terraref/extractors-hyperspectral: Nov 2017 Beta Release

This is the first release of the hyperspectral pipeline. See the repository README for more details. It represents a major improvement relative to the Nov 2016 release.

The hyperspectral calibration procedure is documented at https://github.com/terraref/computing-pipeline/issues/282.

1. Only valid for 300-800nm (range of downwelling radiometer)
2. Raw hyperspectral exposures are calibrated for images in full sunlight. Other times and cloudy days are not well-tested yet.
3. Zenith angles used in the calibration data are: 42.3, 47.6, 53.0, 58.4, 64.0, 75.1, 80.7, 86.5
   • The closer the raw data is to these angles the better the result
4. The calibration needs improvement to obtain accurate absolute reflectances. Environmental conditions (such as shade and specular reflection) and irregular calibration of known targets (such as tilted surfaces and field-based calibration) can bias retrieved reflectances by an unknown factor. However, the scale bias factors out of indices created as ratios of reflectances, e.g., (A-B) / (A+B).

1. Notes from meeting on calibration options
2. First (alpha) calibration proceedure https://github.com/terraref/computing-pipeline/issues/88
3. Second (radiometer based) calibration
   • List of tasks https://github.com/terraref/computing-pipeline/issues/281
   • Algorithm documentation https://github.com/terraref/computing-pipeline/issues/282