This week we've seen how measurements of weather and air quality at high altitudes are gathered using airplanes and balloons. There are ways, however, to get such data remotely, using ground-based instruments. Two of the most advanced are in use here in Northeast Philadelphia this summer.

One of the instruments is called RASS, for Radio Acoustic Sounding System. This instrument emits radio waves - like a radar - and also gives off sound waves - explaining the "acoustic" part of the name. By analyzing how these waves are reflected back, it's possible to estimate wind and temperature in the lowest few thousand feet of the atmosphere. Another instrument is called LIDAR, for LIght Detection And Ranging. As the name implies, lidar sends out light beams, and by analyzing how the light interacts with the air, you can estimate temperature, humidity, and ozone levels in the lowest few miles of the atmosphere.

RASS, Lidar, and other similar remote-sensing devices are now used mainly for research, but one day they will be used routinely to make everyday weather observations.