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I am planning on using 'SHARP IR Distance Sensor - GP2Y0A710K0F' in an outdoor environment. Assuming the casing I design for the sensor is waterproof, can I use this IR sensor without any trouble? If the water is interfering, what can I do to reduce that noise?

The sensor is fixed above the ground and aimed towards the ground like this.

SHARP sensor is aimed towards the ground

  • If this is off topic, where can I ask a technical question like this, and not get rejected by people who did not even bother to answer? – nipunasudha Apr 27 '18 at 8:59
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According to the data sheet for this device, located at Adafruit's web site, the frequency used is 870nm. If you required specific attenuation figures, that might be useful information.

Another web site suggests that thermal IR camera imaging systems (which use a different frequency IR) are attenuated by rain. Some of the IR energy is lost by absorption and some by reflection. I was hesitant to suggest that as the answer due to the different frequencies involved.

Digikey has a document covering wide use of IR sensing. Listed in the document:

The disadvantages of IR technology are:

  1. Line of sight: transmitters and receivers must be almost directly aligned
  2. Blocked by common materials: people, walls, plants, and other objects can block transmission
  3. Short range: performance drops off with longer distances
  4. Light and weather sensitive: direct sunlight, rain, fog, dust, and pollution can affect transmission
  5. Speed: data rate transmission is lower than typical wired and RF transmission

Even though data transmission is not your objective, the considerations apply. A wet surface over which your sensor passes will have the signal attenuated and may also be slightly diffracted.

I found no direct reference to the magnitude of the attenuation. If your sensor is protected from water intrusion and the surface is only slightly wet, you may have minimal problems reading the distance. If the rainfall is at the level of a frog-strangler, there could be sufficient water to eliminate useful readings.

Another search resulted in a similar question on the physics stack exhange, which led to a more comprehensive answer:

IR absorption graph

There is another image on the same page, but both show that at the 870nm frequency, there is lower attenuation than much of the IR spectrum, particularly above 3000nm. The above linked document suggests that the affect of rain (water) is low at near-infrared (970-1940nm) but that's still higher than the device's 870nm figure.

For your objective, shielding the surface from rain (umbrella) or clearing the surface of standing water seems to be the best options. If those are impractical, one would have to experiment to determine how much water flow can be tolerated before the signal is lost or attenuated beyond reception limits.

  • Thank you very much for this comprehensive answer @fred. I will follow the guide you gave and do some experiments with rain. Never thought that the frequency had a connection with my problem. Thank you very much. – nipunasudha Apr 26 '18 at 21:45
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the ir-sensor senses a difference in infrared. the rain will only interfere if its way warmer then the base outside temperature. this is how humans and other mammals trigger infrared sensors on outdoor garden lamps. we emit infrared because our body temp being higher than the temperature of our surroundings.

just a nice quote from this site: https://www.techwalla.com/articles/how-do-ir-sensors-work

All objects emit light according to their temperature--this is called "black body radiation." The hotter the object, the shorter wavelength of light it emits. The Earth emits infrared light at a peak of about nine to 10 micrometers--and so do warm-blooded animals like humans. This light can be used to detect motion or warmth.

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    Thank you for the response @Jelle. I think you misunderstood how the SHARP IR distance sensor works. It uses it's own IR light source and captures the reflection on a surface. Black body radiation has nothing to do with it. – nipunasudha Apr 26 '18 at 20:18
  • i see. i was expecting a standard pir sensor – Jelle Bleeker Apr 29 '18 at 16:36

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