1. Hyperspectral remote sensing (Imaging Spectroscopy)

2. Imaging Spectroscopy
Imaging Spectroscopy is the acquisition of images where for each spatial resolution element in the image a spectrum of the energy arriving at the sensor is measured.
These spectra are used to derive information based on the signature of the interaction of matter and energy expressed in the spectrum.
This spectroscopic approach has been used in the laboratory and in astronomy for more than 100 years.

3. The imaging spectrometer
Hyperspectral images are produced by instruments called imaging spectrometers.
The development of these complex sensors has involved the convergence of two related but distinct technologies: spectroscopy and the remote imaging of Earth and planetary surfaces.

4. Hyperspectral vs multispectral spectrometers
Multipspectral spectrometers have a limited number of spectral bands to operate with (7-64).
Using hyperspectral data (about two hundred bands)
Material on Earth’s and other planetary surface can be identified
forest inventories can be developed for remote regions to support ecological planning and management.
Agriculture

5. Multi- vs. Hyper-
Hyper-: Narrow bands ( 20 nm in resolution) and continuous measurements.

6. Multi- vs. Hyper-
Although most hyperspectral sensors measure hundreds of wavelengths, it is not the number of measured wavelengths that defines a sensor as hyperspectral.
Rather it is the narrowness and contiguous nature of the measurements. For example, a sensor that measured only 20 bands could be considered hyperspectral if those bands were contiguous and, say, 10 nm wide.
If a sensor measured 20 wavelength bands that were, say, 100 nm wide, or that were separated by non-measured wavelength ranges, the sensor would no longer be considered hyperspectral.

8. Moffett Field, California, at the southern end of the San Francisco Bay.
AVIRIS acquired the data on August 20, 1992 when it was flown on a NASA ER-2 plane at an altitude of 20,000 meters (65,000 feet) over

9. One pixel response
The x-axis is channel wavelength in micrometers, also known as microns (one micron = 1000 nm).
The y-axis is radiance, usually expressed in units of microwatts per square centimeter per nanometer per steradian, or uW / (cm^2 * nm * sr).

10. Why imaging spectroscopy?

12. Plotting spectra
Spectral reflectance curve
Scatter plots

13. Plotting spectra
A reflectance spectrum consists of a set of reflectance values, one for each spectral band.
Each of these bands can be considered as 1-D in an n-dimensional spectral space, where n is the number of spectral bands.
If we plot the measured reflectance value for each spectral channel on its respective coordinate axis, we can use these coordinates to specify the location of a point in spectral space that mathematically represents that particular spectrum.
Mathematically, each pixel value is the end point of a vector that begins at the origin of the coordinate system.
Spectra with the same shape but differing overall reflectance (albedo) plot as vectors with the same orientation but with endpoints at different distances from the origin.
Shorter spectral vectors represent darker spectra and longer vectors represent brighter spectra.

14. Plotting spectra It may be difficult to visualize such a plot for
an image involving more than three wavelength
bands, but it is mathematically possible to construct a hyperdimensional spectral space defined by dozens or hundreds of mutually-perpendicular coordinate axes.
Each spectrum being considered occupies a position in this n-dimensional spectral space. Similarity between spectra can be judged by the relative closeness of these positions (spectral distance) or by how small the angle is between the spectral vectors

15. Hyperspectral Systems
Hyperion
On NASA Earth Observing-1 (EO-1) spacecraft (2000).
Pushbroom system
A 705-km sun-synchronous orbit following 1 minute behind LANDSAT 7, essentially viewing the same atmospheric conditions.
nm hyperspectral bands between 400 nm (blue) and 2500 nm (SWIR) and records reflectance in 12-bit format.
30 m x 30 m resolution;
7.5 km hyperspectral swath
Another hyperspectral sensor aboard EO-1, called LEISA, with a 185-km swath at 250 m x 250 m GSD, collects 246 bands in the SWIR portion of the spectrum where water vapour absorption is significant.
This data is used to derive atmospheric correction information for the other sensor datasets.

16. Hyperspectral Systems
AVIRIS
The Airborne Visible InfraRed Imaging Spectrometer (AVIRIS) designed and built by the NASA Jet Propulsion Laboratory (JPL).
A whiskbroom scanner, and it flies on several airborne platforms. The swath and spatial resolution depend on the flying height and over-ground speed of the aircraft.
On the NASA ER-2 jet at 20 km above MSL, AVIRIS covers an 11 km swath at 20 m resolution.
The sensor records radiance levels at 12-bit radiometric resolution for nm bands between 400 nm (blue) nm (mid-IR).

17. Hyperspectral Systems
HyMap
HyVista Corporation, of Sydney, Australia, commercially operates a 128-band whiskbroom hyperspectral scanner.
Spectral range of nm, with a bandwidth of nm rather than 10 as for AVIRIS and Hyperion.
It records data in bit format.
Spatial resolution depends on flying height, but ranges from meters under typical conditions.

18. Enstatite-ferrosilite Subcalcic-Hedenbergite
Hyperspectra of pyroxenes
Enstatite-ferrosilite
(MgFe)2Si2O6
Fe+2 M2 site
Fe+2 M2 site
Fe+2 M2 site
Subcalcic-Hedenbergite
Fe+2 M2 site
(Ca,Fe)(MgFe)Si2O6
Why sub-calcic hedenbergite has M2 absoprtion at 2300 nm while enstatite-ferrosilite have M2 absorption at 1850 nm?
Hedenbergite
Fe+2 => Fe+3 IVCT
Ca(MgFe)Si2O6
Fe+2 M1 site
Fe+2 M2 site
What would happen to the absorption features as we move down from hedenbergite to pigeonite?
Fe+2 M1 site
What would happen to the absorption features in the enstatite-ferrosilite series (Mg2Si2O6 -Fe2Si2O6) as we move towards ferrosilite from enstatite?
IVCT – Intervalence charge transfer, when an excited 3d electron is transferred between neighboring cations in adjacent coordination sites, transient changes in valencies occur, and the process is IVCT

19. Spectra of some pyroxenes (Wo (Wollastonite) – 100% Ca; En (Enstatite) – 100% Mg; Fs (Ferrosilite) % Fe)

20. Molecular vibration of Hydroxyl (OH)
Symmetric stretch (v1 mode 3652 cm-1 or 2.8 μm)
First overtone of v1 at 1.4 μm - Diagnostic
Combination of Metal-OH bend + v1 between Diagnostic
OH – 2v1
Mg-OH
Fe+2 CF splitting

21. Silicates - Amphiboles
Fe2+ - Ti4+ / Fe2+ - Fe3+
Silicates - Amphiboles

22. Silicates – Hydrated and hydroxide
Olivine – Mg silicate
Serpentine – MgFe silicate hydroxide