Hello, I am member of Rov Team. we want to use JSN-SR04T for determine the distance of an object based on operation of the classic pulse echo detection method underwater. Unfortunately JSN-SR04T doesn't work in underwater. The sensor had wrong detected distance of object which is varying distance. For example:
Measured Distance (cm) / Sensor Detected (cm)
20 / 18
35 / 18
50 / 18
87 / 18
We know that, waterproof ultrasonic sensors are designed to work in air, and do not work in water. But at the Malaysia Perlis, faculty members made Underwater Detection by Using Ultrasonic Sensor (JSN-SR04T). They hadn't written about how they solution for the sensor had wrong detected distance of object in their project report. They had just written "Analog output was employed in this experiment, because the value reported on this pin was designed to filter out invalid distance readings that resulted from noise." . I have tried contact the authors of the paper. I sent mail author but they haven’t answer me.
How can we use the sensor (JSN-SR04T) in underwater?
Please contact the authors of the paper and report back. We are waiting with bated breath....
I have tried contact the authors of the paper. I have send mail author but they haven't answer me. I still try contact.
If you want see Underwater Detection by Using Ultrasonic Sensor Project Report's pdf, I will able to send pdf to you
It is that one?
https://www.researchgate.net/publication/320061013_Underwater_detection_by_using_ultrasonic_sensor
Yes, it is. Shall I send full pdf to you
Presumably copyrighted, but if you have author permission to distribute, I'd take a copy.
The JSN-SR04T-2.0 doesn't have analog output, but the non-waterproof US-016 does.
Good descriptions of JSN-SR04T-2.0:
JSN-SR04T | David Pilling
HC-SR04 and JSN-SR04T-2.0 distance sensors • Wolles Elektronikkiste
Some report more reliable JSN operation with 20uS trigger pulse.
Some report that Maxbotix ultrasonic sensors work underwater. The manufacturer has a page describing the challenges.
Many here, myself included, are skeptical that the JSN will work under water, but please give it a go and report back (and, especially, if you get any useful information from the authors).
Thanks for link. And we thought maxbotix's sensor but these sensors are too expensive for us. I study about this task. I will try 20uS trigger pulse. If I advance anything, I will write. Thank You.
Got it and read, thank you anyway.
It remeber me a similar project that used an HC-SR04 to achieve a better precision. It connected to the chip maybe in the same way this paper did. But I cannot find it 
Thanks for the paper. Well, it certainly appears that the team was able to use the JSN-SR04T to measure distance under water between 20cm and 45cm. But there is much in the paper that is not clear.
For example, note the paper claims, without substantiating evidence, that the sensor works out to 500m. Maybe they meant to say 500mm. Edited to add: But that doesn't make any sense either, because the blind distance in water should be about 20 cm x 4.3 = 86 cm = 860 mm. Maybe they meant 500 cm, the approximate max in air... who knows...
It is not clear whether it is a JSN-SR04T or JSN-SR04T-2.0.
Judging from the photos (why is there no schematic?), it looks like they're using the standard trigger and echo pins, so I suspect the use of the word "analog" is a Malaysian->English translation artifact.
They report success measuring an underwater distance of 20 cm, but that's the approximate dead zone for the sensor in air, so it is not clear whether the difference in speed of sound in air vs water (about 4 to 5x faster in water) was accounted for (why didn't they include their code?) and exactly how the tests were conducted.
The 2nd link I posted mentions that different JSN versions have different "detection angles" (why didn't they characterize their sensor); that may affect suitability for your purpose. Smaller is probably better.
Edited to add the bold above. Also, you may want to try the relatively inexpensive DS1603L if its limited range is acceptable. It's intended to be attached to the bottom of a tank, but it also works as a depth sensor according to this: How to read serial data from Non-contact Ultrasonic liquid level sensor - #22 by wvmarle <-- also has a link to a library for the device.
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