Passive multispectral scanner that uses recursive adaptive sampling

A passive multispectral scanner that uses recursive adaptive sampling, comprising:

• one or more directional antennas configured to receive electromagnetic signals within a total frequency range;
• an aiming system coupled to said one or more directional antennas and configured to aim said one or more directional antennas to receive signals from sources emitting at an azimuth angle and an elevation angle relative to a base orientation of said one or more directional antennas, wherein:
• said azimuth angle lies within an azimuth range;
• and
• said elevation angle lies within an elevation range;
• a frequency selection system coupled to said one or more directional antennas and configured to:
• obtain a signal strength in a multiplicity of frequency subranges, wherein each frequency subrange of said multiplicity of frequency subranges lies within said total frequency range;
• and
• a controller comprising a processor and a memory, wherein:
• said controller is coupled to said aiming system and to said frequency selection system;
• and
• said controller is configured to:
• create or update a signal strength data structure in said memory that associates a signal strength with an azimuth, an elevation, and a frequency subrange;
• divide said azimuth range and said elevation range into a grid of points, wherein:
• each point comprises an azimuth within said azimuth range and an elevation within said elevation range;
• and
• said grid of points forms vertices of polygons that form a tessellation of a surface spanned by said azimuth range and said elevation range;
• for each point in said grid of points:
• transmit said azimuth and said elevation associated with each point to said aiming system;
• obtain said signal strength corresponding to each frequency subrange from said frequency selection system;
• and
• update said signal strength data structure with an entry comprising said azimuth, said elevation, said each frequency subrange, and said signal strength;
• and
• for each polygon of said polygons and for each frequency subrange of said multiplicity of frequency subranges:
• estimate a gradient magnitude of said signal strength in said each frequency subrange within said each polygon;
• and
• when said gradient magnitude exceeds a threshold:
• subdivide said each polygon into a subgrid comprising interior points within said each polygon, wherein each interior point of said interior points has an associated interior point azimuth and interior point elevation;
• for each interior point in said subgrid:
• transmit said interior point azimuth and interior point elevation to said aiming system;
• obtain said signal strength corresponding to said each frequency subrange;
• and
• update said signal strength data structure with an entry comprising said interior point azimuth, said interior point elevation, said each frequency subrange, and said signal strength;
• and
• continue subdividing polygons of said subgrid until a gradient magnitude within said polygons is smaller than a minimum, or until a resolution limit of said aiming system is reached.