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					                     Report on CEOS WGCV SAR
                        Subgroup Activities
                                      Presented at

                             27th CEOS WGCV Meeting
                          National Physical Laboratory, UK
                                 June 12 – 15, 2007


Dr. Satish Srivastava
Chair, CEOS WGCV SAR Subgroup
Canadian Space Agency


   Agence spatiale   Canadian Space                  CEOS Working Group on Calibration & Validation (WGCV)
   Canadienne        Agency                                                          27th Meeting, NPL, UK
                                          Page 1
                      CEOS WGCV SAR Subgroup (1)
    Mission: to foster high-quality synthetic aperture radar imagery
     from airborne and space borne SAR systems through
     precision calibration in radiometry, phase, and geometry, and
     validation of high level products.
    Objectives:
    –        Act as a forum for international technical interchange on the
             evolving methodologies, techniques,and equipment of SAR data
             processing, calibration and validation,
    –        To determine standard definitions and calibration-validation
             requirements for SAR systems.
    –        To support changes in CEOS formats and user products as
             appropriate,
    –        To facilitate international cooperative programs in the calibration
             and validation of SAR systems,
    –        To educate the SAR community.

    Agence spatiale   Canadian Space                CEOS Working Group on Calibration & Validation (WGCV)
    Canadienne        Agency                                                        27th Meeting, NPL, UK
                                        Page 2
                     CEOS WGCV SAR Subgroup (2)
 Action Plan:
   – Annual Workshop/Meeting
   – Set up standard CAL/VAL sites – inter-sensor comparison
   – Calibration specification, requirements and techniques for
     Polarimetry, Interferrometry, POLInSAR

 Recent Annual Workshop/Meeting
   – 2006 – Hosted by University of Edinburgh in Edinburgh, UK
   – 2005 – Hosted jointly by DSTO and University of Adelaide in
     Adelaide, Australia
   – 2004 - Hosted by ESA in Ulm, Germany
   – 2003 – ASAR 2003 Workshop, hosted jointly by CSA and CEOS
     WGCV SAR Subgroup in Saint-Hubert, Canada
   – 2002 – Hosted by BNSC in London, UK


   Agence spatiale   Canadian Space            CEOS Working Group on Calibration & Validation (WGCV)
   Canadienne        Agency                                                    27th Meeting, NPL, UK
                                      Page 3
       Next CEOS SAR Subgroup Meeting (1)

 ASAR 2007 Workshop: hosted jointly by Canadian
  Space Agency and CEOS WGCV SAR Subgroup
 To be held in Vancouver, Canada, Sept. 11 – 13, 2007
 Organizers: Canadian Space Agency, CEOS WGCV
  SAR Subgroup, Defence Research and Development
  Canada, Canada Centre for Remote Sensing and
  MacDonald, Detwiller & Associates (MDA)
 Website –
  http://www.space.gc.ca/asc/eng/events/2007/asar.asp



   Agence spatiale   Canadian Space            CEOS Working Group on Calibration & Validation (WGCV)
   Canadienne        Agency                                                    27th Meeting, NPL, UK
                                      Page 4
      Next CEOS SAR Subgroup Meeting (2)
 ASAR 2007 WorkshopTimetable
  –     First Call: February 15, 2007
  –     Abstract Submission: May 25, 2007
  –     Notification of Acceptance: June 8, 2007
  –     Registration: Now Open
  –     Workshop: September 11 – 13, 2007
  –     Paper Submission: October 12, 2007
  –     Distribution of Proceedings: December 2007



  Agence spatiale   Canadian Space            CEOS Working Group on Calibration & Validation (WGCV)
  Canadienne        Agency                                                    27th Meeting, NPL, UK
                                     Page 5
       Next CEOS SAR Subgroup Meeting (3)
 ASAR 2007 Workshop Suggested Topics
  –     Next Generation SAR Systems
  –     New SAR Missions
  –     Innovative SAR Concepts
  –     SAR Hardware and on-board Processing
  –     Polarimetry and Interferrometry
  –     Signal Processing Techniques
  –     SAR User Requirements
  –     SAR Calibration
  –     Validation
  –     Emerging SAR Applications
  –     SAR Data Formats
  –     Calibration Targets
  –     Calibration Performance of on-going Missions
  –     RCS Models and Scatterometers


  Agence spatiale   Canadian Space                 CEOS Working Group on Calibration & Validation (WGCV)
  Canadienne        Agency                                                         27th Meeting, NPL, UK
                                      Page 6
                              Natural Calibration Sites
 International Amazon Rainforest
  Site
   – Data is routinely collected and
     analyzed for calibration monitoring
     of SAR satellites including
     RADARSAT-1
   – Radiometry of the site remains
     stable
 Canadian Boreal Forest Site
   – Radiometric characterization
     completed at C-band using
     RADARSAT-1 data
   – Site seasonally dependent
   – Can be used complimentary to
     Amazon but with a reduced
     radiometric accuracy
   Agence spatiale   Canadian Space               CEOS Working Group on Calibration & Validation (WGCV)
   Canadienne        Agency                                                       27th Meeting, NPL, UK
                                         Page 7
Radiometric Calibration: Amazon Rainforest



 Recognized distributed target reference
      Seasat
      SIR-B
      SIR-C
      ERS-1                                                  Isotropic
      ERS-2 Scatterometer
      JERS-1
                                                         Temporal stability
      RADARSAT-1                                         Spatial uniformity
      ENVISAT
      RADARSAT-2


 Well characterized site radiometrically
      (late 80s early 90s)




       Agence spatiale   Canadian Space             CEOS Working Group on Calibration & Validation (WGCV)
       Canadienne        Agency                                                     27th Meeting, NPL, UK
                                           Page 8
                                   Extraction of In-Flight Elevation Beam Pattern from
                                   Amazon Rainforest images (Antenna pattern correction off)

                                       PR  g(qinc) G2(qel)

                                   RADARSAT-1 acquisitions to date: More than 1600

                                   Comparison of measured pattern vs Calibrated Pattern



                                                                                  0




                                                            Two-Way Gain (dB)
                                                                                 -2
                                                                                 -4
                                                                                 -6
                                                                                 -8
                                                                                -10
                                                                                -12
                                                                                -14
                                                                                -16
                                                 Beam EL1                             7   8   9   10 11 12 13 14 15 16 17 18 19 20
                                                                                                     Elevation Angle (deg.)
Agence spatiale   Canadian Space                                                CEOS Working Group on Calibration & Validation (WGCV)
Canadienne        Agency                                                                                        27th Meeting, NPL, UK
                                                Page 9
Boreal Forest - Hearst Site
  • Northwestern Ontario landmass (Hudson Bay basin)
  • Boreal Forest-Barrens transition
        boreal spruce, balsam fir, jack pine, poplar, birch,
        tamarack, cedar
  • Seasonal Variations




         Agence spatiale   Canadian Space                      CEOS Working Group on Calibration & Validation (WGCV)
         Canadienne        Agency                                                              27th Meeting, NPL, UK
                                                Page 10
RADARSAT-1
Measurement Campaign

• Started in January 2003
• Covering entire range of
  incidence angles (5 beams)
• 2 to 4 products of each beam
  every 24-day cycle




                                                         S7
           EL1 W1 W2 W3 S7

          10°                     49°             EL1
                                                         LANDSAT
                                                        W1

 6

 4

 2

 0

 -2
                                                                                                                                       S7
                                                                                       W2                        W3
 -4

 -6


                                                                W1
                Agence spatialeEL1
 -8


                                                                               CEOS Working Group on Calibration & Validation (WGCV)
-10

-12
                                 Canadian Space
-14             Canadienne       Agency                                                                        27th Meeting, NPL, UK
-16
                                                                Page 11
      5         10                15              20       25             30           35                40               45                50
Year-round Boreal Forest reflectivity

Extractions of g(qinc) from Boreal Forest images
     Assuming beams remain calibrated during acquisitions

                                                                                    Antenna Pattern
                                                                                   Compensation ON


                                                                    W2
                                                                                         W3               S7
  Deriving a BF reflectivity estimate
       Linear fit of each gamma profile
       Then averaged to obtain reflectivity estimate g(qinc)
            EL1
                                            W1

  g ~ centred around Rainforest value (-6.5 dB)
  g dependence conforms to clutter models
  Large variation of reflectivity levels
         Agence spatiale   Canadian Space                  CEOS Working Group on Calibration & Validation (WGCV)
         Canadienne        Agency                                                          27th Meeting, NPL, UK
                                                 Page 12
Seasonal Boreal Forest reflectivity
      4
               Summer period – normalized (dB)
      3

      2
                              EL1                 W1                   W2               W3              S7
      1

      0

      -1

      -2

      -3

      -4
           8    10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50
                                              Incidence Angle (deg.)

 Piece-wise linear over each beam range
           Agence spatiale   Canadian Space                                 CEOS Working Group on Calibration & Validation (WGCV)
           Canadienne        Agency                                                                         27th Meeting, NPL, UK
                                                          Page 13
Deriving estimates seasonal reflectivity
Assumptions                                                                    Model
                         • Seasonally stable                                         g ~ kqinc over incidence
                         • Linear anisotropy                                           angle range of each
                                                                                       tested beams
 Gamma Linear Fit (dB)




                                                                W1                     W3                                    Standard Deviation of
                                                                                                                                 g dependance
                               EL1                                        W2                                                        (dB/deg.)
                                                                                                    S7
                                                                Summer                                                        'Summer'          'Winter'

                                                                                                                  EL1           .0943               .1789

                                                                                                                  W1            .0915               .1784
 Gamma Linear Fit (dB)




                                                                W1                                                W2            .0919               .1978

                                                                                       W3           S7            W3            .0933               .1929

                                                                                                                  S7            .0915               .1953
                               EL1
                                                                 Winter   W2


                             Agence spatiale   Canadian Space                               CEOS Working Group on Calibration & Validation (WGCV)
                             Canadienne        Agency                                                                       27th Meeting, NPL, UK
                                                                           Page 14
Elevation beam pattern extraction tests
   Derived a beam-wise linear reflectivity estimate
   g(qinc), for both reference periods

   G2(qel)  PR / g(qinc)
   In analysis software, substitute constant Rainforest
   reflectivity with 'summer' or 'winter' g reference

   Mostly experimented with EL1, W1 and S7 so far,                               Antenna Pattern
   acquired in both reference periods                                           Compensation OFF



   Procedure (as with Amazon imagery):                         Average peak-peak pattern difference (dB)
                                                                                     100% swath
     • Extract beam pattern
                                                                  'Summer'             'Winter'          Rainforest
     • Compare with calibrated pattern in
                                                     EL1          1.35 (1.26)         1.43 (1.24)           0.83
       Payload Parameters File
                                                                     0.99                1.21               0.68
     • Measure radiometric deviation: peak-peak      W1
       of pattern difference (dB)                    S7              0.81                1.26               0.71




        Agence spatiale   Canadian Space                   CEOS Working Group on Calibration & Validation (WGCV)
        Canadienne        Agency                                                           27th Meeting, NPL, UK
                                           Page 15
EL1 'Summer' example: 1.17 dB PO M0380288
                                0


                                -2


                                -4
  Two-Way Relative Gain (dB)




                                -6


                                -8


                               -10


                               -12


                               -14


                               -16


                               -18


                               -20
                                     7         8           9        10      11   12        13        14       15       16        17         18        19         20

                                                                                      Elevation Angle (deg)

                                         Agence spatiale   Canadian Space                                     CEOS Working Group on Calibration & Validation (WGCV)
                                         Canadienne        Agency                                                                             27th Meeting, NPL, UK
                                                                                           Page 16
EL1 'Winter' example: 1.26 dB PO M0398005
                                0


                                -2


                                -4
  Two-Way Relative Gain (dB)




                                -6


                                -8


                               -10


                               -12


                               -14


                               -16


                               -18


                               -20
                                     7         8           9        10      11   12        13         14      15        16        17         18        19         20

                                                                                      Elevation Angle (deg)

                                         Agence spatiale   Canadian Space                                      CEOS Working Group on Calibration & Validation (WGCV)
                                         Canadienne        Agency                                                                              27th Meeting, NPL, UK
                                                                                            Page 17
W1 'Summer' example: 0.86 dB PO M0375998
                               -1



                               -2



                               -3
  Two-Way Relative Gain (dB)




                               -4



                               -5



                               -6



                               -7



                               -8



                               -9
                                    16        17           18        19     20   21        22        23       24        25         26         27        28            29

                                                                                      Elevation Angle (deg)

                                         Agence spatiale   Canadian Space                                     CEOS Working Group on Calibration & Validation (WGCV)
                                         Canadienne        Agency                                                                             27th Meeting, NPL, UK
                                                                                           Page 18
W1 'Winter' example: 1.33 dB PO M0404092
                                -1



                                -2



                                -3
   Two-way Relative Gain (dB)




                                -4



                                -5



                                -6



                                -7



                                -8



                                -9
                                     16        17           18        19     20   21        22        23       24        25         26         27        28            29

                                                                                       Elevation Angle (deg)

                                          Agence spatiale   Canadian Space                                     CEOS Working Group on Calibration & Validation (WGCV)
                                          Canadienne        Agency                                                                             27th Meeting, NPL, UK
                                                                                            Page 19
S7 'Summer' example: 0.56 dB PO M0379237
                                7




                                6
   Two-Way Relative Gain (dB)




                                5




                                4




                                3




                                2




                                1




                                0
                                    38          38.5            39          39.5   40       40.5      41             41.5           42           42.5          43

                                                                                   Elevation Angle (deg)

                                         Agence spatiale   Canadian Space                                  CEOS Working Group on Calibration & Validation (WGCV)
                                         Canadienne        Agency                                                                          27th Meeting, NPL, UK
                                                                                        Page 20
S7 'Winter' example: 0.88 dB PO M0396745
                                7




                                6
   Two-Way Relative Gain (dB)




                                5




                                4




                                3




                                2




                                1




                                0
                                    38          38.5           39           39.5   40       40.5      41             41.5          42           42.5           43

                                                                                   Elevation Angle (deg)

                                         Agence spatiale   Canadian Space                                  CEOS Working Group on Calibration & Validation (WGCV)
                                         Canadienne        Agency                                                                          27th Meeting, NPL, UK
                                                                                        Page 21
                         Calibration Transponder Sites

 Multi-Transponder Sites in Canada                ENVISAT ASAR Image of Resolute
   – In Fall 2006, ESA relocated an
     ENVISAT ASAR Transponder in
     Resolute Bay in vicinity of a                                                RADARSAT
     RADARSAT Transponder                                                         Transponder

   – Both Transponders are used
     simultaneously by ENVISAT
   – Another ENVISAT ASAR
     Transponder was recently relocated
     in Ottawa, again in vicinity of
     another RADARSAT Transponder                             ENVISAT
   – Two potential sites in Canada for                       Transponder

     inter-sensor comparisons for C-
     band SARs (e.g., RADARSAT-1
     and 2, ENVISAT)
      Agence spatiale   Canadian Space               CEOS Working Group on Calibration & Validation (WGCV)
      Canadienne        Agency                                                       27th Meeting, NPL, UK
                                         Page 22
RADARSAT-1 Precision Transponders for
Image Quality and Calibration Measurements




                                                                        Resolute Bay




                                                     Prince Albert


                                                                                                                     Fredericton

                                                                                                     Ottawa
SAR Impulse Response
                  Agence spatiale   Canadian Space                             CEOS Working Group on Calibration & Validation (WGCV)
                  Canadienne        Agency                                                                     27th Meeting, NPL, UK
                                                              Page 23
  Recommendations from SAR Subgroup (1)

 CEOS SAR Subgroup Workshop/Meeting
  held at Edinburgh in October 2006
  concluded with a set of following
  recommendations to WGCV:

 In order to reduce the extent of the commissioning
  phase of space borne SARs, effort be invested as
  much as possible into pre-launch calibration (e.g.
  antennas, TR modules, etc)
 Data providers should investigate new product types
  that provide complex data in which the noise has
  been removed
  Agence spatiale   Canadian Space             CEOS Working Group on Calibration & Validation (WGCV)
  Canadienne        Agency                                                     27th Meeting, NPL, UK
                                     Page 24
       Recommendations from SAR Subgroup (2)
 In order to facilitate the use of calibrated SAR data (and
  to avoid the problem of continuously changing data
  formats), the data providers should provide:
   –        a reader on the data CD itself
   –        a LUT of calibration conversion factors for each pixel across a
            swath to covert DNs to sigma nought, beta nought and gamma
 CEOS should co-ordinate a central database to log the
  use, location and availability of corner reflectors, in
  order to increase the availability of calibration targets to
  other agencies for appropriate SAR sensors
 Future SAR Missions should be capable of full
  polarimetric imaging
       Agence spatiale   Canadian Space             CEOS Working Group on Calibration & Validation (WGCV)
       Canadienne        Agency                                                     27th Meeting, NPL, UK
                                          Page 25

				
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