Hyperspectral goes to UAV and thermal

Transcription

1 Hyperspectral goes to UAV and thermal Timo Hyvärinen, Hannu Holma and Esko Herrala SPECIM, Spectral Imaging Ltd, Finland

2 Outline Roadmap to more compact, higher performance hyperspectral imagers Push-broom hyperspectral imager design and validation parameters Compact, high performance VNIR imager First thermal spectral imager in a compact format

3 AISA in the market place

4 Roadmap Target: Airborne hyperspectral sensor systems, which are compact enough for installation and operation in standard stabilized gimbals, pods and mini-size UAVs (payload < 20 kg)

5 Roadmap..and provide remarkably higher performance than current compact systems, particularly: - VNIR ( nm), 2000 pix, SNR 800:1 - VNIR ( nm), 2000 pix, SNR 800:1 - SWIR ( nm), 1000 pix - VNIR+SWIR integrated with common fore optics, factory co-aligned - LWIR (8-12 um), high sensitivity, low maintenance

6 Hyperspectral imager parameters Function Design parameter Standard calibration/ FAT parameter Spectrometer quality Light collection efficiency Signal quality Standard data processing input Spectral range Spectral Linearity calibration Spectral resolution Uniformity (vignetting) F-number Transmission Detector sensitivity Pixel well capacity Readout and dark noise Signal linearity Radiometric stability Spectral sensitivity, SNR Radiometric calibration

7 Function Design parameter Standard calibration/ Design parameters FAT Image quality Smile, keystone Airborne mapping capability Physical construction Geometrical aberration ( ) Stray light, ghosts Spot size MTF Polarization sensitivity # spatial pixels FOV Image rate Dimensions, mass Power consumption Standard data processing input

8 Compact VNIR imager 100 mm Weight 1.4 kg Power consumption < 5 W

9 Compact VNIR imager - Characteristics Spectral range/resolution F/# Smile/Keystone/Spot size nm /2.5 nm F/2.4 Polarization sensitivity <±2% SNR nm Frame rate to disk ±0.95um/±0.065 nm/<10 um 800:1 7.2 nm sampling uw/(cm 2 sr nm)@ 7.2 nm sampling nm, nm, nm # spatial pixels 1300 (-> 2000 by end of 2011) FOV Data interface 23.8 degrees (-> 38 degrees) CL 12 bits

10 Compact VNIR imager performance example 48.2 solar zenith, 1.5 air mass 15 ms exposure time (65 images/s)

11 Compact VNIR imager prototype system VNIR imager, GPS/INS, computer, and power supply integrated together. Total 12.7 kg 270x250x250 mm <70 W

12 Compact VNIR imager flight tests Reno, Nevada, USA, March 2011 FOV 23.8 degrees Altitude 3120 m Speed 59 m/s Image rate 104 Hz GSD 0.6 m Exposure 8 ms Spectral sampling 7.2 nm

13 Dual channel VNIR+SWIR ~13 kg ~300x200x200 mm nm with common fore optics Extremely small aberrations F/2.4, high diffraction efficiency, large throughput l plane array Focal Dispersive component Slit Dispersive component Focal plane array Spatial resolution 380 or 1024 pix Reflective front lens

14 Hyperspectral imaging in LWIR (8-12 um) Challenge: instrument radiation Optomechanics (fore lens and spectrograph) in front of the detector array emit broad-band thermal radiation. May be orders of magnitude higher (per pixel) than the spectrally split signal from the target/sample. How to solve this? - Make the signal from target higher, and/or - Reduce the instrument radiation

15 LWIR Push-broom hyperspectral cameras Focal plane array technologies MCT (Mercury Cadmium Telluride) - < 70K operation temp., Stirling cooler - Photon detector - Saturation from too high photon flux - Highly sensitive (low NESR) - Very expensive in 8 12 um Microbolometer - Uncooled - Each pixel is thermometer - No signal saturation - No integration time - Inexpensive - >10 times less sensitive than cooled MCT photon detector

16 LWIR Push-broom hyperspectral cameras Design targets Cooled High performance in NESR (< 20 mw/m 2 sr um), SNR and spectral resolution for - Airborne and ground remote sensing - Industrial killer applications. Compact size and weight even for use in UAVs. Elimination of deeply cooled optics Low maintenance requirements. Uncooled Sufficient performance for - Imaging emission from higher temperature targets (>150 C) - LWIR chemical imaging in reflection mode in labs and industry. Robust construction. Affordable instrument.

17 LWIR Push-broom hyperspectral cameras Key design elements Cooled - MCT array at 55K, extraordinary low dark current - Special custom cold filter for suppression of instrument radiation - Optics temperature precisely stabilized - Background monitoring on chip (BMC) Uncooled - Most advanced, room temp. microbolometer array - F/1 imaging spectrograph - Trade-off in spectral resolution for higher signal

18 LWIR Spectral Imager Characteristics LWIR cooled Spatial pixels LWIR uncooled Spectral range um 8-12 um Spectral resol. 100 nm 400 nm Spectral sampling 50 nm 150 nm Spectral bands Smile, keystone <0.2 pix <0.2 pix Image rate 100 Hz 50 Hz, fixed 20 mw/m 2 sr um 140 mw/m 2 sr um

19 LWIR Push-broom hyperspectral cameras Cooled Uncooled 285x200x175 mm 13.5 kg < 200 W 185x143x100 mm 3.5 kg 3.5 W

20 Cooled Performance NESR SNR

21 AisaOWL took off Flights over Cuprite, NV, USA FOV 24 degrees Ground pixel size 1 m 94 images/s Daytime Data processed to radiance

22 AisaOWL sensor on the ground Outdoor scan in Finland in daytime in March 2011 Ambient temperature ca -15 C AisaOWL sensor on a rotary stage on tripod FOV 24 degrees 94 images/s Data processed to radiance

23 To conclude Push-broom hyperspectral imagers can be made more compact, with increased performance.