**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 conventional altimetry mode and one to process Delay Doppler mode.

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

- Determine surface type.
- Correct tracker ranges for USO frequency drift.
- Compute internal path correction.
- Correct the AGC for instrumental errors.
- Compute Sigma0 scaling factor.
- Compute Doppler correction.
- Correct waveforms by CAL2.

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

- Determine surface type.
- Correct tracker ranges for USO frequency drift.
- Compute internal path correction.
- Correct the AGC for instrumental errors.
- Correct waveforms by CAL1 and CAL2.
- Compute surface locations.
- Apply Doppler correction.
- Apply slant range correction.
- Align the waveforms.
- Perform the Doppler beams stack multi-looking.
- Compute Sigma0 scaling factor.