Betlem Rosich

The ENVISAT advanced synthetic aperture radar system

The European Space Agency has selected an advanced synthetic aperture radar operating at C-band (5.331 GHz) as a payload for the forthcoming ENVISAT mission. The sensor ensures continuity of ERS SAR and features enhanced capability in terms of coverage, range of incidence angles, polarisations and modes of operation. This paper presents the key features of the ENVISAT ASAR system. The ASAR instrument modes of operation are discussed. The ASAR Ground Processor is presented highlighting the concepts for its development and the performance achieved versus the ESA specifications. The selection of processing algorithm for each product is discussed based on the image quality requirements and the throughput.

Sentinel-1 mission operations concept

As part of the European Copernicus programme (formerly Global Monitoring for Environment and Security - GMES), the Sentinel-1 mission, based on a constellation of two SAR satellites, will ensure continuity of C-band SAR observations, building on ESAs and Canadas heritage on satellite SAR systems (ERS, ENVISAT and RADARSAT). 2014 marks the launch of the first Sentinel-1 satellite, which took place from Kourou on 3rd April on a Soyuz launcher. The Sentinel-1 mission operations concept follows the overall Copernicus Space Component operations concept. The mission will be operated based on stable and predefined observation scenarios and associated systematic production schemes. During the Full Operations Capacity of the mission, the observation plans will make optimum use of the maximum SAR duty cycle within the technical constraints of the overall system, with the main objective of satisfying the observation requirements from the Copernicus services and for use by ESA and EU Member States. In addition, a secondary objective is to some extent ensure the continuity of ERS/ENVISAT SAR data exploitation, including in particular the requirements from the scientific communities. For programmatic and technical reasons, a so-called Ramp-Up operations phase has been defined, during which the capacity of the overall system, including the ground segment, will progressively increase, together with the gradual release of the operationally qualified products. The Ramp-Up phase will lead to the Full Operational Capacity of the system with the two-satellite constellation in orbit. The process of collecting the Sentinel-1 observation needs and deriving the baseline observation scenarios is described in the paper at high level. An overview of the main types of services and applications to be supported by Sentinel-1 and the category and sources of observation requirements is provided. The resulting observation plans for the first months of operations are described at high level.

Sentinel-1 mission status

Sentinel-1A has been launched from Kourou on a Soyuz rocket on 3rd April 2014. The second satellite Sentinel-1B is planned to be launched first half of 2016. The In-Orbit Commissioning phase was completed on 23 September 2014, followed by the so-called operational qualification phase (ramp-up). This ramp-up operations phase is a phase during which the capacity of the overall system, including the ground segment operations, is progressively increased, together with the gradual release of the operationally qualified products. The ramp-up phase is being completed at the time of writing this paper (end May 2015); at this stage the routine operations are starting. The Full Operation Capacity (FOC) of the mission will be reached once the In-Orbit Commissioning phase of Sentinel-1B and the subsequent constellation operational qualification phase will have been completed, indicatively by end 2016. The paper provides high-level information on the ongoing mission operations, at the time of the ramp-up phase completion. It described at high level the system operations, incl. ground segment operational activities, as well as some user data access statistics. It presents few examples of mission results achieved during the first year of Sentinel-1A in orbit, in some key application domains.

ASAR instrument performance and product quality status

This paper presents the main characteristics of the advanced synthetic aperture radar (ASAR) instrument on board ENVISAT, ASAR products, the challenges in the ASAR calibration and product validation, the methodology used to perform the sensor performance monitoring and product calibration based on the special ASAR features and dedicated calibration sites and finally a summary on the product quality status will also be provided.

Calibration and early results of the ASAR on ENVISAT

This paper presents the approach for the in-flight calibration of the ENVISAT-1 ASAR and the verification of the ground processing facility PF-ASAR during the commissioning phase. The philosophy presented is a logical progression from the experience gained during calibration of the ERS SARs. The ASAR has a comprehensive internal calibration loop, which is described distinctly from the external calibration and characterisation. The antenna patterns of the various beams have been fully measured during on-ground flight-model testing and have been used for initial performance predictions. In-flight characterisation of the main beams is performed over the South American rainforest. As for ERS, absolute gain calibration is achieved using three fixed and one transportable precision calibration transponders situated in the Netherlands. These transponders are also capable of recording the azimuth beam patterns and supporting the external characterisation mode of ASAR.