Minimize Instrumental Payload

The payload of SENTINEL-6 (JASON-CS) comprises the primary radar altimeter payload with options for supporting instrumentation:

 

Radar Altimeter (POSEIDON-4): The primary measurement system of SENTINEL-6 (JASON-CS), POSEIDON-4 is a fully redundant normal incidence Ku and C band pulse-width limited radar altimeter with the capability of acquiring phase coherent measurements of a surface allowing synthetic-aperture processing to improve along-track sampling and reducing range and Significant Wave Height (SWH) noise as a function of SWH.

Overall performances will be improved with respect to other ocean topography altimeter missions by means of improvements in the design and in an optiminsed pulse timing pattern.

 

The main characteristics of the POSEIDON-4 (SENTINEL-6 Ku/C radar altimeter) are:

 

  • Radar measurement modes: Interleaved mode (simultaneous LRM and SAR, plus reduced-data-rate-SAR RMC

  • Ku-band central frequency of 13.575 GHz, total bandwidth of 320 MHz

  • C-band secondary frequency, used for ionosphere corrections, central frequency of 5.41 GHz, total bandwidth of 320 MHz

  • Tracking modes: closed and open-loop

  • Pulse repetition frequency: approximately 9 kHz (variable from 9.076 to 9.280 kHz)

  • With the current POSEIDON-4 design theoretical performances have been assessed which demonstrates that SENTINEL-6 will improve on its required performances for both LRM and SAR processing.

 

Radiometer

 

The AMR-C multi frequency NASA-JPL instrument extends the capability of the AMR of Jason -2 and -3 to retrieve Total Column of Water Vapour (TCWV) with the capability of minimising long-term drift by means of an on-board calibration mechanism and by periodic pointing of the platform (and radiometer) to deep space to obtain stable reference brightness temperatures. The manoeuvres option will also be used by Jason-3.

 

GNSS

The precise orbit determination (POD) suite is provided from two payloads.

  • The DORIS DGXX-S model will be carried which is a more robust design of the DORIS on board CRYOSAT-2.
  • In line with the previous missions GNSS equipment will be carried. The current option being studied is an enhanced SENTINEL-3B receiver upgraded to 12 channels with the possibility of further enhancement to 18 dual-frequency channels in addition to a capability to receive various dual configurations of GPS (L1, L2 and L5) and Galileo (E1 and E5a) constellation signals simultaneously.

 

Laser Retro-Reflector Array

This is provided by NASA-JPL and is used to support POD by use of global Satellite Laser Ranging (SLR) facilities.

 

 

Star Trackers

Although used as part of the Attitude and Orbit Control System (AOCS), processed star tracker data are a key component in processing POSEIDON-4 SAR data. Three star trackers are available to ensure continuous attitude measurements during Sun and/or Moon blinding.

 

GNS-RO

As an extension to the primary mission objectives, a Radio Occultation (RO) package is used to measure physical properties of the atmosphere such as temperature, pressure and water vapour, by detecting the occultation of GPS signals as they pass through the limb of the atmosphere.