PALSAR, Phased Array type L-band Synthetic Aperture Radar, is an active microwave sensor on board the ALOS satellite mission, launched in 2006. It provides fine resolution mode and ScanSAR mode, which allows a swath three to five times wider than conventional SAR images.
Source: Japan Aerospace Exploration Agency, 2003b.
COSMO-SkyMed
COSMO-SkyMed mission is a group of four satellites equipped with radar sensors for Earth observation for civil and defense use. The mission was developed by the Italian Space Agency (Agenzia Spaziale Italiana) and Telespazio. The program supplies data for emergency management services, environmental resources management, earth topographic mapping, maritime management, natural resources monitoring, surveillance, interferometric products and digital elevation models.
The first two satellites were launched in 2007, the third satellite launched in 2008, and the fourth satellite is under development.
The sensors operate in various wide field and narrow field modes, with multi-polarmetric and multi-temporal capabilities.
Table 18: PALSAR Sensor Characteristics
Fine Mode ScanSAR Mode
Center Frequency 1270 MHz (L-band) 1270 MHz (L-band) Polarization HH or VV
HH+HV or VV+VH
HH or VV
Range Resolution 7 to 44 m 14 to 88 m
100m (multilook)
Observation Swath 40 to 70 km 250 to 350 km
Bit Length 5 bits 5 bits
Table 19: COSMO-SkyMed Imaging Characteristics
Mode Swath Resolution
ScanSAR Hugeregion
200 km x 200 km 100 m pixel
Sources: Telespazio, 2008 and e-GEOS, 2008.
Envisat
In 2002, the European Space Agency launched Envisat (ENVIronmental SATellite), an advanced polar-orbiting Earth
observation satellite which provides measurements of the atmosphere, ocean, land, and ice. Envisat mission provides for continuity of the observations started with the ERS-1 and ERS-2 satellite missions, notably atmospheric chemistry, ocean studies and ice studies.
Envisat flies in a sun-synchronous polar orbit at about 800 km altitude, with a repeat cycle of 35 days.
Envisat is equipped with these instruments:
• ASAR - Advanced Synthetic Aperture Radar operating at C-band.
• MERIS - Programmable, medium-spectral resolution spectrometer operating in the 390 nm to 1040 nm spectral range.
• AATSR - Advanced Along Track Scanning Radiometer continues the collection of ATSR-1 and ATSR-2 sea surface temperature data sets.
• RA-2 - Radar Altimeter 2 determines the two-way delay of the radar echo from the Earth’s surface to a very high precision. Also
measures the power and shape of reflected radar pulses.
• MWR - Microwave radiometer measures the integrated
atmospheric water vapor column and cloud liquid water content, as correction terms for the radar altimeter signal.
ScanSAR Wideregion
100 km x 100 km 30 m pixel
Stripmap HImage
40 km x 40 km 3 - 15 m pixel
Stripmap Pingpong
30 km x 30 km 15 m pixel
Spotlight 1 Classified Classified
Spotlight2 10 km x 10 km 1 m pixel
Table 19: COSMO-SkyMed Imaging Characteristics
Mode Swath Resolution
• GOMOS - Medium resolution spectrometer measures atmospheric constituents in the spectral bands between 250 nm to 675 nm, 756 nm to 773 nm, and 926 nm to 952 nm. It includes two photometers measuring in the spectral bands between 470 nm to 520 nm and 650 nm to 700 nm.
• MIPAS - Michelson Interferometer for Passive Atmospheric Sounding is a Fourier transform spectrometer for measuring gaseous emission spectra in the near to mid infrared range.
• SCIAMACHY - Imaging spectrometer measures trace gases in the troposphere and stratosphere.
• DORIS - Doppler Orbitography and Radio-positioning Integrated by Satellite instrument is a tracking system to determine the precise location of Envisat satellite.
• LRR - Laser Retro-Reflector tracks orbit determination and range measurement calibration.
Source: European Space Agency, 2008b.
ERS-1
ERS-1, a radar satellite, was launched by ESA in July of 1991. ESA, European Space Agency, announced the end of the ERS-1 mission in March 2000.
The ERS-1 was ESA’s first sun-synchronous polar-orbiting mission, acquiring more than 1.5 million Synthetic Aperture Radar scenes. The measurements of sea surface temperatures made by the ERS-1 Along-Track Scanning Radiometer are the most accurate ever from space.
These and other critical measurements are continued by the ERS-2 mission and Envisat.
Source: European Space Agency, 2008a.
One of its primary instruments was the Along-Track Scanning
Radiometer (ATSR). The ATSR monitors changes in vegetation of the Earth’s surface.
The instruments aboard ERS-1 include: SAR Image Mode, SAR Wave Mode, Wind Scatterometer, Radar Altimeter, and Along Track Scanning Radiometer-1 (European Space Agency, 1997).
Some of the information obtained from the ERS-1 and ERS-2 missions include:
• maps of the surface of the Earth through clouds
• physical ocean features and atmospheric phenomena
• maps and ice patterns of polar regions
• database information for use in modeling
• surface elevation changes According to ESA,
. . .ERS-1 provides both global and regional views of the Earth, regardless of cloud coverage and sunlight conditions. An operational near-real-time capability for data acquisition,
processing and dissemination, offering global data sets within three hours of observation, has allowed the development of time-critical applications particularly in weather, marine and ice forecasting, which are of great importance for many industrial activities (European Space Agency, 1995).
Source: European Space Agency, 1995.
ERS-2
ERS-2, a radar satellite, was launched by ESA in April 1995. It has an instrument called GOME, which stands for Global Ozone Monitoring Experiment. This instrument is designed to evaluate atmospheric chemistry. ERS-2, like ERS-1 makes use of the ATSR.
The instruments aboard ERS-2 include: SAR Image Mode, SAR Wave Mode, Wind Scatterometer, Radar Altimeter, Along Track Scanning Radiometer-2, and the Global Ozone Monitoring Experiment.
ERS-2 receiving stations are located all over the world. Facilities that process and archive ERS-2 data are also located around the globe.
One of the benefits of the ERS-2 satellite is that it can provide data from the exact same type of synthetic aperture radar (SAR).
ERS-2 provides many different types of information. See ERS-1 on page 100 for some of the most common types. Data obtained from ERS-2 used in conjunction with that from ERS-1 enables you to perform interferometric tasks. Using the data from the two sensors, DEMs can be created.
For information about ERDAS IMAGINE’s interferometric software, IMAGINE InSAR, see IMAGINE InSAR Theory on page 679.
Source: European Space Agency, 1995.
JERS-1
JERS stands for Japanese Earth Resources Satellite. The JERS-1 satellite obtained data from 1992 to 1998, and has been superseded by the ALOS mission.
See ALOS on page 68 for information about the Advanced Land Observing Satellite (ALOS).
Source: Japan Aerospace Exploration Agency, 2007.
The JERS-1 satellite was launched in February of 1992, with an SAR instrument and a 4-band optical sensor aboard. The SAR sensor’s ground resolution was 18 m, and the optical sensor’s ground resolution was roughly 18 m across-track and 24 m along-track. The revisit time of the satellite was every 44 days. The satellite travelled at an altitude of 568 km, at an inclination of 97.67°.
1 Viewing 15.3° forward
Source: Earth Remote Sensing Data Analysis Center, 2000.
JERS-1 data comes in two different formats: European and Worldwide.
The European data format consists mainly of coverage for Europe and Antarctica. The Worldwide data format has images that were acquired from stations around the globe. According to NASA, “a reduction in transmitter power has limited the use of JERS-1 data” (National Aeronautics and Space Administration, 1996).
Source: Eurimage, 1998; National Aeronautics and Space Administration, 1996.
RADARSAT
The RADARSAT satellite was developed by the Canadian Space Agency and launched in 1995. With the development of RADARSAT-2, the original RADARSAT is also known as RADARSAT-1.
Table 20: JERS-1 Bands and Wavelengths
Band Wavelength
1 0.52 to 0.60 μm
2 0.63 to 0.69 μm
3 0.76 to 0.86 μm
41 0.76 to 0.86 μm
5 1.60 to 1.71 μm
6 2.01 to 2.12 μm
7 2.13 to 2.25 μm
8 2.27 to 2.40 μm
The RADARSAT satellite carries SARs, which are capable of transmitting signals that can be received through clouds and during nighttime hours. RADARSAT satellite has multiple imaging modes for collecting data, which include Fine, Standard, Wide, ScanSAR Narrow, ScanSAR Wide, Extended (H), and Extended (L). The resolution and swath width varies with each one of these modes, but in general, Fine offers the best resolution: 8 m.
The types of RADARSAT image products include: Single Data, Single Look Complex, Path Image, Path Image Plus, Map Image, Precision Map Image, and Orthorectified. You can obtain this data in forms ranging from CD-ROM to print.
The RADARSAT satellite uses a single frequency, C-band. The altitude of the satellite is 496 miles, or 798 km. The satellite is able to image the entire Earth, and its path is repeated every 24 days. The swath width is 500 km. Daily coverage is available of the Arctic, and any area of Canada can be obtained within three days.
Source: RADARSAT, 1999; Space Imaging, 1999c.
RADARSAT-2
RADARSAT-2, launched in 2007, is a SAR satellite developed by the Canadian Space Agency and MacDonald, Dettwiler, and Associates, Ltd. (MDA). The satellite advancements include 3 meter high-resolution imaging, flexibility in polarization selection, left and right-looking imaging options, and superior data storage.
In addition to RADARSAT-1 beam modes, RADARSAT-2 offers Ultra-Fine, Multi-Look Ultra-Fine, Fine Quad-Pol, and Standard Quad-Pol beam modes. Quadrature-polarization means that four images are acquired simultaneously; two co-polarized images (HH and VV) and two cross-polarized images (HV and VH).
Table 21: RADARSAT Beam Mode Resolution
Beam Mode Resolution
Fine Beam Mode 8 m
Standard Beam Mode 25 m
Wide Beam Mode 30 m
ScanSAR Narrow Beam Mode 50 m
ScanSAR Wide Beam Mode 100 m
Extended High Beam Mode 25 m
Low Beam Mode 35 m
Source: RADARSAT-2, 2008.
SIR-A
SIR stands for Spaceborne Imaging Radar. SIR-A was launched and collected data in 1981. The SIR-A mission built on the Seasat SAR mission that preceded it by increasing the incidence angle with which it captured images. The primary goal of the SIR-A mission was to collect geological information. This information did not have as pronounced a layover effect as previous imagery.
An important achievement of SIR-A data is that it was capable of penetrating surfaces to obtain information. For example, NASA says that the L-band capability of SIR-A enabled the discovery of dry river beds in the Sahara Desert.
SIR-1 used L-band, had a swath width of 50 km, a range resolution of 40 m, and an azimuth resolution of 40 m (Atlantis Scientific, Inc., 1997).
For information on the ERDAS IMAGINE software that reduces layover effect, IMAGINE OrthoRadar, see IMAGINE OrthoRadar Theory on page 657.
Source: National Aeronautics and Space Administration, 1995a;
National Aeronautics and Space Administration, 1996; Atlantis Scientific, Inc., 1997.
Table 22: RADARSAT-2 Characteristics Geometry of orbit near-polar, sun-synchronous Orbit Altitude 798 km
Orbit Inclination 98.6 degrees Orbit repeat cycle 24 days
Frequency Band C-band (5.405 GHz) Channel Bandwidth 11.6, 17.3, 30, 50, 100 MHz Channel Polarization HH, HV, VH, VV
Spatial Resolution 3 meters to 100 meters
SIR-B
SIR-B was launched and collected data in 1984. SIR-B improved over SIR-A by using an articulating antenna. This antenna allowed the incidence angle to range between 15 and 60 degrees. This enabled the mapping of surface features using “multiple-incidence angle
backscatter signatures” (National Aeronautics and Space Administration, 1996).
SIR-B used L-band, has a swath width of 10-60 km, a range resolution of 60-10 m, and an azimuth resolution of 25 m (Atlantis Scientific, Inc., 1997).
Source: National Aeronautics and Space Administration, 1995a, National Aeronautics and Space Administration, 1996; Atlantis Scientific, Inc., 1997.
SIR-C
SIR-C sensor was flown onboard two separate NASA Space Shuttle flights in 1994. Flight 1 was notable for a fully polarimetric spaceborne SAR, multi-frequency, X-band, and demonstrated ScanSAR for wide swath array. Flight 2 was notable for the first SAR to re-fly, targeted repeat-pass interferometry, and also demonstrated ScanSAR for wide swath array.
Source: National Aeronautics and Space Administration, 2006.
SIR-C is part of a radar system, SIR-C/X-SAR, which flew in 1994. The system is able to “. . .measure, from space, the radar signature of the surface at three different wavelengths, and to make measurements for different polarizations at two of those wavelengths” (National
Aeronautics and Space Administration, 1997). Moreover, it can supply “. . .images of the magnitude of radar backscatter for four polarization combinations” (National Aeronautics and Space Administration, 1995a).
The data provided by SIR-C/X-SAR allows measurement of the following:
• vegetation type, extent, and deforestation
• soil moisture content
• ocean dynamics, wave and surface wind speeds and directions
• volcanism and tectonic activity
• soil erosion and desertification
The antenna of the system is composed of three antennas: one at L-band, one at C-L-band, and one at X-band. The antenna was assembled by the Jet Propulsion Laboratory. The acquisition of data at three different wavelengths makes C/X-SAR data very useful. The SIR-C and X-SAR do not have to be operated together: they can also be operated independent of one another.
SIR-C/X-SAR data come in resolutions from 10 to 200 m. The swath width of the sensor varies from 15 to 90 km, which depends on the direction the antenna is pointing. The system orbited the Earth at 225 km above the surface.
Source: National Aeronautics and Space Administration, 1995a, National Aeronautics and Space Administration, 1997.
TerraSAR-X
TerraSAR-X, launched in 2007, is a German satellite manufactured in a public private partnership between the German Aerospace Center (DLR), Astrium GmbH, and the German Ministry of Education and Science (BMBF).
TerraSAR-X carries a high frequency X-band SAR instrument based on an active phased array antenna technology. The satellite orbit is sun-synchronous at 514 km altitude at 98 degrees inclination and 11 days repeat cycle.
The satellite sensor operates in several modes; Spotlight, high Resolution Spotlight, Stripmap, and ScanSAR, at varying geometrical resolutions between 1 and 16 meters. It provides single or dual polarization data.
Table 23: SIR-C/X-SAR Bands and Frequencies
Bands Wavelength
L-Band 0.235 m
C-Band 0.058 m
X-Band 0.031 m
Table 24: TerraSAR-X Imaging Characteristics
Mode Swath Resolution
Spotlight (SL) 10 x 10 km scene 1 - 3 meters High Resolution
Spotlight (HS)
5 km x 10 km scene 1 - 2 meters
Stripmap (SM) 30 km strip 3 - 6 meters
ScanSAR (SC) 100 km strip 16 meters
Source: DLR (German Aerospace Center). 2008.