ASAR

Long name Advanced Synthetic-Aperture Radar (ASAR)
Short name N/A
Sensor type Synthetic-aperture radar (SAR)
Platform Environmental Satellite (ENVISAT)
Frequency 5.331 GHz
Band (wavelength) C (5.6 cm)
Polarization VV, HH, VH, VV
Key file name (use to open data set) *.N1
Supported file extensions *.N1, *.txt
Data distributor Eurimage, European Space Agency (ESA), and others
Sections

Data product name and description
Distribution disk files
Returned data for supported format
References

Data product name and description

ASAR has five acquisition modes:
  • Image [IM]
  • Alternating Polarization [AP]
  • Wide Swath [WS]
  • Wave [WV]
  • Global Monitoring [GM]

The [IM], [AP], [WS] and [GM] modes are intended mainly for acquisition over land, coast and polar regions, and [WV] is dedicated to the monitoring of open ocean. The [WV] mode is not supported in CATALYST Professional. Each supported mode is described briefly in the following tables.

Note: The information provided herein is based on the reference documentation cited under References.
Mode Swath width (km) Resolution (range x azimuth, m)* Polarization Description/notes
Image [IM] 100 9.0 x 6.0 Single (VV or HH) Acquired by using a Stripmap technique.
Alternating Polarization [AP] 100 9.0 x 12.0 Dual (VV+HH or VV+VH or HH+HV) Uses a modified ScanSAR technique. Instead of scanning between different elevation subswaths, the [AP] mode (copolar) scans between two polarizations, HH and VV, in a single swath.
Wide Swath [WS] 405

8.0 x 80.0
150 x 150 (MRI)

Single (VV or HH) Acquired by using a ScanSAR technique.
Global Monitoring [GM] 405 1000 x 1000 (MRI) Single (VV or HH) Acquired by using a ScanSAR technique.

* Resolution is always single-look complex (SLC) unless noted otherwise.

The supported acquisition modes are available in five processing levels. Level-0 RAW data is not supported. Wave Mode at processing level 1 (WVS - cross-spectra) is not supported and processing of level 2 applies only to the Wave observation mode (WVW - Ocean spectra) and is, therefore, not supported.

Processing level Acquisition mode Description/notes

0
(RAW)

Not supported Unprocessed and uncalibrated SAR products. The Level 0 product contains Annotated Instrument Source Packets (AISP). These are instrument source packets as received from the instrument, with a small header attached by the front-end processor (FEP).

1B
Single-look complex (SLC)

[IMS]
[APS]
[WSS]

SLC data is considered to be the basic product, because the phase of the radar signal is preserved. The product also maintains the instrument geometry (slant range) and natural pixel sampling.

Absolute calibration parameters are provided in an external file (ASA_XCA*.txt).

1B
Precision image (PRI)

[IMP]
[APP]

PRI data is detected and averaged lightly and spatially to obtain square pixels and projected into the ground-range plane while maintaining path orientation (azimuth, range).

1B
Ellipsoid geocoded image (GEC)

[IMP]
[APP]

Similar to PRI products, except projected onto a map geometry (easting, northing), such as UTM or polar stereographic, by using the WGS84 reference ellipsoid.
1B Medium-resolution image (MRI)

[IMM]
[APM]
[WSM]
[GM1]

Detected and averaged strongly to obtain square pixels and projected onto the ground-range plane while maintaining path orientation. Available at 150-meter resolution, the product is for use specifically in sea-ice and oceanography applications.

Distribution disk files

File name Format Required Contents/details
*.N1 Product-specific binary format Yes Raster data and metadata.
ASA_XCA_AX *.txt Product-specific binary format Yes, required part of the ASA_APS_1P data product only External calibration data. With the ASA_XCA calibration files this part of the name encodes the file-creation date and the date range to which the calibration parameters apply.

Returned data for supported format

ASAR images can be opened directly in their raw vendor format or imported into a PCIDSK (*.pix) file using their key file names (*.N1). For optimal processing, use the PCIDSK format.

The following table describes the data structure after it is imported into a PCIDSK file. Only the fully supported processing level and acquisition modes are listed.

Data product Data returned Details

Level 1A (SLC)
[IMS]

1 x [C16S] Raster channel (Uncalibrated)

1x [GCP] Ground control points
1 x [ORB] Orbital ephemeris data
1 x [ARR] Incidence angle array

N/A

Level 1A (SLC)
[APS]

2 x [C16S] Raster channels (Uncalibrated)
—or—
2 x [C32R] Raster channels

1x [GCP] Ground control points
1 x [ORB] Orbital ephemeris data
1 x [ARR] Incidence angle array

N/A

Level 1A (SLC)
[WSS]

Number of swaths x [C16S] Raster channels (Uncalibrated)
—or—
Number of swaths x [C32R] Raster channels

1x [GCP] Ground control points
1 x [ORB] Orbital ephemeris data

One channel per swath. Number of swaths = 2, 3

Level 1B (PRI)
[IMP]

Level 1B (GEC)
[IMG]

1 x [16U] Raster channel (Uncalibrated)

1x [GCP] Ground control points
1 x [ORB] Orbital ephemeris data
1 x [ARR] Incidence angle array

N/A

Level 1B (PRI)
[APP]

Level 1B (GEC)
[APG]

2 x [16U] Raster channels (Uncalibrated)

1x [GCP] Ground control points
1 x [ORB] Orbital ephemeris data
1 x [ARR] Incidence angle array

N/A

Level 1B (MRI)
[IMM]
[WSM]
[GM1]

1 x [16U] Raster channel (Uncalibrated)

1x [GCP] Ground control points
1 x [ORB] Orbital ephemeris data
1 x [ARR] Incidence angle array

N/A

Level 1B (MRI)
[APM]

2 x [16U] Raster channels (Uncalibrated)
—or—
2 x [32R] Raster channels

1x [GCP] Ground control points
1 x [ORB] Orbital ephemeris data
1 x [ARR] Incidence angle array

N/A

References

Miranda, N., Rosich, B., Meadows, P.J., Haria, K., Small, D., Schubert, A., Lavalle, M., Collard, F., Johnsen, H., Monti Guarnieri, A., D'Aria, D. 2013. The ENVISAT ASAR Mission: A Look at 10 Years of Operation. Proc. ESA Planet Symposium 2013. Edinburgh, UK 9-13 September 2013. SP-722. 17 pages.

European Space Agency (ESA), Envisat ASAR Product Handbook, Issue 2.2. February 2007.

European Space Agency (ESA), Envisat ASAR Product Handbook, Issue 1.1. December 2002.

Rosich, B., Meadows, P. Absolute Calibration of ASAR Level 1 Products Generated with PF-ASAR. European Space Agency (ESA). Issue 1, revision 5. 07 October 2004. Reference ENVI-CLVL-EOPG-TN-03-0010. 26 pages.

Desnos, Y-L., Buck, C., Guijarro, J., Suchail, J-L., Torres, R (2000). ASAR - Envisat’s Advanced Synthetic Aperture Radar. Building on ERS Achievements Towards Future Earth Watch Missions. ESA Bulletin 102 - May 2000. 10 pages.

For more information, visit: European Space Agency (ESA)

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