The text files in this directory contain information on the spatial gradient
of sigma-0 over Greenland from ERS measurements.  Each file is created from
six months of data centered at the beginning of the indicated year.  For 
example, 'ERS_sigo_gradient_1993.txt' is created from data spanning Oct. 1992
to March 1993.  The columns in each file represent the following information:

Column 1: assigned index (lexicographic pixel number)
Column 2: pixel Latitude (deg)
Column 3: pixel Longitude (deg)
Column 4: x pixel index for Lambertian Projection (8.9 km per pixel)
Column 5: y pixel index
Column 6: Sigma-0 gradient in dB/km
Column 7: Gradient direction in radians relative to north