Digital in-line holography allows for high resolution, high magnification imaging of microscopic particles in a relatively large sample volume.

Traditional high magnification imaging techniques result in very narrow depth-of-field and extremely small imaged volumes.

Holography substantially increases the depth-of-field (>1000 fold) over which in-focus images can be acquired, and enables characterization and enumeration of particles within a statistically meaningful sample volume.

The in-line digital holographic imaging system consists of a laser light source, spatial filter, beam expanding optics, objective lens, and a digital camera.

Holograms recorded by the camera are numerically reconstructed using the Kirchoff-Fresnel convolution kernel.

Automated image analysis techniques can then be used to count particles and measure characteristics such as size or shape.

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.

Scattering sensors are calibrated to provide accurate and reproducible measurements of the volume scattering function (VSF).

Digital counts are converted to VSF units m-1 sr-1 through a calibration to NIST-traceable 0.1 µm beads according to the methods described in Twardowski et al. (2012) and Sullivan et al. (2013).

The reproducibility component takes into account replicability of calibration procedures as well as any possible sensor drift that may have occurred. Accuracy estimates include this reproducibility coupled with any possible bias errors from the calibration procedure.

Calibrations are being provided for NASA’s Ocean Ecology Lab. The Laboratory works to ensure the accuracy of ocean-color data from NASA satellite sensors and make it available to users across the world.

The Quantitative-Filter-Technique Integrating-Cavity Absorption-Meter is a newly designed spectrophotometric setup to measure particulate absorption of material on filters (filter pad technique), like phytoplankton, in the field or lab.

The instrument was developed by Dr. Rüdiger Röttgers at the Helmholtz-Zentrum Geesthacht, Germany.

It combines a compact integrating cavity with a spectral detector and light source into a light weight, portable design to allow rapid measurements of particle-loaded filters in the center of an integrating sphere.

This optical concept has been proven to provide the most reliable measurements of particulate absorption when using the quantitative filter technique. It can easily be used onboard ships for direct measurement avoiding possible sample treatment and storage artifacts.