Visible Infrared Research Articles

GPS Multipath Mitigation for Urban Area Using Omnidirectional Infrared Camera

This paper describes a precision positioning technique that can be applied to vehicles in urban areas. The proposed technique mitigates Global Positioning System (GPS) multipath by means of an omnidirectional infrared (IR) camera that can eliminate the need for invisible satellites [a satellite detected by the receiver but without line of sight (LOS)] by using IR images. Some simple GPS multipath mitigation techniques, such as the installation of antennas away from buildings and using choke ring antennas, are well known. Further, various correlator techniques can also be employed. However, when a direct signal cannot be received by the antenna, these techniques do not provide satisfactory results because they presume that the antenna chiefly receives direct signals. On the other hand, the proposed technique can mitigate GPS multipath, even if a direct signal cannot be received because it can recognize the surrounding environment by means of an omnidirectional IR camera. With the IR camera, the sky appears distinctively dark; this facilitates the detection of the borderline between the sky and the surrounding buildings, which are captured in white, due to the difference in the atmospheric transmittance rate between visible light and IR rays. Positioning is performed only with visible satellites having fewer multipath errors and without using invisible satellites. With the proposed system, static and kinematic evaluations in which invisible satellites are discriminated through observation using an omnidirectional IR camera are conducted. Hence, signals are received even if satellites are hidden behind buildings; furthermore, the exclusion of satellites having large errors from the positioning computation becomes possible. The evaluation results confirm the effectiveness of the proposed technique and the feasibility of highly accurate positioning.

Estimating plot-level forest structural attributes using high spectral resolution ASTER satellite data in even-aged Eucalyptus plantations in southern KwaZulu-Natal, South Africa

This study assessed the suitability of both visible and shortwave infrared of ASTER reflectance bands and various vegetation indices for estimating forest structural attributes of Eucalyptus species. The study was conducted in even-aged monoculture plantations of E. grandis and E. nitens in the southern KwaZulu-Natal Midlands of South Africa. Empirical relationships between forest structural attributes, i.e. stems per hectare (SPHA), diameter at breast height (DBH), mean tree height (MTH), basal area and volume, and ASTER data were derived using correlation and canonical correlation analysis (CCA). The results indicated weak relationships between the studied forest structural attributes and ASTER data. In the younger plantation stands (4–6 years) the adjusted R 2 values from CCA regression for SPHA, DBH, MTH, basal area and volume were 54.2, 63.5, 33.8, 25.4 and 30.3, respectively. The adjusted R 2 values in the mature stands (7–9 years) were distinctly weaker with values of 50.7, 55.8, 25.1, 20.2 and 27.3 for SPHA, DBH, MTH, basal area and volume, respectively. The results imply that ASTER satellite data are not applicable to forest structural attribute estimation in commercially managed forest stands.

Hyperspectral Sensing for Assessing Nearshore Water Quality Conditions of Hudson/Raritan Estuary

This study addresses the use of remote sensing hyperspectral data acquired by NASA/Airborne Visible Infra Red Imaging Spectrometer (AVIRIS) to estimate concentrations of optical water quality parameters in the Hudson/Raritan Estuary of New York-New Jersey. Hudson/Raritan estuary is a complex estuarine system where tidal and wind-driven currents are modified by freshwater discharges from the Hudson, Raritan, Hackensack, and Passaic rivers. Hypersectral (high resolution) remote sensing data offers unique advantages for the study of recurrent hydrological phenomena on regional and local scales. The paper describes the bio-optical water quality model constructed linking the water constituent concentrations to (i) the inherent optical properties (IOPs), using the specific inherent optical properties (SIOP), and (ii) to the subsurface light levels. Generation of accurate reflecta nce R(0) from radiance recorded by the AVIRIS is the key parameter for input into inverse modeling for estimation of constituent concent rations. In conjunction with bio-optical model, the linear matrix inversion technique is used for retrieval of estuarine water constituents in terms of chlorophyll, colored dissolved organic matter and inorganic material. The long term goal is to establish a monitoring/management system for retrieval of estuarine water constituents using remotely sensed data. Such efforts are complementary to the development of spectral library for detec tion/identification of harmful algal blooms (HABs) causing eutrophication and pollutions in the world’s coastal and estuarine waters. Results of AVIRIS data analyses in forms of thematic maps of concentrations of water quality parameters can be integrated into the Geographic Information Systems (GIS) of the estuary. GIS is a computer-based geospatial database which can be used as a management tool for monitoring of water quality conditions of the estuary.

Preparation of RF reactively sputtered indium-tin oxide thin films with optical properties suitable for heat mirrors

Technologies are discussed for preparing and characterizing indium-tin oxide (ITO) thin films with properties appropriate for usage as heat mirrors in solar thermal collectors. The samples were prepared by means of radio frequency (RF) reactive sputtering of indium-tin targets in oxygen. The technological parameters were optimized to obtain films with optimal properties for heat mirrors. The optical properties of the films were studied by visible and infra-red (IR) spectrophotometry and laser ellipsometry. The reflectance of the films in the thermal IR range was investigated by a Fourier transform infra-red (FTIR) spectrophotometer. Heating of the substrates during the sputtering and their post deposition annealing in different environments were also studied. The ultimate purpose of the present research being the development of a technological process leading to low-cost ITO thin films with high transparency in the visible and near IR (0.3-2.4 μm) and high reflection in the thermal IR range (2.5-25 μm), we investigated the correlation of the ITO thin films structural and optical properties with the technological process parameters - target composition and heat treatment.

Development of a Positioning Technique for an Urban Area Using Omnidirectional Infrared Camera and Aerial Survey Data

This paper describes an outdoor positioning system for vehicles that can be applied to an urban canyon by using an omnidirectional infrared (IR) camera and a digital surface model (DSM). By means of omnidirectional IR images, this system enables robust positioning in urban areas where satellite invisibility caused by buildings hampers high-precision GPS measurements. The omnidirectional IR camera can generate IR images with an elevation of 20–70° for the surrounding area of 360°. The image captured by the camera is highly robust to light disturbances in the outdoor environment. Through the IR camera, the sky appears distinctively dark; this enables easy detection of the border between the sky and the buildings captured in white due to the difference in the atmospheric transmittance rate between visible light and IR rays. The omnidirectional image, which includes several building profiles, is compared with building-restoration images produced by the corresponding DSM in order to determine the self-position. Field experiments in an urban area show that the proposed outdoor positioning method is valid and effective, even if high-rise buildings cause satellite blockage that affects GPS measurements.

Ice cloud properties in ice‐over‐water cloud systems using Tropical Rainfall Measuring Mission (TRMM) visible and infrared scanner and TRMM Microwave Imager data

A multilayered cloud retrieval system (MCRS) is updated and used to estimate ice water path in maritime ice‐over‐water clouds using Visible and Infrared Scanner (VIRS) and Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) measurements acquired over the Tropics between January and August 1998. Lookup tables of top‐of‐atmosphere 0.65‐μm reflectance are developed for ice‐over‐water cloud systems using radiative transfer calculations for various combinations of ice‐over‐water cloud layers. The liquid and ice water paths, LWP and IWP, respectively, are determined with the MCRS using these lookup tables with a combination of microwave (MW), visible (VIS), and infrared (IR) data. LWP, determined directly from the TMI MW data, is used to define the lower‐level cloud properties to select the proper lookup table. The properties of the upper‐level ice clouds, such as optical depth and effective size, are then derived using the Visible–Infrared Solar‐infrared Split‐Window technique (VISST), which matches the VIRS IR, 3.9 μm, and VIS data to the multilayer cloud lookup table reflectances and a set of emittance parameterizations. Initial comparisons with surface‐based radar retrievals suggest that this enhanced MCRS can significantly improve the accuracy and decrease the IWP in overlapped clouds by 42 and 13% compared to using the single‐layer VISST and an earlier simplified MW–VIS–IR (MVI) differencing method, respectively, for ice‐over‐water cloud systems. The tropical distribution of ice‐over‐water clouds is the same as derived earlier from combined TMI and VIRS data, but the new values of IWP and optical depth are slightly larger than the older MVI values and exceed those of single‐layered clouds by 7 and 11%, respectively. The mean IWP from the MCRS is 8–14% greater than that retrieved from radar retrievals of overlapped clouds over two surface sites, and the standard deviations of the differences are similar to those for single‐layered clouds. Examples of a method for applying the MCRS over land without MW data yield similar differences with the surface retrievals. By combining the MCRS with other techniques that focus primarily on optically thin cirrus over low water clouds, it will be possible to more fully assess the IWP in all conditions over ocean except for precipitating systems.

Proximal Visible and near Infrared Diffuse Reflectance Spectroscopy for Soil—Landscape Modelling

Proximal Visible and near Infrared Diffuse Reflectance Spectroscopy for Soil—Landscape Modelling

Characterization of InN layers grown by high-pressure chemical vapor deposition

Structural and optical properties of indium nitride (InN) layers grown by high-pressure chemical vapor deposition (HPCVD) on sapphire and GaN epilayers have been studied. HPCVD extends processing parameters beyond those accessible by molecular beam epitaxy and metal organic chemical vapor deposition, enabling the growth of epitaxial InN layers at temperatures as high as 1150K for reactor pressures around 15bars, leading to vastly improved material properties. InN layers grown on GaN(0002) epilayers exhibit single-phase InN(0002) x-ray diffraction peaks with full width at half maximum (FWHM) around 430arcsec. Optical characterization of the InN layers by infrared (IR) reflectance reveals free carrier concentrations in the low to mid-10+19-cm−3 and optical dielectric function ε∞=5.8. The optical properties in the visible and near IR spectral ranges were analyzed by transmission spectroscopy, showing an absorption edge around 1.5eV. The shift of the absorption edge correlates with deviations in the InN stoichiometry, indicating that the understanding and control of the point defect chemistry of InN is critical for improved material properties.

Multiscale Fusion of Visible and Thermal IR Images for Illumination-Invariant Face Recognition

This paper describes a new software-based registration and fusion of visible and thermal infrared (IR) image data for face recognition in challenging operating environments that involve illumination variations. The combined use of visible and thermal IR imaging sensors offers a viable means for improving the performance of face recognition techniques based on a single imaging modality. Despite successes in indoor access control applications, imaging in the visible spectrum demonstrates difficulties in recognizing the faces in varying illumination conditions. Thermal IR sensors measure energy radiations from the object, which is less sensitive to illumination changes, and are even operable in darkness. However, thermal images do not provide high-resolution data. Data fusion of visible and thermal images can produce face images robust to illumination variations. However, thermal face images with eyeglasses may fail to provide useful information around the eyes since glass blocks a large portion of thermal energy. In this paper, eyeglass regions are detected using an ellipse fitting method, and replaced with eye template patterns to preserve the details useful for face recognition in the fused image. Software registration of images replaces a special-purpose imaging sensor assembly and produces co-registered image pairs at a reasonable cost for large-scale deployment. Face recognition techniques using visible, thermal IR, and data-fused visible-thermal images are compared using a commercial face recognition software (FaceIt®) and two visible-thermal face image databases (the NIST/Equinox and the UTK-IRIS databases). The proposed multiscale data-fusion technique improved the recognition accuracy under a wide range of illumination changes. Experimental results showed that the eyeglass replacement increased the number of correct first match subjects by 85% (NIST/Equinox) and 67% (UTK-IRIS).

Analysis of the decrease in the tropical mean outgoing shortwave radiation at the top of atmosphere for the period 1984-2000

Abstract. A decadal-scale trend in the tropical radiative energy budget has been observed recently by satellites, which however is not reproduced by climate models. In the present study, we have computed the outgoing shortwave radiation (OSR) at the top of atmosphere (TOA) at 2.5° longitude-latitude resolution and on a mean monthly basis for the 17-year period 1984-2000, by using a deterministic solar radiative transfer model and cloud climatological data from the International Satellite Cloud Climatology Project (ISCCP) D2 database. Anomaly time series for the mean monthly pixel-level OSR fluxes, as well as for the key physical parameters, were constructed. A significant decreasing trend in OSR anomalies, starting mainly from the late 1980s, was found in tropical and subtropical regions (30° S-30° N), indicating a decadal increase in solar planetary heating equal to 1.9±0.3Wm-2/decade, reproducing well the features recorded by satellite observations, in contrast to climate model results. This increase in solar planetary heating, however, is accompanied by a similar increase in planetary cooling, due to increased outgoing longwave radiation, so that there is no change in net radiation. The model computed OSR trend is in good agreement with the corresponding linear decadal decrease of 2.5±0.4Wm-2/decade in tropical mean OSR anomalies derived from ERBE S-10N non-scanner data (edition 2). An attempt was made to identify the physical processes responsible for the decreasing trend in tropical mean OSR. A detailed correlation analysis using pixel-level anomalies of model computed OSR flux and ISCCP cloud cover over the entire tropical and subtropical region (30° S-30° N), gave a correlation coefficient of 0.79, indicating that decreasing cloud cover is the main reason for the tropical OSR trend. According to the ISCCP-D2 data derived from the combined visible/infrared (VIS/IR) analysis, the tropical cloud cover has decreased by 6.6±0.2% per decade, in relative terms. A detailed analysis of the inter-annual and long-term variability of the various parameters determining the OSR at TOA, has shown that the most important contribution to the observed OSR trend comes from a decrease in low-level cloud cover over the period 1984-2000, followed by decreases in middle and high-level cloud cover. Note, however, that there still remain some uncertainties associated with the existence and magnitude of trends in ISCCP-D2 cloud amounts. Opposite but small trends are introduced by increases in cloud scattering optical depth of low and middle clouds.

Resonant nano-cluster devices

The resonance-enhanced absorption (REA) by metal clusters on a surface is an effective technique on which to base bio-optical devices. A four-layer device consisting of a metal mirror, a polymer or glass-type distance layer, a biomolecule interaction layer and a sub-monolayer of biorecognitively bound metal nano-clusters is reported. Experiments indicate a strong influence of the resonator homogeneity on the absorption maximum. Layer stability plays an important role in the overall performance of the device. Techniques and optimised lab protocols to set up biochips that use the REA process in the detection are presented. The sensors show one to three narrow reflection minima in the visible and or infra-red (IR) part of the spectrum and therefore they do not suffer from the spectral limitations associated with spherical gold colloids. Metal clusters (synthesised by thermal step reduction) as well as metal- dielectric shell clusters (synthesised by various shell deposition processes) are used to precisely shift the readout of the device to any frequency in the visible and near IR range. Disposable single-step protein chips, DNA assays as well as complex biochip arrays are established that use various DNARNA, antigen-antibody and protein-protein interaction systems.

A new method for medium-resolution sea ice analysis using weather-influence corrected Special Sensor Microwave/Imager 85 GHz data

A detailed description of a new method for sea ice analysis using Special Sensor Microwave/Imager (SSM/I) brightness temperature measurements (SEA LION algorithm) is given. The SEA LION algorithm uses the normalized brightness temperature polarization difference at 85 GHz. This polarization difference is corrected for the change in brightness temperatures due to sea surface scattering and absorption/emission by atmospheric water (weather influence). This is achieved by taking low-frequency SSM/I data and Numerical Weather Prediction model data for radiative transfer calculations. Tie points are derived from 85 GHz SSM/I data over a period of at least 10 days/one month focused around the period of investigation. The difference between measured and modelled polarization difference is minimized by iteration to obtain the sea ice concentration. The SEA LION algorithm was applied to daily gridded and single overpass 85 GHz SSM/I data. Resulting 12.5 km@12.5 km ice concentrations are compared to those of the NASA-Team and the COMISO-Bootstrap algorithms, to ship observations, and to space-borne visible/infrared (VIS/IR) and active microwave imagery. The SEA LION algorithm ice edge agrees within 10 km with VIS/IR imagery. The across ice-edge SEA LION algorithm ice-concentration gradient is considerably steeper than that of the NASA-Team and COMISO-Bootstrap algorithm ice concentration and agrees with active microwave imagery. Arctic SEA LION ice concentrations compare to those obtained from classified active microwave imagery with a correlation (regression) coefficient of 0.84 (0.77) and a difference of −4.4% (NASA-Team algorithm: 0.85 (0.57) and −8.5%).

VIRTIS-M flight lamps

VIRTIS-M is a visible-infrared (VIS-IR) image spectrometer designed for the Rosetta mission; it intends to provide detailed informations on the physical, chemical, and mineralogical nature of comets and asteroids. The in-flight performances of VIRTIS-M are expected to be influenced by various disturbances, like the initial strong vibrations of the rocket, the long duration of the experiment (from 2003 to 2010), as well as other possible environmental changes; therefore, an in-flight recalibration procedure is mandatory. Quite often in such kinds of missions, a light emission diode (LED) is employed to calibrate the on-board spectrometers by taking advantage of the relative small dimensions, stability, and hardness of these sources. VIRTIS-M is the first image spectrometer that will use a new generation of lamps for internal calibrations. These new lamps are characterized by a wide spectral range with a blackbody-like emission with an effective temperature of about (2400–2600 K), thereby covering the whole VIRTIS-M’s spectral range (0.2–5 μm); i.e., they offer the possibility of a wider spectral calibration in comparison with the quasimonochromatic LED emission. A precise spectral calibration is achieved by adding special filters for visible and infrared ranges in front of the window source, containing many narrow absorption lines. In the present article, we describe the calibration and tests of some flight prototypes of these lamps (VIS and IR), realized by the Officine Galileo and calibrated by the Consiglio Nazionale delle Ricerche–Istituto di Astrofisica Spaziale e Fisica Cosmica.

A new algorithm for the detection of plumes caused by industrial accidents, based on NOAA/AVHRR imagery

The Advanced Very High Resolution Radiometer (AVHRR) on board the NOAA satellites may be used for detecting plumes caused by industrial accidents through the combined use of the visible (0.58-0.68 @m), near infrared (0.72-1.10 @m) and thermal infrared (11.5-12.5 µm) channels of the AVHRR. In this study a model algorithm is developed to identify pixels which correspond to plumes caused by industrial accidents. The novelty of the algorithm is that it combines the visible, the near infrared and the thermal infrared AVHRR channels in order to produce a two-dimensional feature space image in which the plumes can be detected and monitored. The algorithm was evaluated for four industrial accidents: in Enschede, the Netherlands on 13 May 2000; in Genoa, Italy on 13 April 1991; in Lyon, France on 2 June 1987 and in Kalohori, Greece on 24 February 1986. The effectiveness and reliability of the algorithm was found to be satisfactory in all case studies.

Infrared spectra of carbon nitride films

The assignment of the vibrational modes in amorphous carbon nitride (CN) films is discussed by considering CN films deposited using a variety of methods. The infrared (IR) spectra of CN show three main absorption bands. In hydrogenated CN samples, CH x and NH x groups give rise to stretching vibrations at 3000 and 3400 cm −1, respectively. A weaker sharp band is observed approximately 2200 cm −1 due to CN–sp 1 bonds. Finally, there is a broad band between 1000 and 2000 cm −1. It is usually stated that the effect of nitrogen into carbon films is to break the symmetry of the sp 2 carbon bonds making the Raman ‘G’ (graphitic) and ‘D’ (disorder) modes IR active, so the broad band between 1000 and 2000 cm −1 is similar in both IR and Raman spectra. However, it is shown that nitrogen is not necessary to have significant IR activity in the 1000–2000 cm −1 region. Also, Raman spectroscopy in carbon is always a resonant process, so that the spectra depend on the excitation energy. Therefore, the similarity of the visible Raman and IR spectra of some CNs is generally a coincidence. We show that the IR broad band in the 1000–2000 cm −1 region is an electronic effect and is not due to activation of IR forbidden modes due to symmetry breaking. This explains the IR spectra not only of CN films but also of N-free amorphous carbon films and is related to the presence of the system of delocalized π bonds with increasing conjugation.

Areal Snow Cover Estimation over the Himalayan Terrain Using INSAT‐1D VHRR Data

INSAT ‐1D (Indian National Satellite) VHRR (Very High Resolution Radiometer) daytime visible (0.55-0.75μ) and thermal infrared (10.5-12.5μm) data have been used for delineation of areas under snow cover in the Himalayas. The boundary of the Himalayan frontal thrust belt and other with major structural features could also be demarcated in the processed image. Two different image processing techniques, namely thresholding and textural method were adopted to delineate the areas under snow cover. Thresholding technique was better suited here, though textural method has got a no. of advantages e.g. dimensionality increment etc. which is suited particularly for handling single band data. Results also show more and more snow accumulations over the regional lineaments and tectonic patterns (using INSAT VHRR data).

ZAO: an attractive potential substitute for ITO in flat display panels

Al-doped ZnO (ZAO) is an attractive material, as it is cheap and abundant, it is nontoxic, has comparable electrical, optical and infrared (IR) properties to ITO, is cost-effective and is easy to fabricate. In this paper, ZAO films have been prepared by reactive magnetron sputtering. Their electrical conductivity is shown to be in the region of 10 −4 Ω cm. The influence of the substrate-to-target distance and deposition temperature on the resistivity of ZAO films has been studied. Their IR and optical properties have been investigated with UV–VIS and Fourier transformation IR spectrometry. It was shown that the visible transmittance and IR reflectance of ZAO films deposited on polyester at room temperature are comparable to those of ITO films. ZAO films have n-type conductivity. It was found that by adding Al to ZnO the variation in resistivity of ZAO films was decreased, and was usually no more than 1% at 50–400°C in vacuum and 5% at 50–400°C in air.

Visible–infrared and radar imagery fusion for geological application: a new approach using DEM and sun-illumination model

Radar-multispectral imagery fusion has been successfully used in several application fields. In this study, a new technique to merge an ERS-1 (Synthetic Aperture Radar precision image, SAR-PRI) image and a Landsat Thematic Mapper (TM ) image for the geological study of the western Aspromonte (southern Italy) was investigated. Spectral information provided by the TM image can be effectively combined with texture and pattern data from the radar imagery to produce a synergistic image. Landsat bands are normalized for shadowing effects using the semi-empirical Minnaert model and thereafter multiplied by the ERS1 image. The visible-infrared (VIR) and radar fused bands can be composed into colour images. This technique leads to the production of images in which the geologically relevant information were integrated. These images were compared with the imagery produced by the intensity-hue-saturation (IHS) transformation approach, commonly used for image fusion. The sun-illumination normalization method gives bet...

Multisensor Hydrologic Assessment of a Freshwater Wetland

This article evaluates the use of synthetic aperture radar (SAR) and visible/infrared (VIR) satellite imagery for mapping the extent of standing water in the Peace-Athabasca Delta during spring and summer of 1998. SAR images contain data about the geometric and electrical characteristics of the objects, while VIR images contain information about the reflectivity of objects. Radar pulses can also penetrate vegetation to some degree depending on the wavelength and vegetation thickness. It is hypothesized that since Radarsat and SPOT images contain complementary information, flood mapping will be more efficient when the two image types are used in combination. Radarsat SAR and SPOT multispectral imagery from May 1998 and July 1998 were used for the flood mapping. A Radarsat S2 image (27.5° incidence angle) was obtained for May 1998. To evaluate the incidence angle effect on flood mapping, a Radarsat S1 image (27.5° incidence angle) and a Radarsat S7 image (47.0° incidence angle) were obtained for July 1998. The Radarsat scenes were calibrated and filtered, and all imagery were orthorectified to minimize geometric distortion. A Mahalanobis distance algorithm was used to classify the SPOT scenes, the Radarsat scenes, and a combination of the two into open water, flooded vegetation, and nonflooded land. The results indicate that flood mapping in both spring and summer conditions has significantly higher accuracy when Radarsat and SPOT imagery are used in combination, rather than separately. However, it is important to use Radarsat imagery acquired at low incidence angles. Classification of the SPOT scene combined with the Radarsat S1 scene achieved significantly better results than those obtained when the SPOT scene was classified in combination with the Radarsat S7 scene.

Visible?infrared and radar imagery fusion for geological application: A new approach using DEM and sun-illumination model

Radar-multispectral imagery fusion has been successfully used in several application fields. In this study, a new technique to merge an ERS-1 (Synthetic Aperture Radar precision image, SAR-PRI) image and a Landsat Thematic Mapper (TM ) image for the geological study of the western Aspromonte (southern Italy) was investigated. Spectral information provided by the TM image can be effectively combined with texture and pattern data from the radar imagery to produce a synergistic image. Landsat bands are normalized for shadowing effects using the semi-empirical Minnaert model and thereafter multiplied by the ERS1 image. The visible-infrared (VIR) and radar fused bands can be composed into colour images. This technique leads to the production of images in which the geologically relevant information were integrated. These images were compared with the imagery produced by the intensity-hue-saturation (IHS) transformation approach, commonly used for image fusion. The sun-illumination normalization method gives better results in image fusion, enhancing subtle spectral features. Compared to the individual images, the synergistic SAR-TM images produced by this technique improve the interpretation of lithology boundaries and recognition of structural features.