migprefd.c

用于石油地震资料数字处理

        /*if the horizontal spacing interval is in feet, convert it to meter*/
        if(!flag)
        dx*=0.3048;


	/* loops over depth */
	for(iz=0;iz<nz;++iz){

        /*the imaging condition*/
        for(ix=0;ix<nx;ix++){
        for(iw=0,w=fw;iw<nw;w+=dw,iw++){   
                complex tmp;
                float ratio=10.0;
                
                if(fabs(ix+ix2-ixshot)*dx<ratio*iz*dz)
                tmp=cmul(cp[iw][ix],cp1[iw][ix]);
                else tmp=cmplx(0.0,0.0);  
                cresult[ix+ix2][iz]+=tmp.r/ntfft;
        }
        }

/* anothe imaging condition, slightly different from the above one, but quite
slow*/
        
/*
        for(iw=0,w=fw;iw<nw;w+=dw,iw++){
                float kk=0.0;
                complex tmp;
                float ratio=1.5; 
                if(dip<80)ratio=1.5;
                else ratio=1.5;
        
                for(ix=0;ix<nx;ix++){     
                kk+=(pow(cp1[iw][ix].i,2.0)+pow(cp1[iw][ix].r,2.0))/nx;
                }
         
                for(ix=0;ix<nx;ix++){
                tmp=cmul(cp[iw][ix],cp1[iw][ix]);

                if(fabs(ix-ixshot)*dx<ratio*iz*dz||ixshot-ix<0 )

                tmp=crmul(tmp,1.0/(kk+1.0e-10));
  
                else tmp=cmplx(0.0,0.0);
                
                cresult[ix+ix2][iz]+=tmp.r/ntfft;
        
                }
                }
*/      
                
                /*get the average velocity*/ 
                v1=0.0;
                for(ix=0;ix<nx;++ix)
                {v1+=v[iz][ix]/nx;}

                /*compute time-invariant wavefield*/
                for(ix=0;ix<nx;++ix)
                for(iw=0,w=fw;iw<nw;w+=dw,++iw) {
                        kz2=-(1.0/v1)*w*dz;
                        cshift2=cmplx(cos(kz2),sin(kz2));
                        cp[iw][ix]=cmul(cp[iw][ix],cshift2);
                        cp1[iw][ix]=cmul(cp1[iw][ix],cshift2);
                }

                /*wave-propagation using finite-difference method*/
                fdmig( cp, nx, nw,v[iz],fw,dw,dz,dx,dt,dip);
                fdmig( cp1,nx, nw,v[iz],fw,dw,dz,dx,dt,dip);

                /*apply thin lens term here*/
                for(ix=0;ix<nx;++ix)
                for(iw=0,w=fw;iw<nw;w+=dw,++iw){
                        kz2=-(1.0/v[iz][ix]-1.0/v1)*w*dz;
                        cshift2=cmplx(cos(kz2),sin(kz2));
                        cp[iw][ix]=cmul(cp[iw][ix],cshift2);
                        cp1[iw][ix]=cmul(cp1[iw][ix],cshift2);
                }

}

free2complex(cp);
free2complex(cp1);
free2float(v);

nxshot--;

/* time(&t2);
warn("\n %d nxshot has been finished in %f seconds",nxshot,difftime(t2,t1));
*/

if(nxshot)goto loop;


	/* restore header fields and write output */
	for(ix=0; ix<nxo; ix++){
                tr.ns = nz ;
                tr.dt = dz*1000000.0 ;
                tr.d2 = dx;
                tr.offset = 0; 
                tr.cdp = tr.tracl = ix;
		memcpy( (void *) tr.data, (const void *) cresult[ix],nz*FSIZE);
		puttr(&tr);
	}
	

	return(CWP_Exit());	

}



float * ricker(float Freq,float dt,int *Npoint)
{
int i;/* they are the dummy counter*/
float Bpar,t,u,*Amp;
int Np1,N;
        
if(Freq==0.0)Freq=30.0;
if(dt==0.0)dt=0.004;
Bpar=sqrt(6.0)/(PI*Freq);
N=ceil(1.35*Bpar/dt);
Np1=N;
*Npoint=2*N+1;
         
Amp=alloc1float(*Npoint);
        
Amp[Np1]=1.0;
  
for(i=1;i<=N;i++)
{
t=dt*(float)i;
u=2.0*sqrt(6.0)*t/Bpar;
Amp[Np1+i]=Amp[Np1-i]=0.5*(2.0-u*u)*exp(-u*u/4.0);
}

return Amp;

}

void fdmig( complex **cp, int nx, int nw, float *v,float fw,float
        dw,float dz,float dx,float dt,int dip)
{
	int iw,ix,step=1;
	float *s1,*s2,w,coefa[5],coefb[5],v1,vn,trick=0.1;
	complex cp2,cp3,cpnm1,cpnm2;
        complex a1,a2,b1,b2;
        complex endl,endr;
        complex *data,*d,*a,*b,*c;

        s1=alloc1float(nx);
        s2=alloc1float(nx);

        data=alloc1complex(nx);
        d=alloc1complex(nx);
        a=alloc1complex(nx);
        b=alloc1complex(nx);
        c=alloc1complex(nx);

        if(dip==45){
        coefa[0]=0.5;coefb[0]=0.25; 
        step=1;
        }
        
        if(dip==65){
        coefa[0]=0.478242060;coefb[0]=0.376369527;
        step=1;
        }
        
        if(dip==79){
        coefa[0]=coefb[0]=0.4575;
        step=1;
        }

        if(dip==80){
        coefa[1]=0.040315157;coefb[1]=0.873981642;
        coefa[0]=0.457289566;coefb[0]=0.222691983;
        step=2;
        }
        
        if(dip==87){
        coefa[2]=0.00421042;coefb[2]=0.972926132;
        coefa[1]=0.081312882;coefb[1]=0.744418059;
        coefa[0]=0.414236605;coefb[0]=0.150843924;
        step=3;
        }
         
        if(dip==89){
        coefa[3]=0.000523275;coefb[3]=0.994065088;
        coefa[2]=0.014853510;coefb[2]=0.919432661;
        coefa[1]=0.117592008;coefb[1]=0.614520676;
        coefa[0]=0.367013245;coefb[0]=0.105756624;
        step=4;
        }

        if(dip==90){
        coefa[4]=0.000153427;coefb[4]=0.997370236;
        coefa[3]=0.004172967;coefb[3]=0.964827992;
        coefa[2]=0.033860918;coefb[2]=0.824918565;
        coefa[1]=0.143798076;coefb[1]=0.483340757;
        coefa[0]=0.318013812;coefb[0]=0.073588213;
        step=5;
	}

        v1=v[0];vn=v[nx-1];

loop:
         
step--;

        for(iw=0,w=fw;iw<nw;iw++,w+=dw){

                if(fabs(w)<=1.0e-10)w=1.0e-10/dt; 

                for(ix=0;ix<nx;ix++){
                        s1[ix]=(v[ix]*v[ix])*coefb[step]/(dx*dx*w*w)+trick;
                        s2[ix]=-v[ix]*dz*coefa[step]/(w*dx*dx)*0.5;
		}

                for(ix=0;ix<nx;ix++){
                        data[ix]=cp[iw][ix];
                }

                cp2=data[1];
                cp3=data[2];
                cpnm1=data[nx-2];
                cpnm2=data[nx-3];
                a1=crmul(cmul(cp2,conjg(cp3)),2.0);
                b1=cadd(cmul(cp2,conjg(cp2)),cmul(cp3,conjg(cp3)));

                if(b1.r==0.0 && b1.i==0.0)
                        a1=cexp(cmplx(0.0,-w*dx*0.5/v1));
                else
                        a1=cdiv(a1,b1);

                if(a1.i>0.0)a1=cexp(cmplx(0.0,-w*dx*0.5/v1));

                a2=crmul(cmul(cpnm1,conjg(cpnm2)),2.0);
                b2=cadd(cmul(cpnm1,conjg(cpnm1)),cmul(cpnm2,conjg(cpnm2)));

                if(b2.r==0.0 && b2.i==0.0)
                        a2=cexp(cmplx(0.0,-w*dx*0.5/vn));
                else
                        a2=cdiv(a2,b2);

                if(a2.i>0.0)a2=cexp(cmplx(0.0,-w*dx*0.5/vn));


                for(ix=0;ix<nx;ix++){
                        a[ix]=cmplx(s1[ix],s2[ix]);
                        b[ix]=cmplx(1.0-2.0*s1[ix],-2.0*s2[ix]);
                }

                for(ix=1;ix<nx-1;ix++){

		d[ix]=cadd(cadd(cmul(data[ix+1],a[ix+1]),cmul(data[ix-1],a[ix-1])),
		cmul(data[ix],b[ix]));
                }

                d[0]=cadd(cmul(cadd(b[0],cmul(a[0],a1)),data[0]),cmul(data[1],a[1]));

		d[nx-1]=cadd(cmul(cadd(b[nx-1],cmul(a[nx-1],a2)),data[nx-1]),
		cmul(data[nx-2],a[nx-2]));

                for(ix=0;ix<nx;ix++){
                        data[ix]=cmplx(s1[ix],-s2[ix]);
                        b[ix]=cmplx(1.0-2.0*s1[ix],2.0*s2[ix]);
                }
                endl=cadd(b[0],cmul(data[0],a1));
                endr=cadd(b[nx-1],cmul(data[nx-1],a2));

                
                for(ix=1;ix<nx-1;ix++){
                        a[ix]=data[ix+1];
                        c[ix]=data[ix-1];
                }
                a[0]=data[1];
                c[nx-1]=data[nx-2];
                        
                retris(data,a,c,b,endl,endr,nx,d);

                for(ix=0;ix<nx;ix++){
                        cp[iw][ix]=data[ix];
                }

        }

if(step) goto loop;

        free1complex(data);
        free1complex(d);
        free1complex(b);
        free1complex(c);
        free1complex(a);
        free1float(s1);
        free1float(s2);
                
        return;
}
                 

void retris(complex *data,complex *a,complex *c, complex *b,
                complex endl,complex endr, int nx, complex *d)
{
                 
        int ix;
        complex *e,den;
        complex *f;

        e=alloc1complex(nx);
        f=alloc1complex(nx);
        e[0]=cdiv(cneg(a[0]),endl);
        f[0]=cdiv(d[0],endl);

        for(ix=1;ix<nx-1;++ix){
                den=cadd(b[ix],cmul(c[ix],e[ix-1]));
                e[ix]=cdiv(cneg(a[ix]),den);
                f[ix]=cdiv(csub(d[ix],cmul(f[ix-1],c[ix])),den);
        }
                 

	data[nx-1]=cdiv(csub(d[nx-1],cmul(f[nx-2],c[nx-2])),cadd(endr,cmul(c[nx-2],e[nx-2])));
                
        for(ix=nx-2;ix>-1;--ix)
        data[ix]=cadd(cmul(data[ix+1],e[ix]),f[ix]);

        free1complex(e);
        free1complex(f);
        return;  
}