Blip-to-scan Ratio

In radar systems, the blip-to-scan ratio, or blip/scan, is the ratio of the number of times a target appears on a radar display to the number of times it theoretically could be displayed. Alternately it can be defined as the ratio of the number of scans in which an accurate return is received to the total number of scans.

"Blip" refers to the dots drawn on early warning radars based on plan position indicator (PPI) displays. A "scan" is a single search of the entire sky made by the rotating antenna. A radar with a low blip-to-scan ratio draws only a few reflections from an object (mainly aircraft), making it more difficult to detect. For an aircraft flying at high speed and altitude the ratio is further reduced, rendering the aircraft almost invisible to radar. This fact was the primary reason the Lockheed U-2 was slated to be replaced by the much faster Lockheed A-12. However, upgrades to Soviet radar systems increased their blip-to-scan ratios, rendering the A-12 obsolete before it could be deployed.