ASAR On-board Instrument

1
ASAR On-board Instrument

• Instrument Stability and Status
• Instrument Adjustments
• Tracking Changes of Beam Patterns
• Beam Pattern Maintenance

Ramon Torres ENVISAT Programme ESA
ESTEC Noordwijk, The Netherlands
2
Instrument Stability

• Relies on the RF Subsystem internal control and
  the temperature compensation scheme implemented
  in the Antenna Sub-arrays (Before use of the
  Internal Calibration correction)
• ASAR Instrument has proven to be very stable in
  short and long term
• Short term as demonstrated by the internal
  calibration pulses viewed through time
• Long term as demonstrated by the use of the
  Module Stepping calibration mode

3
Reminder ASAR Antenna

• Major element in the ASAR end-to-end product
  quality
• Active antenna with 320 individual subarrays
• T/R module Transmit/Receive in H and V
  polarisation
• 5 panels ? 4 tiles ? 16 subarrays

• Control and operations at tile level
• Temperature compensation scheme based on
  individual sub-array on-ground characterisation
• Radar mode timing
• Pattern definition at row level
• 8 Stripmap beams
• 5 ScanSAR beams

4
Antenna Temperature

• Initial temperatures were lower than predicted
• Increased operations from May 3 achieved
  realistic temperature conditions
• 0?-6? for HR only
• 4?-10? for full
• Low temperatures corresponding to instrument
  switchoffs

5
Short Term Stability Internal Calibration

• Variations in Tx signal and Rx conditions during
  acquisition
• Analysis of the internal calibration pulses
• P1 ? Tx
• P2 ? Rx
• P3 ? RF s/s

6
Short term Stability
?

• Instrument variations are taken into account by
  the ASAR internal calibration, nevertheless
• RF s/s conversion levels are extremely stable (P3
  pulse July 21-August 9)
• Variations of Tx and Rx characteristics due to
  temperature at antenna level are well handled by
  the temperature compensation scheme (P1 and P2
  pulses for row 18, July 21-August 9)

7
Long Term Stability

• Long-term (along the instrument lifetime)
  Sub-array T/R module failures, drifts and
  degradation
• ASAR monitors T/R modules for failures or drifts
  for eventual correction
• Use of Module Stepping Mode
• Sampling all 320 T/R modules sequentially in less
  than 1 s (Tx/Rx Gain/Phase) anywhere in the orbit
• Comparison with reference measurement
• Statistical analysis of variations

8
Long Term Stability - Module Stepping Mode
Tx
Rx

• Individual T/R Modules
• Tx and Rx
• H and V
• Gain and Phase

9
Module Stepping - Last Results - TxH
ltgt 1.5 dB ltgt 3.0 dB ltgt 10.0 dB gtlt 10.0 dB
ltgt 5.65º ltgt 11.2º ltgt 22.5º gtlt 22.5º
10
Module Stepping - Last Results - RxH
?
ltgt 1.5 dB ltgt 3.0 dB ltgt 10.0 dB gtlt 10.0 dB
ltgt 5.65º ltgt 11.2º ltgt 22.5º gtlt 22.5º
11
Module Stepping - Last Results - TxV
ltgt 1.5 dB ltgt 3.0 dB ltgt 10.0 dB gtlt 10.0 dB
ltgt 5.65º ltgt 11.2º ltgt 22.5º gtlt 22.5º
12
Module Stepping - Last Results - RxV
?
ltgt 1.5 dB ltgt 3.0 dB ltgt 10.0 dB gtlt 10.0 dB
ltgt 5.65º ltgt 11.2º ltgt 22.5º gtlt 22.5º
13
Long-term Stability
?

• Analysis on the T/R modules from Sep/02 to Nov/24
• Close to the LSB step both for gain and phase
• Tx / Rx difference from Rx gain droop not
  compensated in calibration modes
• 0.22 dB (Rx gain droop)
• 0.25 dB (gain control)

14
Instrument Adjustments

• Early corrections
• On board beam coefficients for ScanSAR modes
• Up and down converter levels
• Sub-array gain and phase offsets
• Timing parameters
• Wave Mode exit timing

• Control Software patches from operational
  failures
• Historical Swath parameters
• N-2 echo-shift
• Wave mode telemetry
• Alternate Polarisation mode annotation
• Global Monitoring mode exit

• Parameter optimisation from calibration
  activities
• Receiver gain adjustments
• Image and WideSwath bandwidths
• WideSwath timeline

15
Adjustments Early Corrections

• ScanSAR beam coefficients wrongly burnt in the
  on-board EPROMs ? upload of new
• Up and down converter levels too low for Module
  Stepping mode ? upload of new
• Gain and phase offsets to correct on-ground
  deviations and post-launch drifts ? upload
• Timing parameters not compatible with orbit data
  ? upload of new
• Wave Mode exit timing not compatible with
  complete vignette termination ? MPS control

16
Adjustments Parameter Optimisation

• Receiver Gain for all modes and beams in order to
  maximise the dynamic range
• Image Mode Bandwidth increased to maximum 16MHz
  for all beams
• WideSwath Bandwidth increased
• WideSwath Timeline modified by reducing the
  number of pulses per burst to improve azimuth
  ambiguities

17
On-board Software Patches
?

• Historical Swath Parameters ? Switchdowns
• Uploaded 02-Aug-2002. Anomaly solved!
• N-2 Echo Shift ? Large shifts in images
• Uploaded 05-Sep-2002. Anomaly solved!
• Wave Mode telemetry handling between vignettes ?
  Switchdown
• Uploaded 17-Oct-2002. Anomaly solved!
• Alternate Polarisation Annotation of the SWST
  changes ? Shift between polarisations
• Uploaded 11-Nov-2002. Anomaly solved!
• Global Monitoring exit ? Switchdown
• Uploaded completed 9 December at 185616. GM
  operating correctly from 9 December at 190230

18
Tracking Beam Pattern Changes

• Estimation based on Module Stepping results and
  the radiation model of each sub-array based on
• On-ground characterised embedded row pattern for
  elevation
• Uniform distribution for azimuth
• Generation of antenna radiation patterns
• full elevation and azimuth pattern for ambiguity
  analysis
• swath elevation pattern for tracking changes
• swath azimuth pattern for Doppler estimation and
  descalloping
• A single MS generates the full set of antenna
  patterns (Tx/Rx and Hpol/Vpol)

19
Synthesis of Elevation Patterns

• IS1 Pattern
• Elevation VV
• Measured Pre-launch
• Estimated Rainforest
• Simulated from MS
• Elevation HH
• Measured Pre-launch
• Estimated Rainforest
• Simulated from MS
• Conclusion
• MS agrees with RF within 0.2 dB
• Same order as pre-launch patterns

20
Synthesis of Azimuth Patterns

• June 2002 image mode IS3 over Edam, Zwolle and
  Swifterband
• Very good correlation between simulated data and
  transponder flyovers
• Better than 2 db at the level of 20db (?0.02db)
• IS1 synthesised from MS
• Mispointing agrees with doppler

21
Pattern Estimation Conclusions
?

• Rainforest estimation
• Estimation approach based on combinations of
  pattern estimates in different modes (IMWS) with
  a standard deviation of 0.1dB
• Long process as it requires several acquisitions
  per beam and polarisation
• Synthesis from Module Stepping results
• Very good tool to track variations of the antenna
  radiation patterns
• From a 1-second acquisition full set of radiation
  patterns can be generated as frequently as needed
  (no orbit constraint)
• Elevation patterns can be simulated with an error
  of 0.2dB due to limited quality of ground
  characterisation data
• Embedded row patterns measured with only 14 tiles
  and insufficient control of T/R modules
• Azimuth patterns and pointing can be simulated
  better than 0.02dB and 0.01?

22
Antenna Elevation Pattern Maintenance
Reference Module Stepping
Module Stepping
Module Stepping
Module Stepping
Module Stepping
TRM Drifts
TRM Drifts
TRM Drifts
TRM Failures
TRM Failures
TRM Drifts
TRM Failures
(TSS Failures)
MS Analysis
MS Analysis
MS Analysis
Offset/K0
Offset/K0
Offset/K0 Correction
New Coefficients
Offset/K0
Rain Forest
Rain Forest
Far sidelobes
Rain Forest
Far sidelobes
?
Antenna IMBF Test Results
Antenna IMBF Test Results
Rainforest Patterns
Rainforest Patterns
Rainforest Patterns
23
Antenna Azimuth Pattern Maintenance
Reference Module Stepping
Module Stepping
Module Stepping
Module Stepping
Module Stepping
TRM Drifts
TRM Drifts
TRM Drifts
TRM Failures
TRM Failures
TRM Drifts
TRM Failures
(TSS Failures)
Offset/K0
MS Analysis
MS Analysis
New Coefficients
Offset/K0 Correction
Offset/K0
Offset/K0
MS Analysis
Transponder
Transponder
?
Antenna IMBF Test Results
Antenna IMBF Test Results
Synthesised Patterns
Synthesised Patterns
Synthesised Patterns