Airborne Weather Radar — Page 220, Lesson 205

Let's start with the mapping operation of the airborne weather radar. For the basic monochrome AWR — that's the airborne weather radar — with a maximum range of 150 nautical miles, we have two different beams we can use for ground mapping. The first is the cosecant² beam, which is fan-shaped. We use that for mapping up to about 70 nautical miles by selecting the MAP position on the control unit. Beyond 70 nautical miles, we switch to the pencil beam by selecting the MAN position. Both of these modes have manual gain control, which lets you improve the radar information you get on the display. Now, the key to good mapping is adjusting the downward tilt of the antenna for the best target presentation. Here's the physics: little energy reflects from a calm sea, fine sand, and flat terrain. So those surfaces give weak returns. But coastlines, built-up areas, skyscrapers, bridges, and power stations give very bright returns because they reflect strongly. Ice has jagged edges which reflect well, but snow is a poor reflector and actually masks ground features beneath it. And here's a classic trap: when you fly over high ground, the mountains and hills cast a radar shadow — the beam can't reach the far side — and that shadow can produce a false image that looks like a series of lakes. That's the hill shadow effect, shown in Figure 13.16. Now let's move to pre-flight checks. This is critical because electromagnetic radiation is a serious hazard to personnel and to electronic equipment. So before you check the radar on the ground, you must take great care. First, ensure the aircraft is clear of personnel, other aircraft, vehicles, and buildings. Then, select the conical beam with maximum uptilt, switch the radar on, check that you have a picture, and then go back to standby. That's the sequence — conical beam, maximum uptilt, on, verify picture, back to standby.