It’s quite common in research to plot the aircraft noise footprint. It looks like this: http://2.bp.blogspot.com/_3cvpfoj7mb8/TJpQu-_IqfI/AAAAAAAAC7w/hoJ0ZkoVo

It’s quite common in research to plot the aircraft noise footprint. It looks like this: http://2.bp.blogspot.com/_3cvpfoj7mb8/TJpQu-_IqfI/AAAAAAAAC7w/hoJ0ZkoVoDo/s1600/noisecomparison3.jpg http://2.bp.blogspot.com/_3cvpfoj7mb8/TJpQu-_IqfI/AAAAAAAAC7... A significant part of the noise signature is from the jet of hot turbulent air shearing against the surrounding cool air. This happens behind the aircraft. The Doppler effect plays a role too but for jet aircraft the noise is generated behind the aircraft and much is projected backwards. A lot of work has gone into geometries to reduce this shear noise.