Automatic detection of fire smoke using artificial neural networksand threshold approaches applied to AVHRR imagery

Satellite-based remote sensing techniques were developed for identifying smoke from forest fires. Both artificial neural networks (NN) and multithreshold techniques were explored for application with imagery from the Advanced Very High Resolution Radiometer (AVHRR) aboard NOAA satellites. The NN was designed such that it does not only classify a scene into smoke, cloud, or clear background, but also generates continuous outputs representing the mixture portions of these objects. While the NN approach offers many advantages, it is time consuming for application over large areas. A multithreshold algorithm was thus developed as well. The two approaches may be employed separately or in combination depending on the size of an image and smoke conditions. The methods were evaluated in terms of Euclidean distance between the outputs of the NN classification, using error matrices, visual inspection, and comparisons of classified smoke images with fire hot spots. They were applied to process daily AVHRR images acquired across Canada. The results obtained in the 1998 fire season were analyzed and compared with fire hot spots and TOMS-based aerosol index data. Reasonable correspondence was found, but the signals of smoke detected by TOMS and AVHRR are quite different but complementary to each other. In general, AVHRR is most sensitive to low dense smoke plumes located near fires, whereas smoke detected by TOMS is dispersed, thin, elevated, and further away from fires     

Effect of acids and bases on electrophoretic deposition of alumina and zirconia particles in 2-propanol

The effects of acids (monochloroacetic, dichloracetic, trichloroacetic and sulfuric acids) and bases (diethanolamine, triethanolamine, piperidine) on electrophoretic mobility and electrophoretic deposition (EPD) of particles of amphoteric Al₂O₃ and ZrO₂ in anhydrous 2-propanol were studied. It was found that the ζ-potential of Al₂O₃ and ZrO₂ particles had in acidic and alkaline 2-propanol media opposite charge to that in aqueous medium. This phenomenon was explained by the low dissociation constants of acids and bases in 2-propanol. This enables electrosteric stabilization of Al₂O₃ and ZrO₂ particles by acid anions and base cations. Similar electrophoretic behaviour of Al₂O₃ and ZrO₂ particles in 2-propanolic dispersions stabilized by MCAA allowed the preparation of compact, regular layered laminates with high cohesion at the interface of layers.     

Chemical Synthesis,Sintering and Piezoelectric Properties of Ba0.85Ca0.15 Zr0.1Ti0.9O3 Lead‐Free Ceramics

The preparation of Ba_0.85Ca_0.15 Zr_0.1Ti_0.9O₃ (BCZT) powders by wet chemical methods has been investigated, and the powders used to explore relationships between the microstructure and piezoelectric properties (d₃₃ coefficient) of sintered BCZT ceramics. Sol–gel synthesis has been shown to be a successful method for the preparation of BCZT nanopowders with a pure tetragonal perovskite phase structure, specific surface area up to 21.8 m²/g and a mean particle size of 48 nm. These powders were suitable for the fabrication of dense BCZT ceramics with fine‐grain microstructures. The ceramics with the highest density of 95% theoretical density (TD) and grain size of 1.3 μm were prepared by uniaxial pressing followed by a two‐step sintering approach which contributed to the refinement of the BCTZ microstructure. A decrease in the grain size to 0.8–0.9 μm was achieved when samples were prepared using cold isostatic pressing. Using various sintering schedules, BCZT ceramics with broad range of grain sizes (0.8–60.5 μm) were prepared. The highest d₃₃ = 410.8 ± 13.2 pC/N was exhibited by ceramics prepared from sol–gel powder sintered at 1425°C, with the relative density of 89.6%TD and grain size of 36 μm.     

Soil water and plant canopy effects on remotely measured surface temperatures

Abstract.

Thermal infrared remote sensing of diurnal crop canopy temperature variations represents a possible method for determining the availability of soil water to plants. This study was performed to assess the effects of soil water and crop canopy on apparent temperatures observed by means of remote sensors, and to determine the impact of these effects on remote soil water monitoring. Airborne thermal scanner and apparent reflectance data (one date) and ground PRT-5 data (three dates) were collected primarily over barley and other small grain canopies. Plant heights, cover, and available soil water for four layers in the top 20 cm were determined. Analysis of the data showed a close inverse linear relationship between the available water and the day minus night temperature difference δT, for thick barley canopies (plant cover above 90 per cent) only. The use of apparent reflectance values in the visible region did not improve available soil water regression equations substantially. These results suggest that the available water or plant stress could only be accurately determined for thick canopies, and that the reflectance data could probably be used to identify such canopies but would not improve regression estimates of soil water from remote sensing data.     

Land cover dependence in the detection of contaminated pixels insatellite optical data

The detection of partially contaminated pixels over land is necessary for quantitative applications of satellite optical measurements to estimate surface biophysical parameters such as leaf area index or vegetation composition. Threshold-based algorithms suffer from the heterogeneity of land cover and the seasonal variability of the radiation reflected and emitted by the land surface. As an alternative, a method based on a Fourier series approximation to the seasonal trajectory of the normalized difference vegetation index (NDVI) had been previously developed (Cihlar 1996). In this paper, we introduce modifications to the basic algorithm to more closely represent NDVI seasonal trends for different land cover types, as well as a simplified way to determine the time- and pixel-specific contamination thresholds. Based on the tests with 1993-1996 Advanced Very High Resolution Radiometer (AVHRR) data over Canada, the modified procedure effectively detects contaminated pixels for boreal ecosystems after the growing season of interest. The modifications also improved its performance while the growing season is in progress; in this case, at least one complete previous growing season coverage is required to provide the temporal series needed to establish the thresholds. The modified procedure also yields a contamination parameter that may be used to estimate the most likely value for NDVI or other variables for each pixel. It is concluded that the procedure would perform effectively in other areas, provided that the NDVI temporal trajectories of the cover types of interest can he represented by a mathematical model     

Validation of the Geocoding and Compositing System (GEOCOMP) using contextual analysis for AVHRR images

Mapping of remotely-sensed data to a common projection can potentially degrade the quality of the data. The Canada Centre for Remote Sensing (CCRS) has developed the Geocoding and Compositing System (GEOCOMP) to map Advanced Very High Resolution Radiometer (AVHRR) data to a 1 km2 equal area projection. Using data from the Boreal Ecosystem-Atmosphere Study (BOREAS), we tested GEOCOMP's processing of individual pixels and its ability to preserve the spatial integrity of the original AVHRR observations. Our study shows that GEOCOMP processing does not significantly degrade the ability to derive environmental variables and indices using a contextual approach. Errors produced by the GEOCOMP system are largest for scenes with high radiometric contrast and the parts of scenes with large satellite view angles.     

Influence of LA/Ti molar ratio on the complex synthesis of anatase/brookite nanoparticles and their hydrogen production

Heterophase TiO₂ nanoparticles formed in the presence of a very low concentration of a substance with two donor groups were studied and the mechanism of their formation was proposed. The TiO₂ nanoparticles were prepared by low-temperature hydrolysis and polycondensation of Ti (IV) n-propoxide in the presence of lactic acid (LA). The phase composition of the nanoparticles was controlled by the LA/Ti molar ratio ranging from 0.02 to 3.0. At low LA/Ti molar ratios, biphasic anatase-brookite was formed, at average LA/Ti molar ratios, anatase-brookite-rutile particles were formed, and at high molar ratios, pure anatase was formed. By using the low LA/Ti molar ratios, the low-temperature colloidal synthesis made it possible to control the composition of heterophase mesoporous TiO₂ nanoparticles with a high specific surface area and high photocatalytic activity in the production of hydrogen by water splitting. The highest photocatalytic activity was exhibited by anatase-brookite nanoparticles containing 46–65% brookite, synthesized at LA/Ti molar ratios in the range of 0. 033 to 0.1.     

Sintering of Ce,Sm, and Pr Oxide Nanorods

Synthesis of CeO₂, Pr₂O₃, and Sm₂O₃ nanorods and their sintering have been investigated. In a strongly alkaline medium, nanorods of CeO₂, Pr₂O₃, and Sm₂O₃ were prepared from trivalent salts of rare earths (Ce, Pr, Sm) via precipitation synthesis. Nanorods were formed by nanocrystallites of fibrous structure, which were produced by the mechanism of self‐arrangement of hexagonal particles of Re(III) hydroxides. The subsequent transformation of hydroxide into oxide proceeded via self‐preservation of the rod‐like structure. In CeO₂, the fibrous structure was noncohesive during thermal treatment at temperature of 500°C and higher. Regardless of the shape of the CeO₂ particles (spherical versus rod‐like), sintered ceramic was formed by equiaxial grains. The cohesion of the fibrous structure of Pr and Sm oxides was higher than in CeO₂. The rod‐like shape of the particles of Pr and Sm oxides was (partially) preserved during sintering.     

The bidirectional effects of AVHRR measurements over boreal regions

The objectives of this paper are to analyze the bidirectional effects of satellite data over six land-cover types in northern regions, and to test a method for the routine correction of these effects. Analyses and corrections were carried out with both single-day and 10-day composite data obtained by the advanced very high resolution radiometer (AVHRR) from central Canada acquired in 1993/1994, in part, for the boreal ecosystem and atmosphere study (BOREAS). The model of Wu et al. [1995], developed from a separate data set collected at lower latitudes, was employed for correcting the effects. The analysis showed viewing angle dependence in AVHRR channels 1 and 2 from both single-day images and composites. Reflectances at extreme viewing angles are two to four times larger than those observed near nadir. On average, the effects introduce a variation of 30% relative to mean reflectances. Although the effects decrease in the normalized difference vegetation index (NDVI), they are nevertheless significant before the correction. Using the model of Wu et al. [1995], the BRDF-related variability is reduced by about 68% in channel 1 and 71% in channel 2. After a simple adjustment of the model coefficients, a further reduction of 4% (channel 1) and 6% (channel 2) of the BRDF-related variability was achieved for the 10⁶ km² BOREAS region. The effectiveness of the correction with both original and refined model of Wu et al. was found to be weakly dependent on land-cover type. Corrections for coniferous, mixed wood, and cropland are better than other land-cover types (rangelands/pasture, deciduous, and transitional forests) with residual BRDF errors around 0.05 in both channels. Overall, the model (albeit simple) performs reasonably well throughout the growing season. To apply the model, only general knowledge of land-cover type is required, namely forest, cropland, grassland, and bare ground