A dual-field-of-view spectrometer system for reflectance and fluorescence measurement

Transcription

1 A dual-field-of-view spectrometer system for reflectance and fluorescence measurement (1) Alasdair Mac Arthur, (1) Iain Robinson, (2) Micol Rossini, (3) Neville Davies and (3) Ken McDonald (1) Field Spectroscopy Facility, GeoSciences, University of Edinburgh (2) Environmental Remote sensing and Spectroscopy Laboratory, University of Milano-Bicocca (3) Ocean Optics (UK), Oxford

2 Design brief: Use exis9ng op9cal benches Illuminance thousand lx DFOV and cos- conical for variable illumina9on :20 12:26 12:32 12:38 12:45 12:51 12:57 13:03 13:09 13:16 13:22 13:28 13:34 13:40 13:47 Time Deploy on UAVs < 2kg payload Wirelessly controlled Low cost but not cheap Low power Consump9on < 5 W (unless cooled)

3 FSF Piccolo wireless DFOV single spectrometer system measurements on demand or time series Files saved on internal memory and sent to base station Weight 0.8kg Shutter driver & comms control board. FSF design Computer Raspberry Pi Model A Spectrometer Radio Control and data transfer XBee Pro ~1.6 km range 90mm Battery Lithium polymer 14.7 V 1 Ah 60mm Fibre Bifurcated Length up to 5m Diffuser Cosine corrected Downwelling FO shutter Min shutter open/close cycle ~10ms Upwelling FO shutter Ocean Optics USB2000+ Spectral range ~ nm Sampling interval ~ 0.4nm FWHM 1.3nm Digitisation 16-bit Downwelling Upwelling 1. Acquire downwelling spectrum 2. Acquire upwelling spectrum 3. Acquire dark spectrum

4 FSF Piccolo wireless DFOV single spectrometer system For logging applications Ø Weatherproof fore optics and spectrometer enclosure Ø Files saved on internal memory and/or sent to base station For UAV applications weight <0.8kg Ø Housing and weatherproof fore optics can be removed Ø Files saved on internal memory and saved to base station

5 FSF Piccolo wireless DFOV single spectrometer system For logging applications Ø Weatherproof fore optics and spectrometer enclosure Ø Files saved on internal memory and/or sent to base station For UAV applications weight <0.8kg Ø Housing and weatherproof fore optics can be removed Ø Files saved on internal memory and saved to base station

6 FSF Piccolo Doppio wireless DFOV spectrometer system Any two USB controlled spectrometers can be used Spectrometers log simultaneously Can add external cooling to uncooled spectrometers if required Weight (with QE Pro) ~1.9kg For cooled system an additional power supply would be required USB mm 180mm Optical fibre double bifurcated Spectrometer options Any two of USB2000+, HR4000, Maya or QE Pro series e.g. FSF have: HR4000 (uncooled - 25µm slit ) Spectral range Sampling interval FWHM Digitisation QE Pro ~ nm ~ 0.05nm ~0.21nm 16-bit Maya (uncooled - 10µm slit) Spectral range Sampling interval FWHM Digitisation ~ nm ~ 0.1nm ~0.31nm 16-bit QE Pro (cooled - 10µm slit) Spectral range Sampling interval FWHM Digitisation ~ nm ~ 0.1nm ~0.31nm 18-bit

7 FSF Piccolo & P. Doppio wireless DFOV spectrometer systems Controlled from laptop via wireless (on demand or time series) or activated by Tx For logging applications Ø Weatherproof fore optics and spectrometer enclosures Ø Files saved on internal memory and/or sent to base station For UAV applications weight ~1.9kg Ø Housing and weatherproof fore optics can be removed Ø Files saved on internal memory and saved to base station Major advantages of Piccolo series over other systems Upwelling and downwelling measured by same spectrometer Upwelling and downwelling measured near simultaneous Ø Can be within 10ms of each other Both channels measure through same fore optic Downwelling fore optic is cosine corrected Same spectrometers can be used for both logging and UAV applications

8 Piccolo ground control GUI Code provided open source Live data can be viewed Live reflectance can be viewed All data transformed from DN to measurement units on the ground in post processing Auto integration function currently being developed

9 OO additional spectrometer options HR bit standard CCD and uncooled Maya 16-bit back thinned CCD QE Pro 18-bit back thinned and cooled CCD

10 OO spectrometer options Non cooled response will vary with temperature Back thinned CCD effected by etaloning Ø A systematic error from interaction between wvl of light and thickness of CCD 2 possible methods of correction (avoid filters that rely on frequency components) 1) Referencing method Inst. response = measured spectrum (DN) black body (or source cal. file)

11 QE Pro # ) Curve fitting with smoothing spline Inst. response correction per radiance level per wavelength interval 1) curve fit test spectra 2) calc. residuals 3) linear interp. residuals 4) apply correction per rad. level per wvl interval from lookup table

12 QE Pro # Etaloning appears stationary with regard to wvl. Etaloning appears linear with regard to radiance level 2) Curve fitting with smoothing spline Can correct to < ± 0.5%

13 Piccolo and Piccolo Doppio DFOV spectrometer systems for reflectance and fluorescence measurements Conclusions A light weight low cost DFOV spectrometer system is available Can be deployed on UAVs or at fixed locations Can measure reflectance and fluorescence (near) simultaneously through same fibre optic based fore optic = same support for both measurements QE Pro offers a step-change in OEM spectrometer dynamic range Initial findings etaloning appears to be stationary and linear and can be corrected in post processing with uncertainties <±0.5% when detector is temperature controlled Field trials of FSF system with USB2000+ and QE Pro will begin summer 2014 Still to investigate effect of temperature on etaloning (for Maya) Still to investigate if Maya is fit-for-purpose for fluorescence measurements

14 New COST Action ES1309 OPTIMISE (innovative optical Tools for proximal sensing of ecophysiological processes) WG1 Spectral database and wireless data transfer WG2 UAVs as platforms WG3 Reflectance and fluorescence measurement 1 st WG workshops U. of Milano-Bicocca, 8 th to 10 th September