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Agence spatiale Canadian SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 1
Dr. Satish Srivastava
Chair, CEOS WGCV SAR Subgroup
Canadian Space Agency
Report on CEOS WGCV SAR Subgroup Activities
Presented at
27th CEOS WGCV MeetingNational Physical Laboratory, UK
June 12 – 15, 2007
Agence spatiale Canadian SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 2
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 SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 3
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 SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 4
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 SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 5
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 SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 6
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 SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 7
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 SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 8
Recognized distributed target referenceSeasatSIR-BSIR-CERS-1ERS-2 ScatterometerJERS-1RADARSAT-1ENVISATRADARSAT-2
Well characterized site radiometrically
(late 80s early 90s)
IsotropicTemporal stabilitySpatial uniformity
Radiometric Calibration: Amazon Rainforest
Agence spatiale Canadian SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 9
Extraction of In-Flight Elevation Beam Pattern from Amazon Rainforest images (Antenna pattern correction off)
PR (inc) G2(el)
Beam EL1
RADARSAT-1 acquisitions to date: More than 1600
Comparison of measured pattern vs Calibrated Pattern
-16
-14
-12
-10
-8
-6
-4
-2
0
7 8 9 10 11 12 13 14 15 16 17 18 19 20
Elevation Angle (deg.)
Tw
o-W
ay
Ga
in (
dB
)
Agence spatiale Canadian SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 10
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 SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 11
LANDSATW1
EL1
RADARSAT-1Measurement 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
-16
-14
-12
-10
-8
-6
-4
-2
0
2
4
6
5 10 15 20 25 30 35 40 45 50
S7
EL1 W1W2 W3
EL1 W1 W2 W3 S7
10° 49°
Agence spatiale Canadian SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 12
Deriving a BF reflectivity estimate
Linear fit of each gamma profile
Then averaged to obtain reflectivity estimate (inc) EL1
W1
W2W3 S7
Year-round Boreal Forest reflectivity
~ centred around Rainforest value (-6.5 dB)
dependence conforms to clutter models
Large variation of reflectivity levels
Extractions of (inc) from Boreal Forest images Assuming beams remain calibrated during acquisitions
Antenna Pattern Compensation ON
Agence spatiale Canadian SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 13
Piece-wise linear over each beam range
-4
-3
-2
-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.)
EL1 W1 W3 S7
Summer period – normalized (dB)
W2
Seasonal Boreal Forest reflectivity
Agence spatiale Canadian SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 14
Deriving estimates seasonal reflectivity
Model ~ kinc over incidence
angle range of each tested beams
Assumptions• Seasonally stable• Linear anisotropy
Gam
ma
Lin
ear
Fit
(dB
)G
amm
a L
inea
r F
it (d
B)
Summer
Winter
EL1
W1
W2
W3
S7
EL1
W1
W2
W3 S7
Standard Deviation of
dependance
(dB/deg.)
'Summer' 'Winter'
EL1 .0943 .1789
W1 .0915 .1784
W2 .0919 .1978
W3 .0933 .1929
S7 .0915 .1953
Agence spatiale Canadian SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 15
Antenna Pattern Compensation
OFF
Elevation beam pattern extraction tests
Average peak-peak pattern difference (dB)
100% swath
'Summer' 'Winter' Rainforest
EL1 1.35 (1.26) 1.43 (1.24) 0.83
W1 0.99 1.21 0.68
S7 0.81 1.26 0.71
G2(el) PR / (inc)
Procedure (as with Amazon imagery):
• Extract beam pattern• Compare with calibrated pattern in
Payload Parameters File• Measure radiometric deviation: peak-peak
of pattern difference (dB)
In analysis software, substitute constant Rainforest reflectivity with 'summer' or 'winter' reference
Mostly experimented with EL1, W1 and S7 so far, acquired in both reference periods
Derived a beam-wise linear reflectivity estimate inc for both reference periods
Agence spatiale Canadian SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 16
EL1 'Summer' example: 1.17 dB PO M0380288
-20
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
7 8 9 10 11 12 13 14 15 16 17 18 19 20
Elevation Angle (deg)
Tw
o-W
ay
Re
lati
ve
Ga
in (
dB
)
Agence spatiale Canadian SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 17
EL1 'Winter' example: 1.26 dB PO M0398005
-20
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
7 8 9 10 11 12 13 14 15 16 17 18 19 20
Elevation Angle (deg)
Tw
o-W
ay
Re
lati
ve G
ain
(d
B)
Agence spatiale Canadian SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 18
W1 'Summer' example: 0.86 dB PO M0375998
-9
-8
-7
-6
-5
-4
-3
-2
-1
16 17 18 19 20 21 22 23 24 25 26 27 28 29
Elevation Angle (deg)
Tw
o-W
ay
Re
lati
ve G
ain
(d
B)
Agence spatiale Canadian SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 19
W1 'Winter' example: 1.33 dB PO M0404092
-9
-8
-7
-6
-5
-4
-3
-2
-1
16 17 18 19 20 21 22 23 24 25 26 27 28 29
Elevation Angle (deg)
Tw
o-w
ay
Re
lati
ve G
ain
(d
B)
Agence spatiale Canadian SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 20
S7 'Summer' example: 0.56 dB PO M0379237
0
1
2
3
4
5
6
7
38 38.5 39 39.5 40 40.5 41 41.5 42 42.5 43
Elevation Angle (deg)
Tw
o-W
ay
Re
lati
ve G
ain
(d
B)
Agence spatiale Canadian SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 21
S7 'Winter' example: 0.88 dB PO M0396745
0
1
2
3
4
5
6
7
38 38.5 39 39.5 40 40.5 41 41.5 42 42.5 43
Elevation Angle (deg)
Tw
o-W
ay
Re
lati
ve G
ain
(d
B)
Agence spatiale Canadian SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 22
Calibration Transponder Sites
Multi-Transponder Sites in Canada– In Fall 2006, ESA relocated an
ENVISAT ASAR Transponder in Resolute Bay in vicinity of a RADARSAT Transponder
– Both Transponders are used simultaneously by ENVISAT
– Another ENVISAT ASAR Transponder was recently relocated in Ottawa, again in vicinity of another RADARSAT Transponder
– Two potential sites in Canada for inter-sensor comparisons for C-band SARs (e.g., RADARSAT-1 and 2, ENVISAT)
RADARSATTransponder
ENVISATTransponder
ENVISAT ASAR Image of Resolute
Agence spatiale Canadian SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 23
RADARSAT-1 Precision Transponders forImage Quality and Calibration Measurements
Resolute Bay
Ottawa
Fredericton
Prince Albert
SAR Impulse Response
Agence spatiale Canadian SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 24
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 SpaceCanadienne Agency
CEOS Working Group on Calibration & Validation (WGCV)
27th Meeting, NPL, UKPage 25
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