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The following program converts from pixel sample and line indexes to polar stereographic SSM/I grid coordinates to latitude and longitude coordinates. Program II converts from latitude and longitude coordinates to polar stereographic SSM/I grid coordinates to pixel sample lines and indexes.

c Convert xy 11 c c This program converts from Leads ARI grid sample,line c indexes to polar stereographic SSM/I grid coordinates c (in km) and to latitude and longitude. This program is a c version of the program written by C.S. Morris, Jet Propulsion c Laboratory, which appears in the NSIDC SSM/I User's c Guide, Section F, "SSMII Polar Grids". c c Program adapted for Leads ARI grids by F.Fetterer, c NOARL Remote Sensing,Stennis Space Center, March 1991 real*4 x,y,alat,along real*8 e,e2,cdr,pi character*1 grid c Conversion constant, degrees to radians: cdr=57.29577951 c Radius and eccentricity of earth (Hughes ellipsiod, km): re=6378.273 e2=0.006693883 e=SQRT(e2) pi=3.141592654 c Standard parallel - latitude of no distortion slat=70.0 c Puts 135 deg long. at the top of the grid: xlam=-45. print*, 'Type ''P'' for Pacific grid, ''E'' for European' accept*,grid 100 print*,'Type sample, line (9999,9999 to stop)' accept*,sample,rline if (sample.eq.9999.) goto 999 c Transform sample, line coordinates to SSMI grid coordinates if(grid.eq.'P'.or.grid.eq.'p')then y=1975-rline x=-(2250-sample) else y=1300-rline x=sample end if c Comput latitude and longitude: 200 rho=SQRT(x**2+y**2) if(rho.gt.0.1)goto 250 alat=90. along=0. goto 300 250 cm=COSD(slat)/SQRT(1.-e2*(SIND(slat)**2)) t-TAN((pi/4.)-(slat/(2.*cdr)))/((1.-e*SIND(slat))/ & (1.+e*SIND(slat)))**(e/2.) t=rho*t/(re*cm) chi=(pi/2.)-2.*ATAN(T) alat=chi+((e2/2.)+(5.*e2**2./24.)+ & (e2**3./12.))*SIN(2*chi)+((7.*e2**2./ & 48.)+(29.*e2**3/240.))*SIN(4.*chi)+ & (7.*e2**3./120.)*sin(6.*chi) alat=alat*cdr along=xlam+ATAN2D(x,-y) if(along.1t.0.) along = along+360. if(along.gt.360.)along = along-360. 300 print*,' Sample Line SSMI x SSMI y lat & Long' write (6,310)sample,rline,x,y,alat,along print* goto 100 310 format 4f10.2 2f10.4 999 continue end

The program is reproduced from **Fetterer and Hawkins. 1991**. An AVHRR data set for the Arctic leads ARI. *Naval Oceanographic and Atmospheric Research Laboratory, Technical Note 118*. 61
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