# Level 1A

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This is a raw image data level where detector normalization only is performed in each spectral band. This level is normally selected by users wishing to obtain information that has undergone the least possible processing.

The image appears as a square, leading to a panoramic effect for oblique viewing, as the number of pixels remains constant while the East-West image size varies according to viewing angle.

### Corrections

No geometric corrections are performed. Only detector normalization is performed using a linear model which equalizes the difference in sensitivity between CCD detectors (Coupled Charged Detectors).

These basic corrections are systematically performed on all SPOT data.

### Level 1A products are supplied with auxiliary data:

###

#### Image acquisition information

- satellite
- instrument
- spectral band
- GRS (Grid Reference System) designators
- viewing date and time
- angle of incidence and image orientation angle
- geographic coordinates of the four scene corners
- difference in latitude and longitude between the scene center and the nearest GRS node
- sun angles (azimuth and elevation).

#### Scene geometry

- line and column designators
- geographic marks
- attitude rates
- look angles for the beginning and end of the scanline.

#### Scene radiometry

- gains applied to each spectral band
- list of dark current values
- list of CCD normalization coefficients
- absolute calibration coefficients
- histogram of radiometric values
- dynamic range stretching method used and thresholds
- etc

### Use

This preprocessing level is used in particular for stereoplotting and detailed radiometric studies.Stereopairs are available and usable at this level.

### Image size

Level 1A products can be supplied as full scene or as quarter scene. The image is not resampled.

The volume is constant and comprises (for a full scene) 6000 lines each containing 6000 pixels in panchromatic mode, and 3000 lines each containing 3000 pixels in each band of multispectral mode, irrespective of the viewing angle.

### Medium and format

Level 1A products are distributed inSPOT Standard digital product format.

Range
CCT (full scene only) | P and XS
CD-Rom (full scene only) | P and XS
Film | P and XS (auxiliary data on CCT)