1. An airborne underwater mine countermeasure system adapted to operate onboard an aircraft, the airborne underwater mine countermeasure system comprising: a processor onboard the aircraft, the processor coupled to a memory onboard the aircraft, the memory having stored therein software instructions that, when executed by the processor, cause the processor to perform a series of image processing operations including: obtaining input image data of a body of water from an external image sensor; extracting a sequence of 2-D slices from the input image data by applying diffusion equations to generate the sequence of 2-D slices; performing a 3-D connected region analysis on the sequence of 2-D slices, the connected region analysis including analyzing volumetric pixel elements; computing 3-D invariant features in the image data; performing coarse filtering based on the 3-D invariant features, the coarse filtering including: comparing 3-D invariant features in the image data to a store of invariant features associated with known objects, providing a list of found objects in the image data based on the store, and for each of the found objects, providing an indication of how close features of the found object match features in the store; performing fine recognition; and outputting an image processing result having an indication of the presence of any underwater mines within the input image data.