Sentinel-3 is equipped with a GPS receiver, a DORIS received and a Laser Retro Reflector (LRR) for Precise Orbit Determination in support of the altimetry mission (see the Satellite Description section for further information). Observations from all three techniques are equally important to fulfil the stringent orbit accuracy requirements of 2-3 cm in radial direction (see the POD Products and Requirements section for further information).
Satellite Laser Ranging (SLR) is a key technique to calibrate the GPS and DORIS instrument and the overall POD processing chain. With the demanding accuracies of the mission, SLR is needed for the entire mission life-time to perform periodic checks of the biases that could exist between different tracking techniques. For this reason, at the moment the tracking observations from SLR are not incorporated into the orbit determination processing, but instead are used in an independent validation procedure.
The Copernicus POD Service is responsible for the liaison with the ILRS Community, as it is in charge of generating the CPF orbit files for the ILRS tracking stations and is the main user of the SLR measurements to validate the precise orbital products of Sentinel-3.
Due to the sensitivity of the OLCI (Ocean and Land Color Instrument) to high energy laser illumination, the number of ILSR stations tracking Sentinel-3 was limited to those with an energy threshold below 1.7 nJ/cm2 at the satellite. The list of SLR stations that signed the agreement to track Sentinel-3 satellites following this restriction can be found at the ILRS Sentinel-3: Mission support webpage, together with the corresponding Mission Support Request Forms.
Information on the SLR tracking statistics for Sentinel-3 as well as a list of CPOD publications involving Sentinel-3 and ILRS can be found in the SLR Tracking section of the Technical Guide.