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Why do Southern Hemisphere scenes not display the correct UTM designation?


Traditional Universal Transverse Mercator (UTM) convention distinguishes between the Northern and Southern Hemispheres. In the Northern Hemisphere, the UTM zone is a positive value or identified as UTM North. In the Southern Hemisphere, the UTM zone is a negative value or identified as UTM South. UTM North scenes in this convention have a false northing value of 0, while UTM South scenes have a false northing of 10,000,000. This false northing value effectively shifts the negative projection Y coordinates to a positive value.

Because the use of two different false northing values creates a discontinuity of the scenes when trying to mosaic them, Landsat Level-1 products are processed with a northern UTM zone (i.e., a positive UTM zone), regardless of whether the scene is in the Northern or Southern Hemisphere. With this projection, any scene in the Southern Hemisphere will have a negative projection Y coordinate.

The scenes will display correctly in most (if not all) popular imaging software packages; however, users need to understand that simply negating the UTM zone or reassigning the UTM North to UTM South will cause the projection coordinates to be inaccurate. If the UTM zone is switched to a southern zone for a Southern Hemisphere scene, then the projection Y values must also be adjusted by a value of 10,000,000. This will ensure any coordinate transformations are handled correctly.