Table of Contents

Canada and ENVISAT

Satellite - MPB Technologies

MPB Technologies of Pointe Claire, Quebec, built three transponders, part of a system that characterizes the signal from ENVISAT's Advanced Synthetic Aperture Radar (ASAR).

ASAR is characterized by an active array of 320 elements, which can be steered in elevation to make a choice of selective, high-resolution observations of the earth’s surface. An alternating polarization feature allows scenes to be imaged simultaneously in vertical or horizontal polarization. The operating frequency is 5.3 GHz.

The transponders, also known as Active Radar Calibration units, are situated in Flevoland, The Netherlands. By arranging the transponders along an east-west line with about 20 km between adjacent units, all three transponders can be seen within a single swath of the ASAR image mode. Within a few orbits, the transponders can be viewed over a range of 400 km in off-nadir distance.

Each transponder unit is equivalent to a signal repeater that receives, amplifies and re-transmits ASAR signals. However, in order to be used as a precision point target, these units need to possess a very linear response in both amplitude and phase, over the full range of operating temperature. A constant time delay is introduced into the signal path in order to distinguish the retransmitted signals from surrounding clutter, and to allow for self-calibration.

In addition to their gain calibration function, the transponders are also used for the external characterization of the ASAR system. In this mode, they receive signals from one row at a time in the 32-row array, and faithfully store these signals for off-line processing. This calls for high phase stability, as the amplitude and phase characteristics of each row are set for optimum beam formation.

The transponders operate by directing their antennas toward the known satellite position. Typically, they warm up and undergo self-calibration for an hour before each pass, then follow the satellite. After each satellite pass they transmit any collected data to a central site, then shut down to await the next pass.

MPB Technologies Inc. has also built four transponders for the calibration of RADARSAT-1. Three of these are placed across southern Canada, and one is in the harsh environment of the Canadian Arctic. They are under remote control from a central facility in Ottawa.

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Ground Segment - MacDonald Dettwiler and Associates

MacDonald Dettwiler and Associates (MDA) is a long-time partner of the CSA, especially for the RADARSAT program. Their expertise in SAR technology is widely recognized. For the ENVISAT project, they play a more "down-to-earth" role, i.e., within the ground stations. Building on the experience in SAR data handling, they have contributed the Front End Processors which is integrated within the Payload Data Segment to support nominal ENVISAT satellite scientific data acquisition during the mission. Without proper processing of the raw data transmitted to the ground stations, ENVISAT's ASAR antenna would be of little use.

More specifically, they provided eight Front End Processors to be installed in 3 ESA ground stations (ESRIN, Kiruna and Svalbard) and two others to Astrium to be used in the integration of the satellite.; two PF-ASAR Processors, one at Kiruna and the other for the Frascati station, as well as a stand alone PF-ASAR processor, to be used in Calibration/Validation, which can process ERS or ASAR data. They also supply Systems Engineering support to the Prime Contractor, Alcatel Space.

MacDonald Dettwiler is an information company that provides essential information from anywhere in the world, for decision making in the workplace. The company operates its business through two principal groups: The Information Products Group delivers essential land information products and services that encompass legal, asset and geographical information; the Information Systems Group provides mission-critical information systems for monitoring activities on the planet, managing mobile assets and enabling mobile workforces. The company employs 1 800 people through an international network of offices, subsidiaries and distributors.

Ground Segment - Centre for Remote Sensing

The Canada Centre for Remote Sensing will play a key role in the capture of ASAR data through ground stations located in Gatineau, Quebec and Prince Albert, Saskatchewan. In order to achieve this, CCRS implemented a three phase action plan.

They first worked on developing new functionality and to upgrading existing CCRS satellite acquisition management, data reception, archiving and transcription systems, in order to receive, archive and disseminate the ASAR data from the ENVISAT satellite.

Then, through private industry, they conceived a desktop workstation-based low cost capability for the processing and generation of SAR image products from the ENVISAT ASAR sensor. To minimize risk, the development will be implemented in phases. The initial phase will be the development of the Standard Beam Data Processor followed by the development of the Multi Beam Data Processor.

The last step was to provide ENVISAT ASAR data reception, near real-time processing and delivery services to clients--such as the Canadian Ice Service, the Department of Fisheries and Oceans, BC Forest Service--to complement RADARSAT-1 coverage.

The implementation of the ENVISAT ASAR Canadian Ground Segment Implementation Plan will permit the generation of ENVISAT ASAR Level 0 and Level 1 products thus enabling CCRS to meet its operational requirements. It will also provide Canadian industry the opportunity to develop ENVISAT ASAR specific technology and applications, and to provide data to commercial users according to the ESA product distribution policy.

Data Acquisition