The Point-Source Integrating Cavity Absorption Meter (or PSICAM) is a relatively new approach to measuring absorption first proposed by Kirk in 1983.

Unlike classic spectrophotometers the PSICAM uses a diffused light source which is placed in the center of the integrating sphere.

Light is measured through a port on the side of the sphere. Within the integrating cavity it is possible for the detector to act like an irradiance sensor: collecting light from all directions.

The PSICAM has high sensitivity due to its long optical path and can therefore be used to examine low absorption values in the open ocean.

A bandpass filter is used to measure the fluorescence within the sphere to estimate chlorophyll concentration.