Originally Posted by
Mogwi
Hi Andy,
The LRMTS was used to give the weapon aiming kit an accurate slant range, which allowed weapons to be dropped more accurately. These could be (as far as I remember) any of the weapons carried by the Harrier. The target seeker mode allowed a designated target to be highlighted in the HUD, so that the pilot could carry out the attack. I am sure that ex-fast jet will be able to give the definitive answer.
Mog
That's certainly how LRMTS worked on Jag and Tornado: as a means of cueing unguided weapons and providing an accurate range for the trigonometric calculations which generated HUD aiming symbology. The laser transmitter (designed for use at short range when directly overflying the target) was less powerful than those found in targeting pods and ground target markers, but the receiver (designed to detect faint off-board laser signals anywhere in its field of view) was much more sensitive than the "disposable" one found in Paveway guidance heads. So, as the name suggests, LRMTS was suitable for range measurement and detection of off-board targeting laser spots, but not for guiding LGBs.
Why? To aim the LRMTS at a target it was necessary to keep it in the HUD. For designating LGBs this would entail flying well behind the releasing aircraft to avoid being caught in the explosion (bearing in mind that you would quickly catch up with a LGB as it slowed down during the lofted profile) and this would mean an increased range between laser and target, compounding the effect of the low power and making the reflected signal too weak for the LGB to detect. The geometry of the target matters too; lofted LGBs come in quite flat so the laser really needs to be shining onto a vertical surface to give optimum reflectivity. That is sometimes hard to achieve with a modern targeting pod, let alone through a HUD at long range!