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Piccolo3 spectral systems

Piccolo3 spectral systems

Mac Arthur A.(1,2), Hagdorn, M.(1), Taylor R.(3), and Robinson I. (4). (1) GeoSciences, U. of Edinburgh, (2) LEO/IPL U. of Valencia, (3) Physics, U. of Edinburgh, (4) Rutherford Appleton Laboratories

Need for Piccolo3 system design

Light reflected and/or emitted by a surface is an inherent, though possibly a dynamic, property of that surface and of the conditions under which it was illuminated. To further challenge making measurements, those illumination conditions may also be dynamic. However, by measuring the spectral distribution and intensity of that light, both before and after it has interacted with the surface, it may be possible to infer the physical and chemical properties of that surface at time of measurement. These physics fundamentals, along with rapid technological progress, has led to the development of the science and techniques of optical Earth observation (EO) and remote sensing as key to understanding our environment and its change over time.

Earth observation imaging from space-based platforms has provided scientists with a synoptic view of the Earth’s surface providing geographical and spatial relationships and change over time. This has led to a far greater understanding of Earth surface composition and processes and significantly contributed to our understanding of Earth surface dynamics. However, EO images even when taken from latest instrument/satellite platforms tend to have limited spectral sampling band width (FWHM) and ground sampling distance (GSD) resolutions and infrequent though regular temporal coverage. Current operational missions are at best either multi-spectral (with few (10s of) broad spectral bands (bands say 10 nanometres (nm) or more in width)) and low GSDs (10s of meters square) or hyperspectral (with 100s of spectral band (less than say 10 nm in width)) with higher GSDs (100 of meters square). They may also have at best a daily revisit frequency and have high GSDs or less frequent (multiple days) and lower GSDs. There is therefore a mismatch between scales in geographical and physical space and time of observation and Earth surface feature of interest and their dynamics.

Optical observations from space having to pass through a dense and dynamic atmosphere both on its way from the Sun to the Earth surface and on its way back to the space-based sensor. Any interaction between light (photons) and the atoms and molecules or liquids, gasses or solids causes change both in spectral distribution and intensity of the light further, confounded understanding. To better understand these space-base optical observation measurements of both skylight incident on the surface of interest and reflected and/or emitted reflectance or transmission from surface of interest need to be made. Field spectroscopy serves this purpose and is also an independent research tool in its own right. However, field spectrometers have normally been hand-held or backpack mounted and with a single field-of-view1  (Milton et al (2009), Mac Arthur and Robinson (2015)). These spectroscopic approaches:

  • require that a reference measurement, normally of  a sintered PTFE white panel, be made to record the Earth surface illumination conditions and target surface and reference surface be measured in sequence, with significant time lag between reference and target measurement;
  •  normally cause measurement support (area sampled) to be constrained by instrument field of view and limited by height of the fore optic above the surface;
  • sampling in the spatial domain limited by practical access, time constraint and ability for cover wider  areas with some statistical sampling validation;
  • sampling in the temporal and diurnal domains  as spectrally resolving field spectrometers are not normally weather/ field proof of have configurable long term logging functions;

The Piccolo3 dual-field-of-view multi-spectrometer system has been designed to addresses these issue. It has been developed by a team of scientists in GeoSciences, University of Edinburgh with assistance from scientist at the Laboratory for Earth Observation (LEO) at Image Processing Laboratory, University of Valencia and by Alker Fibre Optic Specialists Ltd to address these issues: .

References

1 Milton et al (2009) Progress in Field Spectroscopy. RSE  DOI: 10.1016/j.rse.2007.08.001

Mac Arthur, A. & Robinson, I. (2015) A critique of field spectroscopy and the challenges and opportunities it presents for remote sensing for agriculture, ecosystems, and hydrology. Proceedings of SPIE doi.org/10.1117/12.2201046

1 The Spectra Vista Corporation GER1500 DFOV configuration being one possible exception or the ASD DFOV dual-instrument at significantly greater cost.

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