4.1. Fast Delivery Product Distribution
  4.1.1. System Overview
    4.1.1.1. Introduction
    4.1.1.2 Distribution Objectives
    4.1.1.3 General System Description
  4.1.2. SAR FD products distribution
  4.1.3. LBR FD products distribution
    4.1.3.1. Baseline distribution
    4.1.3.2. Alternative distribution
  4.1.4 Fast Delivery product copies from the PAF'S
  4.1.5. ERS-1 product ordering

4.2. Fast Delivery Product Format

4.3. Fast Delivery Product Descriptions
  4.3.1. AMI Image-16-bit (UI16)
  4.3.2. AMI Image-8-bit (UI8)
  4.3.3. AMI Image noise stat. and drift calibr. (UIND)
  4.3.4. AMI Image chirp replica (UIC)
    4.3.4.1. AMI Image PCD's and Product Annotations
      4.3.4.1.1. PCD at main product header (MPH) lever
      4.3.4.1.2. PCD at Specific Product Header (SPH) level
      4.3.4.1.3. PCD at Data Set Record level
  4.3.5. AMI Wave (UWA)
  4.3.6. AMI Wave noise stat. & drift calibr. (UWAND)
  4.3.7. AMI Wave chirp replica (UWAC)
    4.3.7.1. Comment on Product Confidence
  4.3.8. AMI Wind (UWI)
    4.3.8.1. UWI Product Confidence Measures and Product Annotations
      4.3.8.1.1. UWI PCD at Main Product Header
      4.3.8.1.2. UWI PCD's in Specific Product Header
      4.3.8.1.3. UWI PCD's at Data Set Record level
  4.3.9. Radar Altimeter (URA)
    4.3.9.1. Comment on Product Confidence
    4.3.9.2. URA PCD at main product header (MPH) level
    4.3.9.3. URA FICD at Specifie Header level
    4.3.9.4. URA PCD at Record Level

4.4. Intermediate product
  4.4.1. AMI Wave Intermediate (IWA)
    4.4.1.1. Comment on Product Confidence
Higher level

Product availability and distribution from the Ground Stations to the Ground Segment components comprises (see chapter 5 for product definition):

The LRDTF distributes the raw LBR data to the F- and UK- PAF's on 12-inch optical disks and the raw ATSR data to RAL (UK).

The EECF distributes the LR Fast Delivery Products further to the PAF'S.

The Fast Delivery Products described in this document include all products which are delivered to end users via the Fast Delivery Distribution Systems*. This includes the following products:

• AMI Image-16-bit (VI16)
• AMI Image-8-bit (UI8)
• AMI Wave (UWA)
• AMI Wind (UWI)
• Radar Altimeter (URA)

The following sections describe the product format and the distribution proc‚dures as they are planned today.

One of the ERS-1 Mission Objectives is to provide the user community with the so-called Fast Delivery Products from ERS-1 within 3 hours from observation. However, since the distribution of SAR FD Products can be performed only via satellite link, considering the high cost associated, the SAR FD Products will be delivered within 1 day nominally. The subject distribution system is presently under implementation and therefore the following paragraphe are for information only, at this stage.

The nominal solution for the Fast Delivery product distribution will use land lines for LBR FD Products and a satellite link (ECS/SMS) for SAR FD Products.

Schematically the dissemination system is depicted in Figure 4-1. It includes:

• a number of Ground Stations, plus the EECF and MMCC;
• the Central Facilities, providing concentration, reformatting and network management fonctions;
• a number of data sinks (i.e. nominated centres and other authorised user terminals);
• a limited number of data sources for data up-link to the satellite dissemination system.

FIGURE 4-1

ERS-1 HR FAST DELIVERY PRODUCT DISTRIBUTION SERVICE

SAR FD Products will be generated and transmitted at 2 Mbps using Eutelsat SMS Standard satellite link from Fucino and Kiruna.

Each station will be equipped vith a SAR FD processor and will transmit SAR FD Products to the Transmitting Station of the Distribution System, which could or could not be co-located.

The Network Supervision Centre (NSC) in Frascati will be connected with the Transmitting Station via standard protocole on land lines. The NSC will be co:qnected to the CUS of

EECF for schedule and control purposes.

The distribution network will provide addressing capabilities ensuring reception of SAR FD Products only at the addressees terminale (Receiving Stations).

The dissemination system will initially operate for one hour a day (equivalent to 20 UI16's or 40 UI8's), to be distributed between Kiruna and Fucino depending on actual data requirements. The hour will be allocated during nighttime in order to benefit from lower operation costs and will not strictly adhere to the three hours Fast Delivery deadline.

The receive facilities will be informed of the transmit time of the requested data, and will have the capability of storing at least one full SAR image. The user at the receiving end will have to ensure the downloading of the data to his own facility for further use, but there is no need on his side to be synchronised with the dissemination system..

This dissemination system aims at satisfying the initial requirements for Fast Delivery of products. The system can grow, e.g. by also including the Maspalomas Ground Station, which is upgraded to generate SAR FD products, and can make use of more transmitting time as a function of user demand and related funding.

The baseline approach for the LBR FD product diss‚mination is by use of landlines from the ESA/ERS-1 Ground Stations to EECF to centrally collect the LBR FD products for their injection into the WMO Global Telecommunication System (CTS) via the GTS node in Rome. They will be in the compressed and WMO-BUFR format, for further distribution to the Meteorological Organizations and then to the National Nominated Centres.

EECF at ESRIN therefore will act as a focal data source since all global LBR FD products will bc routed through it.

Additionally, some facilities can receive the LBR FD Products in uncompressed format (as generated at the stations) directly from EECF, provided that the link can be arranged and resources are available.

In case several of these users are identified, it is also possible to broadcast the LBR FD Products through a dedicated low speed (64 or 128 kbs) commercial satellite system'

The LBR FD Products will be anyway temporarily stored at EECF for 6 hours before being overwritten. During this time, which can be expanded if required, they can be retrieved via PSDN.

Copies of the Fast Delivery products can be made on request in off-line mode at the PAF'S. The Fast Delivery products as defined in this document are in that case embedded in a so-called CEOS superstructure format. This superstructure, proposed by the CEOS WGD, has been adopted world-wide as the standard format for Earth Observation Satellite data. The format is described in R-3. The FD product copies are renamed into:

• AMI Image-16-bit (UI16) - SAR.FDC
• AMI Image-8-bit (UI8) - will not be copied
• AMI Wave (UWA) - SWM.FDC
• AMI Wind (UWI) - WSC.FDC
• Radar Altimeter (URA) - ALT.FDC

The contract address for all ERS-1 product orders is:

ERS-1 Help & Order Desk
Earthnet Programme Office, ESRIN
Via Galileo Galilei
00044 Frascati, Italy.

Each product, with the exception of the raw data products stored on HDDT, has the same structure. This product structure consists of three parts.

The MPH has a single 176-byte record with an identical format for all products. The format of the Main Product Header record is given in Table 4-3. The Main Product Header contains information applicable to all processing chain products.

The specific product header is optional. The number and length of the record varies by product type.

All.products have a product data set, consisting of one or more records. Length and number of records is determined by the product type and is given in the Main Product Header.

Data Types:

Table 4.3: MPH FOR ALL PRODUCTS (EXCEPT HDDT PRODUCTS)

Table 4.3: MPH FOR ALL PRODUCTS (EXCEPT HDDT PRODUCTS)

Note 1.

For the LRDPF this means that at least one auxiliary data field in a source packet header is corrupted and for the SARFDP it means that the chirp could not be extracted from the input raw data. For UWI and URA this flag is always set to zero.

Note 2.

Field 4, UTC time at beginning of product, has the following meaning:

• for SAR 2't Z's the time of the firsi processed range line ie. 0-4 Io 0-48 sec before the zero doppler time of the first line of the product,
• for UWI it is the time of the first line of nodes,
• for URA it is the time of the firsi data set record.

If a Ground Station does not have a value for a field, either because the field is not applicable or a value is unavailable, the field is set to:

0 for integer numbers

space for ASCII

0 for bit fields within a byte

0 for special format. Note that there may also exist a 'non-value' definition by the special format itself

If a value exceeds the range of a type, the positive or negative maximum is given.

Data which are stored in Digital Equipment Corporation (DEC) internal storage formats have the following layout-.

• 16-bit or 32-bit integer numbers have the Least Significant Byte first; for example:

data addressed on bit level; for example, Product Confidence Data (PCD), have the bit addresses start at the least significant bit of a byte and increase to the most significant bit in the byte, i.e. the data item with the following description:

These bits are stored in two bytes as follows:

A bit is defined to be set if the bit has a value 1.

Fast Delivery products include all products which are disseminated over an electronic telecommunication link from the Stations or from EECF. This includes the following products:

Description: SAR processed image covering an area of about 100 x 100 km. This is equivalent to the full azimuth swath width (5000 pixels) and 6300 lines. Pixel size is 20 m (ground range) by approximately 16 m (azimuth). The pixel value, proportional to the square root of the image pixel power (magnitude) is represented by 16 bits. Input for this product is On-Ground Range Compressed (OGRC) data. These are data which have been acquired and digitized on the spacecraft prior to range compression and which undergo range compression in the SAR FDP.

Satellite Source: AMI Image mode

Originating Subsystem: SAR FDP

Product Generation: MMCC/EECF defines the start time for each product.

Throughput: Three AMI Image products, either 8- or 16-bit output pixels, per orbit and per SAR FDP. If both SAR FDPs are in image mode, only 8-bit images can be produced.

The throughput requirements are not applicable if the SAR FDP must produce one or more of the following products:

• Extracted Data Product
• Instrument Header Product

Format: One product includes:

• Main Product Header: See Table 4-3.
• Specific Product Header: see Table 4-9.
• 6300 Product Data Set Records: See Table 4-10. One record is one range line. Range lines are stored in ascending time order. Within each range line, pixels closer to the satellite track precede farther range pixels. The intensity of each pixel is represented by 16 bits.

Media: High-Speed Link

Table 4.9: SPECIFIC PRODUCT HEADER FOR U116, U18, UWA, IWA

Note 1 Chirp Replica Quality flag (field 1, bit 6): (see also fields: 1, 8, 9 and 10). These fields refer to chirp cross-correlation. This means cross-correlation with an MMCC/EECF- supplied nominal chirp. These fields are only valid if the chirp replica is successfully extracted and is used (i.e. field 27, bit 1 = 0). When field 27, bit 1 = 1, meaning that the chirp replica is not extracted successfully, then the cross-correlation values, fields 8, 9 and 10, will be set to 0. Also, if field 1 (bit 6) is set (ie. chirp quality failed) then the values in fields 8, 9 and 10 have no significance. The values given in fields 8, 9 and 10 are calculated on the assomptions that the chirp baseband and the chirp extraction index are correct.

The chirp replica quality flag is raised for a correctly extracted chitp, when either of the chirp quality figures (3dB width, sidelobe or ISLR - respectively fields 8, 9 or 10) is greater than the threshold values set by MMCC/EECF.

Note 2: for UIS, these coefficients are used to convert from 16-bit pixels to 8-bit pixels.

Note 3: Raw Data Correction: (fields 38-40) indicate the values before correction of the raw data i.c. arc still biased unsigned intcger6. They are the same as the biases provided by MMCC (in the EXT-SAR table) and they include the nominal encoding bias (Image OGRC=16; Image OBRC=32; Wave OGRC=2; Wave OBRC=8).

Note 4 Input Data Statistic fiag (field 1, bit 7): The dynamic range depending on the number of bits per samples, the following example is given for 5 bits. For 5 bits the values vary from 0 to 31, i.e. an expected mean value of 15.5.

When MMCC/EECF gives a threshold of x%, it is understood as specifying a range of ±x/2 % around 15.5. The MMCC/EECF threshold of y% for the standard deviation is understood as y% of 31.

The input data statistics flag is set = 1

where:

The dynamic range for image OBRC is 63, for image OGRC is 31, for wave OBRC is 15, and for wave OGRC is 3.

Note 5: Output Data Mean fiag (field 1, bit 11). The mean and standard deviation of the output intensity of part of a complete image (typically 1/15^th) are computed but not reported. The actual values are compared to MMCC/EECF given thresholds te set the bit 11 of field l.. The bit is set = 1:

The output mean is given by SPH byte 241-244, the output standard deviation is given by byte 245-248. The dynamic range is 255 for UI8 and 65535 for UI16, IWA, and UWA.

Note 6 for Latitudes and Longitudes. The latitudes and longitudes always refer to the image frame (6300 by 5000 pixels) independent of the size of the actual data contained within the frame.

Note 7 for Clutter Noise (fields 47 and 48): For the case of UWA the normalisation equations are:

clutter = clutter * 255/max_of_spectrum and

spectrum_component = spectrum_component * 255/max_of_spectrum.

Note 8 for field 27: In case of requested chirp from telemetry but extraction fails, the default chirp from MMCC/EECF is used instead.

Note 9 for fields 34, 35 36 and 37:

The chirp phase is expressed in radians: exp{ø} = exp{2π * (aO + al * t + a2 * t² + a3)}.

Since the unit of ø is radians, the expression (..... ) is dimensionless. This implies that a1 must have the dimension of 1/t, a2 that of 1/t², etc. The corresponding units used are Hz, Hz/s, etc.

Table 4.10: DATA SET RECORD FOR U116

Description: SAR processed image covering an area of about 100 x 100 km. This is equivalent to the full azimuth swath width (5000 pixel) and 6300 lines. Pixel size is 20 m (ground range) by approximately 16 m (azimuth). The pixel value, proportional to the square root of the image pixel power (niagnitude) is represented by 8 bits. The data are processed with 16 bits per pixel and are reduced to 8 bits for dissemination. The reduction from 16 to 8 bits is done using coefficients defined by MMCC/EECF. Whether an image is to be produced in 8 or 16 bits is determined by the generation command prior to processing.

Input for this product is OGRC data.

All product parameters are the same as for AMI Image (16-bit) FD Product, except that one pixel is represented by 8 bits.

Format:

Product Data Set: See Table 4-11. One record is one range line. Range lines are stored in ascending time order. Within each range line, pixels closer to the satellite track precede farther range pixels. The intensity of each pixel is represented by 8 bits.

Table 4.11: DATA SET RECORD FOR U18

Description: The data for one single product can be extracted either at the beginning or at the end of a measurement sequence. The product contains mean magnitude and standard deviation of the extracted noise data, and four calibration pulses.

Satellite Source: AMI Image mode

Originating Subsystem: SAR FDP

Product Generation: Generated upon MMCC/EECF commands, which must specify from where the data shall be extracted. The UIND product can be'generated either as a stand-alone command or together with a UI16 or UI8 commande In the latter case, the UIND product is done during azimuth processing of the image product.

Throughput: maximum two products per orbit

Format: One product includes:

• Main Product Header: See Table 4-3.

• Specific Product Header: Contains the noise data statistics. See Table 4-12.

• 4 Product Data Set Records: One data set record contains one complete pulse and is described in Table 4-13. The records are stored in ascending time order.

If a complete pulse cannot be extracted, zeroes are placed in the data set record.

Media: High-Speed Link to user community and MMCC/EECF Link

Comments on Product Confidence: Not Applicable

Table 4.12: SPECIFIC PRODUCT HEADER FOR UIND, UWAND

Table 4.13.- DATA SET RECORD FOR UIND

Description: This product contains two chirps, i.e. two sets of samples of the transmitted pulse. For each image scene, one chirp is extracted from the beginning, and one at the end of the auxiliary data to be processed.

Satellite Source: AMI Image mode

Originating Subsystem: SAR FDP

Product Generation: Automatically generated for every requested AMI Image User FD product; i.e. up to 3 per orbit.

Throughput: same as AMI Image User FD products

Format: One product includes:

• Main Product Header: See Table 4-3.
• 2 Product Data Set Records: One record contains one chirp. The first record is from the beginning and the second from the end of the image scene. The records are described in Table 4-14.

Media: MMCC Link or EECF Link.

Comment on Product Confidence: Not Applicable.

Table 4.14: DATA SET RECORD FOR UIC, UWAC

As far as AMI IMAGE MODE Product Confidence Measures (PCD's) and product an notations are concerned there is no clifference between

UI16: image 16 bits per pixel and

UI8 : image 8 bits per pixel.

In both products one record corresponds to one range line.

The SAR PD processor does not ingest 27,000 lines after tl, but converts the requested time interval (tl,t2) into a number of lines. The product format being fixed, the missing lines (when the actual number of ingested Fines is less than 27,000) are filled with zeros. The product localisation still corresponds to the 27,000 lines (4 corners).

A summary of the above is given in the field 6 of the MPH.

bit 1 : the product is considered as correctly generated when none of the bits 2 to 16 of the MPH field 6 has been raised.

Most of the PCD measurements are reported at specific product header level (see Table 4-9); additional explanations are hereafter included:

- processing equipment status flag (field 1, bits 1 + 2): the value 2 will never show in an actual product, because under such circumstances, no product is generated.

- PRF code change flag (field 1, bit 3): the value of the PRF is read in the telemetry and checked for consistency ( see paragraph : SAR FDP input error handling ):

the first line to be processed is the first line with satellite binary time (SBT, greater than or equal to the start time in the processing command.

Furthermore, the first two lines are ensured to have identical PRF code, sampling window start time code calibration system gain code, receiver gain code and satellite binary code.

The nominal situation is that no PRF change occurs during the processing of a given image. The code is considered to change if there are two cons‚cutive valid lines with identical code which is different from the previous one. Should more than one PRF value be observed, the bit 3 of field number one shall be raised. The actual number of PRF changes within and image is reported in field 3. Remark: The changes of this parameter value are observed, but the first value, accepted as valid (see error handling), is kept constant during the processing of a given product.

- Sampling window change flag (field 1, bit 4): Exactly the same as for the PRF (see above). Actual number.of changes is reported in field 4. Remark: the changes of this

parameter value are observed but the first value accepted as valid (see error handling) is kept constant during the processing of a given product.

- Calibration system and receiver gain change fiag (bit 5): Exactly the same as for thePRF (see above). Actual number of changes is reported in field 5. Remark: the changes of this parameter value are, observed but the first value accepted as valid (see error handling) is kept constant during the processing of a given product.

- Number of missing lines: (field 6). See also paragraph on SAR FDP input data error handling.

The number corresponds either to the number of missing lines (image mode) or missing source packets (wave mode). The identified missing data are padded with -zeroes before processing.

For image mode these lines of zeroes are inserted after range compression is completed, that is after the data is unpacked, range compressed and converted to 8 I, 8 Q signed data.

The SAR FDP uses the format counter to detect missing Fines with proper account for format counter wrap around (16 bit counter).

The SAR always generates 6300 image records; if there is not enough input data to generate the full scene, the image is padded with zeroes up to 6300 records.

- Doppler centroid confidence measure: (fields 1, 11, 12, 53, 54 and 57).

Principle of the measurements: The across-track variation of the position of the centroid of the doppler spectrum is approximated by a first order polynomial, as follows; For a number M of contiguous azimuth lines, the doppler centroid is estimated and the M estimates are averaged. This operation is repeated N times across swath. A first order polynomial is then fitted to the N estimates (straight line approximation). This straight line is described by two parameters:

- doppler centroid value at near range (in Hz)

- slope of doppler centroid across tra:ck in Hz/sec.

The two values are reported in fields 53 and 54.

- Doppler centroid confidence measure flag (field 1, bit 8): The actual value in field 11 is compared to a predicted maximum value.

- Doppler centroid value flag (field 1, bit 9): The actual valise in field 53 is compared to a predicted maximum value.

- Doppler ambiguity confidence measure flag (field 1, bit 10): The actual value in field 12 is compared to a predicted maximum value.

Doppler centroid goodness of fit: The difference between the beam pattern and the actual doppler spectrum (both supposed gaussian), is expressed by calculating the chi-square value of these two distributions. The measure is normalised as follows: Therefore a perfect fit gives a value of zero. The misfit corresponding to a maximum distance (PRF/2) between the 2 gaussian distribution is given a value of 1. The value is reported in field 11.

Doppler ambiguity confidence measure.- To ensure a correct radiometric value of the output pixels, it is mandatory to process the spectrum corresponding to the area actually in the centre of the beam illumination. The spectrum of a sampled signal being:

S( f ± n * PRF )

(PRF being the sampling frequency), the doppler ambignity removal unit determines the actual value of n, by measuring the misregistration of two looks, in range. The misregistrations corresponding to n = -1,0,1, the value of zero being the expected position, are calculated. The two highest values maxl and max2 are used to form a confidence measure:

(maxl - max2)/max1

where maxl > max2. This value is reported in field 12.

The value of n corresponding to the highest correlation peak is reported in field 57:

Remark: the value is the offset to the expected value.

- Input data statistics: (fields 1, 13, 14, 15, 16, 38 to 40).

The I and Q parts of each sample, which may be positive or negative, are biased positive prior to Analog to DigitaJ Conversion. As a result each complex sample after digitization is represented by two N-bit unsigned integers, where N has the following values;

2 for OGRC wave mode echo and noise data

4 for OBRC wave mode echo and noise data

5 for OGRC image mode echo and noise data

6 for all chirp replica and drift calibration pulse data

Since the real and imaginary parts are biased, the mean of all I and Q data sequences will bc approximately 2^N-1/2

The two (assumed) orthogonal channels are noted I and Q. For all samples of these channels, the following quantifies are estimated:

Field 13 = < I > (<> denotes the average)

Field 14 = < Q >

Field 15 = < I * I > - < I > * < I >

Field l6 = < Q * Q > - < Q > * < Q >

- Raw data correction: (fields 38-40) indicate the values before correction of the raw data i.e. are still biased unsigned integers. They are the sarne as the biases provided by MMCC (in the EXT-SAR table) and they include the nominal encoding bias (Image OGRC=16; Image OBRC=32; Wave OCPC=2; Wave OBRC=8).

Field 38 = mean of the I channel

Field 39 = mean of the Q channel

Field 40 = imbalance between the I and Q channels, defined as the

ratio std(I)/std(Q)

To perform raw data correction, the processor subtracts the respective means from the I and Q parts of each data sample. It then multiplies the Q part of each sample by the I/Q standard deviationratio value. (The SAR FDP performs no correction for non-orthogonality of the I and Q demodulation channels).

- Actual chirp replica (fields 27-37): The range compression is performed using either a replica sent to the station (field 27) or a replica extracted from the raw data themselves (fields 28-37). The chirp replica is sent to the stations by means of nine coefficients (fields 29 to 37):

- chirp amplitude (5 coefficients of a fourth order polynomial representation)

- chirp phase ( 4 coefficients of a third order polynomial repr‚sentation)

If the chirp replica is extracted from the raw data themselves the required chirp extraction index parameter is sent to the station.

The value of the extraction index parameter (field 28) is: index = 1 + offset,

where index and offset are numbers of complex samples, and offset points to the position of the start of the chirp samples within the receiving window.

Remark.- sample numbers start at 1.

Use of the chirp index:

The chirp index parameter is part of the product generation command but it is only used if the range matched filter is to be generated using the extracted chirp.

The processor extracts 710 chirp elements out of the available 768 elements; the location of the extracted elements is determined by the index parameter. If the offset is zero, the processor extracts 710 elements starting from the first element.

A chirp is valid if it is extracted from 24 contiguous range Fines. The bit which indicates the first four segments of the chirp replica (bit 3 of byte 23 in telemetry format) is ensured to be set in the first four of the 24 contiguous range Fines.

The processor only uses the extracted chirp to generate the matched filter. It does not do any analysis to estimate the chirp coefficients.

If the range mat'ched filter is to be generated using MMCC/EECF parameter, the proces sor will use the MMCC/EECF supplied chirp coefficients: the index parameter is not used at all in this case.

The chirp replica is represented in 6-bit complex unsigned binary form ( see input data statistics).

As mean values for correction are not delivered by the MMCC/EECF foi the chirp, a value of 31 +j 31 is subtracted from each complex chirp sample to remove the A to D conversion bias.

No gain mismatch correction is performed.

The following measurements are perforrned, on the autocorrelation of the actual replica function, used for range compression (in FD processing, only one range replica function is used for the whole image):

3-dB pulse width:

First side lobe: The left and right side lobes are meas-red and the highest value reported. Remark: the sidelobes of the autocorrelation function have to be symmetric.

ISLR of the reference chirp, provided by MMCC/EECF, and the downlinked chirp cross correlation function:

The 1-D ISLR is computed as follows:

The chirp peak is in the middle of 32 samples.

The peak energy is obtained by �ummation within plus or minus 1.5 * (3 dB Width).

The ISLR is then: 2 * sum from x to 16 where x = 1.5 * (3 dB Width) samples.

For both UI16 and UI8 there is no PCD value at record level.

Description: Power spectrum in polar coordinates. The power spectrum is based on a sample of data covering an area of at least 5 x 5 km. The instrument on the satellite collects data at intervals of approximately 200 to 300 km. The sample patch may be anywhere in the 100-km wide swath in the order of 2 km steps.

Input for this product can be OBRC or OGRC data.

Satellite Source:AMI Wave mode

Originating Subsystem:SAR FDP

Product Generation:Products are generated for MMCC/EECF defined start and stop times.

Throughput: 150 products per orbit.

The throughput requirements are not applicable if the SAR FDP must also produce one or more of the following products:

Extracted Data Product

Instrument Header Product

General Header Product

Format: One product includes:

Main Product Header: See Table 4-3.

Specific Product Header: See Table 4-9.

1 Product Data Set Record: For format see Table 4-15. The data set contains the mean square value of the intensit‚ of all pixels in one sector. A sector is defined in Figure 4-2.

Media: MMCC Link or EECF Link.

FIGURE 4-2 WAVE PRODUCT EXAMPLE

SECTOR A HAS NOMINAL WAVELENGTH OF 658 M AND ANGLE OF 45ş TO 60ş

SECTOR B HAS NOMINAL WAVELENGTH OF 658 M AND ANGLE OF 0ş TO 15ş

SECTOR C HAS NOMINAL WAVELENGTH OF 433 M AND ANGLE OF 60ş TO 75ş

Table 4.15: DATA SET RECORD FOR UWA

Table 4.15: DATA SET RECORD FOR UWA

Field Number of Data Byte (Page 2 of 2)

Description:Mean magnitude and standard deviationof the noise data, as well as four calibration pulses, extracted at the beginning of a measurement sequence (= scene).

It should be mentioned that even when the orbit propagator returns an error code, the raw data are extracted. So within the product the orbit data may be wrong.

Satellite Source:AMI Wave mode

Originating Subsystem:SARFDP

Product Generation:Generated from data of every 15th scene, within each specified processing interval for AMI Wave FD Product generation, starting with the first scene of

every processing interval.

Throughput:ten products per orbit

Format:One product includes:.

Main Product Header: See Table 4-3.

Specific Product Header: Contains the noise data statistics. See Table 4-12.

4 Product Data Set Records: One data set record contains one complete pulse and is described in Table 4-16.

If a complete pulse cannot be extracted, zeroes are placed in the data set record.

Media: MMCC Link or EECF Link.

Comment on Product Confidence:Not Applicable

Table 4.16: DATA SET RECORD FOR UWAND

Description: This product contains one chirp as extracted from the auxili ary data at the beginning of the data to be processed.

Satellite Source: AMI Wave Mode

Originating Subsystem:SAR FDP

Product Generation:Automatically generated for every AMI Wave FD Product

Throughput:150 products per orbit

Format:One product includes:

.Main Product Reader: See Table 4-3.

.1 Product Data Set Record: The single data set record is described in Table 4-14.

Media:MMCC Link or EECF Link.

Comment on Product Confidence:Not Applicable

There are no product confidence measures related to the image spectrum itself.

However the specific product header is identical to the one of the image mode and,therefore contains the same informations (see above).

The SAR processor uses the data subset counter and the satellite binary counter (SBT) to check the packet continuity (data subset counter should increment by 1 and SBT by 1 or 2 between packets).

Duplicate packets are discarded and missing packets are replaced with zeroes. The zeroes are inserted before the data is processed, that is, the data is still in packet form.

In the wave mode case, the extracted chirp is valid if it is extracted from 22 contiguous valid packets.

Description: This product includes the intermecliate and final results of the wind product generation. It consists of an array of wind vectors expressed in wind speed and direction. The product corresponds to a 500 x 500-km area. This area is represented by a 19 x 19 array of cells, with nominal 25-km spacing. The produced wind field corresponds to an ‚quivalent neutral stabilit‚ wind field, referenced to a height of 10 m. For each cell a wind vector is given together with latitude and longitude. The sigma nought and other information needed to convert these to wind fields are also provided for each cell.

Satellite Source:AMI Wind Mode

Originating Subsystem:LRDPF

Product Generation:Products are generated for MMCC/EECF- defined start and stop times with reference to the midbeam.

Throughput:70 products per orbit

Format:One product includes.

Main Product Header: See Table 4-3.

Specific Product Header: See Table 4-17.

361 Product Data Set Records: One cell is stored in one record. See Table 4-18.

Cells are stored in ascending time order within each cell line across-track; cells closer to the satellite track precede farther cells.

Media:MMCC Link or EECF Link.

Comment on Product Confidence:

Product confidence is monitored on a product-wide and cell basis. Factors which apply to the entire product are included in the SPH.

Table 4.1.7: SPECIFIC PRODUCT HEADER FOR UWI

Note:

The units in fields 6 to 11 have uniis of 2.344 Hz, while 234-4 Hz represents the frequency discretisation.

Table 4.17: SPECIFIC PRODUCT HEADER FOR UWI

Table 4.17: SPECIFIC PRODUCT HEADER FOR UWI

Table 4.17: SPECIFIC PRODUCT HEADER FOR UWI

Note

Refer to notes after Table 4-18 for parameter values in the case that these cannot be calculated.

Table 4.18: DATA SET RECORD FOR UWI

Table 4.18: DATA SET RECORD FOR UWI

Table 4.18: DATA SET RECORD FOR UWI

Table 4.18: DATA SET RECORD FOR UWI

Note 1 : for fields 8, 13 and 18: The counter of corrupted or missing source packets is multiplied by -1 when.in wind/wave mode to indicate wind/wave mode op‚ration.

The absolute value of the counter, in wind/wave mode, is always greater than two because the wind/wave mode operation causes two FMA sequences to be lost.

Note 2 : Fields 6, 11 and 16, Look Angle for the three beams: The beam look angle is defined as the angle between the unit vector tangentiel to the local meridian and pointing North and the projection of the vector from the centre of cell node to satellite onto the local tangentiel plane, counting clockwise.

Note 3 : for fields 4, 9 and 14: it should be indicated that the sigma_0 values are derived from the linear values by using: 10log₁₀(linearvalue). If beam is not available then the value is set to -999 999 999.

Note 4 : (field 20: For version 2.502 and onward, starting on date 15 October 1991, the wind direction is given in the meteorological sense. The definitions for the wind directions used for version 2.502 and onward and used for versions before 2.502 are shown in Figure 4-3.

Note 5 : The schematic in figure 4-4 is used to unambiguously interprete the Product Confidence Data flags of field 21 of the UWIDSR. It corresponds to one run of the ambiguity removal.

Note 6 : Rank one solution flag (bit 10): The ambiguity removal unit may result or not in a solution. When no ambiguity removal is performed or ambiguity removal is not successful, the solution with the highest probability (rank 1) is given and this flag raised.

Note 7 : Flag on ambiguity removal method (bit 11 - 12). The ambiguity removal unit may or may not make use of external meteorological data. This flag is raised when meteo data are used. This indicator is set independently of the success of the ambiguity removal indicated by bit 10.

Note 8 : values for fields 7, 12 and 17 are set to 255 if the calculation is not possible.

Note 9 : Rank 1 is solution of minimum residual. A high occurrence of the bit 13 flag set to 1 is related to a low quality of the model.

Remark : it is necessary to indicate when the ambiguity removal is not attempted. This occurs for instance when the distance (in a maximum likelihood sense) between the measurement and the model is too big or when the number NB of the adjacent nodes in a closed area is too small (eg. < 100) to allow for continuity reasoning.

FIGURE 4-3 WIND DIRECTION DEFINITIONS

WIND DIRECTION DEFINITION AS FROM 15-10-1991, FOR VERSIONS 2.502 AND ONWARDS.

WIND DIRECTION DEFINITION BEFORE 15-10-1991, BEFORE VERSION 2.502.

FIGURE 4-4 PCD FLAGS FOR UWI RELATIONS WITII AMBIGUITY REMOVAL

M = Maximum Likelihood Distance of rank 1 solution

V = Estimated Windspeed

N = Number of adjacent nodes

v₁ = Windspeed of rank 1 solution

v* = Windspeed solution chosen by-ambiguity removal

Remark : the case bit 10 = 0, bit 11-12 = 3 and bit 13 = 0, with the given solution v* may occur in the following example. The ambiguity removal is attempted over 6 consecutive products with a displacement of 2 products. After the first 2 products with successful ambiguity removal the results are kept. In case of non-successful ambiguity removal on the next products, the old results (after ambiguity removal) are used, but the indicator of the method used is lost.

Product confidence is. monitored on a product-wide and cell basis. Factors which apply to the entire product, are included in the SPH.

A summary of the above is given in the field 6, bit 1 of the MPH: the product is considered as correctly generated when none of the bits 2 to 16 of the MPH field 6 has been raised.

- Equipment status flag (Table 4-17, bits 1 and 2):

This flag is always zero in the current implementation.

- I/Q Imbalance flag (Table 4-17, bit 4):

Flag on mean power on I and Q: For each beam the I/Q imbalance is estimated by forming the ratio: mean I power / mean Q power.

However, these two values are separately checked against a threshold, without forming the ratio. Therefore 3 * 2 = 6 thresholds are used;

The flag is set when either the I or Q channels exceeds its threshold.

- Internal Calibration level (Table 4-17, bit 5):

This calculation is performed for every beam, once per product.

- Blank Product flag (Table 4-17, bit 6):

When no source packet, as necessary to generate a product in the time interval (tl,t2), is found, a dummy product is generated and this flag is set.

Remark: the above means that if at least one source packet has been found, this flag is not raised.

- Doppler compensation flags (Table 4-17, bits 7 and 8):

The on-board doppler compensation is refined on ground. The overall performance of the doppler compensation scheme is measured by taking the resulting signal power spectrum, averaged over a number of L1 measurernents blocks and comparing its Centre of Gravity and 'Standard Deviation' with those of an externally specified reference spectrum corresponding to an ideal doppler compensation. This is done for all beams and per product.

When no beam and no estimate is available, the following default values are used in Table 4-17:

..In case of lack of input data, the standard deviation fields should not be filled with the best case values

Wind speed (field 19) may lie in the range 0 to 50.8 m/s. The value of 51.0 m/9 (field value of 255) is reserved to indicate that an invalid wind speed was determined.

- So, when no wind extraction is possible, the product is written with the following default values:

Wind speed 255

Wind direction 255.

The product UWI contains various product confidence measures at node level,one record corresponding to one node, as indicated in field 21:

- Forebeam, Midbeam and Aftbeam Flag (Table 4-18, bits 2,3 and 4):

If a source packet is incomplete or too long, it is disregarded. During the calculations of the 3 sigma-nought values, the number of missing or erroneous packets is counted. This flag is set when no source packet contributing to a node has been found, for this beam.

Remark 1: the above means that when at least one source packet, out of a maximum number of 36, is found, the spatial filtering is performed.

Remark 2: This flag is not related to the arcing problem (see later).

The wind extraction software looks at these flags to determine which branch of the algorithm to use:

In case of only one beam data is available, no wind extraction is attempted.

A possible arcing of the transmitting tube (TWT) leads to an automatic switching off of the transmission. As a new transmission is not attempted before 15 sec, an arcing results in loss of data. These missing data are identified by looking at the statistics of the received data; as no transmission occurs, received data feature noise statistics. The corresponding beam data for a given node are flagged.

Remark: above information is not read and therefore not used by the win extraction software.

- Limit of Kp value (bit 8):

Before the wind extraction, the Kp value for each beam, for a given node is estimated. For every beam the actual value is compared to a given limit (e.g. 20%), and this flag raised in case at least one exceeds this limit. In case this flag is raised no wind extraction is attempted.

- Land/sea flag (bit 9):

A high resolution grid (5'x 5') is used to determine the percentage of land contamination within an area surrounding the center of the node, given by its latitude and longitude. The larger zone extends (beyond the 5' x 5' area) outwards at least 25 km. A scatterometer point falling within a given 5' x 5' area, is processed only if no surrounding cell is indicated as land in the larger zone. The land/sea flag is therefore raised when the contamination is more than 0% of land.

- Flag on frame checksum (bit 14):

For every source packet contributing to a node (up to 36), there is an input flag set by the frame synchronizer. This flag is set whether at least one out of these 36 input flags has been set by the frame synchronizer. If a checksum error happens, the calibration and noise data are replaced with defaults.

Description: The product contains an averaged wind speed, wave height, and satellite altitude together with the standard deviations (one per quantity) for single cells along the satellite track. One cell is sampled every 6.725 km and there is a maximum of 20 values measured during 1 second. Seventy seven (77) cells are combined in one product and represent an area of approximately 500 km.

Satellite Source: Radar Altimeter

Originating Subsystem: LRDPF

Product Generation: Products are generated for MMCC/EECF-defined start and stop times.

Throughput: 80 products per orbit

Format: One product includes:

. Main Product Header: See Table 4-3.

. Specific Product Header: See Table 4-19.

. 77 Product Data Set records: See Table 4-20.

Media: MMCC Link or EECF Link. This product is also stored on CCT. For tape format and tape label annotation see Appendix A.

Table 4.19: SPECIFIC PRODUCT HEADER FOR URA

Table 4.19: SPECIFIC PRODUCT HEADER FOR URA

Table 4.20: DATA SET RECORD FOR URA

Table 4.20: DATA SET RECORD FOR URA

Table 4.20: DATA SET RECORD FOR URA

Note for field 15.Units- number of electrons per square meter;

Scaling : written value is 1000log₁₀, so scaling is 10^{writenvalue/1000}

Table 4.20: DATA SET RECORD FOR URA

Note 1: O=no, 1=yes. Fields 5-15 of this record are only valid if bit 8 of Field 17 is set to '1'.

Source Packet level errors:

Only ocean mode valid source packets are processed.

Too long or incomplete source packets are discarded.

Non-Ocean mode valid source packets are reported in a blank record (cell time longitude and latitude are calculated).

Time gaps, due to unavailability or nonvalid satellite, source packet‚ are filled with blank records at about one second intervals.

Checksum errors on valid source packet are reported.

A summary of the above is given in the field 6 of the MPH.

bit 1 : the product is considered as correctly generated when none of the bits 2 to 16 of the MPH field 6 has been raised.

- processing equipment status flag (bits 1 and 2)

This flag is always zero in the current implementation.

- product type flag (bit 3)

This flag is zero (not-set) when at least one data record out of 77 is in ocean mode with N 10 (see above). Under all other circumstances this flag is set. When there is a missing source packet within the series of 77 forming a product, it is replaced with a blank one.

corrupt data flag (bit 4)

This flag is set when at least one data set record out of 77 features a set PCD summary flag. If there are not enough measurements as input in the averaging process, the contents of the wind speed, wave height and altitude fields are to be discarded.

- number of blocks used for averaging (field 11).

The field 11 indicates the actual number of valid measurements blocks which can be used for calculating the various means and standard deviations (see field 12, bits 2, 3, 4 and field 13). As a minimum of 10 is required, the actual written number is:

N if N >= 10 and

0 if N <= 10.

Points to be confirmed:

- validity criteria

- as 0 means "OK", N < 10 should correspond to 1.

- summary PC factor (field 12).

- frame checksum (bit 6) This flag is copied from the DPMC input.

- HTL time constant (bit 7) The RA algorithm derives the height tracking loop time constant from a table; this table gives for a number of sets of parameter loop (parameters alpha and beta), the corresponding time constant. When the search from the 2 input parameters to the time constant does not succeed, bit 7 flag is raised.

- average peakiness (field 13).

The peakiness factor is also calculated N times and averaged to detect sea ice.

Intermediate products are derived during Fast Delivery product generation at the Ground Stations. One of the intermediate products available to users is the:

. AMI Wave Intermediate product (IWA).

This intermediate product is derived during the AMI Wave FD product generation. The products are stored in the Ground Station subsystem that generated the product. Upon request, products are either recorded on CCT, Exabyte cassette tape or sent to MMCC or EECF over high-speed link.

Note: - that the RA FD products can also be stored on ÇCT and can be used like intermediate products.

Description:This product consists of an intermediate wave image generated prior to conversion, to a power spectrum, and the power spectrum, see UWA product. The image contains

320 in azimuth x 400 in range pixels for OGRC

320 in azimuth x 600 in range pixels for OBRC.

The intensity of each pixel is represented by 16 bits.

Satellite Source: AMI Wave Mode

Originating Subsystem:SAR FDP

Product Generation: Products are automatically generated, when AMI Wave FD products are generated.

Throughput:Same as AMI Wave FD Product

Format:One produet includes:

Main Product Header: See Table 4-3.

Specific Product Header: See Table 4-9.

17 Product Data Set Records: The data set records of this product are of two different types. The first 16 records contain 20 range lines each of the intermediate image (see Table 4-21). Within each range line, pixels closer to the satellite track precede farther range pixels. The 17th data set record contains the power spectrum (see Table 4-22).

Media: CCT; for tape - format and tape label annotation see Appendix A,

Table.4.21: DATA SET RECORD 1-16 FOR.IWA

Table 4.22: DATA SET RECORD 17 FOR IWA

There are no product confidence measures related to the image spectrum itself.

However the specific product header is identical to the one of the image mode and there fore contains the same informations (see paragraph 4.3.4.1.2).

The SAR processor uses the data subset counter and the satellite binary counter (SBT) to check the packet continuity (data subset counter should increment by 1 and SBT by 1 or 2 between packets).

Duplicate packets are discarded and missing packets are replaced with zeroes: the zeroes are inserted before the data is processed, that is, the data is still in packet form.

In the wave mode case, the extracted chirp is valid if it is extracted from 22 contiguous valid packets.

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry