From what I read and managed to figure out, the BRC works like this:
1) construct LOS diagram
2) you know target relative bearing - you know the first angle of which sine is needed
3) find target's AOB - you now know the second angle of which sine is also needed
4) find target's speed
5) find target's bearing rate
now:
- since you know ownship speed, point 90 degree mark (innermost disk) on that speed and read speed across the LOS where target bearing angle is - this is the first speed component. You multiplied your speed by sinus of target bearing angle.
- do the same with target's speed and AOB
- add both speeds to get total relative speed across the LOS
- turn bearing rate value to that calculated speed
- read the range estimation
In my opinion that is the basic principle of BRC operation. OFC this is only my guess from what I read, but it's quite possible they did it like this.
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