Page 172 - Aeronautical Engineer Data Book

Aircraft performance 143
Upward refraction from warm surface air
Cut-off rays Isoemission
line
Flight path
Track

Tropopause

Ground
Grazing/
cut-off points

Secondary boom 'carpets' from downwards refractions
100 km
Wind
50 km

50%
100%
Primary carpet
secondary
carpet

'Bouncing' shock waves giving refracted and
reflected booms at greatly reduced sound pressure

Fig. 9.8 Sonic boom characteristics

the upward-heading wave may be refracted
back to the surface, forming a ‘secondary
boom’ at greatly reduced sound pressure.
Shock waves may also bounce, producing
sound levels only slightly above ambient noise
level (see Figure 9.8)