Uncalibrated Source Research Articles

Hydrophone calibration between 1 kHz and 10 kHz using elastic waveguides

Modern techniques for hydrophone calibration from IEC 60565:2020 typically require sensors to be placed in a free field or within a hydrostatically varying chamber. At mid-frequencies (defined as 1 kHz–10 kHz), the wavelength is too long for free-field conditions in tanks available to most manufacturers and academics. A novel technique to calibrate hydrophones is investigated to address the measurement gap between very-low-frequency (0.1 Hz–1 kHz) and high-frequency (10 kHz–200 kHz) techniques. The measurement environment consists of a 12-meter length of copper tubing that is coiled into a 1-meter diameter helix. Propagation in the elastic waveguide decreases the speed of sound within the apparatus and the wavelength relative to its free-space equivalent. This provides a longer reverb-free time within which to make the calibration measurements using a small (<1 m3) volume. To increase the gain of the system, the recorded files are matched filtered against normalized transmission replicas to determine the signal energy at the receiver. The propagation within the waveguide is studied, including investigating the modal dispersion and channel gain. Calibrations are performed on multiple Ocean Sonics icListen hydrophones, including independently calibrated reference units, using an uncalibrated source to determine the accuracy and precision of the system.

A method for establishing absolute full-energy peak efficiency and its confidence interval for HPGe detectors

A method is proposed for establishing the absolute efficiency calibration of a HPGe detector including the confidence interval in the energy range of 79.6–3451.2keV. The calibrations were accomplished with the 133Ba, 60Co, 56Co and 152Eu point-like radioactive sources with only the 60Co source being activity calibrated to an accuracy of 2% at the 90% confidence level. All data sets measured from activity calibrated and uncalibrated sources were fit simultaneously using the linearized least squares method. The proposed fit function accounts for scaling of the data taken with activity uncalibrated sources to the data taken with the high accuracy activity calibrated source. The confidence interval for the fit was found analytically using the covariance matrix. Accuracy of the fit was below 3.5% at the 90% confidence level in the 79.6–3451.2keV energy range.

Combining Probability Forecasts

SummaryLinear pooling is by far the most popular method for combining probability forecasts. However, any non-trivial weighted average of two or more distinct, calibrated probability forecasts is necessarily uncalibrated and lacks sharpness. In view of this, linear pooling requires recalibration, even in the ideal case in which the individual forecasts are calibrated. Towards this end, we propose a beta-transformed linear opinion pool for the aggregation of probability forecasts from distinct, calibrated or uncalibrated sources. The method fits an optimal non-linearly recalibrated forecast combination, by compositing a beta transform and the traditional linear opinion pool. The technique is illustrated in a simulation example and in a case-study on statistical and National Weather Service probability of precipitation forecasts.

Mixing activity-calibrated and uncalibrated gamma-ray sources in efficiency calibration

A method to calibrate the absolute efficiency of HPGe detectors in a large energy range using both activity-calibrated and uncalibrated multienergy gamma-ray radioactive sources is presented. The adopted efficiency calibration function ε( E) has the simple form ln ε(E)=a 0+a 1 ln(E/E B )+a 2 ln 2(E/E B ) . Different parameters a 0 are simultaneously fitted to the activity-calibrated and uncalibrated sources experimental efficiency data by the least-squares method. As an application example, the calibration of a HPGe detector in the 500 to 3500 keV energy range using a 207 Bi activity calibrated source and one uncalibrated 56 Co source is described.