An Assessment of OMPS Performance

1
An Assessment of OMPS Performance
Glen Jaross M. Kowalewski SSAI / NASA C.
Seftor

• Outline
• Update on OMPS
• Technical Difficulties
• Overall Performance
• Key Challenges Going Forward

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Nadir Sensor Optical Overview
Nadir Profiler
Nadir Telescope
Nadir
Limb
MEB
OMPS is a 3-component suite
Nadir Total Column
3
OMPS Hardware Status

• PFM Nadir Sensor Integrated Testing in
  progress
• Engineering risk reduction testing completed Dec
  05
• Environmental testing completed Sept. 06
• Characterization begins Jan. 07

• PFM Limb Sensor Integrated Ready for
  Acceptance Testing
• Engineering risk reduction testing completed Dec
  05
• System level risk reduction tests with MEB
  performed June 06
• De-manifested June 06

• PFM MEB Integrated Ready for Final Testing
• 5 boards in re-spin to correct FPGA related
  design issues
• Risk reduction testing completed Aug 06
• Acceptance Testing starts Oct 07

4
Key Technical Challenges

• Elimination of Limb Sensor
• OMPS (Ozone Mapping and Profiler Suite) designed
  as a system
• Nadir requirements must be relaxed
• Abbreviated EDU program
• risk reduction testing performed with PFM
• Bore sight shifts during vibration and
  thermal/vacuum
• as much as 16 arcmin in cross-track direction
  1.5 pixels spectral
• are they normal, or indications of a workmanship
  problem ?
• Delayed delivery of MEB
• significant sensor testing without flight
  electronics
• use delta-calibration approach

5
Development schedule leads to calibration w/o
flight electronics
Ground Test Electronics
MEB - Flight Electronics
No absolute calibration planned using flight
electronics
6
OMPS Nadir Close cousin of heritage sensors
Relies on Limb Profiler data
Improvements over heritage systems come from use
of external data
7
NPOESS Specifications for OMPS Total Column
Total Column Precision
Total Column Accuracy
OMPS precision performance without Limb is still
under review
8
Error Budgets Allocate Top-Level Accuracy and
Precision Requirements to Algorithm and Sensor
Contractual requirements
EDR accuracy and precision requirements are
flowed down to the sensor and algorithm.
Lower-level allocations
Sensor and algorithm terms are flowed down to
lower levels.
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SDR Algorithm Errors Derived from Sensor Error
Budget

• Most sensor specifications simply pass through
  SDR alg.
• Requirements flow-down assumes temporal
  averaging performed by SDR algorithm

The SDR algorithm is split between Earth data
processing and calibration processing
SDR Trending
YES
SDR Main LOOP
NO
TOMS EP Near-real time calibration
Analysis and trending of calibration data is at
the heart of the algorithm
10
Total Column Accuracy
Individual Sensor and Algorithm Requirements met
(prior to start of Acceptance Testing)
Total Column Precision
Current Best Estimates (CBE) are updated as
testing progresses
11
Nadir Profile Top-level Accuracy Current Best
Estimate (CBE) vs. Allocations

• The Nadir Profile EDR algorithm is the same as
  the heritage SBUV retrieval
• Nadir Profiler must perform as well as SBUV at 1
  mb
• Other pressure levels are shown for reference
  only
• OMPS performance is consistent with SBUV

Nadir Profile Accuracy Error Budget ()
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Nadir Sensor Acceptance Tests

• Verify sensor performance
• Provide necessary calibration parameters

Environmental Phase
Calibration Characterization

• Environmental phase complete
• Calibration to begin early next year

13
Data Analysis Teams
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Key Problems with Heritage Sensors

• Pre-launch Radiometric Calibration
• Largest component of sensor error budget
• Detector Linearity
• difficult to characterize in flight
• Detector Radiation Damage
• Mitigate through design
• Stray Light
• wide-field telescope hyperspectral focal plane
  create a challenge
• difficult to characterize in flight

2 years after OMI launch biggest challenge
correcting stray light
The OMPS program has addressed all 4 issues
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OMPS Radiometric Calibration

• Use of heritage approach
• expect similar results
• 2 independent methods
• Spectralon plate
• Integrating Sphere

Typically agree within 2
The sphere travels, and can be independently
calibrated against other buv sensors
16
Preliminary tests give confidence in final
characterizations
Wavelength Registration
Spectral Bandpass
Gain Linearity
TC NP Bore sight Alignment
Internal LED provides high fidelity linearity
monitoring
17
Stray Light OMPS will be the best-tested buv
sensor

• Point spread functions (PSFs)
• Total Column PSFs matched predictions with some
  differences near the peak
• Nadir Profiler PSFs exhibit more scatter than
  predictions

Model
Use of a tunable laser to characterize the PSFs
contributing to stray light
Measurement
PSFs provide the basic tool for a software
correction, should it become necessary
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Conclusions

• OMPS has its share of sensor issues but no
  show stoppers
• Major pitfalls of the past have been addressed
  in test program
• Every reason to expect slightly better
  performance than TOMS similar performance to
  SBUV
• On-orbit calibration is not challenging, but
  presents a risk because the operational chain is
  new (untested)