Assessing the Performace of ToF Distance Sensors Above Water

In order to showcase the results of the TeraRanger One (TR1) sensor performance above water, a test has been performed. For this test, the TeraRanger One was employed above water at various water surface types, heights, and under two ambient light conditions. The aim of this test was to assess how these conditions influence the performance of the TeraRanger One above water​.

Design of Experiments

  • Two distances:
    • Config 1: 184 cm between the water level and the TR1 sensor
    • Config 2: 47 cm between the water level and the TR1 sensor
  • Graphs used:
    • Created with 1250 distance measurements
    • Same scale
  • Sensor used
    • TR1 Type A
    • Mode used: Precise (600 Hz)
    • Representative of the sensor sold and is taken from stock
  • Two ambient lighting:
    • Low: Nearly dark
    • Medium: Sunny weather (no direct sunlight)
    • Tests have been made inside, with the pool close to windows (see below image).
  • Two water conditions
    • Static: Flat surface

  • Bubbles: Jacuzzi on with bubbles in order to create white foam typical of moving water

Test Results

Config 1: longer distance

  • Real pool bottom level: 229.00 cm from TR1
  • Medium: Sunny weather, no direct sunlight
  • Real water level: 184.00 cm from TR1
  • Two ambient lights: Low and nearly dark

Config 2: shorter distance

  • Ambient light: Medium = sunny weather (no direct sunlight)
  • Real water level: 47.00 cm from TR1
  • Real pool bottom level: 92.00 cm from TR1

Conclusion

Note that the presented graphs are reversed, which means that the measurements with the TeraRanger One were taken from the lower part of the graph, whilst the top green line depicts the bottom level of the pool.

In Config 1, which is the longer distance, the results convey extremely accurate performance with no errors when measuring distance over static water, and under both low and medium ambient light conditions. Graph 1 establishes that measurements made above water with bubbles exhibit a slight noise under lower ambient light, yet, more accurate performance in medium ambient light conditions.

Graph 1 and 2 also show that measurements received from the test are near to the actual water level. Furthermore, no TR1 data measurements were gathered at the pool bottom level.

In Config 2 which is a shorter distance, the data measuring distance over static water exhibits relatively more accurate readings than the one under medium ambient light over water with bubbles. Both measurements again show high proximity to the actual water level, and no data points acquired at the bottom level of pool (Graph 3).

Test on Natural Water - Lake Geneva

To demonstrate that TR1 can also supply stable measurements in natural, outdoor environments, a customer* tested the sensor in real life situations. The experiment was performed above a water surface (Lake Geneva)  using a TR1 sensor attached to a pole on a moving boat. The purpose of this test was to assess whether TR1 performance would be altered in an outdoor, natural environment.

Environment and Setup

Design of Experiments

  • Two distances
    • Config 1: 60 cm between the TR1 sensor and the water level
    • Config 2: 40 cm between the TR1 sensor and the water level
  • Ambient lights: Medium and sunny weather (no direct sunlight)
  • Graphs utilized
    • Made with 3000 distance measurements
    • Same scale

Test Results

Config 1: longer distance

  • Ambient light: Medium = sunny weather with no direct sunlight
  • Real water level: Around 60.00 cm from TR1 (but with waves)

Config 2: shorter distance

  • Ambient light: Information not recorded
  • Real water level: Around 40.00 cm from TR1 (but with waves)

* Many thanks to Valentin Mottier of Ecole Polytechnique Fédérale de Lausanne (EPFL) for the test data

Conclusion

In Config 1 (longer distance), Graph 4 illustrates that statistics correspond with measurements taken 60 cm above water with waves. With minor readings (errors) which go deeper than the surface level of water, the test establishes that TR1 can detect and measure the distance to the water surface without direct sunlight, with waves, and whilst at a speed of 10 km/h.

In Config 2 which is the shorter distance, as the space between the TR1 and water surface lessens (40 cm), more measurements can go through the surface level of the water (errors). Regardless, when the measurements do penetrate the water surface, the readings reach the maximum range of the sensor, which then permits the user to easily filter these errors from the real water level values when working with the data.

The results establish that the majority of measurements from the TR1 are accurate and the errors are very clear. This means that the TR1 can be utilized reliably above water with some filters to exclude error readings.

This information has been sourced, reviewed and adapted from materials provided by Terabee.

For more information on this source, please visit Terabee.

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