11.3 Processing over Many Scans and Maps

A number of attempts were made in the past to clean up moving target indicator residues and switch the videos using maps. Owing to the numbers of resolution cells, typically for surveillance radars between 100 000 and 1 000 000, cathode ray tube storage had to be used and many were more trouble than they were worth. As computers developed, so did memory technology. The experimental drum memories were replaced by stable, reliable semi-conductor memories as they became available.

Currently maps are used also where, in the past, simple range switching was used. Examples are:

• Transmitter power control, azimuth only;

• Antenna beam switching and steering;

• Sensitivity time control for the receivers (see Chapter 7, Receivers);

• Moving target indicator video switching;

  • Areas for rain gates;

• Moving target detector;

  • Clutter maps for each Doppler frequency bin;

  • Filter bandwidth maps;

  • Rain maps;

• Detection control maps and second censoring;

  • Blanking maps;

  • CFAR control;

  • False alarm control;

  • Quality selection;

• Weather or rain intensity maps for air traffic control.

The resolution of the maps has to be great enough to represent the environment around the radar, typically the antenna (noise) beamwidth in azimuth by the effective pulsewidth in range.

For functions where less precision is required, such as rain maps, the amount of memory may be reduced by increasing the area represented by each memory cell.

The choice of the type of memory for each type of map depends on the following:

• Whether the data should be retained after...