"Physical oceanography" encompasses a broad range of subjects, from heat transfer to sound and optics. Knauss brings all these disparate fields together in this comprehensive text. He strikes a balance between purely descriptive texts and mathematically rigorous ones, assuming readers only have knowledge of elementary calculus and physics. This results in a straightforward, readable book that makes the material accessible both to readers specializing in physical oceanography and those from other disciplines who need to understand the fundamental principles of physical oceanography.
Though I'm not an oceanographer, I found Knauss's introduction to the topic to be excellent. The book covers just physical oceanography, so if you're interested in marine ecology, chemical oceanography, or marine geology, you'd best look elsewhere. Overall, it's fascinating to learn how small differences in salinity, temperature, and density drive so much of the dynamics of the Earth's oceans. Knauss does a good job with his derivations. The chapters discussing heat transfer, the conservation equations, and the equations of motion are excellent and illustrative. His discussion of waves is also good. Owing to the complexity of the topics, his discussion of tides and sound is weakest. But anyone looking for an accessible and readable text on physical oceanography with many useful derivations can start here. (Note that Knauss helped create NOAA and later served as its administrator.) Recommended.