基于FPGA的光泵磁梯度仪频率测量方法

The Frequency Measurement Method for Cesium Optically Pumped Magnetic Gradiometer Based on FPGA

磁梯度测量可以在一定程度上消除地磁日变对测量结果的影响,相比于地磁总场探测具有更高的分辨率,在地质勘探、地球物理以及国防军事方面都具有较高的应用价值。本文提出的测量仪以铯光泵磁力仪作为探头,由FPGA搭建采集系统,实现了磁场数据的测量、显示与存储。对现有铯光泵采集系统的频率测量算法进行改进,提出数字插值与移相结合的测频方法,在保证频率测量采样时间的前提上提高了测量精度,减小了测量误差。之后测试了测频模块的精度误差以及探头的一致性等指标。最后通过磁异常探测实验证明磁场梯度测量相比于磁总场探测可以更清晰的反应磁异常的位置大小等信息。

Magnetic-gradient measurement can suppress the influence of the geomagnetic diurnal variation in the measurements to a great extent and thus has higher resolution than traditional total-field measurement.As a result,it has enormous potential in mineral prospecting,geophysics study,and military affairs.This paper introduces a FPGA-based magnetic-gradient measurement system using two Cs-3 optical pumps as magnetometers.The measured magnetic intensity of an optical pump is proportional to its output frequency,so in order to achieve a higher resolution and a stable sampling rate,we propose a frequency measurement method combining the digital interpolation method and the phase shift method.Experiments show that this new method has improved the frequency-measurement performance in terms of accuracy and consistency.And it has also been proved that magnetic-gradient measurement is more accurate than total-field measurement and can provide clearer details of the anomaly,such as its size and position.