Highlighted Article: A condensed version of a paper entitled: “Violating Nyquist: Another Source of Significant Error in the Instrumental Temperature Record”

• From: Watts Up With That?
• By: William Ward
• January 1, 2019

A condensed version of a paper entitled: “Violating Nyquist: Another Source of Significant Error in the Instrumental Temperature Record”

"The 169-year long instrumental temperature record is built upon 2 measurements taken daily at each monitoring station, specifically the maximum temperature (Tmax) and the minimum temperature (Tmin). These daily readings are then averaged to calculate the daily mean temperature as Tmean = (Tmax+Tmin)/2. Tmax and Tmin measurements are also used to calculate monthly and yearly mean temperatures. These mean temperatures are then used to determine warming or cooling trends. This “historical method” of using daily measured Tmax and Tmin values for mean and trend calculations is still used today. However, air temperature is a signal and measurement of signals must comply with the mathematical laws of signal processing. The Nyquist-Shannon Sampling Theorem tells us that we must sample a signal at a rate that is at least 2x the highest frequency component of the signal. This is called the Nyquist Rate. Sampling at a rate less than this introduces aliasing error into our measurement. The slower our sample rate is compared to Nyquist, the greater the error will be in our mean temperature and trend calculations. The Nyquist Sampling Theorem is essential science to every field of technology in use today. Digital audio, digital video, industrial process control, medical instrumentation, flight control systems, digital communications, etc., all rely on the essential math and physics of ..."

A condensed version of a paper entitled: “Violating Nyquist: Another Source of Significant Error in the Instrumental Temperature Record”