Magnetic Anomaly Map of Australia, Seventh Edition, 2020 - Enhanced Products Package - vBzz (PGravTHD) grid

Total magnetic intensity (TMI) data measures variations in the intensity of the Earth's magnetic field caused by the contrasting content of rock-forming minerals in the Earth crust. Magnetic anomalies can be either positive (field stronger than normal) or negative (field weaker) depending on the susceptibility of the rock. The data are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose.This magnetic grid has a cell size of 0.00083 degrees (approximately 88m).The data are in nanoTesla per metre (or nT/m). To constrain long wavelengths in the grid, an independent data set, the Australia-wide Airborne Geophysical Survey (AWAGS) airborne magnetic data, was used to control the base levels of the survey grid. This survey grid is essentially levelled to AWAGS. The data has had a variable reduction to the pole applied to centre the magnetic anomaly over the magnetised body. The VRTP processing followed a differential reduction to pole calculation up to 5th order polynomial. Magnetic inclination and declination were derived from the IGRF-15 geomagnetic reference model using a data representative date and elevation representative of the survey. A further enhancement has been completed to enhance the geological interpretation of the data.

总磁强度（Total Magnetic Intensity, TMI）数据用于量化地壳中成岩矿物成分差异所引发的地球磁场强度变化。磁异常可分为正异常（磁场强度高于正常背景水平）与负异常（磁场强度低于正常背景水平），具体取决于岩石的磁化率。该数据集通过标准流程处理，以确保记录的响应仅由地下岩石引起。处理后得到的数据集可通过解译揭示地下地质结构。经处理的数据由GA地球物理学家开展质量核验，以确保GA发布的最终数据满足使用需求。该磁网格的单元尺寸为0.00083度（约88米），数据单位为纳米特斯拉每米（nT/m）。为约束该网格中的长波长分量，研究人员采用独立数据集——全澳航空地球物理调查（Australia-wide Airborne Geophysical Survey, AWAGS）航空磁测数据——对本次调查网格的基准水平进行校准，本次调查网格基本已与AWAGS数据完成基准平差。该数据已应用可变极化归算（variable reduction to the pole, VRTP），使磁异常中心与对应磁化体的位置重合；本次VRTP处理采用差分极化归算算法，最高拟合至五阶多项式。磁倾角与磁偏角源自IGRF-15地磁参考模型，所用数据的代表日期与高程均匹配本次调查的实际参数。为优化该数据的地质解译效果，研究人员还完成了额外的增强处理。