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.
As an example a reflectance spectrum of a mixture of three common rock forming minerals is shown below. Each mineral is a different molecule that absorbs energy in different regions of the spectrum. From the spectrum the three minerals can be identifed and with radiative transfer analysis the relative concentrations of the minerals can be determined.
The same spectrum is shown below as measured through the multispectral bands of the Landsat Thematic Mapper. The three molecules cannot be unambiguously identified, nor the relative concentrations determined.
The example above was for minerals found on the surface of the Earth. However, imaging spectroscopy is applicable wherever research, environmental and application questions can be posed in terms of molecules, scatterers and energy sources expressed in the solar reflected spectrum.
swath width 11 km
ground sampling 17 m
spectral coverage 400 - 2500 nm
spectral sampling 10 nm
spectral channels 224
AVIRIS is an experimental optical sensor developed by NASA's Jet Propulsion Lab (JPL) that delivers calibrated images of the upwelling spectral radiance in 224 contiguous spectral channels (also called bands) with wavelengths from 0.4 to 2.5 micrometres (µm). The instrument flies aboard a NASA ER-2 airplane (a U2 plane modified for increased performance) at approximately 20 km above sea level, at about 730 km/hr.
The science objectives of the AVIRIS project are broad. In a nutshell, the main objective is to identify, measure, and monitor constituents of the Earth's surface and atmosphere based on molecular absorption and particle scattering signatures. Research with AVIRIS is dominantly directed towards understanding processes related to the global environment and climate change. AVIRIS research areas include:
The Compact Airborne Spectrographic Imager (casi) is a programmable imaging spectrograph that measures electromagnetic radiation between 400nm and 1000nm. The casi uses real-time attitude and Global Positioning System (differential or non-differential) measurements to provide geocoded imagery for information extraction, map output and integration into Geographic Information Systems (GIS). The casi has been used for generating information products for forestry, agriculture, water, military, and target identification applications.
casi is a commercial system developed and manufactured by itres research ltd. of Calgary, Alberta.
casi Agriculture Imagery
False Colour Infrared Composite Southern Alberta, Canada
Pixel resolution is 5 by 5 metres.
Image was geocorrected using aircraft attitude and Global Positioning System measurements.