# Optical Absorbance Signal Intensity at 434nm (PH434SI)

pH is measured using a colorimetric reaction by injecting a pH-dependent indicator solution into a sample of seawater and measuring the absorbance of that mixture at two wavelengths. The ratio of absorbance between those two wavelengths is then used to calculate pH. Optical Absorbance Signal Intensity at 434nm refers to the absorbance of the seawater sample at a wavelength of 434 nm with and without the pH indicator solution.

### Instrument Classes

The following instrument classes include this data product:

Typical Units
unitless

Sampling Regime
Water Column