When was the last time you used a calibrated product? Likely recently. We often check the temperature outside, weigh food at the grocery store, or maybe even use a dial gauge to work on a car. Whatever it is, we rely on these products to give us accurate results so we can make decisions.
This same principle also applies to our icListen digital hydrophones. Every single one of our hydrophones is calibrated. This ensures reliable and repeatable measurements of underwater sound.
What is Calibration?
In simple terms, calibration is a comparison between a known instrument or quantity and a test unit. This allows end users of measurement devices to have confidence in the measurements they take. No measurement is perfectly precise and calibrations also provide users information regarding the precision or uncertainty of their measurements.
Understanding Digital Hydrophone Calibration
Unlike analog hydrophones, digital hydrophones incorporate the entire signal processing chain—preamplifier, digitizer, and sometimes additional processing—into a single instrument. While the calibration methods for analog and digital hydrophones are similar, this provides some unique benefit for digital instruments. Rather than a series of separate components in a system that may each have their own calibration with uncertainties that add together, digital instruments allow calibration of the entire data chain and provide a single, comprehensive uncertainty term that is likely less than for a combination of calibrations.
The Calibration Process at Ocean Sonics
Ocean Sonics follows a rigorous calibration procedure developed by the International Electrotechnical Commission (IEC), a global organization that creates industry standards for electronic devices. The IEC 60565 guideline specifies the procedures for calibrating hydrophones and electroacoustic transducers. Here’s how it works:
- Setup: A reference hydrophone and a projector are placed in a test tank alongside the hydrophone under test. The projector emits a gated sine wave pulse, appropriate for the tank dimensions.
- Orientation Testing: Both the reference and test hydrophones are mounted on rotating fixtures to measure performance at different angles. This allows measurement of the hydrophone directivity.
- Multi-Run Averaging: Measurements are taken multiple times for each hydrophone, with the hydrophone and projector in different orientations. This approach corrects for projector and hydrophone directivity and improves repeatability of the frequency response measurements.
- Data Validation: The reference hydrophone is positioned consistent with its orientation during its own calibration, ensuring accurate comparisons.
The result is a calibration process that delivers precise measurements. Standards like IEC 60565 provide guidelines for calibrating hydrophones and give end users confidence that calibrations meet a high standard of accuracy when they are done in conformance with the standard.
Toward Standardization for Digital Hydrophones
To align with the evolving role of digital hydrophones, Ocean Sonics advocates for updates to international standards like IEC 60565. These updates would include additional guidance on calibrating instruments with digital outputs, and clarifying units of measurement for digital instruments. Such changes would improve the consistency of calibration done between different organizations around the world.
Pioneering Calibration Excellence
By refining our calibration procedures and contributing to the development of future standards, Ocean Sonics continues to set the bar for excellence in underwater acoustics. Our commitment to innovation ensures that every hydrophone we produce is ready to meet the challenges of modern ocean monitoring.
