Spaceborne Infrared Atmospheric Sounder GEO (SIRAS-G) Thomas - PowerPoint PPT Presentation

Spaceborne Infrared Atmospheric Sounder – GEO (SIRAS-G) Thomas Kampe Ball Aerospace & Technologies Corp AIRS Science Team Meeting March 30, 2007

SIRAS-G Instrument Incubator Overview and Objectives Objective  ─ Develop instrument technology for IR atmospheric sounding from GEO and LEO ─ Validate operational performance in a laboratory demonstration ─ Generate a design recommendation for space flight instrument Mechanical cryocooler SIRAS-G IIP Awarded in 2003 Optical Bench & Diamond- turned optics Technology Development Partners: NASA/Jet Propulsion Laboratory Ruled grating 2-D IR FPA TRL in = 2 TRL current = 4 IR Refractive lens elements Ball Aerospace & Technologies Corp. Dec/2006 Page_2

Evolution of the SIRAS-G Program AIRS SIRAS-1999  The Atmospheric Infrared Sounder  Ball supported JPL Grating (AIRS) provides 3-dimensional maps  Designed, built & of air and surface temperature, water Collimator cryogenically tested 12-15.4um Lens Assy Mounting vapor, and cloud properties. Fixture spectrometer AIRS has 2378 spectral channels,  Integrated AIRS detector array  SIRAS-1999 AIRS has a spectral resolution more Spectrometer In Test Developed test facilities for  than 100 times greater than previous Dewar testing the spectrometer at IR sounders cryogenic temperatures SIRAS-G Builds on the success of SIRAS-1999   Demonstrates a complete IR imaging spectrometer operating over the 3.4 – 4.9 um region  Laboratory demo instrument incorporates a 4- mirror reflective collimator, a 4-element refractive camera, a flat grating, and a large area FPA Instrument concept uses several spectrometers to  provide full coverage from 3.4 – 15.4 um Ball Aerospace & Technologies Corp. Page_3

Demo Instrument Optimized for Demo Instrument Optimized for Large Format Array Large Format Array  Teledyne Hawaii 1-RG Array  1024 x 1024 Format Array Full extent of array (1024 pixels)  0.018-um Pixel Pitch  Spatial and spectral resolution elements = 2 pixels  Image of slit is smaller in length Spectral Linear FOV than FPA: used Full extent of array (1000 pixels) (1024 pixels) ─ Avoids illuminating inactive pixels or leads & wires around Active pixels FPA (1016 pixels) ─ Provides margin for alignment of FPA to slit Spatial Linear FOV ─ Since ends of slit are on active image of slit used (1000 pixels) Extent of array superimposed pixels, alignment of the slit can Active pixels used in on array (1016 pixels) spatial/spectral be measured directions ─ Simplifies alignment of FPA to detector housing and optical system Ball Aerospace & Technologies Corp. Page_4

Alignment Fiducials in SIRAS-G OBA Correct Lens Cell Fiducial placement of Lenses No. 2 & 3 alignment Baffle and fiducials is Lens No. 1 Field Stop Collimator Lens No. 4 critical for Mirror 4 efficient assembly Mirror Fiducial Detail Collimator Mirror 1 Fiducial Detail Grating Fiducial Ball Aerospace & Technologies Corp. Page_5

Camera Lens Elements Bonded into Separate Cells  The refractive lens elements for the camera were fabricated by ISP Optics  Delivered on 8/15/2005  All elements meet requirements  As-built data will be used to Germanium Silicon Germanium Cleartran (ZnS) re-optimize system prior to assembly  Lens elements bonded using Dow Corning 93-500 Silicone Adhesive  Low out-gassing  Wide operational temperature range: Remains compliant to 100 K  Extensive BATC heritage Element Bondline Thickness  Bond thicknesses and widths determined from Deluzio sized to minimize stress with Equation temperature Lens 1 Ge, 86 mm dia. 0.037” Lens 2 Si, 92 mm dia. 0.048” Athermal mount design approach documented in SPIE paper: Herbert, J. (2006), Proc. SPIE Vol. 6288, Lens 3 Ge, 92 mm dia. 0.040” 62880J, Current Developments in Lens Design and Lens 4 ZnS, 72 mm dia. 0.030” Optical Engineering VII; Pantazis Z. Mouroulis, Warren J. Smith, R. Barry Johnson; Eds. Ball Aerospace & Technologies Corp. Page_6

Laboratory Demo Instrument All Major Hardware Completed Subsystems have been integrated into the Laboratory Demo Instrument SIRAS-G Flight-like FPA Package Flat Ruled Grating SB-235 CryoCooler WFOV Refractive SIRAS-G Aft-Optics Assy Optical Bench Ball Aerospace & Technologies Corp. Page_7 Camera

Desired Performance Achieved in Cryogenic Testing Measurements show low spectral smile and  keystone distortion Dispersed MWIR spectrum obtained by SIRAS-G  Demo Instrument Spectra calculated using Genspect Measured spectra Pixel 615 4.258 um 4.3 um ( ν 3 ) CO 2 Absorption band SIRAS-G Measured Spectra Ball Aerospace & Technologies Corp. Page_8

Warm Shield Implementation  Lab Demo demonstrated feasibility of Multi-Stage Warm Shields High performance warm shield  eliminates need for true cold shield This is the first known application of  warm shields to IR imaging spectrometers Mature design methodology in place to  support warm shield designs for additional wavelength ranges, etc. Design, geometry and warm shield  positioning well understood for extrapolation to other spectrometers Excel spreadsheet provides insights  into sensitivities Test methodology for validating warm  shield performance under development Ball Aerospace & Technologies Corp. Page_9

What’s a Warm Shield? And, Why Use it? Grating  SIRAS-G do not have a cold stop in the traditional sense of locating the stop at the detector dewar.  The stop is located at the gratings because that improves the control Detector can see Detector Exit Pupil mechanical surfaces of the spectrometer distortions (keystone and smile) Warm Shields  Not having a cold stop introduces thermal background seen by the detectors  This can be reduced by: ─ Using warm shields ─ Reducing the temperature of the cavity  Multi-stage warm shield concept Rays from the dewar are reflected back to the detector originally developed on SIRAS-G instead rays from the warmer hou sing surfaces Ball Aerospace & Technologies Corp. Page_10

Impact of Using Warm Shields (LWIR Pathfinder) 0 0 0 0 Ch 1, Cycle 4b Ch 1, Cycle 4b Ch 1, Cycle 4 Ch 1, Cycle 4 T~= 112.9 K T~= 112.9 K T~= 112.6 K T~= 112.6 K 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Ch 2, Cycle 4b Ch 2, Cycle 4b Ch 2, Cycle 4 Ch 2, Cycle 4 0 0 T~= 112.9 K T~= 112.9 K T~= 112.6 K T~= 112.6 K 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0  Channel 1 and 2 data sets from cycle 4 and 4b. Channel 1 is largely unchanged and channel 2 has much higher near field thermal background Ball Aerospace & Technologies Corp. Page_11

Radiative Transfer Tools Developed to Provide Insight to Instrument Performance Example: Impact of LW Cutoff on Temperature Temperature RMS errors Sounding Objective: 15.0 micron cutoff 20  Evaluate the impact on retrievals of reducing FPA 14.5 micron cutoff performance or eliminating channels near 15 µ m 14.0 micron cutoff • Advantage is potential reduction in cost and/or technical development Layer upper boundary (km) 15 • These channels have greatest sensitivity to temperate in upper troposphere and lower stratosphere (UT/LS) 10 Results:  0.2K improvement in upper troposphere (<220 mb) and lower stratosphere with 650 cm -1 cutoff 5  No significant additional temperature information is obtained with inclusion of the SMW (1650-2250 cm -1 ) water vapor band - < 2250 cm -1 region only sensitive to low level 0 temperature 0 1 2 3 4 Simulated temperature and humidity retrieval error using a linear regression techniques and an - > 2250 cm -1 could improve UT/LS temperature but ensemble of 2000 atmospheric profiles. problem with NLTE in 4.3 µ m region Ball Aerospace & Technologies Corp. Page_12

Spectrometer Co-registration Errors spatial  For an ideal imaging spectrometer, all e.g. Keystone spectral channels would see the same λ ground pixel at the same time LWIR MWIR SWIR  Optical distortion, FPA-to-FPA mechanical alignment errors and relative magnification 20 20 errors in camera optics can lead to 15 15 misregistration of channels 10 10  In regions where strong scene gradients exist (e.g. near clouds), registration errors 5 5 produce spectral artifacts by mixing 0 0 20 20 spectra from neighboring pixels 0 2 4 6 8 0 2 4 6 8  The spectral errors are not random noise 15 15 in the measurement but are correlated 10 10 across the band affecting science data in 5 5 a complex way  The impact of spectrometer registration 0 0 0 2 4 6 8 0 2 4 6 8 errors on science data must be quantified using an end-to-end Temperature retrieval errors measurement simulation approach Ball Aerospace & Technologies Corp. Page_13