Soliton Radar

The Soliton Radar System was a type of radar that could detect biological reactions, invented by Mei Ling. It employed the KdV equation to detect the electromagnetic waves resulting from biological reactions, allowing the user to obtain a variety of information about the immediate area. It could even estimate the interior structure of buildings by bouncing electromagnetic waves from the land structure in question to a satellite. The main difference between the Soliton Radar and the Reactive Radar, used by Solid Snake during the Zanzibar Land Uprising, is that the Soliton Radar could display the direction in which an enemy was facing.

The Soliton Radar was used by Solid Snake during the Shadow Moses Incident, and then again during his mission on the USS Discovery, both times to aid in infiltration. Although during this mission Philanthropy was working independently, it is possible that the United Nations granted them access to the required satellite. Following the Tanker Incident, however, any credibility that Philanthropy had disappeared, and their truly independent work from then on could explain its lack of use during Liquid Ocelot's Insurrection. Raiden also made use of the Soliton Radar during the Big Shell Incident.

Gameplay
The radar is a constant element in Metal Gear 2: Solid Snake (which uses the Reactive Radar), Metal Gear Solid and Metal Gear Solid 2 (both of which use the Soliton Radar) to show the position of the player, and enemies around them. In Metal Gear Solid 3, the radar is not used, due to it not existing in the time that the game is set, being replaced by various other sensors, including a sonar and a motion sensor. It is also absent in Metal Gear Solid 4, having been replaced by the Solid Eye System.

The radar reacts actively to the environment, changing color to reflect the mood of the enemies (blue for normal, yellow for suspicious, and red for alerted) as well as getting "knocked offline" when the player is spotted. It can also be used to view pictures or videos sent to the player, or, in MGS2 only, view the location of bombs (though this requires a separately obtained sensor). Although the radar is completely unaffected by adverse weather, it otherwise has a fragile signal, becoming jammed easily in areas with strong harmonic resonance or in confined spaces such as vents.

Metal Gear Solid 4: Guns of the Patriots
A Soliton Radar file is used by Naomi to hide information for Snake and Otacon. The radar itself is included in the Shadow Moses dream sequence.

Metal Gear Solid: Peace Walker
A Soliton Radar appears in the Metal Gear Solid: Peace Walker TGS demo while playing as Sneaking Suit Snake, although this version has limited usage due to its reliance on batteries. This would appear to be a retcon of Metal Gear Solid, since Mei Ling had previously been stated as having been its creator. In the full game, the radar's specifications are made available after the first mission in Chapter 5, after the main story ends.