Measuring weather

Let's look at an example of a radiosonde. The photo to the right is the Vaisala RS92. This radiosonde is small enough to fit in your hand. Most of that size is from a battery pack, insulation, and electronics. The measurement instruments themselves are quite tiny. The temperature sensor is a platinum wire encased in glass, a filament only a fraction of a millimeter wide. The humidity sensor is polymer based, and the RS92 includes two of them, each 4 by 1.5 millimeters. The two humidity sensors alternate observation time and heating time so that condensed water and ice that causes measurements errors can be removed. The pressure sensor, measuring 3 by 2.5 millimeters is located inside the white housing. It consists of a flexible diaphragm electrode sealing off a vacuum chamber. As pressure changes, the distance and capacitance between the diaphragm and a fixed base electrode changes. Wind direction and speed are calculated by GPS measurements on the sonde and at the ground while the sonde rises and is moved by the wind over time.

The RS92 is tethered 60 meters below the balloon during the ascent so that measurements are not affected by the presence of the balloon. As measurements are made, the data are radioed to the radio antenna at the ground and processed and transferred to a computer for monitoring.

You can check out this National Weather Service website for a tour of weather balloon launch procedures!

Next page   -> in situ, upper air measurements, radiosondes & rawinsondes

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