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Data Sources

The Earth Library is a collection of collections, merging spectral measurments and models from a range of data sources. earthlib provides routines for resampling this collection to match the wavelenghts of many common optical imaging sensors.

Spectral libraries

The following data sources were filtered and resampled prior to inclusion in earthlib.

Below are plots for the primary land cover spectra included in earthlib.

earthlib photosynthetic vegetation spectra

earthlib non-photosynthetic vegetation spectra

earthlib bare ground spectra

earthlib burned spectra

earthlib vegetation spectra

Supported sensors

earthlib satellite instruments

In the figure above, the black lines indicate the full-width of each band, and the colored squares mark the center wavelength for each band. NEON, an imaging spectrometer system, measures the full shortwave spectrum (400-2500 nm) using over 400 spectral bands to measure continuous spectral variance (these bands have been resampled to match the range/centers of the earthlib reference library).

Measurement types

The earthlib spectral library are provided in units of surface reflectance: scaled as floating point values from 0-1. Data from the most commonly-used sensors—like Landsat, Sentinel & MODIS—are provided in Earth Engine as surface reflectance products. These datasets can be unmixed once the data have been rescaled: they're typically provided as unsigned integer values from 0-10000.

A few data sources are not available as surface reflectance products: ASTER data are provided in radiance (a physical measurement unit, uncorrected for atmospheric composition); ALOS-AVNIR-2 data are provided in DN (raw sensor measurments). Though we provide paths to these collections and the wavelengths of these sensors, these data cannot be unmixed as-is using earthlib. You would have to first convert from DN to radiance (in the case of ALOS-AVNIR-2) then apply atmospheric correction (to convert from radiance to reflectance). This workflow isn't supported by earthlib.

Sensors unavailable in Earth Engine

earthlib provides sensor definitions for NEON data (a set of airborne imaging spectrometers) and for a set of data from Planet's Dove constellation (PlanetScope, Dove-R, SuperDove). These are not available as default Earth Engine collections. You can, however, upload data from these providers as custom user data or from community-contributed datasets. So you can unmix these datasets if you have access to them as Earth Engine Image/Collection assets, but there is no default collection ID provided by earthlib.