Meteorological Instrument Performance Characteristics

Dynamic Response » Response to Specific Input Functions » High-frequency Sine Wave

The next figure shows the response to a 2.5 Hz sine wave. Here the attenuation for both response signals is strong, and the phase lag approaches 90°; i.e., the peak of the output wave occurs 1/4 wavelength after the peak of the input wave.

Depiction of a high-frequency sine wave with strong attenuation for both the first and second order response

Depiction of a high-frequency sine wave with strong attenuation for both the first and second order response. Image from NCAR/EOL.

In this case (as with the previous example), the transfer function acts as a low-pass filter by attenuating fluctuations that are fast compared to the characteristic response times. It is worth noting, though, that this transfer function isn’t a very good filter because the attenuation changes very slowly over a large frequency range and the transfer function introduces substantial lag over a similar range.

Using the observed response to controlled signals like step, ramp and sine functions often makes it possible to learn the response characteristics of a sensor. For example, a simple exponential response to a step function can be studied to determine the time constant of that system, as can the offset in response to a ramp function.