Most of the standard regions use conformal (equal-area) projections.
For such projections, the area of each pixel is constant and equation
to the nominal pixel dimension (4.45 km for SASS) squared.  However, 
polar regions use a polar stereographic projection.  This projection 
does not have constant area pixels.  For these regions, SIR-format 
images that contain the pixel area in square km for each pixel are
provided here.