RADARSAT-1 is the first Canadian developed and commercially operated Earth observation satellite with the objective to monitor environmental change and the planet's natural resources in the microwave region. The observational SAR data is useful to both commercial and scientific users in such fields as disaster management, interferometry, agriculture, cartography, hydrology, forestry, oceanography, ice studies and coastal monitoring. The cooperative project involves the Canadian government under the aegis of CSA (Canadian Space Agency), and the private sector. NASA is a partner in the mission, providing launch services; in exchange, NASA is receiving RADARSAT data at ASF (Alaska SAR Facility), Fairbanks, Alaska. 1) 2) 3) 4) 5)
Table 1: Overview of some key RADARSAT applications
Figure 1: Artist's rendition of the deployed RADARSAT-1 spacecraft in orbit (image credit: MDA, CSA)
The S/C prime contractor is Spar Aerospace Ltd. of Toronto, Ontario (Ball Aerospace & Technologies Corp. of Boulder, CO provided the spacecraft bus). The S/C is three-axis-stabilized with attitude sensors (horizon scanners, sun sensors and magnetometers), momentum wheels and yaw maneuver capability (the S/C uses a set of orthogonally mounted reaction wheels operating around a nominal momentum set point to achieve positive three axis control at all times); momentum desaturation is accomplished with magnetic torque rods. S/C pointing accuracy of ±0.1º (roll, pitch and yaw), pointing knowledge of 0.05º. S/C mass = 3200 kg, payload mass = 1540 kg; solar array power = 3.4 kW BOL (2.9 kW EOL); battery: 3 NiCd (each 48 Ah); propellant: 67 kg hydrazine (orbit adjustment and restitution, and yaw maneuver); design life = 5 years. Autonomous spacecraft operations can be sustained for 24 hour periods.
RF communications: Two parallel X-band downlinks for SAR data transmission [8105 MHz for real-time data at 105 Mbit/s, and 8230 MHz for playback data at 85 Mbit/s; modulation in QPSK, signal quantization = 4 bit (I and Q); RF power = 22 W per channel]. TT&C link in S-band. Most data downlinks are in real-time requiring a network of ground receiving stations for global coverage. RADARSAT can provide daily coverage of the Arctic (with the exception of the North Pole), view any part of Canada within three days, and achieve complete coverage at equatorial latitudes every six days using a 500 km wide swath.
Figure 2: The RADARSAT-1 spacecraft and illustration of observation geometries (image credit: DLR)
Launch: The RADARSAT-1 satellite was launched Nov. 4, 1995 on a Delta II vehicle from Vandenberg AFB, CA.
Orbit: Near circular sun-synchronous dawn-dusk orbit at an altitude of 798 km; inclination = 98.6º, local mean solar time of ascending node at 18:00 (6 PM equatorial crossing); period = 100.7 min; repeat cycle = 24 days (subcycles of 7 and 17 days); the dawn-dusk orbit has the following advantages:
- The platform is in near continuous solar illumination, providing equivalent opportunities for image acquisition during ascending and descending passes (energy consumption).
- A late equatorial crossing time reduces reception conflicts with other remote sensing satellites.
• August 2015: RADARSAT-1 was the first satellite to also provide imaging in narrow and wide ScanSAR modes, corresponding to ground swaths of 300 km with a 50 m resolution and 500 km with a 100 m resolution, respectively. 6)
Some background on the RADARSAT Program: In 1980, the Government of Canada approved a new Canadian Earth observation program called RADARSAT. The work then started for developing the mission requirements and continued through the design and development of a complete system for the first satellite mission called RADARSAT-1 (initially named RADARSAT). Through this program, Canada has been providing without interruption C-band SAR data since the launch of RADARSAT-1 in 1995 and of its successor RADARSAT-2 in 2007. There is also a clear commitment on the part of the Canadian government to maintain data continuity in the future with the development of the next generation RADARSAT Constellation Mission. This continuous data supply enables national and international users to obtain information useful for their operational needs. Since the first mission, the RADARSAT program has gained excellent reputation because of the high-quality calibrated imagery at various incidence angles, resolutions and swath widths that the Program delivers on an operational basis to government, commercial and scientific customers worldwide.
• On May 9, 2013, CSA (Canadian Space Agency) reported the end of the RADARSAT-1 mission. Following numerous attempts to resolve the technical issue, the CSA, in consultation with its commercial distributor MDA Geospatial Services Inc. (MDA GSI) has concluded that RADARSAT-1 is no longer operational after 17 years of outstanding service. 7) 8)
During its 90,828 orbits around the earth it provided 625,848 images to more than 600 clients and partners in Canada and 60 countries worldwide. It assisted with information gathering during 244 disaster events and literally mapped the world, providing complete coverage of the World's continents, continental shelves and polar icecaps.
Among its many accomplishments, RADARSAT-1 conducted Antarctic Mapping Missions (AMM) in 1999 and 2000 and delivered the first-ever, unprecedented high-resolution maps of the entire frozen continent. It also delivered the first stereo-radar coverage of the planet's landmass, the first high-resolution interferometric coverage of Canada, and produced complete single season snapshots of all the continents (Ref. 7).
• On March 29, 2013, RADARSAT-1 experienced a technical anomaly and stopped communicating. As a result the spacecraft entered into safe mode. An expert team is trying to determine what is wrong with the aging satellite.
• In 2013, the RADARSat-1 mission continues to deliver important data well beyond its planned lifetime.
- When the Envisat mission of ESA was lost in April 2012, CSA started immediately negotiations with ESA for the use of RADARSAT-1 and for RADARSAT-2 data. 9)
• The RADARSAT-1 mission is operational in 2012 in its 17th year of service (significantly above and beyond mission design). It continues to be of value to the global remote sensing user community. 10)
- CSA has approved continuation of RADARSAT-1 until March 31, 2013, future under review.
- Data received and processed at 47 ground stations with 32 archive facilities globally.
- As of June 25, 2012, RADARSAT-1 completed 86,868 orbits, planned 351,160 user requests corresponding to a total acquisition of 658,391 minutes of SAR data.
- Average system performance maintained better than 95%.
Table 2: RADARSAT-1 operational status in June 2012 (Ref. 10)
• The RADARSAT-1 spacecraft and its payload are operational in 2011. The current mission extension ends on March 31, 2012. Plans are under way for a further extension. 11)
- Image quality maintained at consistent levels for more than 14 years. Level of maintenance is better than the original specification and design goals (point target measurements).
- Radiometric calibration continues to be maintained despite OBR (On-Board Recorder) no longer available for Amazon data acquisitions: an alternate site (Boreal Forest) within reach of Canadian receiving facilities is now used. - In the time frame 1997-2008, the Amazon region was used for calibration data acquisition (10 acquisitions / 24 day cycle). Since 2008, this service was switched to Canadian sites.
- RADARSAT-1 has set a standard for stable, calibrated ScanSAR imagery
- The latest payload parameter file revision was issued in spring of 2009, successfully updating the radiometric calibration of 7 beams.
- Long term results from internal calibration tests suggest very slow degradation of the transmission level.
- Spacecraft health and resource utilization authorizes a continuation of the operations. 12)
• In November 2010, CSA and MDA Geospatial Services made the RADARSAT-1 mosaics available for the general public. Over its operational life of 15 years, the spacecraft has generated an impressive collection of images, some of which were used to produce high-resolution mosaics of areas of interest. The various mosaics (of Canada, USA, Australia, Africa, Antarctica) were acquired in relatively short time spans and provide a snapshot in time that can be used for studying terrestrial geology, geomorphology, vegetation, coastal features, wetlands, urbanization and ice dynamics. 13)
• In the summer of 2010, the SAR calibration and image quality is still being maintained better than original specifications and design goals of the RADARSAT-1 System Specification document. For both single beam and ScanSAR imagery, routine monitoring of image quality and radiometric calibration are done using images of point targets and distributed targets. The RADARSAT-1 calibration system is operated at the satellite operations facility of CSA (Canadian Space Agency) headquarters located in Longueuil, Canada. - The CDPF (Canadian Data Processing Facility), operated by MDA, has remained the reference processing facility for RADARSAT-1 data quality control since the start of the Maintenance Phase in Feb. 1997. 14)
• The RADARSAT-1 mission is operating "nominally" in 2010 in its extended mission phase - completing its 15th anniversary on orbit in Nov. 2010 (launch Nov. 4, 1995). 15)
• RADARSAT-1 archive transcription to the new system started on April 1, 2009 (at CCRS, Ottawa). 16)
• The system is significantly beyond its design life of 5 years. The on-board resources such as fuel and power are in good supply. The bus attitude control performance is nominal even though momentum wheels and all redundant units are unserviceable. The redundant downlink transmitter for TT&C has reduced capability. For the payload, the SAR antenna continues to provide nominal operations and the SAR system while nominal has no redundancy left. Of the two OBRs only one unit remains operational. 17)
RADARSAT-1 was also used for cross-calibration purposes of RADARSAT-2 (launch on Dec. 14, 2007). The current plans are to continue operations of RADARSAT-1 in parallel for sometime so as to provide benefits to users from supply of C-band SAR data from these two satellites. 18) 19) 20) 21) 22)
• As of 2006, the RADARSAT-1 calibration plan is in its 9th year of operation which started in 1997. In this phase, tracking of beam calibration and image quality parameters are performed on a routine basis. Imagery of reference targets (the primary target site is the Amazon rain forest) is used to monitor the performance of the system.
• The RADARSAT-1 radiometric performance and image quality have continued to consistently excel from the early Maintenance Phase to present (2006), in the fourth year of the extended mission. Measured results indicate that image quality performance is maintained better than specification. RADARSAT-1 has and continues to provide crucial images to assist disaster management efforts under the `International Charter for Space and Major Disasters'.
• On Nov. 27, 2002, CSA temporarily discontinued Radarsat-1 imaging operations on 27 November 2002 because of a deteriorating ACS (Attitude Control System) that affects the satellite's ability to deliver precise imaging to global clients. - Radarsat-1 uses a pitch momentum wheel to maintain gyroscopic stiffness, ensuring the three-axis attitude control required for precise pointing of the spacecraft. In September 1999 the primary pitch momentum wheel started suffering from excessive friction and temperature, and as a result, control was shifted to a back-up wheel. This backup pitch momentum wheel recently developed similar problems and was taken off-line on Nov. 27, 2002, leaving the satellite in what the agency called "a safe and controlled tumble." By the end of Dec. 2002, engineers of the CSA's Satellite Operations Directorate had developed new pointing procedures that eliminated the pitch momentum wheel, relying instead on roll and yaw wheels and torque rods to accurately point the spacecraft.
• RADARSAT-1 was used in the period Sept. 3 - Nov. 14, 2000 to conduct AMM-2 (Antarctic Mapping Mission-2). The objective of AMM-2 was to acquire repeat-pass interferometry to estimate ice surface velocity of the outer regions of the continent (see description below).
• Effective as of Feb. 1, 1999, all ScanSAR images generated by the CDPF (Canadian Data Processing Facility) are radiometrically calibrated. Over the last years, various tests and experiments on attitude control, internal calibration and ScanSAR processing have been undertaken to improve the overall SAR system performance.
• In Sept-Oct. 1997, RADARSAT-1 conducted AMM-1 (Antarctic Mapping Mission-1), representing the first mapping of the ice sheet on Antarctica (see description below).
• RADARSAT-1 was declared "operational" on April 1, 1996 after the commissioning phase.
SAR (Multi-Mode pulsed instrument; observation in C-band (5.3 GHz, 5.6 cm wavelength, RF bandwidth: 11.6 MHz, 17.3 MHz, or 30.0 MHz; transmitter power: up to 5 kW), transmitting and receiving horizontally polarized radiation. Choice of three transmit pulses and selection of numerous beams permit a wide range of swath widths, incidence angles and image resolutions. The SAR instrument can operate at a `high duty cycle' capable of imaging for up to 28 minutes per orbit (orbital period of 100.7 minutes). 23)
Some specific mission objectives are:
- To ensure data availability for environmental monitoring
- To create daily sea ice maps based on SAR data collected over the Arctic
- To collect SAR data over selected portions of the globe for the purpose of crop forecasting
- To obtain periodic SAR data coverage of Antarctic sea ice distribution, subject to receiving station or tape recorder availability
- To collect a global set of stereographic SAR images for mapping
- To obtain the first comprehensive map of the Antarctic continental ice sheet based on SAR imagery
- To collect site and time specific SAR data in support of approved research studies or application demonstrations sponsored either individually or jointly by the parties involved
- To collect and make available global data to any persons, on a non-discriminatory basis
- To develop applications of SAR data in a pre-operational environment
- To promote globally the utilization of RADARSAT-1 SAR data and data products and related information of the Earth's surface.
Special SAR design features: calibration, rapid data processing, a passive slotted waveguide antenna to provide one-dimensional elevation beam forming, and the first satellite implementation of a radar technique known as ScanSAR on a long-term operational basis. The SAR antenna dimensions are: 1.5 m x 15 m (built by CAL Corp.). The antenna comprises one fixed and four deployable panels, each with 32 slotted waveguides fed by beam-forming networks which produce the varied coverage swaths of the radar. 24)
ScanSAR is a technique permitting extended observation coverage (wider swath) on command. In this mode, rapid steering of the elevation beam pattern of the antenna is essential. Extended range coverage can be obtained by using a set of contiguous beams, enabling images to swath widths of up to 500 km. This is accomplished at no increase in mean data rate from the sensor, but at the cost of degraded resolution of the resulting image. The principle of ScanSAR is to share radar operational time between two or more separate subswaths in such a way as to obtain full image coverage of each.
Table 3: RADARSAT-1 imaging modes
Legend of Table 3:
- * Nominal: range dependent and processor dependent
- ** Nominal: ground range resolution varies with range
Data transmission and ground segment
Onboard recording capability of the total stream for up to 10 minutes (when the satellite is outside of receiving station range). Downlink: two parallel X-band channels at 105 Mbit/s for real-time data and at 85 Mbit/s of recorded data. The Canadian ground receiving stations are: Prince Albert (Saskatchewan), and Gatineau (Quebec). All RADARSAT-1 reception stations are compatible with ESA's ERS series.
As of 2004, there is a worldwide network of 23 RADARSAT ground receiving stations licensed by RSI. These are: Cordoba (CONAE), Argentina, Alice Springs and Hobart (ACRES), Australia; Cuiaba (INPE), Brazil; Miyum (RSGS), China; Kumamoto (JAXA), Japan; Seoul (KEOC), Korea; Temerloh (MACRES), Malaysia; Tromsoe (KSAT), Norway; Mayagiiez (UPRM), Puerto Rico; Riyadh (KACST), Saudi Arabia; Singapore (CRISP), Singapore; Bangkok (GISTDA), Thailand; Istanbul (ITU), Turkey; West Freugh (QinetiQ), UK; Fairbanks (ASF), McMurdo, (Antarctica), and Miami (CSTARS), USA.
On January 15, 2007, the Russian UniScan network station in Magadan was awarded RADARSAT-1 Station Operations Certification by MDA Geospatial Services Inc. and the Canadian Space Agency. The addition of this second Russian network station increases the global network of RADARSAT-1 receiving stations to 35.
The primary Canadian archive site for RADARSAT data is Gatineau, providing also accommodation for the Canadian Data Processing Facility (CDPF) that is operated by RADARSAT International Ltd. (RSI) of Ottawa. RSI is a private company (a subsidiary of MDA, Richmond, BC), established in 1989 to process, market and distribute RADARSAT data to Canadian commercial users and to international users. RSI also distributes SPOT, Landsat, and JERS-1 data in Canada. RADARSAT-1 data requested by US investigators is being archived and processed at the ASF (Alaska SAR Facility), Fairbanks, AK.
The RADARSAT MMO (Mission Management Office), and the MCF (Mission Control Facility) are located at CSA in Saint-Hubert, Quebec. The TT&C stations are located in Saint-Hubert and in Saskatoon, Saskatchewan. The main function of MMO is to plan user requests for payload (SAR) tasking. It also coordinates the activities of all other operational ground systems necessary to meet user requests in a timely manner.
Figure 3: MMO interfaces with MCF, Order Desks and Ground Stations (image credit: CSA)
The number of RADARSAT-1 ground stations has evolved over years of operation. Presently (2007) there are 35 (29 fixed, 6 transportable) data reception facilities situated worldwide.
AMM-1 (Antarctic Mapping Mission-1)
A stated mission objective of NASA and CSA was to map the entire ice sheet of Antarctica for the first time. So far, complete coverage of Antarctica was not possible with existing or previous spaceborne SAR missions because of their orbit inclination and/or field of view capability. It turns out that the South Pole itself can only be viewed in a left-sided SAR observation configuration (RADARSAT-1 has a nominal right-side SAR observation configuration). Almost 70% of the Earth's fresh water is contained in the Antarctic region - changes in this enormous reservoir directly influence world sea levels and climate.
The nominal mapping campaign of Antarctica began September 26, 1997 and lasted 18 days, followed by another yaw maneuver (pre-nominal acquisitions from Sept. 19-26; post-nominal acquisitions from October 14-20 - collecting exact repeat data for interferometric analyses). Routine operations with the right-looking mode resumed November 4, 1997. During the period September 9-11, 1997, RADARSAT-1 underwent a successful maneuver to rotate its normally right-looking radar array into a left-looking attitude. This shift involved rotating the satellite by 180º in yaw. Although other missions do regular yaw maneuvers to reorient S/C, RADARSAT-1 was the first satellite to perform this maneuver to map the entire Antarctic continent (a region the size of Canada and Alaska combined), including the South Pole.
AMM yielded the first high-resolution (25 m) radar mosaic of Antarctica, the product of which is now termed the "Antarctic Mosaic." The compilation of 8000 RADARSAT-1 images into the mosaic was undertaken by the Byrd Polar Research Center of Ohio State University (Figure 4). This new mosaic provides a detailed look at ice sheet morphology, rock outcrops, research infrastructure, the coastline, and other features of Antarctica (discovery of two new ice streams in East Antarctica). The resulting map is intended to serve as a benchmark for gauging future changes in the polar ice sheet. 25)
Note: Data accumulated during the mission was initially processed at the Alaska SAR Facility and then sent to the Jet Propulsion Laboratory for a quality review. Final processing of the data into map quality mosaics was performed at the Byrd Polar Research Center using a Vexcel software system called the RADARSAT Antarctic Mapping System (RAMS).
From an operational point of view, AMM demonstrated in particular the need for an automated planning capability. The schedule for AMM consisted of 850 acquisitions (swaths) over 18 days, taking more than a work-year to develop manually.
Other left-looking mode data collected. During AMM, a supplementary Background Mission data acquisition plan was implemented to take advantage of this unique opportunity of imaging geological structures from an exactly opposite radar look direction. The regions selected for this short mission were the Alps, the Appalachians, the Canadian Rockies, Central America, the Himalayas, the Japanese island arc, the Canadian Shield and the US Rockies. Later, these same regions were revisited with the same standard 4-beam once the satellite was restored to its right-looking nominal mode of operations to complete the exact opposite look database. 26) 27)
Fine resolution city coverage. The RADARSAT-1 Background Mission archives also contain 10 m resolution data acquired by means of moderately shallow fine-beam modes over some 170 major cities and capital towns. These are considered historical data, which will be useful reference for observing future urban growth (or decay).
Figure 4: Illustration of the Antarctic Mosaic (image credit: CSA)
AMM-2 (Antarctic Mapping Mission-2)
AMM-2, also referred to as MAMM (Modified Antarctic Mapping Mission), is a joint CSA/NASA interferometric mapping mission of Antarctica in the period Sept. 3 - Nov. 14, 2000 using RADARSAT-1. The objective of AMM-1 (1997) was to acquire complete coverage of the Antarctic continent.
The overall objective of AMM-2 was to acquire repeat-pass interferometry to estimate ice surface velocity of the outer regions of the continent, north of 80º S (re-map the perimeter of the continent and the majority of Antarctica's fast moving glaciers). Interferometric SAR calculations required that this area be imaged 6 times during the mission (three times in descending orbit mode and three times in ascending orbit modes over three consecutive 24-day repeat cycles). This amounted to 2400 SAR data swaths of Antarctica over 72 days. Six image scenes were taken of each area of the continent (three pairs of images, each twenty four days apart); they were used to produce interferometric data about the movement of the ice and the changes in the coastline over time. 28) 29)
New acquisition approach: First, data were acquired so that, where possible, the position of structures on the ice sheet could be compared between the 1997 and 2000 data sets so as to measure point velocities. Secondly, and the real challenge of AMM-2, was to acquire interferometric data so as to estimate velocity fields. The second approach required the use of RADARSAT-1 fine and standard beams, and the unprecedented control of the spacecraft orbit and attitude.
Unlike AMM-1, where the satellite was rotated to a south-looking mode, this was not possible for interferometric acquisition of AMM-2. [Note: In the south looking geometry, the RADARSAT-1 satellite's single thruster is pointing "up" and it is therefore impossible to make the orbit adjustments that would be required for maintaining good interferometric baselines.] Hence, the S/C was not rotated resulting in an acquisition limitation to about 80º S. CSA applied applied special orbit maintenance to minimize the baseline over the three acquisition cycles. A total of about 1500 minutes of SAR data were acquired in several beam modes, including "fine beam" modes of RADARSAT-1.
AMM-2 employed ASPEN (Automated Scheduling and Planning Environment) for mission planning. A model of the mission was built which constructed the 24 days of missions operations repeated three times. There were over 800 imaging activities, and approximately 9000 activities in the 24 day schedule overall, including ground station in-view masks, downlinking events, and onboard recorder activities.
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4) RADARSAT Annual Review 1997/98, CSA brochure, p. 19
6) Satish Derivative, Stephen Schiller, Steve Iris, Ahmed Mahmoud, Surrenders Parish, "RADARSAT Program," Proceedings of the IGARSS (International Geoscience and Remote Sensing Symposium) 2015, Milan, Italy, July 26-31, 2015
8) Satish K. Srivastava, Ahmed Mahmood, Stephane Cote, Stephen Schaller, Surendra Parashar, "Seventeen years of accomplisments of RADARSAT-1," Proceedings of IGARSS (IEEE Geoscience and Remote Sensing Society) 2014, Québec, Canada, July 13-18, 2014
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11) Information provided by Ahmed Mahmood, CSA, St. Hubert, Quebec, Canada
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13) Marc Boucher,"RADARSAT-1 Mosaics Released to the Public," Space Ref Canada, Nov. 18, 2010, URL: http://spaceref.ca/missions-and-programs/canadian-space-agency/radarsat-1/radarsat-1-mosaics-released-to-the-public.html
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15) Jeff Hurley, "Operational Review: RADARSAT-1 & -2," SEASAR Workshop 2010, January 25-29, 2010, Frascati, Italy, URL: http://earth.eo.esa.int/workshops/seasar2010/8_Hurley.pdf
16) Ahmed Mahmood, "RADARSAT-1, RADARSAT-2 and RCM," GSCB ()Ground Segment Coordination Body) Workshop, June 18-19, 2009, ESA/ESRIN Frascati, Italy, URL: http://earth.esa.int/gscb/papers/3.3_Mahmood.pdf
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25) RADARSAT-1 Antarctic Mapping Project. http://www-bprc.mps.ohio-state.edu/rsl/radarsat/radarsat.html
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27) A. L. Gray, K. E. Mattar, P. Vachon, R. Bindschadler, K. Jezek, R. Forster, J. P Crawford, "InSAR results from the RADARSAT Antarctic Mapping Mission Data: estimation of glacier motion using a simple registration procedure", Proceedings of IEEE/IGARSS'98, Seattle, WA., July 6-10, 1998.
28) B. D. Smith, B. E. Engelhardt, D. H. Mutz, J. P. Crawford, "Automated Planning for the Modified Antarctic Mapping Mission," IEEE Aerospace Conference, March 2001,
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).