Guido Levrini

C-SAR instrument design for the Sentinel-1 mission

The ESA Sentinels constitute the first series of operational satellites responding to the Earth Observation needs of the EU-ESA Global Monitoring for Environment and Security (GMES) programme. The GMES space component relies on existing and planned space assets as well as on new complementary developments by ESA. This paper describes the Sentinel-1 mission, an imaging synthetic aperture radar (SAR) satellite constellation at C-band. It provides an overview of the mission requirements, its applications and the technical concept for the system.

ENVISAT radar altimeter system

The Altimetry mission on EnviSat will extend the time series of observations started by ERS-1. The new features of the RA2 mission will improve the quality of the measurements in many aspects. The new on-board algorithms for tracking the surface, the larger range window and the extra low resolution mode will all improve data acquisition over the important ice sheet margins and over most land and wetland surfaces. New, in-situ ionospheric corrections from the dual radar frequency will be a significant improvement on the model-based corrections used in previous missions. The more precise DORIS orbit will improve the precision of all measurements, particularly in near real time. The near real time products will be built with the same algorithms than the off-line final precision products, only some auxiliary input data may differ, thus providing already in 3 hours near-high quality Geophysical Data Record Products to support near real time Oceanography.

The EnviSat RA-2/MWR instrument description, processing chain and data products

Within the ESA Ground Segment, all the Radar Altimeter (RA-2) and Microwave Radiometer (MWR) received data will be systematically processed to Level 1B (geolocated and calibrated engineering parameters) and to Level 2 (geophysical data record). All data will be processed in near real time (availability to users within three hours from data take), then reprocessed as Intermediate GDR (within 3 days) and later in off-line (few weeks after data take). The three version of the Level 2 product have the same layout and provide the typical information of the classical GDR altimeter product. The main difference among them is constituted by the increasing quality of the used orbit. Another main feature of the Level 2 RA-2 product is that every received waveform is processed in parallel by four different algorithms (each one optimised for a particular type of surface: ocean, sea ice, ice 1, ice 2). The Level 2 product (in all its versions) contains the results of the four retracking processes. The Level 1b product NRT and Off-line and the Level 2 NRT products are generated in the ESA station, while the IGDR and the Off-line GDR are produced for ESA by the French Processing and Archiving Centre. Concerning the geophysical corrections, it is important to note that the corresponding MWR measurements are used to correct for the wet tropospheric component, while the dry tropospheric component is corrected making use of the pressure field predicted or reconstructed by ECMWF (European Centre for Medium-Range Weather Forecast).

Sentinel-1 CSAR mission status

The Sentinel-1 synthetic aperture radar (SAR) constellation represents a completely new approach to SAR mission design by ESA in direct response to the operational needs for SAR data expressed under the EU-ESA Global Monitoring for Environment and Security (GMES) programme. The Sentinel-1 constellation is expected to provide near daily coverage over Europe and Canada, and weekly global coverage all independent of weather with delivery of radar data within 1 hour of acquisition - all vast improvements with respect to the existing SAR systems. In addition to responding directly to current needs of the GMES program, the design of the Sentinel-1 satellite mission with its focus on stability, reliability, global coverage, consistent operations and quick data delivery is expected to enable the development of new applications and meet the evolving needs of GMES, for instance in the area of climate change and associated monitoring needs. It is expected that Sentinel-1A will be launched in 2012.

Sentinel-1 ESA's new European SAR mission

The ESA Sentinels constitute the first series of operational satellites responding to the Earth Observation needs of the EU-ESA Global Monitoring for Environment and Security (GMES) program. The GMES space component relies on existing and planned space assets as well as on new complementary developments by ESA. This paper describes the Sentinel-1 mission, an imaging synthetic aperture radar (SAR) satellite constellation at C-band. It provides an overview of the mission requirements, its applications and the preliminary technical concept for the system.

The Envisat geophysical validation programme

Envisat is ESAs advanced Earth observing satellite designed to provide measurements of the atmosphere, ocean, land and ice over a five year period. As the successor to the highly successful ERS-1 and ERS-2 satellites it will provide direct continuity of measurement with most ERS instruments. The payload includes three new atmospheric sounding instruments designed primarily for atmospheric chemistry, including measurement of ozone in the stratosphere. There is an advanced SAR which can collect high resolution images with a variable viewing geometry, together with new wide swath and selectable dual-polarisation capabilities. A new imaging spectrometer is included for ocean colour and vegetation monitoring, and there are improved versions of the ERS radar altimeter, microwave radiometer and visible/near infra-red radiometers, together with a new very precise orbit measurement system. An essential preparation of the Envisat data exploitation is the validation of the geophysical data products which, according to the international CEOS standard is defined as the assessment by independent means of the quality of the data products derived from the system output. The geophysical validation programme is a collaborative effort coordinated by the ESA and consists of a number of validation activities proposed under the Announcement of Opportunity for Envisat data exploitation (AO) and of additional activities by investigators under contract. In a number of instrument and discipline-specific working groups correlative observations are planned to compare Envisat measurements with independent measurements.