Meteorological Instrument Performance Characteristics

Dynamic Response » Response to Specific Input Functions » Step Function

An abrupt change in the measurand to a new value, or step-function change, is shown as the red line in the next figure. The first-order response is an exponential (M1, shown by the blue line), but the second-order response (M2, in green) is slower in this case. However, the shape of the second-order response curve, while preserving the exponential behavior, does exhibit differences from the first-order response. These response curves provide good guidance regarding how long it is necessary to wait before errors caused by time response become negligible in a particular application. Response like that shown is commonly seen; for example, temperature sensors on research aircraft often have first-order time constants of a few seconds and this imposes important limitations on the detection of spatial structures using such measurements.

First- and second-order response to an abrupt change in the measurand leading to a step response.

First- and second-order response to an abrupt change in the measurand leading to a step response. Parameters: 𝛕=1, 𝛚=1, 𝛄=1. Image from NCAR/EOL.