw) #5

Eric,

I am using the low-light HD USB camera, I am sure it’s just the limited visibility of the water

You can see that visibility is only about 4’; the first photo is on the surface, our ROV is only 28" tall, in the 2nd picture, it’s only about 1’ below the surface and you can’t see the bottom. Probably nothing I can do, but was looking for options.

Thanks!


(Eric) #6

Yes, i know the feeling. As soon as i dive, i am lost :wink:

The procedure i follow:

  1. Move near the surface (with lights enabled) to the dive location (on visual)

  2. Enable Autopilot (so i can dive without much heading changes)

  3. Swith to my HUD screen and dive, dive, dive (and keep fingers crossed, that i wont get lost)

  4. Sometimes it helps to follow jetties poles or yacht keels and vector my next stop.

  5. When lost, re-surface… reposition and restart procedure.


(Heinz) #7

I always keep a notepad in my control cabinet. Make a rough sketch of the area where you will be diving the ROV and mark the compass headings on the sketch that way you will know what direction to head away from the boat/dock/pier or wherever you are whether the ROV is visible or not.
Some of my most exciting and challenging dives have been done at night and with low visibility but you must know what headings to take while diving the ROV in those conditions.


(undersearobotics.com) #8

There have been lots of good tips shared already. Here’s what I might add:

If you’re new to flying an ROV, I recommend you pick up a copy of the “ROV Manual” by Bob Christ. The latest issue is available for purchase on Amazon but an electronic version of the older issue can be found floating around the internet. Well worth the time spent reading.

As you have already learned, using visual clues for navigating in poor visibility is really the key. Such as pilings, jetties, etc. But if none exist, you can always add your own using a small weight, bright colored line and a small float. Follow the line from the surface to the bottom, fly in one direction, turn 180 degrees and return to the bottom of the line. Repeat in different directions until you’ve covered that area. Then move the marker and repeat.

Of course the best solution for poor visibility is to use sonar. A good forward scanning / imaging sonar isn’t cheap, but if you plan on using your ROV for work in poor visibility, it is a worthwhile investment.


(Wayne Holtzclaw) #9

Thanks guys!

I will definitely take these into consideration.

I have already talked to my daughter about adding sonar, even if it’s something as simple as a fish finder.

I will also check out that book, sounds like it would be a good read for us.

Thanks again!

Wayne


(Kai Hoppe) #10

Hi Wayne,

one simple thing I haven’t heard here yet (too obvious?) is to move the light source to the side, so that it does not directly illuminate the particles in front. I have seen some nice outrigger pictures on this forum. In UW photography this helps a lot.

Also, you said your daughter was successful in taking water samples. You mentioned a “solenoid valve” in another post, how did that work?

Good luck,
Kai


(Wayne Holtzclaw) #11

Kai,

Than-you for your feedback; The problem is I’m pretty close to the surface, so the light refracting from the particles is sun-light, not necessarily the on-board lights. I plan on experimenting with a cover above the camera (fabricated from plastic or such), that will act as a visor for light from above.

As far as the water sampling, she fabricated a PVC tube; threaded end-caps on each end, with (2) Tee’s in the middle. She then potted the solenoids in PVC end caps, leaving only the threaded ports open; and used adapters to attach to the PVC Tee’s. One on the top and one on the side; they are both controlled with a relay. They are normally closed, and open with voltage; one lets water in, the other lets the air out. The tube is mounted near the center of gravity, so the only effects are with buoyancy. Pre-dive she is slightly positively buoyant, after the water sample she is neutrally buoyant. The sample size is approximately 1 liter. The threaded end caps allow sanitizing of the tube prior to taking the next sample. The solenoid relay is controlled by the PixHawk on the channel initially used for the light switch.

I will snap some photos of it when it comes back from the science fair if you are interested.

Thank-you


(undersearobotics.com) #12

Regarding moving lights further away from the camera to avoid back scatter, check out this “cinematic” oriented ROV’s light set up:

http://rovplanet.com/news/news?id=1185


(Kai Hoppe) #13

Hi Wayne,

yes, I would like to see close-up of your solution. It sounds fairly simple (good for me), but I am not sure about the buoyancy issue, esp. if I want to take a larger sample for eDNA analysis.

Thanks for sharing your ideas,
Season´s Greetings,
Kai