ZetaWare, Utilities --- BHT Correction, The Last Resort

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If only BHTs are available with no time-since-circulation information, simply adding 33 °F (18 °C) is actually one of the best correction methods. The expected Teq uncertainty is ±17 °F (±9 °C) . Averaging multiple corrected BHT data from a single depth using either of the latter two methods improves the predicted equilibrium temperature estimate.

ADD 33 °F (18 °C)

The histogram above shows the difference between observed and predicted equilibrium temperature where the correction is obtained by simply adding a constant to the observed BHT (Teq = BHT + 33 °F ) for all data used in this analyses (N = 983 DST-BHT pairs). The constant is the median of the difference between equilibrium temperature and adjacent (±500 ft) measured BHTs. Surprisingly, this correction is less biased and has a smaller residual variance than any correction examined which incorporates depth information.