Casebook 23 April 2005
CSU-CHILL Casebook: 23 April, 2005
On 23 April 2005, as series balloon-borne radar calibration spheres were launched from the CSU-CHILL radar site. These spheres are light-weight, 12 inch diameter, solid styrofoam balls that have been wrapped in household aluminum foil to provide an electromagnetically reflective outer surface. The sphere is suspended from a conventional helium-filled weather balloon that lifts it to heights that permit the radar to obtain a clutter-free view of the target. Since the sphere presents a known radar cross section, observations of its echo strength can be inserted into the point target form of the weather radar equation to solve for the overall radar system gain. (For accurate calculation of the gain figure, only the returned power values obtained when the antenna main beam axis is directly aligned with the sphere must be used.) The sphere appears as a discrete point target on the radar display. The antenna pattern sidelobes exaggerate the echo width in the cross-beam direction. In the VCHILL example image below, the balloon has lifted the sphere to a height of nearly 10 km AGL at a range of 41 km.
