VSR

Velocity Search with Ranging

VSR mode is a new Combined Radar Mode, or CRM, or the Viper radar that can provide additional detection range of nose-on aspect targets. VSR interleaves High Pulse Repetition Frequency, or HPRF, with Medium Pulse Repetition Frequency, or MPRF, but it does not support Situation Awareness Mode, or SAM. The HPRF acts as an alert scan in which the target is detected along with its angle and velocity. The following MPRF scan determines range information. Note that this will only be effective when the nose of the target is in high aspect to you. Once a target is detected in VSR, it can be designated and tracked as a Single Target Track, or STT.

This can be a useful mode to detect and lock onto high aspect targets at greater ranges than possible in Range While Search and Track While Scan CRM modes.

AN/APG-68(V5) Mechanisation – Velocity Search.

Velocity Search is a very misunderstood radar mode, and is considered by many to be a joke, however it can be used in certain situations very effectively. VS is a single mode, it does not have any sub modes of its own. When you designate a target using the TAC, you will transition directly to the STT mode of the radar (this mode is explained in the RWS section).

The premise behind VS is that the fastest contact that are heading towards you are usually your biggest threat. VS will only display targets that are heading towards you.

A major difference in VS is that the range scale on the right hand side of the screen becomes a velocity indicator, and that you have no ability to select a range. The VS radar mode scans out to 80nm. Contacts at the bottom of the screen DO NOT denote that they are closer to you, but indicate that they are approaching at a low speed. Contacts further up the screen indicate that they are approaching at a much higher speed.

Another major problem is that VS scans for contacts with positive closure that means that if you are overtaking another aircraft they will appear on the screen as well, even if they are not facing you. See below for an example of how a contact will appear on the screen.

What is VS useful for?

VS can be used to fish out high speed, high aspect targets. It can help you decide whether to fight, or run away – a target with very high closure on you is most likely going to be hostile. Other than that specific task it is not that useful.

Velocity Search with Ranging (VSR)

VSR is a search submode of the CRM that interleaves high and medium Pulse Repetition Frequency (PRF) waveforms to provide long range detection of forward aspect targets. VSR is designed to detect forward aspect targets only. In order to be displayed in VSR, targets must have a velocity component along the radar’s LOS directed toward the F-16. Hence this mode will only display contacts that are closing; contacts that are moving away (extending) are not displayed.

Contact detection and display in VSR is a two-step process consisting of a high PRF scan followed by a medium PRF scan. The first scan is called the Alert scan during which a contact is first detected and its azimuth and velocity are stored. Immediately after a Confirm scan is initiated with which the range is determined. After the contact has been detected in both Alert and Confirm scans, the target is displayed.

Targets are displayed on the MFD as solid squares in a B-scope presentation similar to RWS. Only contacts that are closing are displayed.

Manual Acquisition is the method by which the pilot selects a target to track in STT. Acquisition from VSR is the same as from RWS, except that a single Designate (TMS up) switches to STT. SAM cannot be entered directly from VSR.

The cursor is used to select a target for STT, initiate SAD (Search Altitude Display), move the antenna search pattern in azimuth, change the search pattern azimuth selection and change the displayed range scale.

Although only closing targets are detected and displayed in VSR search, acquisition of other targets is not specifically inhibited. This allows the pilot to acquire a turning target that was forward aspect or closing in VSR search, but has turned to a tail aspect or extending target by the time acquisition is commanded, or acquire a tail aspect target that just by coincidence happens to be in the same angular line of sight as an alert for a forward aspect target.

Since the VSR mode is specifically tailored for detection of long range closing targets, it is the optimum mode for a corridor search mission. Although it can be operated with larger scan volumes, frame times lengthen and reduce the effectiveness of the mode, so VSR is best utilized with a small search pattern (1 or 2 elevation bars by ±10° or ±30° in azimuth).