Application and Determination of Threshold on Free-Air Correction of Marine Magnetic Survey

Space variation of simulation and practical data are analyzed.The conclusions show that the influence of fish's height change to surveying results is relate with complexity of horizontal gradient of magnetic anomaly.Based on foregoing analysis,threshold is proposed,and rationality and practicability are proved by test data.We suggest that magnetic survey data must be corrected to mean sea level when carry level 1,level 2 and level 3 marine magnetic survey.