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Contents
Introduction What is Hyperspectral Sensing Hyperspectral vs Multispectral Data Cube – A way to visualize the data The Ultimate Benefit Imaging Spectrometry Concept Spectrometry Imaging Spectrometry n-Dimensional Data
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Overview
In previous lessons, you were introduced to extraction of thematic information from the spectral content of digital multiband imagery.
You learned to manipulate various Band combinations for display and analysis Performed simple classification and change
detection using classified and unclassified imagery. Performed advance classification techniques
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Cont…
The same concepts can be applied to hyperspectral imagery, but Hyperspectral image analysis is much more
complex than multispectral
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Objectives
1. Explain the fundamental principles of hyperspectral remote sensing
2. Explain the georeferencing and radiometric calibration of hyperspectral data
3. Identify standard hyperspectral mapping products and applications
4. Explain the basic principles of hyperspectral image analysis
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Introduction
Remote sensing involves examination of features observed in several regions of electromagnetic spectrum. Multispectral remote sensing is based upon use of
several broadly defined spectral regions Hyperspectral remote sensing is based upon
examination of many narrowly defined spectral channels.
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Cont…
Hyperspectral remote sensing combines imaging and spectroscopy Generally 100 to 200 or more narrow spectral
bands (5 – 10 nanometers wide) Compared to multispectral sensors with typically 4
to 12 spectral bands (70 – 100 nm wide)
Generates large data sets Requires new / different analysis methods
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What is Hyperspectral Sensing?
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Multispectral vs Hyperspectral
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Data Cube – A way to visualize the data
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The Ultimate Benefit…
Diagnostic / identifying characteristics are lost in wide bands
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Imaging Spectrometry Concept
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Analysis Approach
Direct identification using diagnostic absorption and reflection features
Comparison to laboratory and field measured spectra
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Spectroscopy
Spectroscopy pertains to the dispersion of an object's light into its component colors (i.e. energies)
Spectroscopy can be used to detect individual absorption features due to specific chemical bonds in a solid, liquid, or gas
By performing this dissection and analysis of an object's light, one can infer the physical properties of that object (such as temperature, mass, luminosity and composition, etc.)
Continuous spectra Discrete spectra
Emission line spectra Absorption line spectra
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Continuous vs Discrete Spectra
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Image Spectroscopy
Imaging spectroscopy is a new tool that can be used to map specific materials by detecting specific chemical bonds
It is an excellent tool for environmental assessments, mineral mapping and exploration, vegetation species and health studies, general land management studies, and others
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Cont…
Hyperspectral imaging is the simultaneous acquisition of images in many narrow, contiguous, spectral bands
Each pixel in the remotely acquired scene has an associated spectrum similar to the spectra of the material / mineral obtained in the laboratory
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Properties of a Spectrometer
Parameters that describe the capability of a spectrometer Spectral range Spectral bandwidth Spectral sampling Signal-to noise ratio
FWHM = Full Width at Half Max
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Spectral resolution – Sampling Interval
Spectral resolution = narrowest spectral feature that can be resolved by a spectrometer (full width at
half maximum FWHM)
Spectral sampling interval = interval, in wavelength units, between data points in the measured spectrum.
Spectral bandwidth used for spectral sampling interval)
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Properties of a Spectrometer
Parameters that describe the capability of a spectrometer Spectral range Spectral bandwidth Spectral sampling Signal-to noise ratio
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Goniometer
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ASD Fieldspec Pro
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ASD Fieldspec Pro
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ASD Fieldspec Pro
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GER 3700
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PIMA II
PIMA (Portable Infrared Mineral Analyser) Spectral range 1300 – 2500 nm Spectral resolution 7nm, interval 2-4 nm
Measurement is made in contact mode Measurement time 20-60 seconds
Produces reflectance spectra Spectra measured on a sample area of about 10 mm by 2
mm Internal illumination (does not need solar illumination) Internal reflectance standard, wavelength calibration uses
internal target
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PIMA II (cont’d)
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Spectral Libraries
SLI’s are collections of spectra different surface materials.
Often grouped by surface type (vegetation vs. soils vs. man-made materials etc.) and sometimes by grain size fraction (influence on spectra).
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Usually measured under laboratory conditions with excellent spectrometers.
Availability Publicly available SLI’s are included in ENVI ASTER speclib on the internet Create own from field/lab measurements Create own from image (point measurements or
average of ROI)
Spectral Libraries (cont’d)
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n-Dimensional Data
Hyperspectral data (or spectra) can be thought of as points in an n-dimensional scatterplot.
The data for a given pixel corresponds to a spectral reflectance for that given pixel.
The distribution of the hyperspectral data in n-space can be used to estimate the number of spectral endmembers and their pure spectral
signatures and to help understand the spectral characteristics of the materials which make up that
signature.
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Vegetation Spectral Reflectance extracted from AVIRIS data
Questions & Discussion
