Calibrating the 2016 IRIS Community Wavefields Experiment Nodal Sensors for Amplitude Statics and Orientation Errors

Date: 4/24/2019

Time: 11:30 AM

Room: Grand Crescent

Gradiometry is an array analysis technique that is complementary to the traditional phased array method. Unlike the phased array that requires several signal cycles to accurately compute wave attributes, gradiometry uses a fraction of a signal cycle to compute wave attributes. This quality dictates the compactness of the gradiometer; which makes it deployable in areas inaccessible to large aperture arrays. However, differences in instrument response, digitizer gains, local site conditions and instrument orientation errors can introduce significant errors while computing wave attributes from gradiometer records. Therefore, it is necessary to correct the gradiometer element records for amplitude and instrument orientation variations due to the stated errors. The array calibration method employed in this study is based on the premise that a common wavefield should be recorded over a small-aperture array using teleseismic observation. Teleseismic P and S waves recorded in the course of the 2016 IRIS community-planned experiment in northern Oklahoma were used to estimate amplitude correction factors (ACFs) and orientation correction factors (OCFs) for the gradiometer sensors and two other gradiometer-sized subarrays’ sensors. These subarrays were embedded in the 13-km aperture nodal array that was also fielded during the 2016 IRIS experiment. In situ estimates of ACFs for the gradiometer vary by 2.3% (coefficient of variation) for the vertical channels and, typically, variability is less than 6% for the horizontal channels. Gradiometer elements’ OCFs generally dispersed by 8^o. For the two subarrays, the vertical component ACFs usually vary up to 3.1%, while their lateral components’ ACFs largely spread up to 4.9%. OCFs for the subarrays generally vary by 9^o. Work is currently going on to calibrate the entire nodal sensors of the experimental arrays. The outcome of this study shows that small-aperture arrays can be calibrated for amplitude statics and instrument orientation errors so that the resulting dataset can be used for high precision gradiometry computations.

Presenting Author: Oluwaseyi J. Bolarinwa

Authors