“photonics in space: a challenge for modern technologies ... · air/spaceborne imaging:...
TRANSCRIPT
12th Engelberg Lectures on Optics 2007
“Photonics in Space: a Challenge for Modern Technologies”
Advanced Optics by Aspherical Elements IIIDriving Force: Applications
Bernhard Braunecker
Leica Research Fellow (retired)
Braunecker Engineering GmbH Rebstein / Switzerland
7th March 2007
09/05/2007 2
Aspheres & Applications
1. Airborne Imaging: Wide Field Lenses2. Spaceborne Communication: Small Field Telescopes3. Spaceborne Ranging: Small Field Telescopes4. Air/Spaceborne Imaging: Hyperspectral Systems
09/05/2007 3
1 Airborne Imaging
ImagingRanging Communication
Airborne
Terrestrial
Spaceborne
Photogrammetry, Remote Sensing
SSO
Berne, 1: 8‘500 (h = 1‘300 m)(15/4 UAG-S)
3 cm ground pixel resolution
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St. Gallen / Switzerland 1: 34‘000 (h = 2‘200 m) (ADS40)
10 cm ground pixel resolution
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Lens Cone 15/4 UAG-S (UltraAviogon)
The lens is for the film camera RC30; the film format is 9“ square. Note the ‚large‘ round exit pupil (the lens looks like a ‚cat‘) at large viewing angles to achieve homogenous illumination across field
09/05/2007 7
Long Tradition at Wild Heerbrugg, later Leica Geosystems
WILD (8.8 / 5.6 SAG) WILD (15/5.6 UAG-AF)
Heinrich WILD (1890-1951)
Ludwig BERTELE (1900-1985)
Klaus HILDEBRAND (1929-1996)
09/05/2007 8
Lenses for RC30
12:21:58
NAG_N3M Scale: 0.50 BRN 20-May-00
50.00 MM
12:41:10
NATNEU Scale: 0.50 BRN 20-May-00
50.00 MM
12:49:05
S11034 Scale: 0.50 BRN 20-May-00
50.00 MM
12:53:29
Satz42 Scale: 0.50 BRN 20-May-00
50.00 MM
NAT303 mm55°
NAG210 mm70°
UAG153 mm90°
SAG88 mm120°
09/05/2007 9
EPOBJ APIMASTOP
Geometrical Invariant: Inv = YOBJ * NA = YIMA * NA‘
NA NA‘
Received Power: ∆W = πS * ρ * T * Inv2
ρS
Radiance
AlbedoTTransmittance
XX OO O
Resolution (Diffraction) : δYOBJ = λ / NA
> Space Bandwidth Product: SBP = (YOBJ / δYOBJ)2 ~ (Inv / λ)2
> Fourier:(Light travels from the first lens to IMA in 1 ns):Data rate R = 1021 pixel/s
WOW
[for UAG lenses with 9“ image plane;140 lp/mm lens spatial resolution]> No of resolvable pixels: N = SBP = 109 (+ spectral => 1012)
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Distortion Measurement
Tolerance ±2μ
over +/- 150mmMean over 4 semi
diagonals
All 4 semi diagonals
No splitting allowed!!Perfect Lens!!
09/05/2007 11
Light fall-off across field-of-view should be minimal
Cos4 - law
Cos1.2 - law
For spectral range 380 nm to 900 nm and aperture f:4
0
20
40
60
80
100
120
0 40 60 80 100 120 140Radial distance (mm)
in %
15/4 UAG-S 30/4 NAT-S
66%
25%
difficult forthe designer
09/05/2007 12
What about Aspherisation?
uagF_HB Scale: 0.50 BRN 15-Jun-04
50.00 MM
Any Aspherisation would allow to
• to improve imaging of object and pupil
• Contrast & Distortion & Image Homogeneity
> But it was not payable!!!
Also a process risk about disturbing glass homogeneity was seen!
09/05/2007 13
Digital Camera ADS40
Electronics
IMU
Video Camera
TelecentricLens
CCD Sensor
Triple CCD lines 24’000 pixel staggered
Line Sensor (Pushbroom Mode)
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Geometrical & Radiometric Calibration
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Drivers for Aspherics
• Less components
Weight / size reduction, 1. Better spectral transmission
• Better quality
Object and pupil imaging
2. Contrast & Telecentricity & Image Homogeneity
• Better functionalityAuxillary tools around with integrated functionality
3. Real-time calibration
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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
400 450 500 550 600 650 700 750 800 850 900
Wavelength[nm]
0 Grad.20Grad. 35 Grad.
1. Total Spectral Transmission
GlassesADS40
Less and thinner Elements wouldimprove Transmission in ‚Blue‘=> Aspheres
Note the perfect image homogeneity!
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2. Improved Imaging Quality
Aspherics 12 / 2.8 (F= 120 mm)
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Thermal stabilised aspherical mirrorcollimator with test pattern monitorsfocus and magnification
3. Aspheric Catadioptric Collimator for ‚Real-time Calibration‘
09/05/2007 19
09/05/2007 20
ADS40 spectral channels - Adria, Italy
Blue 430 - 490 nm Green 535 - 585 nm
Red 610 - 660 nm Infra-red 835 - 885 nm
Flying height:1,500 m / 4,900 ft
Ground sample distance:GSD ≈ 15 cm / 1/2 ft
Flight direction:
RGB
RGI
09/05/2007 21
ADS40 spectral channels - Adria, Italy
Flying height:1,500 m / 4,900 ft
Ground sample distance:GSD ≈ 15 cm / 1/2 ft
Flight direction:
09/05/2007 22
ADS40 color composite - Shinjuku, Tokyo
Flying height:2,000 m / 6,525 ft
Ground sample distance:GSD ≈ 20 cm / 2/3 ft
Flight direction:
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Yokosuka / Japan
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09/05/2007 25
Sydney : 3D - GIS Model (5 cm accuracy)
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•From Airborne to Spaceborne• Glassmaterials
•Radiation resistant glasses
Schott Glass / Cerium doped
• normal glass starts ‚browning‘at dose of 1 Kr (γ, 1 MeV)
• Gxx- glasses at 1 Mr
• Gxx with x.x% Ce-oxid
•BK7G18 SSK5G06 BK7G25
•LAK9G15 K5G20 LF5G15
•BAK1G12 F2G12 SK4G13
•SF5G10 SK5G06 SF6G05
•SK10G10 SF8G07 KZFS4G20
09/05/2007 27
Radiation stabilized glasses
BK7G18SF6G05
09/05/2007 28
2 Spaceborne Communication
CommunicationRanging Imaging
Spaceborne
Terrestrial
Airborne
09/05/2007 29
Some Basic Telescope ConceptsMirrors Example
NewtonianIsaac N.
1643-1727
Paraboliccc
GregorianJames Gregory
1638-1675
Paraboliccc
Elliptic cc
CassegrainLaurent C. 1629-1693
Paraboliccc
Hyperboliccx
Herschel
Ritchey-Chretien
Cassegrain
Hyperboliccc
Hyperboliccx
Hubble
George R. 1864-1941Henri Ch. 1879-1956
09/05/2007 30
Corrector Plate
Bernhard Schmidt
1879-1935 Maksutov Cassegrain
Modern catadioptricMaksutov Cassegraininstrument of Leica Geosystems
Space Telescope for Optical Communication
LaserSensorStarsensor
Fine pointing mirror
Afocal 10-14 x Keplerian / foldedObjective
• Off axis Cassegrain
(Parabolic cv + Hyperbolic cx)
‚Eyepiece‘
• (Parabolic off axis cv)
Coudé Mount
•Tilt axis
The Fine pointing mirror is at the Exitpupil AP
09/05/2007 32
Corrector Plate
13:05:29
TelescopeScale: 0.58
Positions: 1-2
BIM 01-Jun-05
43.10 MM
Waves
0.0000
1.0000
0.5000
WAVEFRONT ABERRATION
anamorphic plate
Field = ( 0.000, 0.000) Degrees
Wavelength = 1060.0 nm
Defocusing = 0.000000 mm
Corrector plate:Free form aspheric
09/05/2007 33
System Improvement
RMS-Wavefront quality @ λ = 1064 nm On axis Full field
No correction λ / 33 λ / 7
With Correction plate λ / 70 λ / 20
The aspheric „free form“ correction plate reduces
• wavefront error and field distortion
• it can be mounted on a glass plate or directly polished on the folding mirror
09/05/2007 34
Space Telescope for Optical Communication
LaserSensorStarsensor
Fine pointing mirror
Contraves Space AGCoarse pointing mirrorNo corrector plate
09/05/2007 35
3 Spaceborne Ranging
Ranging Imaging Communication
Space borne
Terrestrial
Airborne
09/05/2007 36
BepiColombo Mercury Mission / BELA
09/05/2007 37
Instrument Comparison
NASA ESA MOLA-1 MOLA-2 GLAS MLA BELA
Mars Mars Earth Mercury Mercury 26 Kg 26 Kg (300 Kg) 6.8 Kg 5.5 Kg
Note: MLA has 4 subapertures
09/05/2007 38
Laser Altimeter
ACCURACY: 1 m
ALTITUDE: 400-1‘500 km
REFLECTANCE: 5 %
FOOTPRINT: <100 m
GROUND SPEED: 2.5 km/s
RATE: 10 – 20 Measurements/s
SOLAR IRRADIANCE: 10x earth
09/05/2007 39
Transmitter Accommodation
Cassegrain Ritchey-Chrétien Variant
ZnSe- Lenslet Array
Alternative Transmitter Concept
Spectral filter 1: UV- reflective
Spectral filter 2: Au: IR- reflective
Spatial filter 3: Sensor Aperture
• Efficient use of collecting apertur
• Weight & Volume reduction
• Useable for Sensor array
Lidar 1064 nm
IR
UV
Goal: Avoid heat load by minimizing absorption in Filter 1 (UV), ZnSe Plate and Filter 2 (IR)09/05/2007 40
09/05/2007 41
Fiber + Sensor Array
ZnSe- Lenslet Array
Spectral filter 4: Fabry-Perot at 1064 nm ; BW 1 nm
Detector Array
Mini Baffles
09/05/2007 42
Honeycomb structure• No need for large external baffle byhexagonal tube array
Emitter
Fiber
Honeycomb Tube Baffle
09/05/2007 43
Pump LASER
Range Accuracy / Sensitivity Improvement
Lenslet Array
Fiber Laser Array Sensor Array
• Lidar strategy
• Pre-pulse 1 monitors ‚time of arrival‘
• Main-pulse 2 probes target
• Post-pulse 3 optically amplifies return pulse 2
• ‚Clock‘ or timebase of central importance
Leica Patent (Brn)
09/05/2007 44
Cassegrain Telescope
Lenslet Array
New Terminal Conceptsfor space applications
09/05/2007 45
4 Air / Spaceborne Hyperspectral Imaging
ImagingRanging Communication
Spaceborne
Airborne
Terrestrial
09/05/2007 46
APEX / K. Itten, J.Nieke
Pupils
09/05/2007 47
Principle of HS Imager, a pupil manipulator
Source Object Pupil 2 Slit Pupil 1 CCD
SpectrometerGround Imager
•Chromatic spectrum of a ground pixel is spread along track, Swath line of all ground pixels across track
Scrambler
The ‚scrambler‘ makes the recorded intensity independant to polarisation fluctuations by theatmosphere. It eliminates depolarisation effects of the Optics and allows a better radiometricresolution.
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MERIS• ‚Off axis‘ Catadioptric Maksutov Cassegrain
• Rowland circle spectrometer
09/05/2007 49
Leica Prototype6 Modules (FoV= ± 7°), each with GroundImager & Spectrometer, to cover a wideangle FoV of 84°.
Priority levels:
•P1: Noise Equivalent Albedo < 10-4
•P2: 400 –1100 nm; 1.2 nm resolution
•P3: 250 m ground pixel at 650 km orbit
Integration Sphere
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New Applications: Multiplex Processor
White Source
Object Pupil Image Pupil CCD
A B C
B C A
C A B
A B C
B C A
C A B
¤
¤
¤Matched filter
A
B
C¤ ¤ ¤
¤ ¤ ¤
¤ ¤ ¤
The different pattern A,B,C,.. in the object plane are simultaneously detected as colour coded autocorrelation peaks. Using SF10 and 400-700 nm, one canprocess about 30 holograms of different objects of spatial bandwidth of 6 lp/mm
See B. Braunecker, O. Bryngdahl, Optics Communications, Vol 40,Number 5, p.332 (1982)
09/05/2007 51
Hyperspectral Imaging
– Future Trends• Seamless adaption HS Imager as next generation of Digital Sensors• Better Balance of system performance between radiometric, spectral and
spatial range/resolution– Improve Ground imager (wide angular viewing)– Look for alternative spectroscopic concepts
• New Technologies:– Use Glass ceramics with n>1.9, transparent to 5 mue for unifying
visual and IR channels– Use Aspheres in GI and Spectrometer– Use monolithic concepts to improve pointing stability
• Look for new applications besides remote sensing
09/05/2007 52
Conclusions & Outlook
• APPLICATIONS– Imaging
• Film Digital / Color Hyperspectral– Ranging / Communication
• Miniaturisation, but keeping the large collecting aperture Integration
• OPTICS– Wide Angle Lens Systems : Spheres Rotational symmetric Aspheres– Small Angle Mirror Systems: Conical Aspheres Free Form Aspheres
• SYSTEMS– Sensorfusion of Imaging & Ranging & Tracking &…– „Time Base / Clock“ of central relevance of remote sensing systems