The Reststrahlen effect has been investigated for detecting regions of recently disturbed earth, by taking images where
metallic objects had been buried in a sandy soil and comparing with images of undisturbed soil. The images were taken
with a Long wave Infrared (LWIR) Hyperspectral Sensor, the Hyper-Cam.
Advanced multispectral, or hyperspectral, camera systems are being used to identify objects of interest on the basis of spectral characteristics. This paper will describe developments in the field of a real time spectral matched filtering. Matched filtering relies on there being a measurable difference between the spectrum of the target and that of background materials such as soil, vegetation, concrete and tarmac. If prior knowledge is available then the target can be found by matching the two spectra numerically. Previous work has identified the most robust and effective matched filtering technique. Software has been written to interface with a pushbroom hyperspectral sensor to enable fast spectrally tracking of objects. False alarms have been reduced by means of additional processing. Example detections of a number of unclassified objects will be presented.
Benefits for the detection of difficult targets have been demonstrated for multispectral and polarimetric imagery in differing conditions. The spectral differences between target and background have been seen to provide an enhancement to target discrimination. However, false alarms can occur mainly due to spectral variations in background materials. Complimentarily, polarimetric imagery has been used to detect man made targets by exploiting the reflective characteristics of man-made objects and the suppression of background clutter; but the detection process can be limited by the geometry and nature of targets. A data gathering SWIR Multispectral-Polarimetric sensor has been built to investigate whether adding polarimetric to multispectral information decreases background induced false alarms whilst maintaining good detection statistics for low contrast targets.
This paper will describe the development of a real time matched filtering technique for hyperspectral imagery.
Advanced multispectral, or hyperspectral, camera systems can potentially be used to identify objects of interest on the
basis of spectral characteristics. Matched filtering relies on there being a measurable difference between the spectrum of
the target and that of background materials such as soil, vegetation, concrete and tarmac. If prior knowledge is available
then the target can be found by numerically matching the two spectra. Tests have been carried out to evaluate the
effectiveness of a technique that utilises a specific type of spectral matched filter. Some results from the tests will be
presented that indicate how our technique is affected by changes in environmental and illumination conditions. Example
detections of a number of unclassified objects will be presented.
Highly efficient target detection algorithms in hyperspectral remote sensing technology, particularly for the long range detection of very low observable objects which exhibit extremely small detection cross sections, are in great demand. This is more so for a near or real time application. This paper is concerned with global anomaly detections (GAD), and conventional methods to achieve better detection using multiple approach fusion (MAF), which fuses detection outputs from various detectors using either logical operators, or, via a model based estimation of the joint detection statistics from all detectors, is found to be not good enough. This work emphasises the need to integrate a more comprehensive background modelling into the GAD to develop a robust anomaly detector (AD). Then, the detection output from this detector is fused with other detectors via MAF for a further improvement of detection performance. The MUF2 algorithm is formulated exactly using this 2-level fusion mechanism, in which mixture modelling and spectral unmixing fusion have been employed. The significance of background modelling in GAD has been highlighted in this work using real data. The result has shown a factor of 2-5 reduction in detection performance when a very small amount of target pixels (~0.1%) is misclassified as background. This is because anomalies are defined with reference to a model of the background, and subsequently two new background classification techniques have been proposed in this work. The effectiveness of the MUF2 has been assessed using three representative data sets which contain various different types of targets, ranging from vehicles to small plates embedded in backgrounds with various degrees of homogeneity. The performance of MUF2 has been shown to be more superior than the conventional GAD frequently in orders of magnitude, regardless of the background homogeneity and target types. The current version of the MUF2 is run under Matlab and it takes ~2 minutes to process a 20K pixel imagery.
This work forms part of the research programme supported by the EMRS DTC established by the UK MOD.
In the literature of spectral unmixing (SU), particularly for remote sensing applications, there are claims that both geometric and statistical techniques using independency as cost functions1-4, are very applicable for analysing hyperspectral imagery. These claims are vigorously examined and verified in this paper, using sets of simulated and real data. The objective is to study how effective these two SU approaches are with respected to the modality and independency of the source data. The data sets are carefully designed such that only one parameter is varied at a time. The 'goodness' of the unmixed result is judged by using the well-known Amari index (AI), together with a 3D visualisation of the deduced simplex in eigenvector space. A total of seven different algorithms, of which one is geometric and the others are statistically independent based have been studied. Two of the statistical algorithms use non-negative constraint of modelling errors (NMF & NNICA) as cost functions and the other four employ the independent component analysis (ICA) principle to minimise mutual information (MI) as the objective function. The result has shown that, the ICA based statistical technique is very effective to find the correct endmember (EM) even for the highly intermixed imagery, provided that the sources are completely independent. Modality of the data source is found to only have a second order impact on the unmixing capabilities of ICA based algorithms. All ICA based algorithms are seen to fail when the MI of sources are above 1, and the NMF type of algorithms are found even more sensitive to the dependency of sources. Typical independency of species found in the natural environment is in the range of 15-30. This indicates that, conventional statistical ICA and matrix factorisation (MF) techniques, are really not very suitable for the spectral unmixing of hyperspectral (HSI) data. Future work is proposed to investigate the idea of a dependent component clustering technique, a fused geometric and statistical approach, and couple these with a modification of the conventional ICA based algorithms to model the independency of the mixing, rather than the sources. This work formulates part of the research programme supported by the EMRS DTC established by the UK MOD.
Most target detection algorithms employed in hyperspectral remote sensing rely on a measurable difference between the spectral signature of the target and background. Matched filter techniques which utilise a set of library spectra as filter for target detection are often found to be unsatisfactory because of material variability and atmospheric effects in the field data. The aim of this paper is to report an algorithm which extracts features directly from the scene to act as matched filters for target detection. Methods based upon spectral unmixing using geometric simplex volume maximisation (SVM) and independent component analysis (ICA) were employed to generate features of the scene. Target and background like features are then differentiated, and automatically selected, from the endmember set of the unmixed result according to their statistics. Anomalies are then detected from the selected endmember set and their corresponding spectral characteristics are subsequently extracted from the scene, serving as a bank of matched filters for detection. This method, given the acronym SAFED, has a number of advantages for target detection, compared to previous techniques which use orthogonal subspace of the background feature. This paper reports the detection capability of this new technique by using an example simulated hyperspectral scene. Similar results using hyperspectral military data show high detection accuracy with negligible false alarms. Further potential applications of this technique for false alarm rate (FAR) reduction via multiple approach fusion (MAF), and, as a means for thresholding the anomaly detection technique, are outlined.
This paper reports the result of a study on how atmospheric correction techniques (ACT) enhance target detection in hyperspectral remote sensing, using different sets of real data. Based on the data employed in this study, it has been shown that ACT can reduce the masking effect of the atmosphere and effectively improving spectral contrast. By using the standard Kmeans cluster based unsupervised classifier, it has been shown that the accuracy of the classification obtained from the atmospheric corrected data is almost an order of magnitude better than that achieved using the radiance data. This enhancement is entirely due to the improved separability of the classes in the atmospherically corrected data. Moreover, it has been found that intrinsic information concerning the nature of the imaged surface can be retrieved from the atmospherically corrected data. This has been done to within an error of 5% by using a model based atmospheric correction package ATCOR.
The Advanced Technology Centre (ATC) is responsible for developing IR signature prediction capabilities for its parent body, BAE SYSTEMS. To achieve this, the SIRUS code has been developed and used on a variety of projects for well over a decade. SIRUS is capable of providing accurate IR predictions for air breathing and rocket motor propelled vehicles. SIRUS models various physical components to derive its predictions. A key component is the radiance reflected from the surface of the modeled vehicle. This is modeled by fitting parameters to the measured Bi-Directional Reflectance Function (BDRF) of the surface material(s). The ATC have successfully implemented a parameterization scheme based on the published OPTASM model, and this is described. However, inconsistencies between reflectance measurements and values calculated from the parameterized fit have led to an elliptical parameter enhancement. The implementation of this is also described. Finally, an end-to-end measurement-parameterization capability is described, based on measurements taken with SOC600 instrumentation.
A modified mid-size low by-pass aero-engine running on a sea level test bed was used for measurements with non-intrusive demonstrator systems and currently used gas sampling analysis techniques. A novel open-path White mirror system was developed and installed in the test bed to enhance the sensitivity of non-intrusive FTIR spectrometry. A comparison was made of the different measurement techniques at several engine thrust levels i.e. gas concentrations. This included the emission and absorption mode of the FTIR-spectrometers with the multi-path reflection compartment as well as the single emission mode. A new calibration procedure with a hot cell filled with CO (temperatures 300 to 750 K) was developed and used to calibrate the FTIR instruments. Retrieval results from FTIR measurements were obtained by using a rectangular and Gaussian distribution profile of temperature and gas concentrations in the plume. The FTIR measurement results for CO2, CO, and NO have been proven to be in agreement with the intrusive data. The deviations were generally in the order of plus or minus 30%, i.e. comparable to the day-to-day variations of the engine emissions. NO2 could be detected in the absorption mode only.
The capability of taking non-intrusive species measurements in a jet plume of a modified mid-size low by-pass aero-engine running on a sea level test bed at several thrust levels was demonstrated. Also conventional intrusive measurements were performed with a spatially resolved method using a traversing single-point sampling probe which fulfills ICAO standards. The FTIR spectrometry measurements included both emission and absorption mode with a multi-path reflection compartment as well as the single emission mode. Due to the lack of a common/unique definition for the exhaust plume diameter it was found that the column density was the best measure to compare the different techniques. The FTIR engine measurement results for CO2, CO, and NO have been proven to be in agreement with the intrusive data within plus or minus 30%. Several error sources during the radiometric radiance calibration were identified which lead to uncertainties in the FTIR retrievals, namely (1) incomplete knowledge of the optical surface emissivities, (2) incomplete knowledge and inhomogeneities of the optical surface temperature, and (3) undefined instrumental drifts and non-linearities during the calibration.
Klaus Schaefer, Joerg Heland, Roger Burrows, John Black, Marc Bernard, Gary Bishop, Volker Tank, Erwin Lindermeir, Dave Lister, Robert Falk, Peter Wiesen, Moira Hilton
The environment impact of air traffic and economical aspects require aircraft engines to be developed which have reduced trace gas emissions and, at the same time, increased efficiency. Each new engine must be shown to meet the environmental requirements laid down by regulatory bodies, and exhaust gas measurements must be performed for the certification. The goal of the EC project AEROJET is to demonstrate the equivalence of remote measurement techniques to conventional extractive methods for both gaseous and particulate measurements. The different remote measurement techniques will be compared and calibrated. A demonstrator measurement system for exhaust gases, temperature and particulates including data-analysis software will be regarded as result of this project.
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