For complete details download pdf of Envisat chapter from Eurimage Products and Services Guide
Envisat Technical Status Report
On 1 March 2002, the European Space Agency launched Envisat, an advanced polar-orbiting Earth observation satellite which will provide measurements of the atmosphere, ocean, land, and ice over a five year period.
The Envisat satellite has an ambitious and innovative payload that will ensure the continuity of the data measurements of the ESA ERS satellites. Envisat data will support Earth science research, allow monitoring of the evolution of environmental and climatic changes, and facilitate the development of operational and commercial applications.
The ENVISAT orbit provides a 35-day repeat cycle, the same as the ERS-2 mission. Since the orbit track spacing varies with latitude (the spacing at 60° latitude is half that at the equator), the density of observations and/or revisit rate is significantly greater at higher latitudes than at the equator. The flexible swath positioning in Image Mode greatly increases the revisit frequency compared to ERS. Coverage is also affected by the different swath widths.
An Advanced Synthetic Aperture Radar (ASAR), operating in C-band, ASAR ensures continuity with the image mode (SAR) and the wave mode of the ERS-1/2 AMI. It features enhanced capability in terms of coverage, range of incidence angles, polarisation, and modes of operation.
ASAR operates simultaneously with the other ENVISAT instruments. The diagram below shows the swath positioning of ASAR together with AATSR (not distributed by Eurimage) and MERIS coverage. Overlap with AATSR is quite limited, but ASAR IS1 to IS5 and most of Wide Swath Mode coverage falls within the MERIS cover.
Improvements in image and wave mode beam elevation steerage allow the selection of different swaths, providing a swath coverage of over 400-km wide using ScanSAR techniques. Transmit and receive polarisation can be selected allowing scenes to be imaged simultaneously with alternating polarisation.
An additional ASAR measurement mode, called Alternating Polarisation Mode, has also been defined which employs a modified ScanSAR technique. Instead of scanning between different elevation sub-swaths, the Alternating Polarisation Mode (co-polar) scans between two polarisations, HH and VV, within a single swath (which is preselected, as for the Image Mode). In addition, there are two cross-polar modes, where the transmit pulses are all H or all V polarisation, with the receive chain operating alternatively in H and V, as in the CO-polar mode.
Alternating Polarisation Mode (AP) gives two co-registered images per acquisition, from any of 7 selectable swaths. HH/VV HH/HV or VV/VH polarisation pairs possible. Spatial resolution of approximately 30 m (for precision product)
For Image Mode and Alternating Polarization:
Level 0 (Raw)
Data from image mode after frame synchronisation. Includes the instrument source packet and input data required for processing.
Single-Look Complex (SLC)
For SAR image quality assessment, calibration and interferometric or wind/wave applications and the derivation of higher-level products. Absolute calibration parameters are provided.
Precision Image (PRI)
A multi-look, ground range, digital image suitable for most applications.
Ellipsoid Geocoded Image (GEC)
Similar to a Precision Image, but with rectification to a map projection. Geocoded using a map projection selectable by the user, such as UTM, or Polar Stereographic. Absolute calibration parameters are provided.
Medium-Resolution Image (MRI)
Available at 150 m resolution, specifically aimed at sea ice and oceanography applications. Absolute calibration parameters are provided.
Wide Swath products are available only as Raw or PRI.
For complete details download pdf of Envisat chapter from Eurimage Products and Services Guide
See Radar images in the Image Gallery
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