MEASUREMENT INTERVAL AND THE ACCURATE ASSESSMENT OF GROUND TEMPERATURE TRENDS

High frequency, multi-year ground temperature measurements (every eigh t hours) obtained for the Norman Wells to Zama Pipeline Thermal Monito ring Program were used to create synthetic 'manual' data subsets with measurement intervals between 30 and 90 days. Mean annual temperatures were estimated from the subsets using cubic spline interpolation. By repeatedly producing collections of subsets with a given long term mea surement interval, the uncertainty about the underlying temperature wa ve when sampled at that interval could be summarized using standard st atistical measures (averages and standard deviations). Analysis of dat a from 0.5-5.3 m deep sensors indicates a predictable pattern of uncer tainty for any given measurement interval. The annual temperature regi me is estimated with increasing precision at greater depths for a give n time interval. The standard deviation of the temperature estimates t ends to be greatest where the change in curvature of the true temperat ure time series is greatest. At all depths, the standard deviation of both the instantaneous and the mean annual temperature estimates is a nearly constant proportion of the annual variation at that depth. The magnitude of error that will result for a given measurement interval c an be estimated using the annual temperature range.