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    24-Jul-2014
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Geolocation Grid ADSRs
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ASAR external calibration data
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Level 0 MDSR
SPH for auxiliary data with N=1 DSDs
ASAR WVI Product SPH
SQ ADSRs
Wave Mode Geolocation ADS
ASAR Wave Mode Products Base SPH
Slant Range to Ground Range conversion parameters
SQ ADSRs
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
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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
Descalloping
Range-Doppler
ASAR Level 0 Products
Level 0 Instrument Source Packet Description
Product Evolution History
Definitions and Conventions
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
References
Notes
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
Throughput
Latency
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
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Level 1B Products
Summary of Applications vs Products
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2.2 Organisation of Products

The data from all the ENVISAT instruments is classified according to a hierarchical data product scheme. Details of this scheme are as follows:

Raw Data is data as it is received from the satellite (serial data stream, not demultiplexed). Raw data is recorded from the X and Ka band demodulator output interfaces and stored on High-Density Data Tapes (HDDTs). The Raw Data is not considered a product, and its structure is not defined in this document.

Level 0 is reformatted, time-ordered satellite data (no overlap), in computer-compatible format. The Level 0 product is the lowest level product in the ENVISAT PDS. Table 2.7 in the section "Level 0 Products" shows a full list of ASAR Level 0 products.

Level 1B products are geolocated engineering foundation products in which data has been converted to engineering units, auxiliary data has been separated from measurements, and selected calibrations have been applied to the data. These products are the foundation from which higher level products are derived.

The Level 0 product is transformed into a Level 1B Product by application of algorithms and calibration data to form a baseline engineering product. The Level 1B product may be based on the whole of the source Level 0 product, or only a selected set of instrument packets from within the Level 0 product, based on a time range or other selection criteria.

Level 1B products may be produced in the following ways:

  • Unconsolidated: generated in Near Real Time (NRT); an intermediate step in near real time processing, used for instrument performance monitoring. It is produced in NRT using available NRT auxiliary data (i.e., may not contain the most precise orbit vectors or calibration information).
  • Fully Consolidated: generated off-line, time ordered, no overlap, no data gaps (except where the instrument has been turned off), fully validated; the basis for any further off-line processing. It is produced using the most precise auxiliary information available. It is compiled to respect the defined product boundaries (e.g., ascending node to ascending node at the equator for full orbit products).
  • Partially Consolidated: a product that has been consolidated in all ways except that it does not use the most precise auxiliary data possible to perform processing. Since several different levels of accuracy exist for auxiliary data (e.g., 5 possible orbit state vector sources), varying levels of consolidation may exist for a product.

Level 1B products make up the majority of ASAR products, and are outlined in the section "Level 1B Products" 2.6. . Table 2.39 in that section provides a summary of these products.

Level 2 consists of geolocated geophysical products:

  • Near Real Time: generated in near real time from unconsolidated Level 1B products
  • Off-line: generated from consolidated Level 1B products

In general, the Level 1B product is transformed into one or more Level 2 products through higher-level processing to convert engineering units into geophysical quantities and to form a more directly interpretable and useful measurement data set. The Level 1B products used are created at the time of Level 2 processing.

The general rule for product structure is that NRT and off-line versions of Level 2 products share the same structure, the only difference being that the off-line product is of better quality due to the fact that more accurate (fully consolidated) data is used during production than for the NRT product; and that the start and stop times of the data may be different to reflect consolidation of the data to standardised portions of the orbit. Level 2 products may be processed systematically or upon user request.

At present, there is only one ASAR Level 2 product, which is the "Wave Mode Ocean Wave Spectra" product (ASA_WVW_2P). This is discussed more fully in the section "Level 2 Products and Algorithms." 2.7.

Browse

Browse products are decimated images which can be ordered from the ENVISAT inventory. These products are very small to support electronic transmission while querying the catalogues. They may be further reduced in size through the use of standardised data compression algorithms.

Browse products will be generated systematically for ASAR (except wave mode) and will contain image lines derived from a data segment (up to a full orbit of data).

The user will view the browse product to assist in ordering the required products by displaying scenes starting anywhere in the browse product. A comprehensive description of the Browse products is provided in the section entitled "Browse Products." 2.6.2.1.3.

Figure2.9 below shows the generalised product tree:

The Generalised Product Tree
Figure 2.9 The Generalised Product Tree

As discussed in the Introduction 2.1. , ASAR products can be classified according to the mode in which the SAR instrument is operating. These are:

  • Image (IM) Mode - these products are high-resolution, narrow swath products based on data acquired at one of seven subswaths.

    The Precision Image product is a multi-look, ground range, digital image (in either Horizontal Polarisation Transmitted/Horizontal Polarisation Received (HH) or Vertical Polarisation Transmitted/ Vertical Polarisation Received (VV) polarisation) suitable for most applications. It is intended for multi-temporal analysis and for deriving backscatter coefficients. Engineering corrections and relative calibration are applied to compensate for well understood sources of system variability. Absolute calibration parameters are provided in the product annotations.

    The Ellipsoid Geocoded Image product is similar to a Precision Image, but with rectification to a map projection. It is geocoded using a map projection selectable by the user, such as UTM, or Polar Stereographic.Absolute calibration parameters are provided in the product annotations.

    Single-Look Complex (SLC) image data is intended for SAR image quality assessment, calibration and interferometric or wind/wave applications. A small number of corrections and interpolations are performed on the data in order to allow freedom in the derivation of higher-level products. Absolute calibration parameters are provided in the product annotations.

    A Medium-Resolution Image product will be available at 150 m resolution, which is specifically aimed at sea ice and oceanography applications. Absolute calibration parameters are provided in the product annotations.

  • Alternating Polarisation (AP) Mode - these products are similar to Image Mode products but include a second image acquired using a second polarisation combination. The raw data is acquired in bursts of alternating polarisation.

    The polarisation combinations are:

    • the co-polarisation submode (one image HH and one image VV)
    • the cross-H polarisation submode (one image HH and one image HV)
    • the cross-V polarisation submode (one image VV and one image VH)

    Products contain two images corresponding to one of the three polarisation combination submodes, at reduced spatial resolution in comparison to Image Mode.

  • Wide Swath (WS) Mode - these products provide greater swath width at reduced spatial resolution through the use of the ScanSAR technique.

    The standard product available for Wide Swath Mode will be a 150 m resolution image with the full 405 km swath width.

  • Wave (WV) Mode - these products are similar to those in Image Mode but are much smaller, covering an area of approximately 5 km by 5 km. Wave mode products may also contain secondary information like cross spectra.

    ASAR Wave Mode products are based on small high-resolution, complex images of ocean scenes also called imagettes. These are processed to derive spectra of the ocean backscatter and consequently the wavelength and direction of ocean waves.

    An SLC Imagette and Imagette Cross Spectrum is the basic Level 1B product from the ASAR Wave Mode. A minimum number of corrections and interpolations are performed on the SLC data in order to allow freedom in the derivation of higher-level products. Absolute calibration parameters are provided in the product annotations.

    ASAR Ocean Wave Mode Spectra are available as a Level 2 product. A Level 2 product is an ocean wave wavelength and direction measurement.

  • Global Monitoring (GM) Mode - is similar to WS mode, but has a lower data rate since the data is subsampled on board the satellite.

    The Global-Monitoring Mode product is a 1 km resolution image with a 405 km swath width, suitable for dissemination by electronic links in near real time.

The nominal characteristics of the various ASAR measurement modes are summarised in the following table:

Table 2.4 Nominal characteristics of ASAR measurement modes
ASAR Image Mode (IM)
VV or HH polarisation images from any of 7 selectable swaths. Swath width between approximately 56 km (swath 7) and 100 km (swath 1) across-track. Spatial resolution of approximately 30 m (for precision product).
ASAR Alternating Polarisation Mode (AP)
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)
ASAR Wide Swath Mode (WS)
400 km by 400 km wide swath image. Spatial resolution of approximately 150 m by 150 m for nominal product. VV or HH polarisation.
ASAR Global Monitoring Mode (GM)
Spatial resolution of approximately 1000 m in azimuth by 1000 m in range for nominal product. Up to a full orbit of coverage, HH or VV polarisation.
ASAR Wave Mode (WV)
A small imagette (dimensions range between 10 km by 5 km, to 5 km by 5 km) is acquired at regular intervals of 100 km along-track. The imagette can be positioned anywhere in an Image Mode swath. Up to two positions in a single swath or in different swaths may be specified, with acquisitions alternating between one and the other (successive imagettes will hence have a separation of 200 km between acquisitions at a given position). HH or VV polarisation may be chosen. Imagettes are converted to wave spectra for ocean monitoring.

Table 2.5 below gives a summary of the ASAR products, categorised by product level, and Table 2.5 below gives a product summary categorised by mode. As for all ENVISAT instruments, the interface for browsing and ordering these products is via the PDS User Service Facility (USF).

Table 2.5 Summary of ASAR data products
Mode
Product Level
Product ID Product Name
IM Level 0 ASA_IM_0P 2.5.1.2.2.1.
ASAR Image Mode source packets
AP Level 0 ASA_APH_0P 2.5.1.2.2.2.
ASAR Alternating Polarisation Mode source packets
cross-polarised H (HH/HV= H transmit H and V received)
AP Level 0 ASA_APV_0P 2.5.1.2.2.2.
ASAR Alternating Polarisation Mode source packets
cross-polarised V(VV/VH= V transmit V and H received)
AP Level 0 ASA_APC_0P 2.5.1.2.2.2.
ASAR Alternating Polarisation Mode source packets
co-polarised C (HH/VV= H and H received/V transmit and V received)
WS Level 0 ASA_WS_0P 2.5.1.2.2.3.
ASAR Wide Swath Mode source packets
WV Level 0 ASA_WV_0P 2.5.1.2.3.2.
ASAR Wave Mode (low rate)
GM Level 0 ASA_GM_0P 2.5.1.2.3.1.
ASAR Global Monitoring Mode (low rate)
IM Level 1b ASA_IMP 1P 2.6.2.1.1.2.1.2.
ASAR Image Mode Precision Image (high-resolution)
IM Level 1b ASA_IMS_1P 2.6.2.1.1.2.1.1.
ASAR Image Single-look Complex (high-resolution)
IM Level 1b ASA_IMG_1P 2.6.2.1.1.2.1.3.
ASAR Image Mode ellipsoid Geocoded image (high-resolution)
AP Level 1b ASA_APP_1P 2.6.2.1.1.2.1.5. ASAR Alternating Polarisation Precision image
AP Level 1b ASA_APG_1P 2.6.2.1.1.2.1.6.
ASAR Alternating Polarisation Mode Ellipsoid Geocoded image
AP Level 1b ASA_APS_1P 2.6.2.1.1.2.1.4.
ASAR Alternating Polarisation Mode Complex image (high-resolution)
WS Level 1b ASA_WSM_1P 2.6.2.1.1.3.1.3.
ASAR Wide Swath standard image
IM Level 1b ASA_IMM_1P 2.6.2.1.1.3.1.1.
ASAR Image Mode Medium-resolution image
AP Level 1b ASA_APM_1P 2.6.2.1.1.3.1.2.
ASAR Alternating Polarisation Medium-resolution image
WV Level 1b ASA_WVI_1P 2.6.2.1.2.1.1.
ASAR Wave Mode SLC imagette and Imagette Cross Spectra
WV Level 1b ASA_WVS_1P 2.6.2.1.2.1.2.
ASAR Wave Mode Imagette Cross Spectra
GM Level 1b ASA_GMI_1P 2.6.2.1.1.3.1.4.
ASAR Global Monitoring Mode Image
WV Level 2 ASA_WVW_2P ASAR Wave Mode Ocean Wave Spectra
GM browse ASA_GM_BP 2.6.2.1.3.1.4.
ASAR Global Monitoring Mode Browse Image
IM browse ASA_IM_BP 2.6.2.1.3.1.1.
ASAR Image Mode Browse Image
AP browse ASA_AP_BP 2.6.2.1.3.1.2.
ASAR Alternating Polarisation Browse Image
WS browse ASA_WS_BP 2.6.2.1.3.1.3.
ASAR Wide Swath Browse Image

To view the summary table that provides the standard specifications for ASAR data products, see "Products and Algorithms Introduction." 2.1.

The Image Mode (IM), Alternating Polarisation mode (AP), and the Wide Swath modes (WS) are all high data rate products. Figure2.10 below gives the generalised product tree for high data rate products.

ASAR High Data Rate Product Tree
Figure 2.10 ASAR high data rate product tree

The Global Monitoring (GM) and Wave Modes (WV) are low data rate products. The generalised trees for these products is given below in Figure2.11 .

ASAR Low Data Rate Product Tree
Figure 2.11 ASAR low data rate product tree