Data Acquisition and Processing - Helicopter Geophysical Survey, Ringvassøy

Abstract

In July 2002, a helicopter geophysical survey was carried out over Ringvassøy, Troms county. The purpose of the surveys was to provide geophysical information for mineral exploration. The data were collected and processed by Geological Survey of Norway (NGU). A total of about 1589 line-km of electromagnetic (EM), very low frequency EM (VLF), radiometric, and magnetic data were acquired using a nominal 200-m line spacing. The nominal flying height was 60 m above ground level (AGL), and lines were flown in alternating directions at headings of South and North. Noise levels were within survey specifications.\rAll initial processing was carried out on a flight-by-flight basis. Magnetic data, consisting of total field measurements collected by a cesium vapor magnetometer, were corrected by removing diurnal variations as recorded at a magnetic base station at Hansnes, Ringvassøy. Radiometric data were reduced using three-channel processing according to procedures recommended by the International Atomic Agency Association. VLF data were reduced by removing a first-order trend along each line. EM data were leveled using data from frequent high altitude excursions above 300-m AGL. All final processed data were gridded using 50-m square cells. Geophysical maps were produced at a scale of 1:50 000 and are considered as standalone products.\rThis report covers aspects of data acquistion and processing.