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ASAR Data Formats Products
Geolocation Grid ADSRs
Doppler Centroid parameters
Chirp parameters
Antenna Elevation pattern
ASAR external characterization data
ASAR external calibration data
Level 0 SPH
Level 0 MDSR
SPH for auxiliary data with N=1 DSDs
Wave Mode Geolocation ADS
ASAR Wave Mode Products Base SPH
Slant Range to Ground Range conversion parameters
Measurement Data Set containing spectra. 1 MDSR per spectra.
Ocean Wave Spectra
Map Projection parameters
ASAR Image Products SPH
Measurement Data Set 1
Auxilliary Products
ASA_XCH_AX: ASAR External characterization data
ASA_XCA_AX: ASAR External calibration data
ASA_INS_AX: ASAR Instrument characterization
ASA_CON_AX: ASAR Processor Configuration
Browse Products
ASA_WS__BP: ASAR Wide Swath Browse Image
ASA_IM__BP: ASAR Image Mode Browse Image
ASA_GM__BP: ASAR Global Monitoring Mode Browse Image
ASA_AP__BP: ASAR Alternating Polarization Browse Image
Level 0 Products
ASA_WV__0P: ASAR Wave Mode Level 0
ASA_WS__0P: ASAR Wide Swath Mode Level 0
ASA_MS__0P: ASAR Level 0 Module Stepping Mode
ASA_IM__0P: ASAR Image Mode Level 0
ASA_GM__0P: ASAR Global Monitoring Mode Level 0
ASA_EC__0P: ASAR Level 0 External Characterization
ASA_APV_0P: ASAR Alternating Polarization Level 0 (Cross polar V)
ASA_APH_0P: ASAR Alternating Polarization Level 0 (Cross polar H)
ASA_APC_0P: ASAR Alternating Polarization Level 0 (Copolar)
Level 1 Products
ASA_IMS_1P: ASAR Image Mode Single Look Complex
ASA_IMP_1P: ASAR Image Mode Precision Image
ASA_IMM_1P: ASAR Image Mode Medium Resolution Image
ASA_IMG_1P: ASAR Image Mode Ellipsoid Geocoded Image
ASA_GM1_1P: ASAR Global Monitoring Mode Image
ASA_APS_1P: ASAR Alternating Polarization Mode Single Look Complex
ASA_APP_1P: ASAR Alternating Polarization Mode Precision Image
ASA_APM_1P: ASAR Alternating Polarization Medium Resolution Image product
ASA_WSS_1P: Wide Swath Mode SLC Image
ASA_WVS_1P: ASAR Wave Mode Imagette Cross Spectra
ASA_WSM_1P: ASAR Wide Swath Medium Resolution Image
ASA_APG_1P: ASAR Alternating Polarization Ellipsoid Geocoded Image
Level 2 Products
ASA_WVW_2P: ASAR Wave Mode Wave Spectra
ASAR Glossary Terms
Sea Ice Glossary
Land Glossary
Oceans Glossary
Geometry Glossary
ASAR Instrument Glossary
Acronyms and Abbreviations
ASAR Frequently Asked Questions
The ASAR Instrument
Instrument Characteristics and Performance
Inflight Performance Verification
Preflight Characteristics and Expected Performance
Instrument Description
Internal Data Flow
ASAR Instrument Functionality
Payload Description and Position on the Platform
ASAR Products and Algorithms
Auxiliary Products
Common Auxiliary Data Sets
Auxiliary Data Sets for Level 1B Processing
Summary of Auxiliary Data Sets
Instrument-specific Topics
Level 2 Product and Algorithms
Level 2 Product
ASAR Level 2 Algorithms
Level 1B Products
ASAR Level 0 Products
Level 0 Instrument Source Packet Description
Product Evolution History
Definitions and Conventions
Organisation of Products
ASAR Data Handling Cookbook
Hints and Algorithms for Higher Level Processing
Hints and Algorithms for Data Use
ASAR Characterisation and Calibration
The Derivation of Backscattering Coefficients and RCSs in ASAR Products
External Characterisation
Internal Calibration
Pre-flight Characterisation Measurements
ASAR Latency Throughput and Data Volume
Data Volume
Products and Algorithms Introduction
Child Products
The ASAR User Guide
Image Gallery
Further Reading
How to Use ASAR Data
Software Tools
How to Choose ASAR Data
Special Features of ASAR
Geophysical Coverage
Principles of Measurement
Scientific Background
Geophysical Measurements
ASAR Product Handbook
ASAR instrument characterization data
Wave Mode processing parameters
ASAR processor configuration data
Main Processing parameters
ASA_WVI_1P: ASAR Wave Mode SLC Imagette and Imagette Cross Spectra
Product Terms
RADAR and SAR Glossary
Level 1B Products
Summary of Applications vs Products
Site Map
Frequently asked questions
Terms of use
Contact us


1.1.1 Geophysical Measurements

The ENVISAT mission has both global and regional objectives, with the corresponding need to provide data to scientific and application users on various time scales.

Following on from the very successful ERS-1/2 SARs, ASAR is an all-weather, day-and-night, high-resolution imaging instrument that will provide radar backscatter measurements indicative of terrain structure, surface roughness, and dielectric constant. Important new capabilities of ASAR include beam steering for acquiring images with different incidence angles, dual polarisation, and wide swath coverage.

Important contributions of ASAR to the global mission include:

  • measuring sea state conditions at various scales
  • mapping ice sheet characteristics and dynamics
  • mapping sea ice distribution and dynamics
  • detecting large scale vegetation changes
  • monitoring natural and man-made pollution over the ocean

ASAR will make a major contribution to the regional mission by providing continuous and reliable data sets for applications such as:

  • offshore operations in sea ice
  • snow and ice mapping
  • coastal protection and pollution monitoring
  • ship traffic monitoring
  • agriculture and forest monitoring
  • soil moisture monitoring
  • geological exploration
  • topographic mapping
  • predicting, tracking and responding to natural hazards
  • surface deformation

Some of the global and regional objectives (sea state condition, sea ice applications, marine pollution, maritime traffic, hazard monitoring, etc.) require near real-time (NRT) data products (within a few hours from sensing). Some of these products are generated systematically since they are assimilated by meteorological offices (e.g. wave and wind information from wave mode acquisitions) while others are generated according to user requests. Other applications (e.g., agriculture, soil moisture, etc.) require fast turnaround data services (within a few days).

As well as using ASAR to satisfy specific operational and commercial requirements, major systematic data collection programmes will be undertaken, to build up archives for scientific research purposes.

ASAR will provide continuity of the ERS SAR Image and Wave Modes but with the opportunity for better temporal frequency of coverage. The nominal spatial resolution (30 m) and swath coverage of ASAR Image Mode (100 km) are the same as the ERS Image Mode, and ASAR will also be in a 35-day repeat orbit. However, using beam steering, it will be possible to obtain images of the same area on the ground from different orbits with different incidence angles. This gives a revisit frequency varying from daily coverage near the poles to weekly coverage at the equator.

ASAR has dual polarisation capabilities and a special Alternating Polarisation Mode has been implemented that permits half of the looks from a scene to be acquired with horizontal and half with vertical polarisation, thereby considerably increasing the target classification capability (especially if used in conjunction with multi-temporal imaging).

Wide area coverage will be achieved by switching between different swaths using the ScanSAR technique. This will enable 405 km coverage at resolutions of either 150 m or 1 km. At the 1 km resolution the data rate is low enough for tape recording on board the spacecraft and the recording capacity will be sufficient for downloading low-resolution global coverage through a single receiving station.

Incidence Angle

In contrast to the ERS SARs, which had a fixed swath position (23° mid-swath incidence angle), ASAR Image Mode will provide data acquisition in seven different swath positions (i.e., IS1 to IS7), giving incidence angles ranging from 15° to 45°. This subject is discussed in the section "Selectable Incidence Angles"

Dual Polarisation

Imaging radars can transmit horizontal or vertical electric field vectors, and receive either horizontal or vertical return signals, or both. The basic physical processes responsible for the like-polarised return are quasi-specular surface reflection and surface or volume scattering. The cross-polarised return is usually weaker, and often associated with multiple scattering due to surface roughness or multiple volume scattering. Scattering mechanisms and the returns from different surfaces may also vary markedly with incidence angle. For a further discussion of this topic see the section entitled "Dual Polarisation."

Wide Area and Frequent Coverage

ASAR medium and low-resolution images, provided by the Wide Swath and Global Monitoring Modes, open up new possibilities for applications requiring large area coverage and/or more frequent revisit. Both modes will provide 405 km swath coverage with a spatial resolution of 150 m for the Wide Swath and 1000 m for the Global Monitoring. For applications where higher resolution is necessary, better than a 5-day repeat interval is possible for approximately 100 km x 100 km areas using Image Mode. For a further discussion on this topic, see the section entitled "Wide Area Coverage and Frequency of Coverage."


ASAR offers continuity with 35-day repeat images for SAR interferometry, although interferometric pairs will need to be taken with the same incidence angles. The availability of ASAR interferometric pairs acquired at higher incidence angles will be useful for improving the visibility of steeper slopes, and there will also be new possibilities for low-resolution interferometry. For a further discussion on this topic, see the section entitled "Interferometry."

Wave Spectra

ASAR Wave Mode will provide wave spectra derived from imagettes of minimum size (5 km x 5 km), similar to the ERS AMI-Wave Mode, spaced 100 km along-track in VV polarisation. For a further discussion on this topic, see the section entitled "Wave Spectra."