Lecture 1. In situ Measurements (1). Saturday, 0900‐1030 h. Starting from a base in the radiative transfer equation, the fundamental measurement of the underwater radiance field will be introduced. Historical observations will be traced through two recent developments. These measurements will be used to introduce (or reintroduce) various integrated radiometric quantities: the planar and scalar irradiances, the average cosines, and reflectances. Variations in the radiance distribution along a path (say in the vertical) brings together consideration of the fundamental inherent optical properties, the absorption coefficient and volume scattering function, as well as the beam and diffuse attenuation coefficients and scattering coefficients over various solid angles. Modern methods for the independent measurement of these quantities will be presented and discussed. Attempts at optical closure field experiments will be presented. Bibliography Ocean Optics Web Book. http://www.oceanopticsbook.info/view/introduction/overview