This text is designed to meet the needs of students interested in remote sensing as a tool for the study of military and intelligence problems. It focuses on the technology of remote sensing, both for students who will be working in systems acquisition offices and for those who might eventually need to be "informed consumers" of the products derived from remote sensing systems. I hope it will also be useful for those who eventually work in this field. Here in the second edition, the book maintains, as much as possible, a focus on the physics of remote sensing. As a physicist, I'm more interested in the technology of acquiring data than the final applications. Therefore, this work differs from related textbooks that favor civilian applications, particularly geology, agriculture, weather (atmosphere), and oceanography. I have instead concentrated on satellite systems, including power, data storage, and telemetry systems, because this knowledge is important for those trying to develop new remote sensing systems. For example, one of the ongoing themes is how bandwidth constraints define what you can and cannot do in terms of remote sensing.

From a tactical perspective, low-spatial-resolution systems are not very interesting, so this text focuses on systems with high spatial resolution. This is not to deny the utility of, say, weather systems for the military, but that is a domain of a different sort, and one I leave to that community. (As a consequence, for example, I leave out passive microwave sensing as a topic.) Similarly, although oceanography is clearly important to the Navy, that too is a topic I leave to others. I have completely ignored the technology of film-based imaging systems, aside from a discussion of the historical reconnaissance satellite systems.

Part of the motivation for creating this textbook was and is the ongoing discrepancy between the content of such books and the current state of the art. When I started teaching remote sensing and crafting what has become this text, the IKONOS satellite had not yet been launched. At the time of publication of the first edition, there were no high-spatial-resolution imaging radar systems, but now I have an illustration from TerraSAR-X at a 30-cm resolution. The launch of SkySat 1 by Skybox Imaging (now Terra Bella, a Google company, as of November 21, 2013) clearly signals many upcoming changes in imaging from space that are not ready to be discussed here. These larger fleets of satellites and newer focal plane technology imply more persistent imaging. Video from space is a consequence of these new hardware designs, with promising but uncertain utility. Also signaled by the success of Skybox imaging: remote sensing appears to be emerging as the third field, following communications and navigation, to become economically viable in space. This text is organized according to a fairly typical progression - visible optical systems in the visible realm, followed by infrared and radar systems. New to this textbook is a full chapter on LiDAR. The necessary physics is developed for each domain, followed by a look at a few operational systems that are appropriate. Somewhat unusual for a text of this sort is a chapter on how orbital mechanics influences remote sensing, but ongoing experience shows that this topic is essential.

I have added a radiometry component to the infrared (IR), radar (SAR), and LiDAR sections. The IR section clearly needed this to address detection issues and make temperature measurements more clearly founded. The imaging radar material clearly needed the radar range equation, just as the LiDAR chapter needed its corresponding range equation.

Finally: The first edition was pretty much a solo effort on my part. The second edition has benefitted from the support of my technical team - my thanks to Angela Kim, Jeremy Metcalf, Chad Miller, and Scott Runyon for their contributions. Thanks to Donna Aikens and Jean Ferreira for help with the many copyright issues. The reviewers did a great job and identified a number of annoying elements in my writing style that clearly needed to be adjusted. Thanks to the editor, Scott McNeill, for his persistence and diligence.