Progress in Field Spectroscopy

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1 Progress in Field Spectroscopy Ted Milton School of Geography University of Southampton NASA JPL Reflectomobile

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4 Progress in Instrument Design

5 Challenges in Instrument Design SNR in SWIR Temperature effects Polarisation sensitivity Field-of-view & PSF Radiometry

6 However, users still complain about... Total cost of ownership Sunlight-unreadable screens Problems with optical fibres Steps in spectra

7 Roles for Field Spectroscopy in EO Scaling-up from individual elements of the scene to areas the size of a pixel Iron Chlorite 50 Mean Reflectance (%) (offset for clarity) Mean Reflectance 100W Lamp (%) Mean Reflectance 100W Lamp rotated (%) Mean Reflectance Contact Probe (%) Pima Reflectance Wavelength (nm)

8 Roles for Field Spectroscopy in EO Scaling-up from individual elements of the scene to areas the size of a pixel; Using those pixel-scale data to: validate numerical models validate sensor calibration post-launch correct remotely sensed data for the effect of the atmosphere Field spectroscopy also provides a tool for sensitivity analysis; and is an effective aid to teaching the physical principles of remote sensing.

9 Measurement of reflectance factors Reference panels need calibrating (spectral and angular). Reference panels deteriorate over time. Reflectance factors are not an inherent property of the target.... need to pay more attention to the spectral irradiance distribution.

10 The problem of sub-visual clouds Cause the amount of irradiance to change rapidly. Cause the angular distribution of irradiance to vary. Significant source of error Possible solutions: dual-beam methodology monitor or model the irradiance

11 Dealing with sub-visual clouds Simultaneous measurement Simultaneous estimation Milton & Rollin, 2006

12 The challenge of angular measurements... NASA JPL PARABOLA III

13 Some goniospectrometer designs The NPL GRASS goniometer

14 University of Zurich RSL dual-beam goniometer

15 Goniospectrometry using a CCD array

16 An Instrument Package for Field Spectroscopy Instrument 1. Constant panel set-up Purpose Time series of irradiance spectra (plus direct/diffuse). 2. Mobile spectrometer Spatial variation of reflectance 3. Goniospectrometer Angular variation of reflectance 4. Sky camera Permanent visual record 5. Sun photometer AOT and EWT

17 Spectral characterisation of large uniform areas 1. White Sands, New Mexico. 2. Railroad Valley, Nevada. 3. Lunar Lake, Nevada. 4. Salar de Uyuni, Bolivia. 5. Salar de Arizaro, Argentina. 6. Tuz Gölü, Turkey. 7. Lake Eyre, Australia. 8. La Crau sèche, France. 9. Dunhuang, China. 10. Dome Concordia, Antarctica.

18 Seasonal change in playa surface properties Thome et al., 1993 APRIL NOVEMBER

19 Example : How stable are inert surfaces? Disused airfield Concrete, Asphalt, Grass Mobile platform Dual-beam GER1500 Karen Anderson PhD

20 Seasonal change in hemispherical-conical reflectance

21 First clue to what we think is affecting the concrete reflectance is found in the met. data...

22 Each sequence shows a small variation with solar zenith angle. Not large enough to account for the difference between am and pm. Neither is the spatial uncertainty of location...

23 Development of an onshore breeze in the afternoon. Reflectance of concrete affected by what? change in air mass?...surface moisture? Algae and cyanobacteria on the surface Anderson and Milton (2006) Int. J. Rem. Sens., 27,

24 SpecNet mobile tram system Gamon et al., 2006 Remote Sensing of Environment, 103,

25 Conclusion Progress is slow... Methodologies still immature. Field spectroscopy remains difficult and expensive. Barely begun to address the issues of sampling in time and space. Potential contribution of field spectroscopy to a physically-based global remote sensing system is immense.