2.1.1 Child Products

2.1.1.1 Definition

Child products are the result of the extraction from existing Level 0, Level lB or Level 2 parent products, and they own the same format and file name principles as any other ENVISAT Payload Data Segment (PDS) product (child product does not apply to future products). Also, there is no child product extraction from Auxiliary Data. The child products are generated by the Archiving Facility (ARF) and they consist of one segment, or separated consecutive scenes.

The product structure is provided in the previous section, entitled "Products and Algorithms Introduction"

Each child product contains an integer number of granules, which is a part of the product that corresponds to the time window covered by a Data Set Record (DSR) of the Location Annotation Data Set (LADS). The start time of the granule is the time label of the LADS DSR. For the Advanced Synthetic Aperture Radar (ASAR) instrument, the stop time of the granule immediately precedes the time label of the following LADS DSR in the product.

In table 2.2 below, examples are given for full scenes, relative to the specific product mode described, and scenes the size of only one granule.

Table 2.2 Child product scene sizes

Products	Full Scene Size	Granule Size
IM, AP	100 Km x 100 Km (10 granules)	10% of the full scene 10 Km along-track
WS, GM	400 Km x 400 Km (10 granules)	10% of the full scene 40 Km along-track
WV	One imagette for ASAR WV ( one granule )	One imagette for ASAR WV

The Extracted Instrument Header (EIH) product is extracted from a Level 0 product. It contains a suite of Instrument Source Packet (ISP) fields for a selected time interval. Its structure is the following:

• Main Product Header (MPH): It is identical to the MPH of the Level 0 product from which the data is being extracted, except for the time and positioning information which are updated to reflect the extracted region.

• Specific Product Header (SPH): It contains sensing time information, offset and length in MDS-DSR of each field (one or several fields) extracted from ISP of the parent product.

• Measurement Data Set (MDS): Each Data Set Record (DSR) of the MDS contains one or several fields extracted from ISP.

• The file name also changes to "C"; that is ASA_IMM_1C.

2.1.1.2 Child Product Extraction Requirements

As was first discussed in the Introduction, the ASAR child product is extracted from a parent product already archived in the ARF. However, the ARF does not archive the child product, and it does not update the inventory. After completion of the instruction, the ARF sends back an instruction report to the Centre Monitoring and Control (CMC).

The ASAR child products extraction criteria is defined as follows:

Table 2.3 ASAR child product extraction criteria

Product Level	Time	Location	Bands	Data Set	Extracted Ins. Header
Level 0	Yes	Yes	No	No	Yes
Level 1B and Level 2	Yes	Yes	No	Yes	N/A

2.1.1.2.1 Data Set Selection

The ARF shall select the Data Set (DS) of the parent product based on data set names in each Data Set Descriptor (DSD) of the Specific Product Header (SPH) 2.3.2.3. to extract child products with a DS extraction criterion. All Global ADS (GADS) shall be kept in the child product.

2.1.1.2.2 ISP Subsets Selection (Extracted Instrument Headers)

The ARF shall extract from the Level 0 products the Extracted Instrument Headers (EIH) , by selection of one or several sets of selected Instrument Source Packets (ISPs).

2.1.1.2.3 Common Archiving Facility Requirements

1. The external auxiliary data DSD records shall always be kept in the child product.
2. The GADS shall always be kept in the child product.
3. The MPH of the extracted child product shall be copied from the parent product, and then updated with the following parameters:
   • sensing start day and start time (t0)
   • sensing stop day and stop time (TL)
   • duration of the product (t 140)
   • processing centre
   • processing time
   • total size
   • size of each DS
   • number of DS
4. The name of the extracted child product shall be updated according to the parameters updated in the MPH.
5. The SPH shall be copied from the parent product.

• Time information.
• Location information of the products determined by reading the LADS in Level 1B or Level 2 products, if the product has a LADS. This information contains at least the four corners of the product area expressed in latitude and longitude, including the first and last sample latitude and longitude (determined from the LADS).

The following parameters shall be updated for each DSD describing a data set in the extracted child product:

• filename: set to "NOT _USED" if the DS corresponding to the DSD is empty, when the DS is not kept during a data set extraction
• data set offset
• total size of data set
• number of DSRs within the data set