CubeSat-Scale Hyperspectral Imager for Middle Atmosphere Investigations

Transcription

1 CubeSat-Scale Hyperspectral Imager for Middle Atmosphere Investigations Rick Doe 1, Steve Watchorn 2, John Noto 2, Robert Kerr 2, Karl van Dyk 1, Kyle Leveque 1, and Christopher Sioris 3 1 SRI International 2 Scientific Solutions, Inc. 3 Environment Canada 2009 CUBESAT DEVELOPER S CONFERENCE, SAN LUIS OBISPO, CA

2 The Earth s Atmosphere 3 km

3 Characteristics of the Middle Atmosphere Coldest temperatures on Earth Convectively unstable Breaking gravity waves drive planetary wind circulation Competition between eddy and molecular diffusion Meteoric deposition of trace metals (Na, Fe, K) Inaccessible to satellites and balloons

4 Coldest Temperature in the Atmosphere PRESSURE (T) km TEMPERATURE ( K)

5 Mesospheric Temperature Minimum is Controlled by CO 2 IR Radiation 280 CO 2 cooling CO 2 cooling O 3 heating O 3 heating TEMPERATURE ( K)

6 Mesopause Temperature Minimum is a Harbinger of Climate Change CO 2 Doubling 3 km CO 2 Halving Roble and Dickinson, GRL, 16, 12, , 1989.

7 Gravity Waves in the Middle Atmosphere 3 km 87 km Middle atmosphere gravity waves couple energy and momentum fluxes from the troposphere to the thermosphere GW climatology helps improves our understanding of mean wind flow and tides, turbulence, heat and chemical transport, and higher altitude gravity waves ( km)

8 Target Species for Middle Atmosphere Remote Sensing 3 km OH, Atomic Metals (Na & K), O, and O 2

9 Spectral Signatures are Sensitive to Mesopause Temperature Sodium ( km) Molecular Oxygen (97 km)

10 Candidate Techniques for CubeSat-Based Middle Atmospheric Studies Imagers (limited spectral information) Traditional Slit Grating Spectrograph (large) Interferometer (luminosity advantage)

11 Classic Michelson Interferometer Peaks and Nulls in Fringe Pattern Probed by Moving Mirror Recovered Spectra is Fourier Transform of Fringe Pattern Moving Parts!

12 SHS Interferometer - No Scanning Required Tilted gratings replace mirrors to provide crossed wavefronts at exit aperture Wedge angle, grating density, and optical path adjusted to tune SHS to desired wavelength, resolution, and coverage Fringe pattern (Fourier Transform of Spectra) acquired without scanning Robust design

13 Spatial Heterodyne Spectrometer (SHS) Monolithic design can be locked down with no alignment issues or moving parts Fused silica design first created for space-based limb imaging of OH by NASA, U Wisconsin, and NRL SHS Instrument Operating on STPSat-1 since March 2007

14 In Hand Na-Optimized SHS Monolith mm Light Baffle Light Baffle

15 Notional CubeSat HSI (CHSI) Layout Spatial Heteodyne Spectrometer Monolith CubeSat Envelope 100 mm Light Baffle Imaging Light Baffle Detector (CCD) Order Sorting Prefilter Aperture Slit

16 CubeSat HSI Orientation Cross-Track 100 mm Spatial Dimension INERTIAL FRAME Orbit Velocity Nadir Light Baffle Spectral Dimension Light Baffle IMAGE PLANE

17 Ideal SHS Fringe Pattern for Imaging Spectroscopy 100 mm Light Baffle Spatial Dimension Light Baffle Spectral Dimension

18 Prototype Sodium CHSI Field Test 100 mm Light Baffle Light Baffle

19 Raw Fringe Pattern from Prototype of Sodium CHSI 100 mm Light Baffle Light Baffle

20 Recovered Na Spectra from CHSI Prototype nm 100 mm Light Baffle nm Light Baffle

21 CubeSat-Optimized Na Monolith Design Grating Blk 1 PG Spacer 1 Prism 1 Spectral Coverage: nm Spectral Resolution: 0.13 nm PW Spacer 1 15 mm BS Half 1 BS Half 2 PW Spacer 2 Prism 2 PG Spacer 2 Grating Blk 2 34 mm

22 CubeSat-Optimized Monolith Mass Model

23 Front Optic Selection 50 mm FL for 10 spatial field of view on grating Low-distortion Leica rangefinder lens 28 mm back focus distance sufficient to illuminate grating

24 Spatial Coverage

25 Starlight Xpress Lodestar CCD Camera Astronomy grade 752 X 580 pixel Sony ICX429AL CCD Low noise, 16-bit dynamic range, 10 Hz max sampling On-chip binning to enhance SNR and minimize telemetry Extensive Linux libraries for image processing

26 CCD Camera Performance Dark Noise, 50º C 1 s Integration Read Noise, 50º C 1 ms Integration

27 Reimaging Optics Selection Transfers SHS fringe pattern to CCD focal plane Large aperture (F/1.4) to maximize sensitivity Close-up diopter added to decrease standoff distance Bolex 36-mm macro lens with +10 diopter adapter

28 Payload Miniaturization for 1.5 U Form Factor Miniaturized with Folding mirrors Folded electronics Repackaged lens

29 1.5 U CHSI Payload Model

30 Flight Processing Goals Optimize spectral and spatial binning for best science at acceptable telemetry and power loads Investigate on-orbit photometric correction (flat fields, dewarping) Perform on-orbit FFTs to extract band feature intensity Analyze recovered bands to extract temperature

31 Temperature Extraction from O 2 Spectra

32 CHSI Requires Nadir Orientation with CCD Spatial Axis Perpendicular to Ram Direction

33 Path Forward Design Integrated Cruciform Optimize foreoptic mechanical support Assess processing power associated with image manipulation Build vibration and thermal test unit