Spectral discrimination of vegetation types in a coastal wetland

Spectral imaging technology, which records simultaneously spectral and spatial information about an object, was initially developed for remote sensing and has since been successfully applied to other areas of research. Although relatively new to the field of conservation, this non-invasive method of investigation has already provided promising results in the analysis of paintings and written documents, the characterization of materials and digital documentation. This article reviews the published literature relating to the application of multispectral and hyperspectral imaging for the study and conservation of works of art and presents some new perspectives offered by this innovative and fast-developing technology.

Multispectral and hyperspectral imaging technologies in conservation: current research and potential applications

Use of coupled canopy structure dynamic and radiative transfer models to estimate biophysical canopy characteristics

Performance of different spectral and textural aerial photograph features in multi-source forest inventory

Hyperion images are currently processed to level 1a (from level 0 or raw data). These level 1a images are files of radiometrically corrected data in units of either watts/(sr /spl times/ micron /spl times/ m/sup 2/) /spl times/ 40 for VNIR bands or watts/(sr /spl times/ micron /spl times/ m/sup 2/) /spl times/ 80 for SWIR bands. Each distributed Hyperion level 1a image tape contains a log file, called "(EO-1 identifier).fix.log", that reports the bad or corrupted pixels (called known bad pixels) found during the pre-flight checking, and details how they were fixed. All bad pixels should be corrected in a level 1a image. However, bad pixels are still evident. In addition, there are dark vertical stripes in the image that are not reported in the log file. In this paper, we introduce a method to detect and correct the bad pixels and vertical stripes (we will refer to these occurrences as abnormal pixels). Images from the Greater Victoria Watershed and other EVEOSD test sites are used to determine how stationary the locations of the abnormal pixels are. After abnormal pixel correction a Hyperion image is ready for geometric correction, atmospheric correction, and further analysis.

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Detection and correction of abnormal pixels in Hyperion images

The beginning of the next millennium promises an explosion in the quantity and quality of global data available from imaging remote sensing systems. The scientific and commercial communities become aware of unique hyperspectral imaging data acquisition opportunities. A brief profile of over 80 high resolution spaceborne and airborne earth observation sensor systems (H less than 800 km) planned to be operating in the year 2000 and beyond are presented in this paper. This overview covers multi- and hyperspectral civil, land and ocean nadir viewing observation sensors in the spectral range from the ultraviolet to the thermic infrared. A summary of the performance of each system, from image parameters (spectral and ground resolution) to the image generating procedure (spectral selection mode, image acquisition mode) is presented. At this point some caution is due since not all these concepts and plans will come to pass. The cuts in the government budget and the containment of commercial plans for new sensor systems will affect the realization of the present plans. However, the year 2000 will see at least four large area vegetation and ocean mappers, three landsat-like systems and two commercial high resolution systems in polar orbit simultaneously. A fleet of over 40 airborne sensor systems gives the final polished form of the future data acquisition opportunities.

Imaging Spaceborne and Airborne Sensor Systems in the Beginning of the Next Century.

In the past decade imaging spectrometers for observation of the Earth were developed to use the complete information of a spectrum as a major tool in the study of physical and biological processes of the Earth. Instead of a few relatively broad spectral bands (line detector), this imager concept provides for the detection of many contiguous narrow spectral bands by applying the technology of matrix detectors. The change from one-dimensional to two-dimensional solid-state imagers makes it necessary to carry out the specific signal-to-noise ratio (SNR) analysis of such detectors. A simulation of maximum and minimum radiances for typical spectral signatures of the Earth (water, vegetation) and the verification of these radiances with modular optoelectronic scanner data provide the means for calculation of electrons generated at the matrix detector. For a hypothetical sensor, water-minimum and vegetation-maximum signals are calculated, and the degradation of the SNR caused by image smear of two-dimensional solid-state imagers is demonstrated.

Noise contributions for imaging spectrometers

Until now incandescent lamp, sun and moon calibrations have been successfully applied for in-flight calibration of spaceborne Earth observation imaging sensors. The performance development of LEDs in the past decade guided to higher luminous efficiencies, broader spectral coverage, lower degradation of light output over time and lower power consumption. These advantages make LEDs to a candidate for radiometric and spectral calibration of spaceborne spectrometers. For analysing LEDs for space in-flight calibration a set of LEDs has been characterised and a simulation of space radiation quantities (i.e. proton and electron radiation for a polar low-Earth orbit) has been carried out. Additional vacuum tests (outgassing behaviour) demonstrated a possible application of LEDs with epoxy housing for the future space environment. Further on, a concept for long-term temperature stabilisation has been developed for solving the main problem of LED in-flight calibration, i.e. the temperature dependency of the irradiance. Consequently, this study demonstrates that (1) a degradation of LEDs due to space environment is not expected, that (2) long-term temperature stability of LEDs can be ensured, and that (3) the higher blue part of ‘white’ LEDs would best suit ocean-colour scientists needs.

Spaceborne spectrometer calibration with LEDs

In the last decade imaging spectrometers for Earth observation were developed by different government agencies because of the ability to use the full information of a spectrum as a major tool in the study of physical and biological processes of the Earth. Instead of a few relatively broad spectral bands, the new imager concepts provide the detection of many contiguous narrow spectral bands by applying the technology of 2D detectors. The step from 1D to 2D solid-state imagers makes it necessary to include the typical behavior of these advanced imagers on the signal-to-noise (SN) ratio analysis. A simulation of maximum and minimum radiances for typical spectral signatures of the Earth and the verification of these radiances with Modular Optoelectronic Scanner data give the source for the calculation of electronics generated at the imager's detector. Different sensors will be compared concerning water-minimum and vegetation-maximum signals, and the degradation of the SN ratio due to image-smear of 2D solid-state imagers is demonstrated. A developed smear parameter gives a tool for analyzing the spectrometer performance during the conceptual phase.

Jens Nieke

Papers

Imaging Spaceborne and Airborne Sensor Systems in the Beginning of the Next Century.

Noise contributions for imaging spectrometers

Spaceborne spectrometer calibration with LEDs

Signal-to-noise ratio reduction due to image smear concerning spaceborne imaging spectrometers for remote sensing of the Earth