A system and method of indirect underwater acoustic ocean surveillance is sclosed requiring at least two sonar platforms, usually ships, travelling some distance apart. At least one of the platforms transmits sonar pulses, portions of which are scattered off the ocean floor to at least one companion sonar receiver platform. The receiver platform is provided with means to analyze the received scattered sonic pulses to determine if a submerged object such as a submarine is obstructing a portion of the pulse, thus casting an acoustic shadow. With accurate positioning information supplied by a navigation information system such as the NAVSTAR GLOBAL POSITIONING SYSTEM (GPS), and by combining pulse measurements over several positions the system will be able to locate, identify, and track the obstructing object by analyzing these acoustic shadows or silhouettes. Geometric silhouette reconstruction techniques and other mathematical techniques may be employed to construct an image of the submerged object.

A system that extends the use of a navigation system which uses radio waves to a an environment which is otherwise inaccessible to radio-based position, location, or navigation services. This system provides beacons which dynamically determine their positions and broadcast data to any number of underwater users. By receiving and processing the beacon data or the signal upon which it is modulated, the user dynamically determines its own position within a geodetically-based time-space coordinate system. Extending externally-generated navigation information to an underwater user need not be limited to the Global Positioning System or its signal structure. Underwater extensions of LORAN, Omega, and other navigation services are also amenable to the technique.

Stealthcraft are detected by illuminating backgrounds with narrow radar or sonar beams and monitoring this background illumination for the changes that result when these beams are absorbed by such targets, and are ranged by triangulation using two such beams.

The autonomous survey system (AutoSurvey) is used to automatically maximize area coverage with swath sensors and to minimize survey time while ensuring the collected data meets specified quality constraints. The autonomous survey system (AutoSurvey) evaluates the effects of the environment and system performance on the collected survey data by modulizing the data collection into a series of modules--data collection and error detection, data georectification, data quality validation, swath-edge fit, next-line way point generation, and the autopilot. All of these processes are implemented in near real-time, allowing unfettered survey progress. The data is applied directly between processes, providing operator independent system operation; the autosurvey system directly controls the survey vessel via the autopilot. Through the real-time data acquisition the system provides automation of the operator quality and coverage assessment tasks and also provides quantified data assessment. The operator is able to adjust the system operating parameters to compensate for ambient conditions and to determine subsequent navigation way points as a function of the specified survey criteria.

An active impulse magnetometer includes a magnetic field transmitter which generates a low frequency magnetic impulse waveform. A separate magnetometer receiver responds to the transmitted waveform, and produces a receive waveform which is transformed by a Fast Fourier Transform device into the frequency domain. The transformed signal is processed to indicate the presence of any detected objects.