Apply Orbit Correction

Apply Orbit File Operator

The orbit state vectors provided in the metadata of a SAR product are generally not accurate and can be refined with the precise orbit files which are available days-to-weeks after the generation of the product. 

The orbit file provides accurate satellite position and velocity information. Based on this information, the orbit state vectors in the abstract metadata of the product are updated.

Orbit Files Supported

The operator currently only supports ASAR and ERS products. 

• For Sentinel-1, Restituted orbit files and Preceise orbit files may be applied. Precise orbits are produced a few weeks after acquisition. Orbit files are automatically download from Array's servers. If an orbit file is not found, you may try looking for it in https://qc.sentinel1.eo.esa.int/  and placing the downloaded file into the auxdata folder.
• For ASAR product, DORIS precise orbit file generated by the Centre de Traitement Doris Poseidon (CTDP) and Delft University can be applied. It provides the satellite positions and velocities in ECEF coordinates every 60 seconds.
• For ERS product, DELFT precise orbit file generated by Delft Institute for Earth-Oriented Space Research (DEOS) can be applied. It provides the satellite ephemeris information (latitude, longitude, height) every 60 seconds. The operator first converts the satellite position from (latitude, longitude, height) to ECEF coordinates, then computes the velocity information numerically.
• Also for ERS product, PRARE precise orbit file generated by Delft University can be applied. It provides the same information every 30 seconds.

Major Processing Steps

To refine the orbit state vectors, the following steps are performed:

1. Get the start time of the source product;
2. Find orbit file with user specified type and the product start time;
3. For each orbit state vector, get its zero Doppler time;
4. Compute new orbit state vector with 8th order Lagrange interpolation using data for the 9 nearest orbit positions around the zero Doppler time.

Parameters Used

The following parameters are used by the operator:

1. Orbit Type: User can select the type of orbit file for the application. Currently the following orbit file types are supported:
   • SENTINEL-1 Restituted
   • SENTINEL-1 Precise
   • DORIS_VOR
   • DORIS_POR
   • DELFT_PRECISE_ENVISAT
   • DELFT_PRECISE_ERS_1
   • DELFT_PRECISE_ERS_2
   • PRARE_PRECISE_ERS_1
   • PRARE_PRECISE_ERS_2