tempo instrument update dennis nicks, tempo pm may 21-22, 2014 (303) 939-4467 [email protected]
TRANSCRIPT
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Instrument design is maturing with PDR in July 2014• Performance estimates have been updated based on design maturity• Updated operating parameters to optimize instrument performance
At NASA KDP-B Instrument cost risk is perceived to be too high• Ball, LaRC, and SAO worked closely to evaluate current instrument
performance and science performance• SAO and LaRC are able to accept the current instrument performance with
little impact to science• SNR, Spectral Stability, dark current
• Issues remain with stray light – need to work with LaRC/SAO on definitions and resolution
Mission Level INR requirements have been allocated to subsystems• Instrument pointing performance has been rolled up into Mission Level INR –
everything closes
TEMPO Instrument Status
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TEMPO Design Maturation Since Last Science Meeting
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Design Presented at 7/2013 Science Team Meeting
Pre-PDR Design as of 5/2014
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Detector Update
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Parameter SRR Value PDR Baseline
Notes
Frame Integration Time 95.83 ms 118 ms
A longer frame integration time marginally improves SNR performance and gives flexibility for seasonable variations in lighting conditions.
Image Frame Rate 10 Hz 8.19 Hz Includes frame integration time and frame transfer time of 4.17 ms. 10 Hz is the maximum frame rate.
Image Frame Time 2.70 s 2.69 s Includes integration time, frame transfer time, and coadds.
Number of Coadds 27 22 Number of coadds must adjust with integration time to meet the coverage time requirement.
Scan Mirror Step Size 115 urad 114 µrad
The measure of E/W overlap and the requirement has changed since SRR. New requirement will be 6µrad based on INRWG analysis presented
by Benton Ellis on 4/30/2014.
Number of Scan Mirror Steps 1267 1278
Number of scan mirror steps increased slightly due to the slightly smaller scan mirror step size.
Coverage Time 59.14 min 59.39 min
A more careful accounting of coverage time is now being done, courtesy of Roger Drake. Coverage time includes book keeping for flight software
timing margin from the end of a scan to the beginning of a scan (10 seconds), scan mirror move time at the end and beginning of a scan
(4.75 s), scan mirror step/settle (50 ms), ICE commanding step/settle (50 ms).
TEMPO Parameter Evolution
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Previous SNR model assumed aggressive mirror reflectivity and grating efficiencies• Dielectric coatings for mirrors allow for high performance over a broad
spectral range• However they often increase spectral features and polarization
TEMPO design has more optical elements• Polarization wave plate and corrector lens in front of FPA
New TEMPO SNR estimates assume “as manufactured” grating efficiency of 55% (was 60%) and mirror reflectivity curves – based on GeoTASO• Lower risk posture is highly desirable given the Earth Venture cost cap• Allows adequate design space between SNR requirement (minimum optical
throughput) and saturation requirement (maximum optical throughput)• Worked with SAO and LaRC to assess impacts to science
• Impact to primary chemical species is negligible• Secondary chemical species that have been removed can be added back when
cost risk is less of a concern
SNR
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Original TEMPO Requirements:Total System Optical Throughput
The margined curves (red) indicate that no system throughput will meet the SNR requirement with 20% margin and the saturation requirement with 10% margin
Having a gap between curves of less than 10% translates to coating tolerances that are likely not achievable
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Dark Current requirement at 290-300 nm affects the SNR requirement (need for higher optical throughput)• Dark current is within requirements for the rest of the spectral range
After discussions – the Dark Current requirement has been dropped for wavelengths below 300 nm.
Dark Current
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New SNR Requirements vs Performance
New SNR requirements are result of BATC/SAO/LaRC negotiations• Utilizes the new operating parameters• Allows for manufacturability of optical elements and coatings• Uses new retrieval assumptions from SAO / Xiong• Reduces instrument project cost risk
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ISD 6.7.7 Spectral StabilityThe instrument shall have a spectral stability better than 0.02nm (1-sigma) for all data collected that mets the requirements in Section 6.6.1 and Section 6.7.1 over any 24-hour time period
New:ISD 6.6.7 Spectral Stability of Radiances versus IrradiancesThe Instrument shall have a spectral stability of radiances compared to irradiances of better than 0.2 nm (1-sigma) for all data collected that meet the requirements in Section 6.6.1 and Section 6.7.1 over any 24-hour time (midnight-midnight) period.
ISD 6.6.8 Spectral Stability of RadiancesThe Instrument shall have a spectral stability for radiances of better than 0.1 nm (1-sigma) for all data collected that meet the requirements in Section 6.6.1 and Section 6.7.1 over any 24-hour time (midnight-midnight) period. ISD 6.6.9 Spectral Stability of IrradiancesThe Instrument shall have a spectral stability for irradiances of better than 0.1 nm (1-sigma) for all data collected that meets the requirements in Section 6.6.1 and Section 6.7.1 over any 24-hour time (midnight-midnight) period.
Spectral Stability Requirement
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The single Spectral Stability requirement over a 24 hour period was extremely challenging• The design already had a low-CTE structure, athermal optics and an active
thermal design• Would require extremely precise thermal control over all solar geometries
Worked with science team to rephrase the requirement to allow for easier compliance while still meeting science requirements• Specify spectral stability for radiance measurements (Earth View), irradiance
measurements (solar cal) and allowable shifts between radiance and irradiance
Change allows for smart instrument design / operational trades with no impact to science
Spectral Stability
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ISD 6.6.7 Stray LightThe Instrument shall have a stray light response less than 2% of the Instrument response over the spectral range of 290 to 740 nm for the hemispherical angle of incidence for the nominal radiances in Table 1.
The definition of stray light is the ratio of the sum of contributions from sources (e.g., scatter, ghosts from lenses, windows, and focal plane reflections) originating from outside the point source function being evaluated to the signal inside the point source image area of interest. For the purposes here, inside the point source image area is defined as a box on the focal plane 15 x 15 pixels centered on the point source.
Stray Light Requirement
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Design / Trade Studies• Includes baffling design iteration• Scatter from surface roughness/particulate contamination• Waveplate angle of rotation
Ghosting contributors New analysis indicates that the largest stray light contributor for
TEMPO is the grating• Used BRDF measurements of “as manufactured” grating• BRDS model fitting• Grating efficiency / orders
Requirement is worded as Point Spread Function (PSF) stray light• Less than 2% of the instrument response over the spectral range of 290-740
nm
Stray Light Status
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System Stray Light Compliance
System Level Requirement
Optical Surface Scatter/Ghosting
Grating Scatter/Artifacts
Mechanical Surface Scatter
< 2%
< 0.75% < 1.0% < 0.25%
Goal Allocations
Wavelength (nm)
Grating Model
AOptical Ghosting
SL (%)
BOptical Surf.
Scatter SL (%)
CGrating SL
(%)
DMechanical Surf. SL* (%)
Model Contingency** (%) Total (%)
Total w/Contingency (%)
303 ZW_base 0.05 0.43 0.75 0.25 1.01 1.48 2.49ZW_1 0.05 0.43 1.13 0.25 1.01 1.87 2.87
400 ZW_base 0.25 0.40 0.95 0.25 1.26 1.85 3.10ZW_1 0.25 0.40 1.40 0.25 1.26 2.30 3.56
497 ZW_base 0.07 0.30 1.00 0.25 1.24 1.62 2.86ZW_1 0.07 0.30 1.39 0.25 1.24 2.01 3.25
Preliminary Results from F. Grochocki
* Stray light contributions from mechanical surfaces have not been analyzed – 0.25% allocation is assumed
** Model contingency = √ (0.5 ( 𝐴+𝐵+𝐷 ) )2+( (𝐶𝑚𝑎𝑥+𝐶𝑚𝑖𝑛 )2 )
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Current estimates based on PSF show some areas of non-compliance
Further discussions with Science Team at LaRC and SAO indicated that PSF interpretation may not be correct• 15 x 15 pixel box confuses the interpretation of the requirement and may be
deleted• May be more correctly interpreted in a broadband sense, where measured
stray light needs to be <2% of signal electrons • Most challenging at the 290 – 300 nm range where there is low signal
Ball / SAO / LaRC are working stray light requirement interpretation• Discussions are on-going regarding the wording of the stray light requirement
Stray Light Summary
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KTP Summary: Science Performance (1 of 3)
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KTP Reqt Current Est Notes
Long Term Radiometric Drift
< 0.9% over mission Not yet available Expect estimate next month with finalized pointing requirements
RAD Spectral Stability < 0.1 nm (1-sigma) over 24 hrs
< 0.1 nm (1-sigma) over 24 hrs
Preliminary analysis – to be verified by STOP analysis
IRD Spectral Stability < 0.1 nm (1-sigma) over 24 hrs
< 0.1 nm (1-sigma) over 24 hrs
Preliminary analysis – to be verified by STOP analysis
RAD-IRD Spectral Stability
< 0.2 nm (1-sigma) over 24 hrs
< 0.2 nm (1-sigma) over 24 hrs
Preliminary analysis – to be verified by STOP analysis
Bandwidth < 0.6 nm 0.575 nm Based on expected slit width, slit width variability, and optical spot size specification
Bandwidth Symmetry < 6% ≤ 6% Holding 9% reserve against requirement. Performance estimates are not yet available.
Radiometric Calibration Accuracy
< 4% (1-sigma) 2.8% (1-sigma) Radiance / 3.2% (1-sigma) Irradiance
Relative Radiometric Uncertainty
< 0.5 (RMS) / Required SNR Not yet available Error budget holds 10% reserve against requirement. Performance estimates are not yet available.
KTP Summary: Science Performance (2 of 3)
* C.F. = Chance Farm at Geodetic 36.5° N, 100° W
KTP Reqt Current Estimate Notes
FOR GNA, between 58° N and 18° N Compliant Allocated for worst-case orbit
GSD ≤ 2.22 km, ≤ 5.15 km @ C.F.* 2.21 km, 5.11 km @ C.F.* Allocated for worst-case orbit
E/W Step Overlap
5% (3-sigma) 5% ISD Requirement update
MTF > 0.16 @ 0.5 cyc/N-S GSD> 0.3 @ 0.5 cyc/E-W GSD
0.19 @ 0.5 cyc/N-S GSD0.36 @ 0.5 cyc/E-W GSD
Trend
Spectral Sampling
≥ 2.7 pixels / FWHM 2.9 pixels / FWHM Consistent with nominal slit width and dispersion
LPS 290 – 490 nm: < 5% (1-sigma)540 – 690 nm: < 20% (1-sigma)
290 – 490 nm: < 4% (1-sigma)540 – 690 nm: < 15% (1-sigma)
Current design estimate
SNR See SNR chart See SNR chart See SNR chart
Stray Light < 2% 2.0 – 2.9% Preliminary analysis results of PSF stray light modelling
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KTP Summary: Science Performance (3 of 3)
SNR Wavelength
SNR Requirement
SNR PerformanceThis Month Notes
290 19.6 24 Significant updates based
300 46.1 56 on realistic optical and
305 161.9 196 QE information.
310 377 456
320 1220 1473
330 2003 2419
340 2013 2431
350 1414 2299
420 836 1734
430 675 1401
450 733 1423 450 nm is a new reqmt.
490 1176 1411
540 1109 1340
600 987 1193
650 898 1085
690 820 975
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Instrument design is maturing quickly• Instrument is designed for high structural / thermal stability• Instrument performance is based on “as-manufactured” optical
components based on GeoTASO experience Some changes to TEMPO performance requirements
were required to reduce perceived cost risk• Worked closely with Science Team to relax requirements without
severely impacting science• Science analysis / algorithm development descopes can be
added back if cost risk allows• Low risk posture highly desirable at NASA HQ
Summary
5/21/2014
