NOTE: The Level-1B product is an output from Level-1 processing and is an internal product only. It is not available to users and is considered only as an input to Level-2 processing.

The Level-1 calibration chain computes all calibration corrections. One part of these calibration corrections is characterised on the ground and one part is measured in flight.

There are three types of calibrations:

• calibration due to internal calibration of the instrument (CAL1)
• calibration due to the gain profile range window (CAL2)
• calibration due to the calibration of the Automatic Gain Control (AGC) correction tables.

These calibration corrections are applied in the Level-1 measurement chains.

There are two types of Level-1 processing measurement chains: one to process LRM and SAR-C band data and another to process SAR-Ku band data. LRM mode is useful over open-ocean surfaces where topography is homogeneous.

The main processing steps of the LRM and SAR-C Level-1 measurement chains are:

1. Determine surface type.
2. Correct tracker ranges for USO frequency drift.
3. Compute internal path correction.
4. Correct the AGC for instrumental errors.
5. Compute Sigma0 scaling factor.
6. Compute Doppler correction.
7. Correct waveforms by CAL2.

The main processing steps of the SAR-Ku Level-1 measurement chain are:

1. Determine surface type.
2. Correct tracker ranges for USO frequency drift.
3. Compute internal path correction.
4. Correct the AGC for instrumental errors.
5. Correct waveforms by CAL1 and CAL2.
6. Compute surface locations.
7. Apply Doppler correction.
8. Apply slant range correction.
9. Align the waveforms.
10. Perform the Doppler beams stack multi-looking.
11. Compute Sigma0 scaling factor.