2.6.2 Level 1B Products

2.6.2.1 Level 1B High Level Organisation of Products

Table 2.39 below gives a listing of all Level 1B products, as was first disclosed in Section 2.1 "Products and Algorithms Introduction." 2.1.

The following processing steps are applied to the Level 0 data to form the SAR Level 1B image:

• data decompression
• replica construction and power estimation
• calibration pulse processing
• noise power estimation
• raw data correction (I/Q bias removal, I/Q gain imbalance correction, I/Q non-orthogonality correction)
• antenna elevation pattern compensation (not applied for SLC images)
• image formation (SPECAN or Range/Doppler)
• geolocation
• conversion to map projection (geocoded products only)

The image formation algorithm used is either the Range Doppler Algorithm 2.6.1.2.3. or the SPECAN 2.6.1.2.4. algorithm, depending upon the product requested.

All of the above-mentioned algorithms are discussed in detail in Subsection entitled "ASAR Level 1B Algorithms." 2.6.1.

During preprocessing, PF-ASAR performs raw data analysis, noise processing, and the processing of the ASAR calibration pulse data. Chirp replicas and antenna pattern gain factors are obtained from the calibration pulse processing. The signal data for all modes is FBAQ decoded; prior to processing (from 2, 3 or 4 bits back to 8 bits).

As far as the Wave Mode (WV) is concerned, the products generated are not detected, but Single-Look Complex (SLC). They allow for further Cross Spectra processing, following the algorithm developed by NORUT (Norway) and provide complete speckle compensation and potential capability to resolve the propagation ambiguity observed on the corresponding ERS products.

2.6.2.1.1 Level 1B Image Products

The general product structure, used in all ENVISAT products, is given in "Definitions and Conventions." 2.3.2.1. For the engineering quantities associated with these products, refer to "Level 1B Engineering Quantities." 2.6.2.2.

Advanced Synthetic Aperture Radar (ASAR) Image Products can be grouped into those produced as stand-alone products 2.6.2.1.1.2. , and those produced as stripline products 2.6.2.1.1.3. . All ASAR Image Products are stored in time-increasing order, except the geocoded products, which are oriented such that the first pixel of the first line is the most north-west pixel. Image products can be generated from various ASAR modes, as outlined in the section entitled "Products and Algorithms Introduction." 2.1.

2.6.2.1.1.1 Image Product Structure

All ASAR Image products follow a standard structure as described in figure2.42 , shown below:

The Main Product Header (MPH) is the same as for all ENVISAT products, and it is provided in the Data Formats 6.6.1. section. The Specific Product Header (SPH) used for image products is also given in the Data Formats(Chapter 6. ) section. The Data Set Names (DS_NAMES) in table 2.40 below may appear in the ASAR Image Product SPH Data Set Descriptors (DSDs):

Table 2.40 ASAR image products data set descriptor names

2.6.2.1.1.1.1 Image Product Data Sets

Data Sets (DS) are in mixed-binary format. ASCII values may be included in the Data Sets, but they do not follow the Keyword-value format of the MPH and SPH, nor are they contained within quotation marks.

The Data Sets which make up the ASAR image product structure are the following:

• Summary Quality ADSs
• Main Processing parameters ADS
• Doppler Centroid Coefficients 2.6.1.2.2. ADS
  
• Slant Range to Ground Range Conversion ADS
  
• Chirp parameters ADS
  
• Antenna Elevation Pattern ADS
  
• Geolocation Grid ADS (or LADS)
  
• Map Projection GADS
  
• Measurement Data Set (MDS)
  

The details relating to the layout of each of these Data Set Records (DSRs), is given in the Data Formats(Chapter 6. ) section.

2.6.2.1.1.2 Stand-Alone (On-Request) Image Products

Stand-alone image products are produced by request only and are created directly from the Level 0 data. They are ordered as a scene. All of these products share a common format.

Table 2.41 below lists the type of image formation algorithm applied to the various stand-alone products.

Table 2.41 Image formation algorithms for stand-alone products

2.6.2.1.1.2.1 Stand-Alone Product Types

2.6.2.1.1.2.1.1 Image Mode Single-Look Complex

The format for this product is given in the Data Formats(Chapter 6. ) section, and the engineering quantities are given in the section entitled "Level 1B Engineering Quantities." 2.6.2.2.1.2.1.

Figure2.43 is an example of an ASA_IMS_1P product as seen using EnviView: 1.2.1.2.

Figure 2.43 ASA_IMS_1P sample product (as seen in EnviView)

2.6.2.1.1.2.1.2 Image Mode Precision Image

The format for this product is given in the Data Formats(Chapter 6. ) section, and the engineering quantities are given in the section entitled "Level 1B Engineering Quantities." 2.6.2.2.1.3.1.

Figure2.44 is an example of an ASA_IMP_1P product as seen using EnviView 1.2.1.2. .

Figure 2.44 ASA_IM_1P sample product (as seen with EnviView)

2.6.2.1.1.2.1.3 Image Mode Ellipsoid Geocoded Image

The format for this product is given in the Data Formats(Chapter 6. ) section, and the engineering quantities are given in the section entitled "Level 1B Engineering Quantities" 2.6.2.2.1.4.1. .

Figure2.45 is an example of an ASA_IMG_1P product as see with EnviView 1.2.1.2.

Figure 2.45 ASA_IMG_1P sample product (as seen with EnviView)

2.6.2.1.1.2.1.4 Alternating Polarisation Mode Single-Look Complex

The format for this product is given in the Data Formats(Chapter 6. ) section, and the engineering quantities are given in the section entitled "Level 1B Engineering Quantities." 2.6.2.2.1.2.2.

Figure2.46 is an example of an ASA_APS_1P product as with EnviView 1.2.1.2.

Figure 2.46 ASA_APS_1P sample image (as seen in EnviView)

2.6.2.1.1.2.1.5 Alternating Polarisation Mode Precision Image

Figure2.47 is an example of as ASA_APP_1P product as seen with EnviView 1.2.1.2. .

Figure 2.47 ASA_APP_1P sample product (as seen with EnviView)

2.6.2.1.1.2.1.6 Alternating Polarisation Ellipsoid Geocoded Image

The format for this product is given in the Data Formats(Chapter 6. ) section, and the engineering quantities are given in the section entitled "Level 1B Engineering Quantities." 2.6.2.2.1.4.2.

Figure 2.48 ASA_APG_1P sample product (as seen with EnviView)

2.6.2.1.1.2.2 Input Data

The input for all of the stand-alone products is the Level 0 data corresponding to the particular mode and auxiliary data.

( Refer to table 2.5.1.2. in the section "Level 0 Products" for a listing of the Level 0 products )

2.6.2.1.1.2.3 Auxiliary Data Used

The auxiliary data required to create the stand-alone products is listed in table 2.42 shown below. The description of the main auxiliary data records is provided in the "Auxiliary Data Sets for Level 1B Processing" 2.9.2. section, and the formats are provided in the Data Formats(Chapter 6. ) section. The description of the orbit state vectors, including their formats, is provided in the section "Common Auxiliary Data Sets." 2.9.3.

Table 2.42 ASAR auxiliary data for image product processing

2.6.2.1.1.3 Stripline Processed Image Products

Stripline image products contain image data for an entire segment, up to a maximum size of 10 minutes per product for IM, AP and WS and up to a full orbit (100 minutes) for GM. The PF-HS concatenates together several sub-images called slices received from PF-ASAR on a data set by data set basis in order to form the entire stripline image.

Each slice produced by PF-ASAR follows the standard stand-alone image product format described previously. After concatenation of slices to form the stripline, the structure of the stripline image is identical to that of the stand-alone image products except the data sets contain data concatenated from several slices in time ordered sequence.

Stripline Formation:

Each slice delivered to the PF-HS is in the form of a separate product (i.e., format shown in figure2.42 "ASAR image product structure"). Thus the steps performed by the PF-HS to create the stripline product from the individual slices is as follows:

1. Data Sets of the same type for each slice are concatenated in zero Doppler time order sequence.

2. The SPH from the first slice is adopted as the SPH for the stripline. The following positioning information will be updated to reflect the size of the full stripline product:

• Stripline continuity indicator (set to 000)
• Slice number (set to +001)
• Number of slices (set to 001)
• Last Zero Doppler Azimuth time of product (can be read from SPH of last slice);
• Geodetic latitude and longitudes for the first, last, and middle samples of the last line of the stripline image (as read from the SPH of the last slice in the stripline).
  

In addition, the following parameters must be updated for each DSD describing a data set contained in the product:

• Data set offset (gives location of a data set relative to the start of the product);
• Total size of a data set;
• Number of DSRs within a data set.

3. The MPH from the first slice is adopted for the whole strip. Several fields in the MPH will need to be updated. These fields are:

• sensing stop time (can be read from MPH of last slice); {This is the on-board sensing time of the input source packets used to create each slice. On-board sensing time is also used for the sensing stop time field and to calculate the product duration. The goal is to provide input data times so that the data could be reprocessed at a later date if desired.}
• duration of product sensing (sensing stop time - sensing start time of MPH of first slice);
• total size of product.

Child Product Extraction:

Child product extraction is performed as per specified in the section "Child Products. 2.1.1. "

Processing Performed

The same processing steps are applied to stripline products as for stand-alone products. In addition a final concatenation step and MPH/SPH update step is performed by the PF-HS. The image formation algorithm used is the SPECAN 2.6.1.2.4. algorithm, as shown in table 2.43 below:

Table 2.43 Image formation algorithms for stripline products

2.6.2.1.1.3.1 Stripline Product Types

The medium-resolution products are systematically generated in the PDHS from Level 0 data collected when the instrument is in Wide Swath Mode (WS), alternating polarisation (AP), or Image Mode (IM) narrow swath. The product covers a continuous area along the imaging swath up to a maximum size of 10 minutes per product.

2.6.2.1.1.3.1.1 Image Mode Medium-resolution Image

Figure2.49 is an example of a simulated ASA_IMM_1P product as seen with EnviView. 1.2.1.2.

Figure 2.49 ASA_IMM_1P sample product (as seen with EnviView)

2.6.2.1.1.3.1.2 Alternating Polarisation Medium-resolution Image

Figure2.50 is an example of an ASA_APM_1P product as seen with EnviView. 1.2.1.2.

Figure 2.50 ASA_APM_1P product sample (as seen in EnviView)

2.6.2.1.1.3.1.3 Wide Swath Medium-resolution Image

Figure2.51 is an example of as ASA_WSM_1P product as seen with EnviView. 1.2.1.2.

Figure 2.51 ASA_WSM_1P sample product (as seen with EnviView)

2.6.2.1.1.3.1.4 Global Monitoring Mode Image Product

The format for this product is given in the Data Formats(Chapter 6. ) section, and the engineering quantities are given in the section entitled "Level 1B Engineering Quantities." 2.6.2.2.1.5.1.

Figure2.52 is an example of an ASA_GMI_1P product as seen with EnviView. 1.2.1.2.

Figure 2.52 ASA_GMI_1P sample product (as seen with EnviView)

2.6.2.1.1.3.2 Input Data

The input for all of the strip-line products is the Level 0 data corresponding to the particular mode and auxiliary data.

( Refer to table 2.7 in the section "Level 0 Products" for a listing of the Level 0 products )

2.6.2.1.1.3.3 Auxiliary Data Used

The same data used for on-request (stand-alone) products is required for the production of stripline products, as indicated above 2.42 . The description of the main auxiliary data records is provided in the "Auxiliary Data Sets for Level 1B Processing" 2.9.2. section, and the formats are provided in the Data Formats(Chapter 6. ) section. The description of the orbit state vectors, including their formats, is provided in the section "Common Auxiliary Data Sets." 2.9.3.

2.6.2.1.1.3.4 Product Structure

The product structure and contents for stripline products is identical to the on-request products. The stripline image product structure is shown in Figure2.53 below.

For a detailed description of the contents of the data sets refer to the sections for stand-alone products 2.6.2.1.1.1.1. discussed above.

A by-product of the creation of Strip-line products are the Browse images. A full discussion of these images, identified as: ASA_IM_BP, ASA_AP_BP, ASA_WS_BP and ASA_GM_BP, can be found in the section "Browse Products." 2.6.2.1.3. The table which shows the correlation between these two product forms is reproduced here for convenient reference:

2.6.2.1.2 Level 1B Wave Products

The general product structure, used in all ENVISAT products, is given in "Definitions and Conventions." 2.3.2.1. For the engineering quantities associated with these products, refer to "Level 1B Engineering Quantities" 2.6.2.2. .

Wave Mode (WV) products are not detected, but Single Look Complex (SLC). They allow for further Cross Spectra processing, following the algorithm developed by NORUT (Norway,) and provide complete speckle compensation and potential capability to resolve the propagation ambiguity observed on the corresponding ERS products. For a discussion of the processing steps carried out in the generation of the Level 1B products refer to the section entitled "ASAR Level 1B Algorithm Descriptions." 2.6.1.2.

Wave Mode (WV) products are those products produced from data acquired while the ASAR instrument is operating in Wave Mode. During Wave Mode operation, the ASAR instrument acquires small measurements called wave cells which are approximately 5 km along-track by (up to) 10 km in across-track. The wave cells are acquired at 100 km intervals. The cells may have alternating positions in the same swath or be in alternating swaths. In theory, up to 400 of these wave cells may be acquired per orbit, but in practice it is anticipated that the average number of acquisitions per orbit will be substantially lower. Each wave cell is processed into a small SLC image called an imagette and each imagette is further processed using the cross-spectra methodology to produce the cross-spectra of the imagette. In addition, each imagette can be processed to generate the Level 2 ocean wave spectra product.

2.6.2.1.2.1 Product Types

The two Level 1B Wave Mode products are shown below:

2.6.2.1.2.1.1 Wave Mode SLC Imagette and Imagette Cross-Spectra

Figure2.54 below is an example of as ASA_WVI_1P product as seen using EnviView: 1.2.1.2.

Figure 2.54 ASA_WV1_1P sample product (as seen with EnviView)

2.6.2.1.2.1.2 Wave Mode Imagette Cross-Spectra

Figure2.55 below is an example of an ASA_WVS_1P product spectral view ( see the spectral view section in "EnviView" )

Figure 2.55 ASA_WVS_1P spectral view ( as seen with EnviView )

2.6.2.1.2.2 Input Data

For the SLC Image and Cross Spectra product, the input data is the Level 0 Wave Mode product ( ASA_WV_0P 2.5.1.2.3.2. ) plus auxiliary data. (See table 2.7 in the section entitled "ASAR Level 0 Products" for a listing of all of the Level 0 products.)

The Cross Spectra product is simply an extraction of the Cross Spectra MDS and all ADSs from the SLC Image and Cross Spectra Product.

2.6.2.1.2.3 Auxiliary Data Used

The auxiliary data used to create the Wave Mode products is the same as that used to create the on-request SLC Image Mode product (see "Strip-line Auxiliary Data Used" in "Level 1b Image Products" 2.6.2.1.1.3.3. ). Auxiliary data formats are described in the section "Auxiliary Data Sets for Level 1B Processing" 2.9.2. .

2.6.2.1.2.4 Processing Performed

The processing steps applied to create the SLC imagette are the same as those used to create the on-request SLC Image Mode product (see the section entitled "ASAR Strip Line Product Processing" 2.6.1.2.5. ). The processing steps required to create the Cross Spectra products are discussed in the section entitled "ASAR Level 1B Algorithm Descriptions"

2.6.2.1.2.4.1 Wave Mode Error Handling

If PF-ASAR is unable to produce an imagette or cross spectra, the following method is used to indicate the error and the location of the error within the product:

• CASE 1: PF-ASAR is able to produce the imagette but not the cross / wavespectra:
  • The MDSR containing the cross/wave spectra is given the correct time stamp (corresponding to the first line of the imagette), the Quality Flag is set to -1, and all entries pertaining to the cross spectra are set to zero.
  • Fields in all ADSRs pertaining to the cross / wave spectra are set to zero.
  • The Attachment Flags of the SQ ADSR and the Geolocation ADSR corresponding to the wave cell are set to 1.
  • The SPECTRA_FAILED counter in the SPH is incremented.
• CASE 2: PF-ASAR is unable to produce neither the imagette nor the cross /wave spectra:
  • The MDS which was supposed to hold the imagette is still created. It contains only 1 MDSR which consists only of the time stamp corresponding to the estimated location of where the imagette would have been located, a range line number of 1, and the Quality flag set to -1. If it is not possible to determine the approximate time stamp for the MDSR, the time stamp may be set to zeros.
  • The MDSR which was to have held the cross / wave spectra is still produced, but it is zero filled and the Quality Flag set to -1 (as in CASE 1). The time stamp is identical to that used in the single MDSR of the imagette MDS.
  • Information in all ADSRs is set to zeros, and the Attachment flag of each ADSR is set to 1. The time stamp for each ADSR is identical to that of the single MDSR of the imagette MDS.
  • The SPECTRA_FAILED and IMAGETTES_FAILED counters in the SPH are incremented.

The rationale for the error handling described above is that:

1. PF-ASAR should not fail completely just because one imagette or cross /wave spectra in a series could not be produced;
2. for extraction purposes, the number of MDSs containing imagettes and the number of DSRs in the other data sets must be the same;
3. by setting the MDSRs and ADSRs (if appropriate) to zero, a placeholder is inserted in the product which allows one to identify unambiguously which wave cell failed, in both the WVI product and in further extracted products.

2.6.2.1.2.5 Product Structure

The standard Wave Mode product structure is shown in Figure2.56 below:

Figure 2.56 Wave Mode Products Structure

2.6.2.1.2.5.1 Main Product Header

2.6.2.1.2.5.2 Specific Product Header

As explained in "Definitions and Conventions" 2.3.2.3. , the SPH is defined for each product and provides additional information, applicable to the whole product, related to the processing. A description of the Level 1B Wave products' SPH, which includes the formulae used to reconstruct the wavelengths as well as the table of related Data Set Descriptors (DSDs) , refer to the ASAR_Wave_Base_SPH in the Data Formats 6.6.22. section.

2.6.2.1.2.5.3 Data Set Names

The Data Set Names, shown in Table 2.46 below, may appear in the ASAR Wave Product SPH Data Set Descriptors (DSDs) 2.3.2.4. :

For the table of DSDs, refer to ASAR_Wave_Base_SPH in the Data Formats 6.6.22. section.

2.6.2.1.2.5.4 Data Sets

The data sets 2.3.2.5. which make up the ASAR Wave product structure are shown below.

• Cross-Spectrum MDS
• Wave Mode Processing parameters ADS
• Wave Mode Geolocation Grid ADS (or LADS)
• Wave Mode Summary Quality Annotation Data Set Records (SQ ADSRs) - There is one Wave Mode SQ ADSR per wave cell. The ADSR contains information pertaining to both the imagette and the spectrum. This table, known as the ASAR_Wave_SQ_ADSR, consists of the ASAR image SQ information, defined in the table ASAR_SQ1_Image_ADSR, plus new information pertaining to the cross spectra.

The formats for all of these Data Sets can be found in the Data Formats(Chapter 6. ) section.

2.6.2.1.2.5.4.1 MDS Containing Imagettes

The structure of the Measurement Data Set (MDS) for the SLC Imagette and Imagette Cross Spectra (ASA_WVI_1P) 2.6.2.1.2.1.1. product, which contains an imagette, will be identical to that specified in the "Level 1b Image Products" Section 2.6.2.1.1.1. . Note that there is one MDS per imagette and up to 400 MDSs per product. The MDSs are not included for the Imagette Cross Spectra (ASA_WVS_1P) 2.6.2.1.2.1.2. product.

If PF-ASAR is unable to produce an imagette, the MDS will consist of only one MDSR with the time stamp corresponding to what the first line of the imagette would have been, a range line number of 1, and the quality flag set to -1.

2.6.2.1.3 Browse Products

The general product structure, used in all ENVISAT products, is given in "Definitions and Conventions." 2.3.2.1.

Browse products are a special form of Stripline product, produced from Level 0 products. As first discussed in the section entitled "Organisation of Products," they are decimated images which can be ordered from the ENVISAT inventory.

They are systematically generated at the same time as the corresponding medium-resolution Level 1B, as by-products of this process. For a discussion of the Level 1B Stripline products, refer to "Level 1B Image Products." 2.6.2.1.1.3. The Level 1B and browse pairs that are produced together are shown in table 2.47 below:

Browse products are also created as individual slices and then concatenated together by the PF-HS. However, browse products are intended only as a user aid when ordering data. Thus, many of the Annotation Data Sets (ADS) pertaining to detailed processing records may be discarded by the PF-HS for the browse product. There is no additional auxiliary data required.

The 4 browse products listed in Table 2.47 above, are described under the following sections

2.6.2.1.3.1 Product Types

2.6.2.1.3.1.1 Image Mode Browse Image

This low-resolution product will be produced systematically together with the Image Mode medium-resolution Product (ASA_IMM_1P).

These products will be amenable to dissemination by electronic links in near real-time (NRT). Possible use of data compression algorithms will be considered. The product covers a continuous area along the imaging swath and is derived by block averaging the medium-resolution product.

The format for this product is given in the Data Formats(Chapter 6. ) section.

Below in Figure2.57 is an example of an ASA_IM_BP browse image as seen with EnviView. 1.2.1.2.

Figure 2.57 ASA_IM_BP sample product (as seen with EnviView)

2.6.2.1.3.1.2 Alternating Polarisation Browse Image

This low-resolution compressed image product will be produced systematically together with the AP medium-resolution Product. This product will be provided via electronic link in near real-time. The product will contain only one of the polarisation options rather than two. The polarisation used will be that of the MDS1 of the APM product. This means the polarisation may vary depending upon which polarisation option is chosen for MDS1 for the medium-resolution AP product.

Possible use of data compression algorithms will be considered. The product covers a continuous area along the imaging swath and is generated by subsampling from the medium-resolution product.

Note: This product may contain only one of the two available polarisations from the original Level 0 data.

The format for this product is given in the Data Formats(Chapter 6. ) section.

Below in Figure2.58 is an example of an ASA_AP_BP browse image as seen with EnviView. 1.2.1.2.

Figure 2.58 ASA_AP_BP sample product (as seen with EnviView)

2.6.2.1.3.1.3 Wide Swath Browse Image

This low-resolution product will be produced systematically together with the WS medium-resolution Product.

These products will be amenable to dissemination by electronic links in near real-time. Possible use of data compression algorithm will be considered. The product covers a continuous area along the imaging swath. The product is generated by subsampling from the medium-resolution product.

The format for this product is given in the Data Formats(Chapter 6. ) section.

2.6.2.1.3.1.4 Global Monitoring Mode Browse Image

This low-resolution product will be produced systematically together with the GM Image Product from Level 0 GM data. The image is intended for browse purposes only (pixel spacing is approximately 1000 m).

These products will be amenable to dissemination by electronic links in near real-time. Possible use of data compression algorithms will be considered. The product covers a continuous area along the imaging swath.

The format for this product is given in the Data Formats(Chapter 6. ) section.

2.6.2.1.3.2 Processing Performed

The following processing steps are applied after the medium-resolution slice has been created:

• block averaging of medium-resolution slice (by PF-ASAR)
  
• concatenation of browse slices by PF-HS

2.6.2.1.3.3 Product Structure

The structure of the browse product is the same as for the regular Stripline products except that some data sets have been removed. The structure of the product is shown in figure2.59 below. For a detailed description of the contents of the data sets, refer to the sections for on-request products in "Stand-Alone Products" in "Level 1B High Organisation of Products 2.6.2.1.1.1.1. "

2.6.2.1.3.3.1 Browse SQ ADS

The SQ ADS for the browse product is simply the SQ for the medium-resolution image from which the browse was created. No fields are updated or changed during the formation of the browse product.

If the browse product is created from an Alternation Polarisation (AP) medium-resolution product containing 2 Measurement Data Sets (MDSs), which means using both polarisations (H and V), then both SQ ADSs are left in the browse product to provide a complete quality record.

2.6.2.1.3.3.2 Subsampled Geolocation Grid ADS

2.6.2.2 Level 1B Engineering Quantities

2.6.2.2.1 Image Products

2.6.2.2.1.1 Medium Resolution Products

2.6.2.2.1.1.1 Image Mode Medium-resolution Image (ASA_IMM_1P)

This Strip-line ASAR product is systematically generated in the PDHS. This product, processed to approximately 150-m resolution, features an ENL (radiometric resolution) good enough for ice applications.

2.6.2.2.1.1.2 Alternating Polarisation Medium-resolution Image (ASA_APM_1P)

This stripline product is processed to approximately 150 m resolution using the SPECAN 2.6.1.2.4. algorithm and contains radiometric resolution good enough for ice applications and covers a continuous area along the imaging swath. This product may also be generated on request with one, or both, polarisations included in the product.

2.6.2.2.1.1.3 Wide Swath Medium-resolution Image (ASA_WSM_1P)

This is the standard product for ASAR Wide Swath Mode and it is systematically generated in the PDHS using the ScanSAR technique and processed to 150-m resolution. The swath width is approximately 400 km.

2.6.2.2.1.2 Single-Look Complex (SLC) Products

2.6.2.2.1.2.1 Image Mode Single-Look Complex (ASA_IMS_1P)

The Image Mode Single-Look Complex (ASA_IMS_1P) products are stand alone, phase-preserved images. They are generated using up-to-date auxiliary parameters (at time of processing), using the Range-Doppler 2.6.1.2.3. algorithm

Intended use: SAR image quality assessment, calibration and interferometric applications. A minimum number of corrections and interpolations are performed on the data, so as to allow the end-user maximum freedom to derive higher level products. Complex output data is retained to avoid loss of information. Absolute calibration parameters, when available (depending on external calibration activities) shall be provided in the product annotations.

2.6.2.2.1.2.2 Alternating Polarisation Mode Single-Look Complex (ASA_APS_1P)

This stand-alone narrow swath product uses the Range Doppler 2.6.1.2.3. algorithm and the most up to date processing parameters available at the time of processing. The product can be used to derive higher level product.

Intended use: SAR image quality assessment, calibration, and interferometric applications, if allowed by the instrument acquisition. A minimum number of corrections and interpolations are performed on the data in order to allow the end-user maximum freedom to derive higher level products. Complex output data is retained to avoid loss of information. Absolute calibration parameters, when available (depending on external calibration activities) shall be provided in the product annotations.

2.6.2.2.1.3 Precision Image Products

2.6.2.2.1.3.1 Image Mode Precision Image (ASA_IMP_1P)

This stand-alone image is generated using the Range/Doppler 2.6.1.2.3. algorithm. The processing uses up to date (at time of processing) auxiliary parameters and corrects for antenna elevation gain, and range spreading loss.

Engineering corrections and relative calibration are applied to compensate for well-understood sources of system variability. Absolute calibration parameters, when available (depending on external calibration activities) shall be provided in the product annotations.

Max size: 134 Mbytes per scene
Coverage: 100 km * 100 km (max)

2.6.2.2.1.3.2 Alternating Polarisation Mode Precision Image (ASA_APP_1P)

This is a stand-alone multi-look, ground range, narrow swath digital image generated using the SPECAN 2.6.1.2.4. algorithm and the most up to date auxiliary information available at the time of processing. Engineering corrections and relative calibration (antenna elevation gain, range spreading loss) are applied to compensate for well-understood sources of system variability. Generation of this product uses a technique to allow half the looks of an image to be acquired in horizontal polarisation and the other half in vertical polarisation and processed to 30-m resolution (with the exception of IS1). Absolute calibration parameters, when available (depending on external calibration activities), shall be provided in the product annotations.

2.6.2.2.1.4 Ellipsoid Geocoded Products

2.6.2.2.1.4.1 Image Mode Ellipsoid Geocoded Image (ASA_IMG_1P)

This stand-alone Image Mode Geocoded SAR image is generated in either HH or VV polarisation, using the Range/Doppler 2.6.1.2.3. algorithm with the best available instrument corrections. The product is intended for mapping applications and other uses requiring map projection images. Absolute calibration parameters, when available, shall be provided in the product annotation. All processing information in the geocoded product corresponds to the intermediate product created during processing. Only the Geolocation Grid ADS and Map Projection ADS are updated to reflect the map projection information.

The six available map projections are:

• Universal Transverse Mercator
• Universal Polar Stereographic
• Lambert Conformal Conic
• Transverse Mercator
• Mercator
• Polar Stereographic

Engineering corrections and relative calibration are applied to compensate for well-understood sources of system variability. Absolute calibration parameters, when available (depending on external calibration activities) shall be provided in the product annotations.

2.6.2.2.1.4.2 Alternating Polarisation Ellipsoid Geocoded Image (ASA_APG_1P)

This is a multi-look image generated upon request using the SPECAN 2.6.1.2.4. algorithm and the most up to date auxiliary information available at the time of processing. Engineering corrections and relative calibration (antenna elevation gain, range spreading loss) are applied. The product contains two CO-registered images corresponding to one of the three possible polarisation combinations (HH and VV, HH and HV, VV and VH). Absolute calibration parameters (when available) shall be provided in the product annotation. All processing information in the geocoded product corresponds to the intermediate product created during processing. Only the Geolocation Grid ADS and Map Projection ADS are updated to reflect the map projection information.

2.6.2.2.1.5 Global Monitoring Products

2.6.2.2.1.5.1 Global Monitoring Mode Image Product (ASA_GM1_1P)

This strip-line product is the standard for ASAR Global Monitoring Mode. It is processed to approximately 1 km resolution using the SPECAN 2.6.1.2.4. algorithm. The swath width is approximately 400 km.

2.6.2.2.2 Wave Products

2.6.2.2.2.1 Imagette Cross-Spectra Products

2.6.2.2.2.1.1 Wave Mode SLC Imagette and Imagette Cross-Spectra (ASA_WVI_1P)

This is the basic Level 1B Wave Mode product. The product includes up to 400 single-look, complex, slant range, imagettes generated from Level 0 data and up to 400 imagette power spectra computed using the cross-spectra methodology. The auxiliary parameters used are the most up-to-date at the time of processing. A minimum number of corrections and interpolations are performed in order to allow the end-user maximum freedom to derive higher level products. Complex output data is retained to avoid loss of information. Absolute calibration parameters, when available (depending on external calibration activities), shall be provided in the product annotations.

Imagette power spectrum is equivalent to the ERS UWA product with revisited algorithm (cross-spectra) taking into account the higher quality of the SLC imagette.

Note: Starting from an SLC imagette, generation of an ERs UWA-type product might be ensured by a simple look detection and summation.

2.6.2.2.2.2 Single-Look Complex (SLC) Imagette Products

2.6.2.2.2.2.1 Wave Mode Imagette Cross-Spectra (ASA_WVS_1P)

This image power spectrum product contains up to 400 cross-spectra extracted from the SLC Imagette and Imagette Cross-Spectra product, shown above. It contains only the cross-spectra derived using cross-spectra methodology.

2.6.2.3 Level 1B Essential Product Confidence Data

Product Confidence Data (PCD) data is designed to demonstrate whether the product has met certain minimum quality standards. As such it should be differentiated from mere processing statistics. For example, a processing statistic might be the percentage of pixels in an image which are corrupted. A PCD flag would only be set if the number of bad pixels exceeded a predefined threshold (e.g., 10%).

Product Confidence Data may be located in the MPH, the SPH, and/or within a specific Annotation Data Set attached to a product. A signed character is used at the start of each MDSR in a Data Set to indicate the quality of the DSR (for Level 1B and Level 2 products only, if needed). The value of -1 is reserved to indicate that the DSR is blank.

Product Confidence Data in the MPH is designed to very simply provide the user with an assessment of the overall product quality by reporting if errors have occurred during the processing. To obtain a detailed description of the errors which occurred, the user refers to the SPH or the detailed PCD structures of the product.

The thresholds used when evaluating PCD information are stored in the processor configuration files for each processor that generates products.

PCD in the MPH

The MPH is a generic header (i.e., instrument unspecific), and so any PCD contained within must be applicable to all instrument types.

• PCD applications include:
  • summary quality - high-level quality indicator for product
  • acquisition and de-multiplexing - this is related to the data commutation and downlink performance aspects which are independent of product type
  • processing flag - high-level error detected during product generation
  • error in auxiliary data

PCD in the Data Set Record (DSR)

The PCD in the DSR, which was called measurement confidence data (MCD) in ERS, is referred to as PCD in the ENVISAT payload data segment. The DSR PCD provides details on individual source packet quality. It is related directly to the engineering aspects and details of the ground processing algorithms. PCD data includes: error codes, error flags and threshold values for product data, and processor thresholds from processor parameters.

Payload data is found in INSERTLINKTO SQ_ADSR. The flags are listed in table 2.64 below.

Processor thresholds are shown in ASA_CON_AX 6.5.1. data.