Abstract: A system and method of signal detection from a given point, in which a radiative aperture, such as a sonar sensor, radar antenna, acoustic sensor, or the like, receives radiation from the point at more than one range. At each range, the signal incident on each point within the aperture is weighted by the cosine of the angle between a surface normal at the point on the aperture, and a vector from the point on the aperture to the given point. The physical size and shape of the aperture may also be changed to cause the aperture to subtend the same solid angle having the given point as the vertex, at each range. In this manner, the signal from the given point becomes aperture shape independent, facilitating object recognition and imaging.

Abstract: Vehicle attitude is estimated relative to a ground surface over which the vehicle is traveling. An actual image of the ground surface over which the vehicle is traveling is compared with stored or predicted model images of the ground surface. The model images have corresponding known vehicle attitudes associated therewith. For one of the model images that most closely matches the actual image, the known vehicle attitude associated therewith is an estimate of an actual vehicle attitude relative to the ground surface over which the vehicle is traveling.

Abstract: A correlation image detector is provided that co-registers sonar images by finding peaks in correlation images. To obtain the peaks, the mean of the absolute values of the correlation coefficients in the correlation image is found and the Rayleigh parameter is determined from the mean. Based on the Rayleigh parameter, an appropriate threshold can be determined using a desired probability of false detection. The threshold can be chosen such that the probability of a single false detection over the expected life of the mission for which correlation detection is being performed is extremely low, e.g., one in a million. The peak value in the image is determined and a correlation is considered detected when the peak value is greater than the product of the threshold and the Rayleigh parameter. If a detection occurs, the correlation image detector returns the transformation that co-registers the two images.

Abstract: Systems and methods for coherent image correlation are provided. The systems include sonars with overlapping frequencies that observe terrain from overlapping aspects to form sonar images. First and second sonar images are formed and are grazing angle compensated. The first image is formed using the open or closed aperture theorem. Forming the second image using the open or closed aperture theorem constraint is optional. If the first and second images are not aligned, a range of possible rotations can be defined and image pairs can be created for a sampling of rotational angles. In addition, the images can be aspect compensated to remove windowing and beam pattern effects, if necessary. Once both images are grazing angle compensated and aligned, values are calculated for each possible image shift. To obtain a correlation image, the correlation coefficient for each possible image shift is calculated.

Abstract: Systems and methods for obtaining target elevation information are disclosed. The systems and methods use multiple vertical transmitters and one or more receivers to infer changes in the elevation plane and the height of objects. Changes in elevation and heights of objects are inferred from path length differences between the transmitters and a particular backscattering point. Using known geometric information regarding the configuration of the transmitters, propagation time differences can be estimated via time delay estimation methods in either the time or frequency domain. Appropriate modulation schemes are used such that the multiple signals transmitted are separable upon reception.