radarsat-1: an end-of-mission review of the imaging and...

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RADARSAT-1:

An End-of-Mission Review of the Imaging and Calibration Performance of a Magnificent Canadian Instrument

S. Cote, S. Srivastava Canadian Space Agency S. Muir Calian Technologies Ltd

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RADARSAT-1

• Canada's first operational EO satellite

• Launched November 1995 - Operational April 1996

• HH, C-Band, right-looking

• Mission Lifetime: 5.25 yrs

• Actual Lifetime: 17.3 yrs

• Sun-synchronous, Dawn–Dusk LEO

• Altitude: 798 km

• Period: 100.7 minutes

• Repeat Cycle: 24 days

• Orbits per day: 14

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Outline

• Calibration Activities Closeout

• Image Quality (point target) review

• Radiometric performance review

• Internal calibration history

• Conclusion

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February 6, 2013: First occurrence of an anomaly related to a power degradation of the low power transmitter (LPT) induced by failure to load chirp information needed for imagery.

March 29, between 06:05 and 07:28 UTC: Last complete communication with spacecraft: RADARSAT-1 was assumed to be in safe-hold mode.

March 5: After several occurrences (22) of LPT anomaly, decision was taken to reconfigure the payload in order to use the redundant unit.

March 6: Redundant LPT was successfully activated. This did not immediately stop the anomaly from occurring: two other instances happened less than 24 hours after reconfiguration.

March 7-8: Images acquired with the redundant LPT were of good general IQ. Plan had begun to assess the calibration and imaging performance of the reconfigured payload using point target and distributed target scenes.

March 9-26: No anomalies, nominal payload imaging.

March 27-28: Five planned outages for battery reconditioning were executed during that period (routine outages performed each spring). Spacecraft was back to nominal after procedures.

May 2013

Recent events affecting the spacecraft

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Nominal IQ and Calibration operations have ceased shortly after final loss of communication with the spacecraft (29 Mar 2013):

• Acquisition planning, image analysis, trend analysis, transponder scheduling; • Longer-term projects such as comparative radiometric level validations with R2,

and prototyping of new beam pattern corrections (payload update 33); • Close-out and final issuance of cal-val reports, procedures, databases, SW.

Over the last couple of years, the Calibration Operations had already begun consolidating its activities for RADARSAT-1:

• Decommissioning of Resolute and Prince Albert transponders; • Upgrade of Fredericton transponder and re-deployment in St Hubert.

Closeout of IQ and Calibration Operations

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Last Boreal Forest scene acquired

Standard 1

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Last transponder scene acquired

Transponder response

TT&C antenna reflection

CSA

Extended High 6

8

0

5

10

15

20

25

30

35

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2D IS

LR (d

B)

Range and Azimuth 3 dB Impulse Response Width (30, 17.28, 11.58 MHz)

Range and Azimuth Peak Side Lobe Ratio 2D Integrated Side Lobe Ratio

IQ Performance: Impulse Response Indicators

0

5

10

15

20

25

30

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

PSLR

(dB)

Azimuth

Range

Specification

5

10

15

20

25

30

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

Rang

e IR

W (

m)

30.0 MHz 17.28 MHz 11.58 MHz

5

10

15

20

25

30

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

Azim

uth

IRW

(m)

30.0 MHz 17.28 MHz 11.58 MHz

9

0

50

100

150

200

250

300

350

400

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

Abso

lute

Loca

tion

Erro

r (m

) Azimuth

Range

2D

Beam Absolute Location

Accuracy (m)

(predicted orbit)

Wide 60

Standard 52

Fine 56

Low Incidence 72

High Incidence 56

Geolocation accuracy

Geometric distortion since Jan. 2007: 39.0 m (design goal: < 40 m) • Based on Ottawa scenes with transponder and Gatineau antenna.

After last range bias adjustment performed in Jan. 2007, directional location error bias was on average: +0.8 m.

Average of absolute location error since Jan. 2007: 60 m.

Requirement: 750 m.

10

-20

-15

-10

-5

0

Jul-9

8

Jul-9

9

Jul-0

0

Jul-0

1

Jul-0

2

Jul-0

3

Jul-0

4

Jul-0

5

Jul-0

6

Jul-0

7

Jul-0

8

Jul-0

9

Jul-1

0

Jul-1

1

Jul-1

2

Imag

e Fo

otpr

int O

ffse

t rel

ativ

e to

SPA

Swat

hs

(km

, Eas

t pos

itive

)FS

Image footprint offset relative to SPA (Swath Planning Application)

At end of mission, the centre of a delivered product was around 4 km to the West of the intended swath in SPA at the latitude of the calibration sites.

Current trend towards a ‘0 km offset’ was part of a long-term oscillation between the simplified orbit model of the SPA and the actual RADARSAT-1 orbit propagator.

Image footprint offset slowly continued its decrease of 1 km/year, which would have led to a 0 km offset by Aug 2016.

Northern latitudes

Boreal Forest and transponder sites

Collision avoidance

manoeuvre Aug. 2010

Manoeuvre overburn anomaly

Apr. 2004

SPA orbit model update, Dec. 2004

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DGCF, 2000-present, from all transponders

DGCF (dB) = RCStrue - RCSest

-3

-2

-1

0

1

2

3

4

5

6

7

8

9

10

11

DGCF

(dB)

Ice buildup on antennas (NT0)

R2 upgrade of Ottawa unit, deployed before recalibration

Damaged radome horn covers (SK0)

Azimuth positioner

issue on ascending

passes only (NT0)

- 0.084 dB - 0.029 dB

St Hubert not calibrated for R1

Radiometric stability from transponder data

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Elevation Angle (deg.)

Two-

Way

Gai

n (d

B)

In-orbit measurements of elevation beam pattern: averaging of image lines, then subtracting the backscatter profile of the area

Difference pattern Radiometric deviation (rel. radiometric accuracy (maintained within 1 dB)

Current reference pattern

Relative radiometric accuracy

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Since late 2008, relative radiometric accuracy measurements (elevation beam pattern shape monitoring) was performed using an area in the Canadian boreal forest.

This site was exploited following the end of On-Board Recorder operations in early 2009, which prevented routine data acquisition at the Amazon.

Anticipating On-Board Recorder limitations, Canadian areas had been studied since 2003 for beam pattern shape monitoring potential.

To overcome seasonal backscatter variations, monthly backscatter models of the area have been derived and updated over the years.

Acquisitions were increased during summer season, a period of higher confidence level of the measurements.

Statistics at the area since 2003 indicate that certain in-scene deviations, as characterized, cannot originate from antenna pattern deviations, but from short-term fluctuations of the area’s backscatter. These could therefore be excluded from beam pattern measurements, refining radiometric accuracy estimates.

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Measured at the boreal forest since since the last Payload update (March 2009).

Rel. Rad. Acc. (dB)

µ

EL1 1.00 S1 0.55 S2 0.53 S3 0.45 S4 0.44 S5 0.60 S6 0.50 S7 0.65 W1 1.19 W2 0.74 W3 0.74 EH3 0.44 EH4 0.45 EH6 0.28

F1N-F1-F1F 0.65 F2N-F2-F2F 0.83 F3N-F3-F3F 0.97 F4N-F4-F4F 0.76 F5N-F5-F5F 0.78


Data acquired before F3 recalibration (Payload 32 )

Fine beam patterns were not systematically tested at the boreal forest : swath sizes were not sufficiently large to overcome physical non-uniformities through averaging.

Fine beam pattern levels were verified with transponder data, which showed no noticeable variation.

Amazon data acquired between 1997 and 2008 showed Fine beams to be very stable radiometrically.

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Relative radiometric accuracy measurements at the boreal forest site since last Payload update in March 2009

Highest confidence level and best accuracy for elevation beam pattern measurements at the boreal forest: June to September

0.2

0.4

0.6

0.8

1

1.2

1.4

Rela

tive

Radi

omet

ric A

ccur

acy

(dB)

16

88

90

92

94

96

98

100

102

0 5 10 15 20 25 30 35 40

Mea

n sig

nal S

tren

gth

(dB)

AGC Attenuation Setting (dB)

1999

2001

2002-1

2002-2

2003

2004

2005

2006-1

2006-2

2007

2009

Low Power Transmitter

Limiter &

LNA A/D and AGC

SAR Antenna

Decrease of cal. attenuator setting

Cal. attenuator

Noise dominates

Low relative noise

Non-imaging data acquisitions were used to test receiver linearity, and gain variation in limiter and Low Noise Amplifier

Cal attenuator settings + AGC attenuator: 40 dB range

Results very similar year to year, no noticeable cyclic variations, but small signal decrease over 10 years:

0.5 dB (30.0 MHz BW) 0.7 dB (17.3 MHz BW) 1.0 dB (11.6 MHz BW)

30.0 MHz

Internal calibration (1999-2009)

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On-line tracking of gain variation for in-processor compensation (every 8th pulse, excludes limiter and Low Noise Amplifier)

Pulse replica energy was slowly degrading: < 0.1 dB/year

Decays are different for each bandwidth, in close agreement with the long-term internal cal results. Signal decrease over 10 years:

0.5 dB (30.0 MHz BW) 0.8 dB (17.3 MHz BW) 0.9 dB (11.6 MHz BW)

30.0 MHz 9000 samples

-0.05 dB/yr 65.68 dB in 1996


-0.08 dB/yr 65.61 dB in 1996


-0.09 dB/yr 65.57 dB in 1996

Low Power Transmitter

Limiter &

LNA A/D and AGC

SAR Antenna

Internal calibration (1999-2009)

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Imaging and cal-val performance: 1997-2013

Until end of RADARSAT-1 operations, imaging and calibration performance showed no sign of degradation, except for the very slow decrease of transmitted power:

• Through the nominal mission (1997-2001), and successive extended missions (2001-2013), image quality parameters remained very stable (resolution, focusing, location accuracy), and within initial specifications and design goals;

• Relative radiometric accuracy, monitored at the Amazon (1997-2008) and then at the boreal forest, (2008-2013), was maintained within the 1 dB design goal;

• Long-term transponder DGCF data indicate good stability of the end-to-end SAR system gain over the years.

The R1 IQ Operations represent a prime example of comprehensive, consistent SAR calibration monitoring and maintenance over a long duration (16+ years):

• Cal Plan was maintained while the IQ Ops System (including transponders) and image processor underwent various upgrades;

• RADARSAT-1 has set a standard for operational provision of stable and calibrated data, including ScanSAR;

• Consistent use of a single area of the Amazon (CEOS 2004), then of the Canadian Boreal Forest, permitted long-term characterization of the areas, for the benefit of present and future cal-val operations.

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Robert Hawkins (CCRS)

Peter Hoang (CCRS then CSA)

Tom Lukowski (CCRS then DND)

Tony Luscombe (MDA)

Dean Flett (CIS)

Rob Gray and Nick Shepherd (Altrix)

René Périard, Gordon Fitzgerald (RSI)

Celine Fabi (RSI, then CIS)

Pierre Le Dantec (RSI)

The RADARSAT-1 Image Quality Working Group

radarsat-1: an end-of-mission review of the imaging and...

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