Space Dorothy appears on Weather Radar

On August 6th, 2015, PiBalloonIII was launched from the Trinity Valley Community College in Terrell, TX. Launch took place at approximately 11:15AM. The balloon drifted south, towards Athens, and then cut west for a burst near Ennis. Burst happened at ~2:33PM, and the payloads were on the ground shortly thereafter.

Space Dorothy was two draw-string bags filled with ~150 ping pong balls. A 5″ foil tail was attached to each ping pong ball to help with reflectivity. The bags were mounted above the parachute, so they would be turned up-side-down when the balloon burst.

This map shows the launch from Terrell, the burst point, landing site (final K5UTD-11 position), and the debris field based on local area reports. Several residents called after seeing my phone number written on the side of ping pong balls.

flight

This album shows the differential reflectivity between horizontal and vertical polarization on weather radar. At the 1.5° tilt, the altitude was approximately 8kft. At the 2.5°, 3.6° and 4.5° tilts, the approximate altitudes of the beam were 12kft, 17kft, and 21kft respectively.

As you can see, there is a cluster of debris that intersects the expected flight path of the ping pong balls shortly after burst. Because the ping pong balls have little mass and a foil tail, they took much longer to descend than the primary payloads.

Despite original looks at the radar being inconclusive, a further analysis of the Level 2 data proved to be quite useful. The filtering on the WSR-88D most likely filtered out most of the ping pong balls on the Base Reflectivity and Base Velocity products, but the Differential Reflectivity appears to have far less filtering, allowing these reflections to be seen. Apparently 152 ping pong balls can actually appear on weather radar.

These images were rendered with GR2Analyst. The data was pulled from KFWS on 8/6/2015 between 1900 and 2030 UTC.