•••••UCL

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Doc No.
CS-IS-MSL-GS-2001
Issue.
Date.
1.0
11 Dec 2003
CryoSat L2
L2 Prototype Input & Output Definition Document
Author:
S.G. Baker, MSSL
Checked:
R. Scott, ESYS
Approved:
P. Viau, ESA
Issue:
1.0
Date:
11 Dec 2003
ID:
esa
CS-IS-MSL-GS-2001
A
UCl
Climate Physics Group
Mullard Space Science Laboratory
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Document History
Version
Date
0.1
Interim update following changes to [RI 5}
0.3
SGB
2319102 SGB
11/10/02 SGB
0.4
28110/02 SGB
Minor Updates - First full issue
0.5
1412103
0.6
0.2
Updated by
916102
Reason
Created
Updated tofollow algorithm developments
Interim update following changes to [RI 5}
2613103
SGB
SGB
0.7
25/4/03
SGB
Issued for internal review comments
0.9
915103
SGB
Issued for ESA and CSAG review I approval
1.0
11/12/03
SGB
Full Issue following review by CSAG & ESA
Updates following changes to LI b and [RI 2}
Entries in italics denote non-deliverable versions provided for information or internally.
Detailed chanze hist
Version
Section
Updated by
Modification
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Contents
Table of Contents
1 Introduction
1.1
1.2
1.3
1.4
PurposeAnd Scope
ApplicableReferences
Definitions,Acronymsand Abbreviations
Conventions
2 IPF2 External Interfaces
2.1 List Of IPF2 External Interfaces
2.1.l
2.1.2
Inputs
Outputs
3 File Formats
3.1 File Headers
3.1.1
3.1.2
CryoSat Products Fixed Header
StandardVariableHeaderAnd MPH Format
4
4
4
5
7
8
9
10
10
11
11
12
12
4 L 1b Data Products
13
5 L2 Data Products
14
5.1 The L2 File Format
5.2 The L2 SPH
5.3 L2 MOS
5.3.1
L2 Parametersand Flag Words
6 Auxiliary Input Data Files
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
6.10
Auxiliary Data File Format
Constants
IPF Database Parameters
Job Order File
Processor ConfigurationFile
Sea Ice Concentration
Mean Sea Level
Snow Depth Climatology
Slope Model Files
DEMs
7 Internal Interfaces To ESL Processing
7.1 IntermediateInputs
7.2 IntermediateOutputs
15
15
16
20
35
35
36
.36
36
36
37
37
37
38
39
40
40
40
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1
Introduction
1.1
Purpose And Scope
.m
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1
The CryoSat Instrument Processing Facility (IPF) processes LO SIRAL data to level 2. The
Processing chains to process the LOdata to L 1b are called the IPF 1. The processors which convert
Llb data to Level 2 are called the IPF2. This document defines the main external data interfaces
for the IPF2 activity.
This issue is the second delivery in the IPF2 contract aligned with the mature vB algorithm
specifications and applicable to the vB delivery, of the ESL IPF2 code, in January 2004.
Notes for this issue:Datacontent has been updatedto matchthe changesto the L1b productand to take accountof CSAG
review comments.
1.2
R1
R2
R3
R4
RS
R6
R7
R8
R9
R10
R11
R12
R13
R14
R15
R16
Applicable References
ESL IPF1 IODD: CS-IS-MSL-GS-0001 (ESL-IODD)
CryoSat Data Products Requirements:CS-RS-UCL-SY-0003,CryoSat SAG, Draft 2
Earth Explorer Mission ConventionsDocument: CS-MA-DMS-GS-0001
Earth Explorer: Ground Segment File Format Guidelines : CS-TN-ESA-GS-0154(Is 1.3)
SIRAL Software InterfaceControl Document:SIRAL-ASPl-IR-0052,24/07/2002 lss 7
Mission CFI, General Software User Manual: CS-MA-DMS-GS-0002
Mission CFI, EXPLORER_LIBSoftware User Manual: CS-MA-DMS-GS-0003
Mission CFI, EXPLORER_ORBITSoftware User Manual: CS-MA-DMS-GS-0004
EXPLORER_GEO_CORRECTIONSCFI Software User Manual: CS-MA-CLS-GS-0001
EXPLORER_RETRACKERCFI Software User Manual: CS-MA-CLS-GS-0002
CryoSat IPF1 Products Format Specification[CS-RS-ACS-GS-5106)
CryoSat PDS Generic Processor ICD [CS-ID-ACS-GS-0118)"PROC_ICD"
CryoSat PDS L1b Processor ICD [CS-ID-ACS-GS-0116] "L1B_ICD"
CryoSat PDS L2 Processor ICD [CS-ID-ACS-GS-5121) "L2_1CD"
CS-TN-MSL-GS-2001,CryoSat Level 2 prototype processorFRAPPEdata structures
ENVISAT:Product Data ConventionsPO-RS-MDA-GS-2009-Annex-A
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1.3
Definitions, Acronyms and Abbreviations
AGC
Automatic Gain Control (output value of)
API
Application ProgrammersInterface
CEOS
Committeefor Earth ObservationStandards
CFI
Customer Furnished Item
CRYMPS
CRYOSAT Mission PerformanceSimulator
DORIS
Doppler Orbitographyand RadiopositioningIntegratedby Satellite
D-PAF
German Processingand Archiving Facility
DEM
Digital Elevation Model
DSR
Data Set Record
ENVISAT
ENVlronmentalSATellite (ESA mission)
ESA
European Space Agency
ERS
European Remote Sensing (satellites)
ESTEC
European Space agency Technical Centre
FBR
Full Bit Rate (ProcessedSIRAL data before stacking of echoes= Level 1)
FRAPPE
Flexible Radar Altimeter Processorfor PerformanceEvaluation
GDR
GeophysicalData Record (Altimeter Level 2.0 GeophysicalProduct)
GEF
Global Earth Fixed (referenceframe)
GMMI I GUI
Graphical Man-MachineInterfaceI Graphical User Interface
HSRRA
High Spatial Resolution RadarAltimeter (CRYOSATconcept simulator)
IERF
InternationalEarth ReferenceFrame
IFF
Inertial Fixed Frame (a referenceframe)
IPF1
Instrument ProcessingFacility up to level 1b (part of the PDS)
IRS
Instrumentand Retrieval Simulation
ISP
InstrumentSource Packet
LO /L1b/L2
ProcessingLevels 0 I 1b I 2
LEF
Local Earth Fixed (a referenceframe)
LLPA
Long Loop PerformanceAnalysis
LRM
Low Rate Mode i.e. Pulse Limited operation of the altimeter
MOS
MeasurementData Set
MPH
Main Product Header
MS
Mission Simulation
MSSL
Mullard Space Science Laboratory
PDS
Payload Data Segment
PH
Product Header
PRI
Pulse Repetition Interval
RA-2
Radar Altimeter on ENVISAT
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RMS
Root Mean Square
SAR
Synthetic Aperture Radar
SARin
Interferometric Synthetic Aperture Radar
SAT
Site Acceptance Tests
SCCS
Software Configuration Control System
SOD
System Design Document
SIRAL
SAR/Interferometric Radar Altimeter
SP
Source Packet
SPH
Specific Product Header
srf
a Satellite Reference Frame TBD
TAI
International Atomic Time
ToD
True of Date (reference frame)
UCL
University College London
VDU
Video Display Unit
WGS84
World Geodetic System 1984
XML
extensible Markup Language
CS-IS-MSL-GS-2001
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1.3
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1.4
Conventions
Bit numbering 0 = LSB, and hence 15 = MSB (2-byte int) or 31=MSB (4-byte int). This convention
is required by [R4]. and referred to as 'PDS' convention. Note that the documentation on CryoSat
telemetry uses the opposite convention (which we call Space Segment or 'SS' convention).
All file formats will follow the CryoSat mission guidelines [R4]
In the tables describing record formats within this document we use a syntax similar to the 'C'
programming language to describe the parameter type.
Hence the column labelled" Type 'C' "may contain the following entries:
Type 'C'
code
code meaning
length
UC
unsigned character
I byte
us
unsigned short integer
2 bytes
SS
signed short integer
2 bytes
ul
unsigned long integer
4 bytes
sl
signed long integer
4 bytes
ull
unsigned long long integer
8 bytes
sll
signed long long integer
8 bytes
[n]
denotes an array of length n
MDSR Time Stamp is formatted as defined for the ENVISAT Mission [Rl 5]. However, it is a TAI
Time with a datum of 1Jan2000 at 00:00 (TAI), and not a MJD as used in ENVISAT.
expressed as 3 integers:Day(sl), seconds-of-day(ul) and microseconds(ul).
Note that:
i) Time in File headers (MPH, SPH) is in UTC and not TAI
ii) time correlations between UTC and TAI are provided via Orbit files - these must account for the
correct offsets due to leap seconds
iii) 1Jan2000 at 00:00 UTC = 1Jan2000 at 00:32 TAI
The reference ellipsoid is WGS84.
Longitude: expressed in the range -180 to +180, +ve East does not contain 180.0, -ve West does
contain -180.0. (same definition as ENVISAT)
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2
IPF2 External Interfaces
The IPF2 is a science data processing chain forming part of the Payload Data Segment which in
turn is a component of the CryoSat Mission Ground Segment (GS). Logically the IPF2 lies inside
the PDS so that all external IPF2 interfaces are with the PDS.
Telemetry
Receiving
Stations
Figure 2-1. The Context of the IPF2 Processor
The main input data format is CryoSat Lib products. For development and testing these files have
the correct format as defined within the CryoSat Ground Segment (IPFl development). The data
content of these files is created by simulators and/or data editors.
In addition to the main L2 data output the environment allows two other kinds of output:
• an output stream for log files : to provide job tracability and record processing messages
• switchable Breakpoint files for certain IPF2 algorithms : to provide de-bugging information
and visibility of internal parameters. The latter are not archived by the PDS.
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2.1
List Of IPF2 External Interfaces
Here we only consider data interfaces. Control interfaces, including the processing run instruction
(or Job Control Card) and error and progress reporting, are discussed elsewhere.
IPF Database file.
(Instrument characterisation &
Platform Data)
L2
Processing
Chains
Figure 2.1-1. L2 Data Interfaces
Input files are accessed either directly or indirectly through CFI library functions. Where files are
accessed directly the system must have a full description of the file and record structure. Where
files are accessed indirectly the system only needs to know about the CFI routine interface.
CFI routines are available for the Mean Sea Surface and Geoid heights [R10].
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2.1
Inputs
Input Data Type
Access Direct I CFI
Defined in
direct
[RI]
Mean Sea Surface height
CFI library
[R10]
Geoid height
CFI library
[R10]
Physical and Geophysical Constants
direct
[RI]
Radar Altimeter Parameter Database (Characterisation
data)
direct
[RI]
Processor configuration (Algorithm Tunable Constants)
direct
[R14]
Snow depth climatology
direct
TBD
DEMs
direct
TBD
Slope Models
direct
section 6.9
Sea Ice Concentration Files
direct
TBD
LI b Data Files (partitioned by mode)
Most input files are defined by other sources therefore their format is defined in external reference
documents. However to aid understanding herein some auxiliary data formats may be included in
Appendix TBD.
2.1.2
Outputs
The format of these output products is part of the IPF2 design. These formats are defined in this
document.
Output Data Type
Comment
Defined in
CryoSat L2 data
distributed to users
Section 5
Incomplete L2 SAR data
i/p to 2nd pass SAR
processing
Section 5
Breakpoint Files
for testing only
aAppx TBD
others TBC
documentation).
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3
File Formats
All files are formatted in accordance with the mission file format guidelines [R3][R4].
NB: For the prototyping work file headers are not used - the definition is not yet sufficiently stable.
All Product files consist of a Header block and a Data block. Generally the Headers wlll be ASCII
text and the data block may be binary or ASCII format. Each product will additionally have a
separate XML Header File (ASCII text). The Fixed portion of the XML header will be the same
for all CRYOSAT files. File organisation is illustrated by the diagram below.
CryoSat Product
Variable Header (Data Products only)
Specific Product
Header
Figure 3-1. CryoSat Data File Structure.
3.1
File Headers
File headers shall be in ASCII text. The main L2 product will have a file header, and XML product
headers shall be contained in a separate file.
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3.1
CryoSatProductsFixedHeader
Fixed headers shall be in ASCII text using XML syntax. Details TBD
3.1.2
StandardVariableHeaderAnd MPHFormat
The Variable Header shall contain an MPH which is the same format for all CryoSat data files and
a SPH Which varies with the file type. The XML variable header shall be an XML version of the
MPH and SPH in the main product file. The MPH and SPH will be similar in layout to ENVISA T
products.
Variable headers are TBD
Table 3.1.2-1: MPH content
Field
Description
1
<MPH>
2
TBD
3
<FILE_ TYPE> Type_code<!FILE_ TYPE>
4
TBD
n
<SPH_SIZE>size_in_bytes</SPH_SIZE>
n+l
</MPH>
Values
Bytes
Total
Length
Total
NB
For the L2 prototyping development files shall consist only of a single binary MDS. The file type
may be determined from the filename. Number ofrecords in a file may be determined from its size.
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4
L 1b Data Products
The L 1b data is output from the IPF 1 in 3 different formats corresponding to 3 modes of operation:
SAR, SARin and LRM.
Llb data is described in the ESL-IODD [R1]. (this issue is inline with v3.3)
For this prototype we are using an interim L1b format which differs from the IPF Ll b product in
the following ways :
• No file headers are used.
• Some data fields and flags may contain zero
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5
L2 Data Products
The L2 data is the main output from the L2 processor.
The format of the L2 data is independent of the SIRAL instrument operating mode.
"'!
SIR_LRM_2_
LRM
L2 LRM soecProc J
SIN
L2 SIN specProc
SIR_SIN_2_
L2 SARI specProc
SIR_SAR_2A
f-- . -
L2 Data
- • I
-
L2 SAR2 specProc
SIR_SAR_2B
L2 Data
Figure 5-1. Outline of L2 Product Generation
Final L2 SAR data requires 2 processing passes. In the second pass the Ocean Height is
interpolated to all measurements over sea ice. The output from the 2 passes are distinguished by
the file type strings 'SIR_SAR_2A' and 'SIR_SAR_2B'.
The data format is identical but
SIR_SAR_2A has some zero-filled parameters. Hence all 4 output types have the same format but
at this stage are still partitioned by mode.
To produce a consolidated L2 GDR product the mode-dependent segments around an orbit are
merged together. Two 'flavours' ofGDR are possible depending on which type ofL2 SAR data is
used. 'SIR_GDR_2A' results if SIR_SAR_2A data is used, and 'SIR_GDR_2B' products are
produced when SIR_SAR_2B data is used. This is illustrated in figure 5-2.
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5.1
consolidation ANX-ANX
SIR_LRM_2_
MERGE
SIR_SAR_2A
SIR_SAR_2B
Figure 5-2. Consolidation of L2 data
5.1
The L2 File Format
The L2 product will consist of two files: an XML header file and the L2 data file. The L2 data file
has an MPH, an SPH and a MDS containing a variable number of records. This is true for the
mode-segmented L2 files as well as for the consolidated GDR products.
The frequency of L2 data records is approximately 20/second.
L2 data files are partitioned in whole-orbit segments cut at the ascending equator crossing (ANX).
Therefore each L2 product will be approximately 4,948 seconds long.
Filename: the format will follow Earth Explorer Mission standards (which is similar to ENVISAT).
Hence the name of the data file will be of the form:
MM_CCCC_TTTTTTTTTT_yyyymmddThhmmss_YYYYMMDDTHHMMSS_vvvv.DBL
where the ten-character type string will be SIR_GDR_2A or SIR_GDR_2B.
5.2
The L2 SPH
The SPH is not yet defined. The ESL IPF code outputs an 'interim' L2 product with only the MDS.
Headers are added by the Postprocessor. The definition will be in [Rl4].
Table 5.2-1: L2 SPH
Field
Symb
Descriptor
Values
Size
(bytes)
Tot. Size
(bytes)
6
1.
<SPH>
6
2.
</SPH>
7
The SPH should contain the COM (centre of Mass Offset) value used in the processing.
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L2 MOS
The L2 Measurement Dataset has a single format which is independent of mode. However the
meaning of some fields is mode dependent.
NB: There is no 'Blocking' of high-rate data in the record (as in Llb). All L2 parameters are
output at the same frequency giving a 'flat' record structure.
Product parameters are grouped
Location Group
Measurements Group
Auxiliary Measurements Group
External Corrections Group
Internal Corrections Group
according to function into 5 sub-structures as follows:
time and orbit location
derived from instrument measurement parameters
from auxiliary data or models
geophysical corrections
calibration corrections etc
The record structure is illustrated in the following diagram. The repetition frequency of each substructure is 1.
Figure 5.3-1. L2 MDS record structure.
In the following table the symbol column provides a cross reference to parameters defined in [R2]
or in the Ll IODD [Rl].
Table 5.3-1: L2 MDS Record Structure
ID
Descriptor
Symb
Unit
Type 'C'
Size
(bytes)
Tot. Size
(bytes)
TAI
sl+2*ul
12
12
(ratio)
sl
4
4
Time and Orbit group
1.
tk
Data Record Time (MDSR Time Stamp)
USO Correction factor (definition tbd)
2.
3.
p3
Mode ID (Instrument mode information)
-
us
2
2
4.
p3
Source Sequence Counter (from telemetry)
-
us
2
2
5.
SJ
Instrument Config (including loop status)
-
ul
4
4
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·····•·······.·
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'
' ·\. ~~
nt··,
Doc No.
Issue.
CS-IS-MSL-GS-2001
1.0
~.'
...
, ..·I·.
1... ·.
Date.
section.
11 Dec 2003
5.3
::...~·
:
~
Table 5.3-1: L2 MDS Record Structure
ID
6.
.
Descrrptor
Sym b
K
Surface Sample counter (Record Counter)
U .
mt
T
'C'
ype
Size
(b ytes)
Tot. Size
(bytes)
-
ul
4
4
I
7.
r(l) <Pe Latitude of measurement
10·1µ-degree
sl
4
4
I
8.
r(l) Ae Longitudeof measurement
10·1µ-degree
sl
4
4
9.
r<l)h
mm
sl
4
4
Instantaneousaltitude rate derived from orbit
mm/sec
sl
4
4
mm/sec
sl
3*4
12
e
I0.
~ltitude of COG above reference ellipsoid
(mterpolatedvalue)
11.
vg
Satellitevelocity vector[3] (in JERF)
12.
ma
Real beam directionvector[3] (in CRF)
um
sl
3*4
12
13.
mb
Interferometerbaseline vector[3] (in CRF)
µm
sl
3*4
12
Level 2 MeasurementConfidenceData (flag
word)
_
ul
4
4
mm
sl
4
4
dB/100
sl
4
4
-
sl
4
4
14.
Measurements group
15.
h
Height of surface w.r.t.ellipsoid
16.
Sigma 0
17.
spare (reserved for future use)
18.
Peakiness
1/100
sl
4
4
19.
Retracked range correction
mm
sl
4
4
20.
Retracked Sigma 0 correction
dB/100
sl
4
4
21.
Retracker output 3
tbd
sl
4
4
22.
Retracker output 4
tbd
sl
4
4
23.
Retracker output 5
tbd
sl
4
4
24.
Retracker output 6
tbd
sl
4
4
25.
Retracker output 7
tbd
sl
4
4
26.
Retracker output 8
tbd
sl
4
4
27.
Retracker output 9
tbd
sl
4
4
28.
Retracker output 10
tbd
sl
4
4
29.
Retracker output 11
tbd
sl
4
4
30.
Retracker output 12
tbd
sl
4
4
31.
Retracker output 13
tbd
sl
4
4
dB/100
sl
4
4
32.
CT8
Power echo shape parameter
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5.3
Table 5.3-1: L2 MDS Record Structure
ID
33.
Symb
8
I
Descriptor
Size
(bytes)
Tot. Size
(bytes)
SS
50*2
100
µradians
sl
4
4
1/1000
sl
4
4
Unit
I Beam behaviour parameter [50]a
Type'C'
34.
x-Track Angle (interferometric angle computed
at Retrack point)
35.
Coherence ( at Retrack point)
36.
Interpolated Ocean Height
mm
sl
4
4
37.
Freeboard
(initially =0)
mm
sl
4
4
38.
Surface Height Anomaly
mm
sl
4
4
39.
Interpolated Sea Surface Height Anomaly
mm
sl
4
4
40.
Interpolation error for Ocean Height
mm
us
2
2
41.
Number of interpolation points used -forward
us
2
2
42.
Number of interpolation points used -backward
us
2
2
43.
Radius of interpolation -forward (in time)
ms
us
2
2
44.
Radius of interpolation -backward (in time)
ms
us
2
2
45.
Interpolation error flag
us
2
2
46.
Measurement mode (SAR I SARin I LRM )
ul
4
4
47.
Measurement Quality Flags
ul
4
4
48.
Retracker Flags
ul
4
4
49.
Height Status Flags
ul
4
4
50.
SAR Freeboard Status Flags
ul
4
4
51.
Measurement Spares
UC
16xl
16
%/1000
sl
4
4
mm
sl
4
4
sl
4
4
Auxiliary Measurements
group
52.
Ice concentration parameter
53.
Snow Depth
54.
Discriminator result (enumerated type)
55.
SARin Discriminator Parameter I
tbd
sl
4
4
56.
SARin Discriminator Parameter 2
tbd
sl
4
4
57.
SARin Discriminator Parameter 3
tbd
sl
4
4
58.
SARin Discriminator Parameter 4
tbd
sl
4
4
59.
SARin Discriminator Parameter 5
tbd
sl
4
4
60.
SARin Discriminator Parameter 6
tbd
sl
4
4
61.
SARin Discriminator Parameter 7
tbd
sl
4
4
Page 18
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I' ~.w~J',
~ltI
Doc No.
Issue.
Date.
Section.
('''.\/l:~~'~' ,.
Climate
Physics
Group
A''•~
CS-IS-MSL-GS-2001
1.0
11 Dec 2003
5.3
Table 5.3-1: L2 MDS Record Structure
ID
I
I
Symb
Descriptor
Type'C'
Size
(bytes)
Tot. Size
(bytes)
62.
SARin Discriminator Parameter 8
tbd
sl
4
4
63.
SARin Discriminator Parameter 9
tbd
sl
4
4
64.
SARin Discriminator Parameter 10
tbd
sl
4
4
65.
Discriminator status flag
-
ul
4
4
66.
Slope model correction attitude
µdeg
sl
4
4
67.
Slope model correction azimuth
µdeg
sl
4
4
68.
Uncorrected Latitude
µdeg
sl
4
4
69.
Uncorrected Longitude
µdeg
sl
4
4
70.
Ambiguity indicator
-
ul
4
4
71.
MSS from model
mm
sl
4
4
72.
Geoid from standard model
mm
sl
4
4
73.
DEM elevation (interpolated)
mm
sl
4
4
74.
DEM identifier (used in SARin)
-
ul
4
4
75.
Auxiliary Spares
-
UC
16xl
16
External Corrections
I
Unit
group
76.
C3
Dry Tropospheric Correction
mm
sl
4
4
77.
C4
Wet Tropospheric Correction
mm
sl
4
4
78.
C10
Inverse Barometric Correction
mm
sl
4
4
79.
CJ
DORIS Ionospheric Correction
mm
sl
4
4
80.
Cz
Model Ionospheric Correction
mm
sl
4
4
81.
C5
Ocean Tide 1
mm
sl
4
4
-
sl
4
4
82.
Spare (reserved for alternative tide correction)
83.
Cg
Ocean Loading Tide
mm
sl
4
4
84.
C7
Solid Earth Tide
mm
sl
4
4
Geocentric Polar Tide
mm
sl
4
4
Surface type flag
-
ul
4
4
87.
Correction status flags
-
ul
4
4
88.
Correction error flags
-
ul
4
4
89.
Spare
UC
12xl
12
85.
86.
dsi
Internal Corrections
group
Page 19
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•••••
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Issue.
Date.
Section.
Climate
Physics
Group
MSSL
CS-IS-MSL-GS-2001
1.0
11 Dec 2003
5.3
Table 5.3-1: L2 MDS Record Structure
ID
Symb
Descriptor
I
4
I
4
I
4
sl
I
4
I
4
I
sl
I
4
I
4
I
sl
I
4
I
4
Internal Phase Correction
I milli-radians I
sl
I
4
I
4
C17
I External Phase Correction
I milli-radians I
sl
I
4
I
4
Pi
I Noise
I
sl
I
4
I
4
C9
Doppler range correction (inc slope)
91.
CJ2
Instrument Range Correction, t-r antenna
I
mm
I
sl
92.
C13
Instrument Range Correction,
I
mm
I
93.
C14
Instrument Sigma 0 correction, t-r antenna
I
dB/lOO
94.
C15
Instrument Sigma 0 correction, r only antenna
I
dB/100
95.
CJ6
96.
97.
I
Tot.Size
(bytes)
4
90.
98.
Size
(bytes)
Type'C'
Unit
1 Spare
power measurement
r only antenna
sl
mm
I
dB/100
I
I
UC
I
12xl
I
12
notes:
i. COM offset is contained in the SPH.
ii. Doppler Range correction is computed from the line-of-sight vector and thus includes slope
model component where slope model is used.
5.3.1
L2 Parameters and Flag Words
field 1. MDSR Time Stamp - corresponding to ground bounce time of the individual pulse, or
middle of group of pulses for LRM. See section 1.4 for definition.
field 2. USO Correction factor (definition tbd) - this is the correction factor for USO drift
field 3. Mode ID - (us giving 16 bits) Identifies the SIRAL instrument measurement mode. see
Page 20
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Climate
Physics
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····.1.'.!
,~:U'
Doc No.
Issue.
Date.
Section.
CS-IS-MSL-GS-2001
1.0
11Dec2003
5.3
Table 5.3.1-1:
Table 5.3.1-1: Mode ID
Definition
Instrument mode - derivedfrom configuration
bits in the LO
PDS
Bit
SS
Bit
Setting
000001 = 1 = LRM
000010 = 2 =SAR
000011 = 3 = SARin
001011 = 11 = CALl-LRM
001100 = 12 =CALI-SAR
001101=13 = CALl-SARin
010110 = 22 = CAL2-SAR
010111=23 = CAL2-SARin
100001=33 = CAL3
15-10
0-5
SARin degraded case
9
6
set to 1 if one receive chain is missing
Reserved
8
7
set to 0
CAL4Mode
7
8
set to 1 for CAL4 packets
Platform attitude control
6-5
00 =unknown
9-10 01 =Local Normal Pointing mode (affirmed)
10 =Yaw Steering mode (affirmed)
Reserved
4-0
11-15 set to 0
field 4.
Source Sequence Counter - passed through from the L 1b record. Originally read from the
LO Echo telemetry packet (of the master channel in the case of SARin). This is a 16384
cyclic modulo counter, starting from 0, incrementing by 1. A separate counter is
maintained for each instrument mode.
field 5. Instrument Config flag - (ul giving 31 bits) This is derived from flags in the LO packets
for tracking and the echo [Rl]. see Table 5.3.1-2:
Table 5.3.1-2: Instrument Configuration Flag
Definition
PDS
Bit
SS
Bit
Setting
00 = 0 = unknown
0l = 1 = chain l
IO= 2 =chain 2
11=3 =both
31-30
0-1
Reserved
29
2
set to 0
Reserved
28
3
set to 0
27-26
4-5
Reception_chain_to_use
Bandwidth
'
00 =unknown
01=320MHz
10=40MHz
Page 21
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Section.
Climate
Physics
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CS-IS-MSL-GS-2001
1.0
11 Dec 2003
5.3
Table 5.3.1-2: Instrument Configuration Flag
PDS
Bit
SS
Bit
Reserved
25
6
set to 0
Reserved
24
7
set to 0
Definition
Setting
23-22
8-9
00 = 0 = unknown
01 =I =LRM
10 = 2 =SAR
11=3 = SARin
External Calibration
21
10
0 = no, I = External calibration
Reserved
20
11
set to 0
Loop_status
19
12
0 = closed loop
I= open loop
Loss of echo (from cycle report)
18
13
O= OK, 1 = loss of echo
Real-time error (from cycle report)
17
14
O= OK, 1 =real time computation error
(computing cycle too long)
Echo saturation error (from cycle report)
16
15
O= OK, I = echo saturation detected
Reception_Band_Attenuation
15
16
0 = not attenuated
I = attenuated
Cycle Report General Error
14
17
0 = cycle report is 0
I = cycle report is not 0
Tracking_mode
Reserved
13-0
18-31 set to 0
field 6. Record counter - will increment from 1 for each record in the L2 product.
field 7. Latitude of measurement - Corrected for off-nadir position of the retracked point; in
SARin by using the inferred x-track angle and in LRM using slope models. The Llb
field 8.
field 9.
field 10.
field 11.
field 12.
field 13.
Latitude (at Nadir) is preserved in field 68. Units are 10-1 µdegrees at User request.
Longitude of measurement - (as for Latitude). Longitude (at Nadir) is preserved in field
69.
Altitude - Altitude of the Satellite CoG above reference ellipsoid at Nadir. This is not
modified by SARin or LRM processing.
Altitude rate - instantaneous rate of change of Altitude with time (from Llb)
Satellite velocity vector -described in the International Terrestrial Reference Frame in the
International Earth Fixed System. From Orbit CFI call. This is not a unit vector as the
velocity magnitude is also required.
Real beam direction vector - described in the CryoSat Reference Frame (see [R2] section
2.4). From CFI call. This is a unit vector and note that the units are micro-metres.
Interferometric baseline vector - described in the Cryosat Reference Frame. From CFI
call. This is a unit vector and note that the units are micro-metres.
Page 22
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UCL
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l::.
Climate
Physics
Group
·~~.··I
• ~ ' .Jll.jf; '
Doc No.
CS-IS-MSL-GS-2001
Issue.
Date.
1.0
11 Dec 2003
Section.
5.3
field 14.L2 MCD - Measurement confidence flags. See Table 5.3.1-3:
Table 5.3.1-3: Level 2 Measurement Confidence Data
PDS
Bit
SS
Bit
Block degraded
31
0
Blank Block
30
I
O= OK, I= Blank block inserted for record
padding
Datation degraded
29
2
O= OK, 1= datation is bad or not set
Orbit propagation error
28
3
0= OK, I= error (returned by CFI or by
independent check)
Orbit file change
27
4
O= OK, l= Orbit file has changed w.r.t. previous
record
Orbit discontinuity
26
5
O= OK, l= discontinuity (eg gap)
Echo Saturation
25
6
O= OK, 1= saturated
(from echo saturation flag in the telemetry)
Other Echo error (e.g. empty waveform)
24
7
O= OK, I= echo error
Receive Ch 1 error for SARin
23
8
O= OK, 1= degraded or missing
Receive Ch2 error for SARin
22
9
O= OK, 1= degraded or missing
I
Window Delay Inconsistency
21
IO
O= OK, l= degraded, Value out of range or
computation error
I
AGC Inconsistency
20
11
O= OK, l= degraded, Value out of range or
computation error
I
CAL 1 Correction Missing
19
12
O= OK, 1= missing - not applied
I
CALI from IPF DB used
18
13
O= default not used
1= default from IPF DB used
I
DORIS USO correction missing
17
14
O= OK, correction available
I= correction factor not available
I
External COM correction missing
16
15
O= OK, correction available
1= correction not available
I
I
I
TRK Echo Error
15
16
O= OK, 1= degraded tracking echo
Echo Rx I Error
14
17
O= OK, 1=bad raw echo
Echo Rx2 Error
13
18
O= OK, 1= bad raw echo
I
NPM Inconsistency
12
19
O= OK, 1= degraded, Value out of range or
computation error
I
Azimuth Calibration
11
20
O= OK, Azimuth calibration
l= No Azimuth calibration
Definition
I
I
-from LO
Missing
Setting
O= OK, I= degraded (set if the block should not
be processed)"
applied
Page 23
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•••••
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Date.
CS-IS-MSL-GS-2001
1.0
11 Dec 2003
Section.
5.3
Doc No.
Issue.
Climate
Physics
Group
Table 5.3.1-3: Level 2 Measurement Confidence Data
PDS
Bit
SS
Bit
Azimuth Calibration from IPF DB
10
21
O=default not used
l= default from IPF DB used
Range window'' calibration function Missing
9
22
0= OK, calibrated
1= No Calibration applied.
Range window calibration function from IPF
DB
8
23
O=default not used
l= default from IPF DB used
reserved
7
24
set to 0
CAL 2 Correction Missing
6
25
O= OK, I= missing - not applied
CAL 2 from IPF DB used
5
26
O= default not used
I= default from IPF DB used
Power scaling error
4
27
O= OK, I= Error in power scaling
Attitude Correction Missing
3
28
0= OK, Attitude correction applied
l= Not corrected
reserved
2
29
set to 0
reserved
I
30
set to 0
Definition
Setting
reserved
31
set to 0
0
me
01ocKis not nrocesseu - me conamons ror
a. inrncates mat me uezraoauon or me 01ocKis senous so tnat
this must be defined.
b. the frequency dependent phase and amplitude correction function applicable to the range window
field
field
field
field
15.
16.
17.
18.
field 19.
field 20.
field 21.
field 22.
field 23.
Height of surface : At measurement point w .r.t. the reference ellipsoid.
Sigma 0 : fully corrected including instrument gain corrections and retracker correction.
spare : reserved for future use
Peakiness : of the echo in the Lib product. Note that this will require different
interpretation for SAR and SARin echoes which are not the 'usual' pulse-limited echo
shape.
Retracked range correction : the offset of the retracked point on the echo from the
reference point of the range window. This is a 1-way correction in mm.
Retracked Sigma 0 correction : correction to SigmaOresulting from the actual echo power
being different from the nominal, or expected, echo power.
Retracker output 3 : reserved for other retracker algorithm output parameters LRM = amplitude estimate
SARin=tbd
SAR = unused =O
Retracker output 4 : reserved for other retracker algorithm output parameters LRM =leading edge width (sigma c)
SARin=tbd
SAR = unused =0
Retracker output 5 : reserved for other retracker algorithm output parameters Page 24
•••••
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MSSL
field 24.
field 25.
field 26.
field 27.
field 28.
field 29.
field 30.
field 31.
field 32.
field 33.
Doc No.
CS-IS-MSL-GS-2001
Issue.
Date.
Section.
1.0
11 Dec 2003
5.3
LRM =tbd
SARin=tbd
SAR = unused =0
Retracker output 6 : reserved for other retracker algorithm output parameters LRM = reserved for U 10 the.
SARin= tbd
SAR = unused =0
Retracker output 7 : reserved for other retracker algorithm output parameters LRM =reserved for SSB the.
SARin= tbd
SAR = unused =0
Retracker output 8 : reserved for other retracker algorithm output parameters LRM = unused = 0
SARin=tbd
SAR = unused =0
Retracker output 9 : reserved for other retracker algorithm output parameters LRM = unused = 0
SARin=tbd
SAR = unused =0
Retracker output 10 : reserved for other retracker algorithm output parameters LRM = unused = 0
SARin= tbd
SAR = unused =0
Retracker output 11 : reserved for other retracker algorithm output parameters LRM = unused = 0
SARin= tbd
SAR = unused =0
Retracker output 12 : reserved for other retracker algorithm output parameters LRM = unused = 0
SARin=tbd
SAR = unused =0
Retracker output 13 : reserved for other retracker algorithm output parameters LRM = unused = 0
SARin= tbd
SAR = unused =0
Power echo shape parameter : TBD
Beam Behaviour parameter - an array of 50 integers to characterise the shape of the set of
Doppler echoes from a common surface location prior to stacking (averaging).
Currently the first 5 numbers are defined as follows, while the remainder are reserved for
future use:Table 5.3.1-4: Beam Behaviour Parameters
Index Name
[O]
STACK_HALF _WIDTH
Description
standard deviation [type=us]
Page 25
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Doc No.
Issue.
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Section.
Climate
Physics
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CS-IS-MSL-GS-2001
1.0
11 Dec 2003
5.3
Table 5.3.1-4: Beam Behaviour Parameters
Index Name
Description
[I)
STACK_CENTRE
beam in stack at maximum of the fitted Gaussian [type=us)
[2]
STACK_AMPLITUDE
stack scaled amplitude [type=us)
[3]
STACK_SKEWNESS
Stack skewness [type=ss] val/100, -99900 (TBD) if cannot be computed
[4]
STACK_KURTOSIS
Stack kurtosis [type=ss] val/100, -99900 (TBD) if cannot be computed
field 34. x-Track Angle : from the interferometric processing in SARin mode. This is the inferred
cross-track angle corresponding to the Retrack point of the SARin echo. This can be used
in combination with the Altitude to derive a horizontal offset from Nadir. The Latitude
and Longitude in field 7. and field 8. include this offset. Set to zero for SAR and LRM.
field 35. Coherence: derived from the SARin echoes at the Retrack point, this provides a measure
of confidence in the interferometric result. Set to 0 for SAR and LRM modes.
<<<question - should this be =Ifor SAR & LRM? (i.e. '1000' )>>>
field 36. Interpolated Ocean Height (or MSS) : the ocean height interpolated from the SAR data or
read from a MSS model (TBD) which is used in conjunction with surface height (field
15.) to compute a freeboard.
field 37. Freeboard : SAR mode computed freeboard of the Sea Ice. Initially (e.g. for launch plus
1 year) this will be set to zero, when there is greater confidence in the knowledge of the
Arctic basin sea surface height then freeboard will be computed in the L2 products. Set
to 0 in SARin and LRM modes.
field 38. Surface Height Anomaly : TBD
field 39. Interpolated Sea Surface Height Anomaly: TBD
field 40. Interpolation error for Ocean Height: height error in mm associated with the interpolated
Ocean Height.
field 41. Number of interpolation points used -forward : the number of measurement points in front
of current record that were used to interpolate the Ocean Height to this record.
field 42. Number of interpolation points used -backward : the number of measurement points
behind current record that were used to interpolate the Ocean Height to this record.
field 43. Radius of interpolation -forward (in time): maximum distance, in front of current
location, of points used to interpolate the Ocean Height to this record. Units are in time
(ms) which can be converted to km by multiplying by the satellite ground-speed.
field 44. Radius of interpolation -backward (in time): maximum distance, behind current location,
of points used to interpolate the Ocean Height to this record. Units are in time (ms) which
can be converted to km by multiplying by the satellite ground-speed.
field 45. Interpolation error flag : Indicates errors in ocean height interpolation.
field 46. Measurement mode (LRM I SAR I SARin): LRM=l, SAR=2, SARin=3
field 47. Measurement Quality Flags : Used to indicate errors with any component parameters in
Page 26
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•••••
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Climate
Physics
Group
Doc No.
Issue.
Date.
CS-IS-MSL-GS-2001
Section.
5.3
1.0
11 Dec 2003
this group.
Table 5.3.1-5: Measurement Quality flags
PDS
Bit
SS Bit
Height error
15
0
0 =no, 1 =yes
SigmaO error
14
1
0 =no, 1 =yes
SWH or Slope error
13
2
0 =no, 1 =yes
Peakiness error
12
3
0 =no, 1 =yes
Echo shape error
11
4
0 =no, 1 =yes
x-track angle error
10
5
0 = no, 1 = ambiguous angle
Coherence error
9
6
0 =no, 1 =yes
8-0
7-15
Definition
unused
Setting
set to 0
field 48. Retracker Flags : Indicate errors from the retracker algorithms in each mode.
Table 5.3.1-6: Retracker flags
PDS
Bit
SS Bit
Overall retracker failure flag
31
0
0 =no, 1 =yes
Low or zero power in waveform flag
30
1
0 =no, 1 =yes
Low peakiness flag
29
2
0 =no, 1 =yes
High peakiness flag
28
3
0 =no, 1 =yes
High noise flag
27
4
0 =no, 1 =yes
Low variance flag
26
5
0 =no, 1 =yes
Bad leading edge flag
25
6
0 =no, 1 =yes
Retrack position out of range
24
7
0 =no, 1 =yes
Abnormal beam behaviour parameters
23
8
0 =no, 1 =yes
Bad backscatter calculation
22
9
0 =no, 1 =yes
Reserved SWH
21
IO
0 =no, 1 =yes
Reserved UIO
20
11
0 =no, 1 =yes
Reserved SSB
19
12
0 =no, 1 =yes
Spare 4
18
13
0 =no, 1 =yes
SARin Retrack interpolation failure flag
17
14
0 =no, 1 =yes
SARin low coherence flag
16
15
0 =no, 1 =yes
Spare 6
15
16
0 =no, 1 =yes
Definition
Setting
Page 27
•••••
UCL
MSSL
Climate
Physics
Group
J
.'l ~ ''lt.f
-~·
·bl' : ~..
~>~
~~~;
''
Doc No.
CS-IS-MSL-GS-2001
Issue.
Date.
Section.
1.0
11 Dec 2003
5.3
,
Table 5.3.1-6: Retracker flags
PDS
Bit
SS Bit
Spare 7
14
17
0 =no, I= yes
Spare 8
13
18
0 =no, I= yes
Spare 9
12
19
0 =no, I= yes
Spare IO
11
20
0 =no, I= yes
Spare 11
10
21
0 =no, I= yes
SAR spare 12
9
22
0 =no, I= yes
SAR spare 13
8
23
0 =no, I= yes
SAR spare 14
7
24
0 =no, I= yes
SAR spare 15
6
25
0 =no, I= yes
SAR spare 16
5
26
0 =no, I= yes
SAR spare 17
4
27
0 =no, l =yes
SAR spare 18
3
28
0 =no, I= yes
SAR spare 19
2
29
0 =no, I= yes
LRM Retracker was CFI Ocean
I
30
0 =no, I= yes
LRM Retracker was OCOG
0
31
0 =no, 1 =yes
Definition
Setting
field 49 .Height Status Flags : Shows if corrections have been applied to the height field 15.
Table 5.3.1-7: Height Status flag
PDS
Bit
SS Bit
Corrected for internal calibration
31
0
0 =no, 1 =yes
Corrected for Radial Doppler
30
1
0 =no, 1 =yes
Corrected for Dry Tropo
29
2
0 =no, 1 =yes
Corrected for Wet Tropo
28
3
0 =no, 1 =yes
Corrected for Inverse Barometer
27
4
0 =no, 1 =yes
Corrected for Ionosphere - DORIS
26
5
0 =no, 1 =yes
Corrected for Ionosphere - Model
25
6
0 =no, 1 =yes
Ocean tide 1 used
24
7
0 =no, 1 =yes
Ocean tide 2 used
23
8
0 =no, 1 =yes
Ocean loading tide used
22
9
0 =no, 1 =yes
Definition
Setting
Page 28
•••••
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,,,~.m
f~,~~
Climate
Physics
Group
,, · t.\; 1w~; ,
i.
I
Doc No.
CS-IS-MSL-GS-2001
Issue.
Date .
1.0
11 Dec 2003
Section.
5.3
Table 5.3.1-7: Height Status flag
PDS
Bit
SS Bit
Solid earth tide used
21
10
0 =no, 1 =yes
Geocentric Polar tide used
20
11
0 =no, 1 =yes
Slope Doppler corrected
19
12
0 =no, 1 =yes
Mode specific window offset applied
18
13
0 =no, 1 =yes
SAR retracker applied
17
14
0 =no, 1 =yes
SARin retracker applied
16
15
0 =no, 1 =yes
LRM retracker applied
15
16
0 =no, 1 =yes
LRM Ocean bias applied
14
17
0 =no, 1 =yes
LRM Ice bias applied
13
18
0 =no, 1 =yes
SAR Ocean bias applied
12
19
0 =no, 1 =yes
SAR Ice bias applied
11
20
0 =no, 1 =yes
SARin Ocean bias applied
10
21
0 =no, 1 =yes
SARin Ice bias applied
9
22
0 =no, 1 =yes
LRM Slope model data valid
8
23
0 =no, 1 =yes
SARin baseline downward flag
7
24
0 =no, 1 =yes
SARin baseline forward flag
6
25
0 =no, 1 =yes
SARin out ofrange flag
5
26
0 =no, 1 =yes
Definition
Unused
4-0
Setting
27-31 set to 0
field 50.SAR Freeboard Status Flags: flags to indicate availability and reliability of the freeboard
measurement
Table 5.3.1-8: Freeboard Status flag
PDS
Bit
SS Bit
Freeboard measurement unavailable
31
0
0 =no, 1 =yes
Freeboard measurement unreliable
30
1
0 =no, 1 =yes
Freeboard measurement is in northern
geographical boundary
29
2
0 =no, 1 =yes
Freeboard measurement is in southern
geographical boundary
28
3
0 =no, I= yes
Definition
spare - tbd
27 - 0
Setting
4 - 31 set to 0
Page 29
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field 51. Measurement Spares : reserved for possible future use
field 52. Ice concentration parameter : a percentage estimate of Sea Ice concentration merged from
model data.
field 53. Snow Depth: in mm merged from a cJimatology model data. This can be used (by L2
product User) to adjust the freeboard estimate.
field 54. Discriminator result : enumerated type code showing the result of the discriminator
algorithm in each chain.
Table 5.3.1-9: Discriminator result
Value Definition
1
Result of LRM discrimination is undefined
2
Result of LRM discrimination is ocean
3
Result of LRM discrimination is land ice plateau
101
Result of SARIN discrimination is undefined
102
Result of SARIN discrimination is altimeter mode
201
Result of SAR discrimination is undefined.
202
Result of SAR discrimination is ocean.
203
Result of SAR discrimination is Sea Ice.
204
Result of SAR discrimination is Leads.
field 55. SARin Discriminator Parameter 1 : reserved for output parameters from the SARin
discriminator algorithm - TBD.
field 56. SARin Discriminator Parameter 2 : TBD
field 57. SARin Discriminator Parameter 3: TBD
field 58. SARin Discriminator Parameter 4 : TBD
field 59. SARin Discriminator Parameter 5: TBD
field 60. SARin Discriminator Parameter 6: TBD
field 61. SARin Discriminator Parameter 7 : TBD
field 62. SARin Discriminator Parameter 8 : TBD
field 63. SARin Discriminator Parameter 9: TBD
field 64. SARin Discriminator Parameter IO : TBD
field 65. Discriminator status flag: shows quality of the discriminator result for each chain.
Table 5.3.1-10: Discriminator flags
PDS
Bit
SS Bit
Overall discriminator failure flag
31
0
0 =no, 1 =yes
LRM discriminator flags TBD
30
1
0 =no, 1 =yes
Definition
Setting
Page 30
•••••
UCL
MSSL
i,'~~,._
lsc~·itt~
Climate
Physics
Group
I
i/
, .
~,..~"
~
.
I
,;.
',
!
'
Table 5.3.1-10: Discriminator
I
Issue.
Date.
1.0
11 Dec 2003
Section.
5.3
flags
SS Bit
TBD - reserved for LRM
29-22
2-9
set to 0
SARin Low Variance flag
21
10
0 =no, 1 =yes
SARin Bad Leading Edge flag
20
11
0 =no, 1 =yes
SARin High Noise flag
19
12
0 =no, I =yes
SARin Low Peakiness flag
18
13
0 =no, I= yes
SARin Hi Peakiness flag
17
14
0 =no, I= yes
SARin Low Power flag
16
15
0 =no, 1 =yes
TBD - reserved for SARin
I
CS-IS-MSL-GS-2001
PDS
Bit
Definition
I
Doc No.
15-12
Setting
16-19 set to 0
SAR very high peakiness flag
11
20
0 =no, 1 =yes
SAR very low peakiness flag
10
21
0 =no, 1 =yes
SAR Low or zero power flag
9
22
0 =no, 1 =yes
SAR abnormal beam behaviour parameters
8
23
0 =no, I= yes
SAR ice concentration unavailable
7
24
0 =no, 1 =yes
SAR ice concentration unreliable
6
25
0 =no, 1 =yes
SAR signal to noise ratio too low
5
26
0 =no, 1 =yes
Waveform is too wide
4
27
0 =no, I= yes
No votes for any available waveform
classification
3
28
0 =no, I= yes
Voting for discrimination classification tied
2
29
0 =no, I= yes
TBD
I
30
set to 0
SAR partial match
0
31
0 =no, 1 =yes
field 66. Slope model correction attitude : attitude angle of nearest echoing point on surface as
determined from slope models in LRM processing. 0 if model not present or invalid. Set
to 0 for SAR and SARin but may be used in the event of SARin mode with only 1 receive
chain operating.
field 67. Slope model correction azimuth : as for attitude
field 68. Uncorrected Latitude : of the Nadir position - this allows for removal of the slope
corrected position if desired.
field 69. Uncorrected Longitude : of the Nadir position - this allows for removal of the slope
corrected position if desired.
field 70. Ambiguity indicator : to flag the case where the interferometric angle may be ambiguous
Page 31
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11 Dec 2003
5.3
due to phase wrapping.
Table 5.3.1-11: SARinAmbiguity
Indicator flags
PDS
Bit
SS Bit
Overall Ambiguity
31
0
0 =no, I= yes
TBD Ambiguity
30
I
0 =no, I= yes
29-22
2-9
set to 0
DEM not available
21
IO
0 =no, I= yes
Different elevations
20
11
0 =no, I= yes
19-0
12-31
Definition
unused
unused
Setting
set to 0
field 71. MSS from model : from the ocean model supplied in the CFI library.
field 72. Geoid from standard model : from the Geoid model supplied in the CFI library.
field 73. DEM elevation: interpolated from a DEM (model tbd) to act as a check against the SARin
derived elevation. Set in SARin mode only, =0 for LRM & SAR.
field 74. DEM identifier: to identify the DEM model used in SARin
field 75. Auxiliary Spares : reserved for possible future use
field 76. Dry Tropospheric Correction - added to range measurement to correct for the propagation
delay to the radar pulse, caused by the dry-gas component of the Earth's atmosphere.
field 77. Wet Tropospheric Correction - added to range measurement to correct for the propagation
delay to the radar pulse, caused by the H20 component of the Earth's atmosphere.
field 78. Inverse Barometric Correction - added to range measurement to correct for the depression
of the ocean surface caused by the local barometric pressure.
field 79. DORIS Ionospheric Correction - added to range measurement to correct for the delay to
the Radar pulse caused by free electrons in the ionosphere. Computed from the
concurrent DORIS data.
field 80. Model Ionospheric Correction - added to range measurement to correct for the delay to
the Radar pulse caused by free electrons in the ionosphere. Computed from an
Ionospheric model.
field 81. Ocean Tide 1 - added to the range to remove the effect of local tide and adjust the
measurement to the mean sea surface.
field 82. Spare - reserved for possible future use.
field 83. Ocean Loading Tide - added to the range to remove the effect oflocal tidal distortion to
the Earth's crust.
field 84. Solid Earth Tide - added to the range to remove the effect of local tidal distortion in the
Earth's crust.
field 85. Geocentric Polar Tide - added to the range to remove a 'wobble' effect of the poles w.r.t.
Earth centre caused by tidal forces.
field 86. Surface type flag - enumerated key to classify surface at nadir.
field 87. Correction status flag - used to show which correction algorithms have been called, see
Page 32
UCL
•••••
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(f''-~ffi:
·~.\0~•1
Climate
Physics
Group
·\I .
fl
~/.
Doc No.
Issue.
Date.
CS-IS-MSL-GS-2001
1.0
11 Dec 2003
Section.
5.3
Table 5.3.1-12:. First 11 fields are as in Llb.
field 88. Correction error flag - used to show if a correction algorithms returned an error when
called see Table 5.3.1-13:. First 11 fields are as in Llb.
field 89. Correction spares - reserved for future use.
Table 5.3.1-12: Correction status flags
PDS
Bit
SS Bit
Dry Tropospheric Correction Called
31
0
0 =no, l =yes
Wet Tropospheric Correction Called
30
l
0 =no, l =yes
Inverse Barometric Correction Called
29
2
0 =no, l =yes
DORIS Ionospheric Correction Called
28
3
0 =no, l =yes
Model Ionospheric Correction Called
27
4
0 =no, l =yes
Ocean Tide l Called
26
5
0 =no, l =yes
Ocean Tide 2 Called
25
6
0 =no, l =yes
Ocean Loading Tide Called
24
7
0 =no, l =yes
Solid Earth Tide Called
23
8
0 =no, l =yes
Geocentric Polar Tide Called
22
9
0 =no, l =yes
Surface type flag Called
21
10
0 =no, l =yes
Ice concentration model called
20
11
0 =no, l =yes
Snow depth model Called
19
12
0 =no, l =yes
MSS model called
18
13
0 =no, 1 =yes
Geoid model Called
17
14
0 =no, l =yes
DEM model called
16
15
0 =no, 1 =yes
Slope model Called
15
16
0 =no, 1 =yes
14-0
17-31
Definition
reserved
Setting
set to 0
Table 5.3.1-13: Correction error flags
PDS
Bit
SS Bit
Dry Tropospheric Correction Error
31
0
0 = OK, l = error
Wet Tropospheric Correction Error
30
1
0 = OK, 1 = error
Inverse Barometric Correction Error
29
2
0 = OK, l = error
DORIS Ionospheric Correction Error
28
3
O=OK, 1 =error
Definition
Setting
Page 33
~
UCL
MSSL
~~Jt
..{f'i~,
·~1~r:,
Doc No.
Issue.
Climate
Physics
Group
Date.
Section.
i
CS-IS-MSL-GS-2001
1.0
11Dec2003
!
5.3
Table 5.3.1-13: Correction error flags
PDS
Bit
SS Bit
Model Ionospheric Correction Error
27
4
0 = OK, 1 = error
Ocean Tide 1 Error
26
5
0 = OK, 1 = error
Ocean Tide 2 Error
25
6
0 = OK, 1 = error
Ocean Loading Tide Error
24
7
0 =OK, 1 =error
Solid Earth Tide Error
23
8
0 =OK, 1 =error
Geocentric Polar Tide Error
22
9
0 =OK, I =error
Surface type flag Error
21
10
0 =OK, I =error
Ice concentration Error
20
11
0 =OK, I =error
Snow depth Error
19
12
0 =OK, I =error
MSS model Error
18
13
0 = OK, 1 = error
Geoid model Error
17
14
0 = OK, I = error
DEM model Error
16
15
0 = OK, I = error
Slope model Error
15
16
0 = OK, I = error
14-0
17-31
Definition
I
Setting
!
:
I
reserved
set to 0
Page 34
UCL
••••••
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6
Doc No.
Issue.
Date.
Section.
Climate
Physics
Group
CS-IS-MSL-GS-2001
1.0
11Dec2003
6
Auxiliary Input Data Files
A number of auxiliary data files are required for the L2 processing. These are:-
Job Order - Specifies the type of processing to perform and names the input files.
Physical constants - Physical and geophysical constants. These should remain fixed throughout
the mission.
IPF Database - Parameters which characterise the SIRAL instrument such as Radar frequency and
bandwidth.
Processor configuration file - Parameters controlling run-time processing options or
performance.
Sea Ice Concentration file - An input to the SAR processing chain to facilitate surface type
discrimination.
Mean Sea Level file - Provides the Global (Including Arctic) ice-free mean sea level to allow
freeboard computation.
Snow Depth file - Aids ice thickness determination as snow cover on sea ice affects freeboard/
thickness ratio.
Slope Models - corrects LRM mode data for the direction of echoing point when over sloping
terrain.
DEMs - used by SARin chain to help resolve ambiguity in the interferometric phase difference.
6.1
Auxiliary Data File Format
Auxiliary files will have a mission standard [R16] and an SPH [R16] followed by a single data set
record.
Table 6.1.0-1: Auxiliary Data File SPH
Field
Descriptor
Symb
Values
Size
(bytes)
Tot. Size
(bytes)
TBD
The SPH shall contain
TheMDS type
MDS record length
Number ofMDS records
Page 35
• .-
<'.:>••·••••••··
. '\\ . I ~
~ ~~~i
·~'u.,..~,, 1'' 'Jt..i.,;.
:
Climate
Physics
Group
•••••
UCL
MSSL
6.2
1111 '·
••••
i
:
Doc No.
Issue.
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Section.
CS-IS-MSL-GS-2001
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11 Dec 2003
6.2
!
.
i
i
Constants
Table 6.2-1: Physical and Geophysical Constants
Units
c
299792458.0
mis
PI
3.14159265358979
grav_accl_mu
3.9860044 el4
m"3 s"-2
Boltzmanns_ Const
l .380662e-23
J/K
Ref_elp
WGS84
-
Name of Reference Ellipsoid
ellipse_semi_maj
6378137.0000
m
WGS84
ellipse_semi_min
6356752.3142
m
WGS84
Deg2Rad
0.017453292
-
conversion of degrees to
radians
a.
I
speed oflight (c_vacuo)
circular ratio
Jt
Gravitational Constant x Earth
Mass= G *Mass of Eartha
Boltzmann's Constant
stancarus oocumem
IPF Database Parameters
I
This file is used by the IPFl system as well as IPF2. (see [Rl3])
I
I
6.4
I
1nK;:)
-
used by
algorithm
note: ellipse flattening is calculated from the two axes.
In the operational IPF system this is a common file with the IPFl processing. (see [R12])
6.3
I
description
value
Mnemonic
I'
Job Order File
This file defines the processing job type and identifies the input filenames. It is very similar to the
Llb JobOrder file. (see [R12])
6.5
Processor Configuration
File
This file defines all the run-time parameters and thresholds used to "tune" the IPF2 algorithms in
the LRM, SAR and SARin processing chains.
These are currently detailed in [R14]
:
Page 36
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6.6
Climate
Physics
Group
·~·v
..
1-
,~\L
~-'
Doc No.
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Section.
CS-IS-MSL-GS-2001
1.0
11Dec2003
6.6
Sea Ice Concentration
Two options are available and the preferred is option 1, but this requires processing the 5 channels
of daily Brightness Temperatures to ice concentration, supplied on a 25km stereographic grid in
HDF format. If no daily ice concentration files are available then either a default climatology can
be used (UCL can generate this) or use the last available daily data files.
1) Near Real- Time SSM/I daily SSM/I brightness temperatures available from: http://nsidc.org/
data/docs/daac/nsidc008 l_ssmi_nrt_seaice.gd.html They point out that the most recent daily
datasets (usually the previous day) do not have quality checks. They suggest that if this
is required, then you should wait at least 3 days for the required dataset. Also, they indicate that
the near real time products may have different values compared to the standard data products they
release with data latency of -4months. The ice concentration files are generated following the
NASA Team algorithm (Cavalieri, D.J., P.Gloersen and W.J.Cambell, Determination of sea ice
parameters with the NIMBUS 7 SMMR, J.G.R, 89, (D4), 5355-5369, 1984).
2) The Near Real-Time SSM/I EASE-Grid Daily Global Ice Concentration and Snow Extent
product: http://nsidc.org/data/nise I .html.
Sea ice concentration and snow extent maps are provided in two 25 km azimuthal, equal-area
projections: the Southern Hemisphere 25 km low resolution. (SI) and Northern Hemisphere 25 km
low resolution (NI) Equal-Area Scalable Earth-Grids (EASE-Grids). Data in Hierarchical Data
Format - Earth Observing System (HDF-EOS) format, and browse files in GIF and HDF formats,
are updated daily and are available via ftp for two weeks after initial posting.
6.7
Mean Sea Level
UCL will supply the MSL derived MSS from ERS-2 radar altimeter data containing the latitude,
longitude and MSL spanning a period of nearly 4 years (Cycles 0 to 41 corresponding to dates
between May 95 and April 1999). For ESA the lHz datafiles without detrending will be
concatenated together and supplied as one file. The provisional aim is to grid the data onto a 0.0625
degree grid, using the CFI routine to assign the nearest neighbour value to the acquired CryoSat
nadir record locations.
This proposal is to be subjected to an investigation and may be changed if the method is deemed
unsuitable.
6.8
Snow Depth Climatology
UCL could supply 12 files of monthly data containing the latitude, longitude and snow depth. A
new API is required to interpolate the model files to any given record location.
(An alternative is to regrid the climatology on a 25km (the) grid, and use the CFI routine to assign
the nearest neighbour value to the acquired CryoSat nadir record locations. However this is
Page 37
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Issue.
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Section.
CS-IS-MSL-GS-2001
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6.9
deemed to be higher risk as it restricts the interpolation method and may not be suitable for the task
required).
6.9
Slope Model Files
A slope model is a pair of two-dimensional arrays of single-precision numbers representing range
slopes. The X and Y components of slope are accessed separately.
The slope model is created from a digital elevation model. The data are processed, essentially by
differentiation, so that for each pair of array elements corresponding to a position, a unique pair of
derivatives can be assigned. The required geometry of the slope models uses a hemispherical
cartesian coordinate system. The slope model is therefore defined on the X,Y plane, but the
transformation from the DEM coordinates to the X,Y plane must be performed when creating the
model.
The X,Y coordinate mapping is ambiguous with respect to the hemisphere of the Earth under
consideration. Therefore a 'hemisphere flag' is included in the slopes file.
A slope model is required for both Antarctica and for Greenland. The accuracy of the slopes will
depend upon the quality of the source DEMs used. The slope models shall be derived from the best
available DEMs. Note that slope models will continue to evolve, and ENVISA T RA-2 and CryoSat
SIRAL data will also be used to improve and update the models. Thus the Auxiliary Files used may
be updated during the processing phase.
The horizontal sampling of the models shall be up to lKm. This is appropriate for the best
altimetric DEMs of Antarctica and Greenland derived from ERS geodetic mission data. With this
sampling resolution, we can estimate the size of the slope files as follows:
Greenland (Model number= 1) is a land mass of 2000 by 3000 km extent. At lkm resolution, we
can represent its slopes by an array of approximately 2000 x 3000 numbers. These are specified as
floats, and so the file will be approximately 48 Megabyte in size. The whole of Antarctica (Model
number= 2) can be contained within a square of 6670 kms per side. At lkm resolution this file will
be a little over 360 Megabyte.
These sizes refer to the simplest possible implementation of the slope models as pairs of rectangular
2-dimensional arrays of real numbers. Coding with variable resolution, taking into account areas
of low slope variability could be exploited. Also areas of ocean within the model could be
eliminated. The models are probably too large to be held in memory, and so an efficient cacheing
scheme may be needed. One way to achieve this is to note that radar altimeter data is normally
processed one orbit at a time. Thus it should be possible to pre-load a narrow along-orbit strip of
the range slope models for each orbit. The strip would need to extend a number points either side
of the orbit track to satisfy the requirements for the interpolation requirementsof the algorithm.
Slopes of I in I0,000 lead to slope corrections at the - 5 millimetre level, and so the slopes in the
Page 38
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Issue.
Date.
Section.
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11 Dec 2003
6.10
models may be safely represented as single-precision, 32-bit floating-point numbers, as the 24-bit
precision available translates to approximately 8 decimal significant figures. Slopes of greater than
a few degrees will not be tracked at high precision (if at all) by the LRM mode , and so precision
in areas of high surface slope is less important.
The number of models required initially is 2, 1 for Greenland, and 1 for Antarctica. However we
require that the system shall be able to take additional slope models as more and better models
become available. Hence we recommend that the number of slope models in the system be variable.
The minimum number of slope models to be handled by the system should be 10.
6.10
DEMs
Gridded Digital Elevation Models of Antarctica and Greenland. Initially there will only be these
two models but we require that the system can take additional models and that the minimum
number be 10. These models will be the best available. File sizes will be half of the corresponding
slope models described above.
Page 39
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7
Climate
Physics
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Doc No.
Issue.
Date.
Section.
CS-IS-MSL-GS-2001
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11Dec2003
7
Internal Interfaces To ESL Processing
This section defines TBD intermediate data interfaces.
7.1
Intermediate Inputs
TBD
Input to pass 2 of the Sealce chain is exactly the same L2 data structure defined in section 5.3
7.2
Intermediate Outputs
TBD
Output from pass 1 of the Sealce chain is exactly the same L2 data structure defined in section 5.3
Break point files - to be detailed in a later issue.
Page 40
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