Tanami MainEW - TMI RTP grid (AWAGS)

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 0.00036 degrees (approximately 40m).The data are in nanoTesla (or nT). The data used to produce this grid was acquired in 2018 by the NT Government, and consisted of 97969 line-kilometres of data at 200m line spacing and 60m terrain clearance. 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-11 geomagnetic reference model using a data representative date and elevation representative of the survey.

总磁强度（Total Magnetic Intensity, TMI）数据用于表征地壳内造岩矿物成分差异引发的地球磁场强度变化。磁异常可分为正异常（磁场强度高于正常值）与负异常（磁场强度低于正常值）两类，其分类取决于岩石的磁化率。该数据通过标准化方法进行处理，以确保所记录的响应仅源于地下岩石。处理后得到的数据集可通过解译揭示地下地质构造。经处理的数据由GA地球物理学家开展质量核查，以确保GA发布的最终数据符合使用要求。该磁网格的单元尺寸为0.00036度（约合40米），数据单位为纳特斯拉（nanoTesla, nT）。该网格的原始数据由NT政府于2018年采集，总测线长度达97969线公里，测线间距为200米，地形离地高度为60米。为约束网格中的长波长信号，本次处理引入了独立数据集——全澳航空地球物理调查（Australia-wide Airborne Geophysical Survey, AWAGS）航空磁测数据，用于校准本次调查网格的基准水平，本次调查网格基本已与AWAGS数据集完成平差校正。该数据已施加可变极化归算（variable reduction to the pole, VRTP）处理，使磁异常中心位于磁化体正上方。此次VRTP处理采用差分极化归算方法，最高可至5阶多项式展开。磁倾角与磁偏角由IGRF-11地磁参考场模型（International Geomagnetic Reference Field, IGRF-11）推导得到，所用数据的代表日期与高程均匹配本次调查的实际情况。