Data Compilation And Processing

The basic processing of airborne data will be done on the same day the survey flights are flown. This basic processing includes quality control and checking of data, correcting of errors, geophysical calculations and calibrations to final units, so all those steps which are due to aircraft and measuring equipment. Final levelling is done after the whole area is surveyed.After each flight files from aircraft’s PC are copied to Iomega ZIP disk. This ZIP disk is the primary archive media. Data from magnetic base station and GPS base station will also be copied to this disk. Data from this disk is then copied to the processing portable PC.Most of our programs are made in-house. Besides our own software we use GEOSOFT’s OASIS Montaj and AVS/UNIRAS graphical library mainly for map presentation ,data checking and for tie line correction and Exploranium NASVD library for spectral decomposition.A preliminary check program is run to check the data and to make a GEOSOFT binary file (.GBN) for visual checking using OASIS Montaj program. The magnetic field of the magnetic base station is checked using a graphical program which plots the magnetic data to the screen. By this program it is possible to remove civilization effects and noise using median filtering or interactive processing if necessary.A differential correction is applied to GPS data using ASHTECH’s PNAV program and GPS base station data. After this it is possible to cut the flight lines according to the flight area boundaries by interactive processing. Then methodological corrections can be applied to the profile data.Final processing is carried out using desktop PCs and Alpha AXP DEC 3000 UNIX workstation.For radiometric data dead-time, background, cosmic background, stripping, temperature, barometric and height corrections are applied and then the final pulse counts are converted to ground concentrations and dose rates. Radon reduction is carried out using data from upward looking detector.Spectral noise is filtered by NASVD technique. Final levelling is carried out by in-house made automatic levelling program.For magnetic data automatic compensation, lag correction, transient correction and direction correction are applied. Finally magnetic data is levelled by in-house made program which compares adjacent profiles and calculates medians of differences to level profiles. This correction term is always a constant for one flight line. Final levelling is done using tie lines and after that IGRF is removed.Digital terrain model is calculated from geocentric GPS heights and radio altimeter clearance heights. The accuracy of GPS height is much better than that of barometric height. GPS gives only geocentric height but it can be converted to final sea level heights by using some control points.If EM is used, time constant correction, zero level correction and calibration to final units are applied to the data. Also the effect of a conductive body of the aeroplane is corrected by complex coefficients.After methodological corrections the profile data is final, ready for map production and interpretation.Profile data is stored as GEOSOFT XYZ-files, in ASCII. Interpolating is done with OASIS and grids will be stored as GEOSOFT GXF-files. The type of coloured contours is black contours over colour image. Data is archived on a CD-ROM.