I had an extensive talk with my professor about this.
The reason for this tilting/rotation is the USGS satellite imagery is already geocoded (Geocoding is the process of transforming a description of a location—such as a pair of coordinates, an address, or a name of a place—to a location on the earth's surface) or you may say the geometric distortions have already been rectified.
Sources of geometric distortion:
- aspect ratio
- non-linear mirror velocity
- detector geometry & scanning sequence
- panoramic effect
- earth curvature
motions of the aircraft/satellite or target
- attitude changes (pitch, roll, yaw)
- position variations (altitude, slew)
- earth rotation
Distortions appear as:
- changes of scale over the image
irregularities in the angular relationships among the image elements
displacement of objects in an image
occlusion of one image element by another
For an illustration: The image 1 is the raw imagery whereas the image 2 is the geocoded one.