Ϊ�о�������ζԺ��յ����Ӧ��Ӱ�죬���ö�άƵ�򽻴��������޲�ַ���( FDFD) ����ģ���е�ų��ֲ�����������ò���ȫ����˹��Ԥ�����˫�����ݶȷ�������ϡ�踴���Դ��������顣���ɽ����ɽ������������Σ�ͬʱ�ı��¶ȴ�С���Ƚϲ�ͬ�¶ȶԵ����Ӧ��Ӱ��̶ȡ��ڴ˻���֮�ϣ��������У���������÷������м򵥿��ٵ��ŵ㣬�ֲ��˺�ʱ�޴�Ĵ����εķ��ݷ����IJ��㡣��������µĵ���У����Ľ���������÷�������׼ȷָʾ�����쳣�Ĵ��ڡ�

To study the effect of undulate topographies on helicopter-borne electromagnetic ( HEM) response�� we use the staggered-grid finite difference method in frequency domain ( FDFD) ��simulate the electromagnetic distribution of two dimensional models��and use the in-complete Cholesky decomposition procedures and the Bi-conjugate gradient solver to calculate largely sparse linear matrix�� Two topographies of hill and valley with various slope angles are used to compare the effects of electromagnet in different slopes�� We offer a linear correction method�� with simple and quick characters��which wakes up the deficiency of the inversion method with topographies to consume too much time�� We check the terrain correction at random topographies��which proves the method effective to indicate the place with anomaly��