# Level 1B

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This is the basic preprocessing level including radiometric and geometric corrections. Geometric corrections take the viewing characteristics into account.

Level 1B corrections have cancelled the panoramic effect linked to distortions resulting from high viewing angles

### Corrections

This level includes the radiometric corrections mentioned for level 1A.
Geometric corrections associated with systematic distortion introduced by the system: panoramic effect, earth rotation and earth curvature effects, variation in orbital altitude, with respect to the reference ellipsoid.
The geometry of the image is brought to a constant sampling interval.

### Accuracy

The root mean square error in location accuracy is around 500 metres for vertical viewing. The internal relative error on distances is 0.0005 (RMS).

### Use

This level is used for photointerpretation and thematic studies. Image analysis can be performed visually or digitally, with computer assistance. Stereopairs are available and usable visually at this level.

### Full scene size

Level 1A products can be supplied as full scenes or as quarter scenes.
The image is resampled at regular intervals of 10 or 20 metres according to the spectral mode (panchromatic or multispectral).
The number of pixels is therefore altered: it varies from 6400 to 8500 in panchromatic mode and from 3200 to 4250 in multispectral mode according to the viewing angle, giving an image size of 60 kilometers in the North-South direction and 60 to 80 kilometers in the East-West direction.
The oblique part of the image is obtained by adding zero value border pixels.
The scene center is placed on the 3000th or 1500th line, depending on the spectral mode, and each scene is split at an interval of 3000 or 1500 lines, starting from scene center.
For a given "J" on the SPOT GRS, latitude is constant.

### Medium and format

Level 1B products are distributed under the SPOT Standard digital product format.

Range
CCT (full scene only) | P and XS
CD-Rom (full scene only) | P and XS
Film | P and XS
Paper print | P and XS